Soft tissue surgery in dogs encompasses a wide range of procedures, from elective spay and neuter to emergency GI resection. The asepsis standard differs substantially across this range, and applying the wrong standard in either direction, too strict where it is unnecessary or too lax where it is essential, produces inefficiency or infection respectively.

What this covers: The perioperative asepsis protocol for soft tissue surgery in dogs, including wound classification, procedure-specific SSI risk factors, patient preparation, intraoperative standards, and tract-specific considerations for GI, urinary, and respiratory surgery.Evidence base: PMC6802975 SSI incidence study in dogs undergoing soft tissue surgery; ATDove SSI risk factor review; The Veterinary Nurse SSI preparation and prevention; wound classification framework.SSI rate context: Clean soft tissue procedures (elective, no tract entry): 2 to 5% in veterinary literature. Clean-contaminated (controlled tract entry): 5 to 10%. Contaminated and dirty: 4 to 18% depending on degree and source of contamination.

Key takeaways

• Wound class determines the asepsis standard and SSI risk baseline for each procedure.
• Procedure duration over 60 minutes is a documented independent SSI risk factor in dogs.
• Tract entry (GI, urinary, respiratory) elevates wound class and requires protocol modification.
• Patient risk factors (endocrinopathy, obesity, ASA score) compound procedure SSI risk.
• Skin antisepsis, instrument sterilization, and sterile technique apply to all soft tissue cases.
• Antibiotic prophylaxis is indicated for clean-contaminated and above; not routine for clean.
• Lavage before closure is standard for contaminated and dirty procedures.

Wound classification for canine soft tissue surgery

The CDC surgical wound classification system provides the framework for matching asepsis standard to procedure type:

For all classes, the full standard surgical asepsis protocol applies. Class II and above require additional considerations for lavage, potentially antimicrobial prophylaxis, and wound management decisions.

Patient risk factors for soft tissue SSI in dogs

Procedure class is not the only determinant of SSI risk. Published veterinary literature documents the following patient-level risk factors:

Endocrinopathies:

Hyperadrenocorticism (Cushing's disease) is the most strongly documented patient risk factor for SSI in dogs. Dogs with Cushing's disease have substantially higher SSI rates than dogs without endocrinopathy undergoing the same procedure. Hypothyroidism and diabetes mellitus also elevate risk.

Obesity:

Obese dogs have thicker subcutaneous tissue layers, reduced subcutaneous blood supply, and potentially reduced immune competence. These factors elevate SSI risk and complicate wound closure.

ASA score:

Higher ASA physical status classification (indicating more severe systemic disease) is an independent predictor of SSI in the veterinary literature, consistent with human surgical data.

Procedure duration:

Surgery duration over 60 minutes is a documented independent SSI risk factor in dogs (PMC6802975). The relationship holds when controlling for procedure type and patient factors. Efficient technique that minimizes operative time is itself an infection prevention measure.

Active infection at another site:

Presence of concurrent infection (urinary tract infection, skin infection, dental disease) elevates SSI risk through bacteremia risk and potential immune system distraction.

Pre-operative preparation for canine soft tissue surgery

Patient preparation

Clipping:

Clip margins should extend at least 5 to 10 cm beyond the anticipated incision. For abdominal procedures, clip from mid-sternum to pubis and lateral extension to include both flanks.

Clip immediately before surgery. Do not use razors.

Skin antisepsis:

Standard three-pass centrifugal scrub sequence. CHG-alcohol combination preferred for most body sites due to residual activity. PVI preferred for ophthalmic, ear, and some oral procedures.

For abdominal surgery in female dogs: include the vulvar region in the prep area and apply a sterile drape or cover to minimize contamination from normal vulvar flora.

Pre-operative fasting:

Standard pre-anaesthetic fasting (minimum 8 to 12 hours for solid food) reduces GI content volume and aspiration risk, but also reduces contamination load if GI tract is entered or perforated.

Antibiotic prophylaxis

Clean procedures (Class I):

Antimicrobial prophylaxis is not routinely indicated for clean elective soft tissue surgery in healthy dogs. Standard aseptic technique applied correctly produces SSI rates within the 2 to 5% expected range without prophylaxis.

Clean-contaminated procedures (Class II):

Prophylaxis is indicated. Selection based on likely pathogens for the specific tract entered:

• GI surgery: cover gram-negative bacteria and anaerobes (e.g., ampicillin-sulbactam or cefoxitin)
• Urinary tract: cover gram-negative uropathogens (e.g., enrofloxacin or ampicillin)
• Respiratory: cover typical respiratory pathogens

Contaminated and dirty (Class III and IV):

Therapeutic antimicrobial therapy, not prophylaxis. Culture and sensitivity where possible.

Intraoperative asepsis for canine soft tissue surgery

Sterile field management

Standard sterile field principles apply: sterile instruments, sterile gown and gloves, correct draping, sterile technique throughout.

Abdominal procedures:

• Impervious draping to isolate the abdominal incision from the flanks and thorax
• Saline-moistened laparotomy sponges used to pack off adjacent organs during GI work
• Any instrument or sponge that contacts the bowel lumen should be considered contaminated and removed from the sterile field

Soft tissue exposure:

During deep tissue dissection, retractors should be wetted to reduce tissue trauma. Minimize tissue handling. Atraumatic technique reduces devitalized tissue at the wound site, reducing the substrate available for bacterial colonization.

GI tract entry

When the GI tract is entered under controlled conditions (enterotomy, intestinal resection and anastomosis):

• Isolate the segment being operated on with intestinal forceps or umbilical tape to minimize luminal content spillage
• Double-glove change after GI closure and before abdominal closure
• Copious lavage before abdominal closure
• Instrument change: instruments that contacted the GI lumen are removed from the sterile field

For core aseptic technique, including the sterile field maintenance and instrument handling standards that apply throughout the intraoperative phase for all procedure types, that guide covers the intraoperative technique framework.

The canine skin antisepsis protocol is a critical foundation for all soft tissue cases. For skin antisepsis preparation for dogs, including the complete centrifugal scrub technique, agent selection, contact time requirements, and common preparation errors specific to canine patients, that guide covers the step-by-step preparation protocol.

Lavage before closure

Wound lavage before closure is standard for all Class II and above procedures and should be considered for extended Class I procedures.

Purpose: Remove debris, blood clots, and bacteria that accumulated during the procedure.

Volume: 300 to 500 mL minimum for abdominal procedures; larger volumes for grossly contaminated cases.

Agent: Sterile saline is the standard baseline. For contaminated or dirty cases, antiseptic lavage may be used before closure.

Dead space management

Eliminating dead space at closure reduces the blood and fluid accumulation that supports bacterial growth. Techniques:

• Obliterating subcutaneous dead space with walking sutures where anatomically appropriate
• Closed-suction drains for large dead space that cannot be eliminated
• Omentum mobilization to fill dead space in abdominal procedures when indicated

Tract-specific asepsis considerations

Pyometra surgery

Pyometra presents as a Class IV (dirty) procedure with pre-existing uterine infection. Additional considerations:

• Culture the uterine exudate intraoperatively for culture and sensitivity
• Minimize spillage during ovariohysterectomy
• Copious lavage if spillage occurs
• Therapeutic antibiotics, not prophylaxis
• Consider active infection control precautions for the post-operative patient

Cystotomy

Class II (clean-contaminated) procedure. Urine culture before surgery when possible to guide antimicrobial selection. Double-glove change after bladder closure. Lavage before abdominal closure.

For asepsis during soft tissue surgery in cats for comparison, including the feline-specific considerations that differ from the canine soft tissue asepsis protocol, that guide covers the cat-specific approach.

Frequently asked questions

Does wound class change if an unplanned event occurs during surgery?

Yes. An unexpected GI perforation during an elective procedure reclassifies the wound from Class I to Class III. This changes the intraoperative lavage requirement, post-operative monitoring intensity, and possibly the antimicrobial plan. The surgeon should acknowledge the reclassification and adjust the protocol accordingly.

Is skin closure method relevant to SSI risk in soft tissue surgery?

Yes. Subcutaneous closure technique affects dead space and wound tension. Excessive tension at the skin closure impairs blood supply to the wound edge, reducing local immune competence. Some evidence suggests that minimizing subcutaneous suture material reduces wound reaction and SSI risk, though specific data in veterinary soft tissue surgery is limited.

How should contaminated wound cases be handled in terms of OR scheduling?

Contaminated and dirty-infected cases should be scheduled last in the surgical day where possible, to allow full terminal cleaning of the OR after the procedure. If this is not possible, thorough terminal cleaning (not just between-case cleaning) should follow a contaminated or dirty procedure before the next sterile case.

For surgical asepsis standards for all canine surgery, including the five-domain surgical asepsis framework that underlies the procedure-specific applications covered in this guide, that guide covers the full standard.

Applying the correct asepsis standard to the correct procedure class requires not just knowing the protocol but consistently executing it without the errors that most commonly compromise soft tissue surgical asepsis in practice.

For common errors in soft tissue asepsis, including the most common aseptic error categories documented in small animal surgical practice and how to prevent them, that guide covers the error taxonomy that applies throughout soft tissue surgery.

Soft tissue surgery in dogs spans a wide range of contamination risk, and the asepsis protocol must be matched to that range. The same core principles apply to every case: sterile instruments, correct technique, appropriate skin prep, and matched antimicrobial strategy. What changes is the intensity, duration, and lavage requirement based on wound class and patient risk. Matching the protocol to the procedure is as important as applying it correctly.

Resources

The following sources were used as reference and background for this article:

• NIH/PMC. Incidence of SSI in dogs undergoing soft tissue surgery: risk factors and economic impact. pmc.ncbi.nlm.nih.gov
• ATDove. Surgical Site Infection. atdove.org
• The Veterinary Nurse. Surgical site infections: preparation, technique and perioperative prevention. theveterinarynurse.com
• WSAVA 2014. Maintaining a Sterile Operating Environment. vin.com

The operating room is the highest-stakes aseptic environment in any veterinary facility. Every design decision, behavioral protocol, and maintenance schedule either supports or undermines the sterile field established during surgery.

OR asepsis is not only about what happens during the procedure. It is the result of physical infrastructure, access control, airflow engineering, surface disinfection, and team behavior working together.

What this covers: The physical and procedural standards that govern asepsis in the veterinary operating room, from facility design and airflow engineering through traffic management, between-case disinfection, and SSI surveillance.Standard reference: ASHRAE Standard 170 (Ventilation of Health Care Facilities) provides the primary engineering reference for OR ventilation design. Veterinary ORs are typically designed to align with or adapt from this standard.Clinical context: OR asepsis standards exist at the intersection of facility design, infection control, and team behavior. A well-designed OR used with poor behavioral compliance will not prevent SSI. A team with excellent technique in a poorly designed OR faces preventable contamination challenges.Scope: Applies to dedicated surgical suites in small animal veterinary hospitals and specialty referral centers.

Key takeaways

• OR location and flow design are the foundation of environmental asepsis: Surgical suites should be positioned to minimize patient transport through high-traffic clinical areas and to allow unidirectional patient flow.
• Positive pressure ventilation is the standard for veterinary ORs: Air pressure inside the OR must exceed adjacent areas to prevent corridor air from entering the sterile environment.
• HEPA filtration is the recommended standard for veterinary surgical suites: Minimum MERV 16 filtration is specified in ASHRAE 170 for ORs; HEPA-equivalent filtration is used in most well-equipped veterinary facilities.
• Air changes per hour matter, not just filtration: ASHRAE 170 specifies a minimum of 20 total air changes per hour during occupied surgical conditions, with a minimum of 4 outdoor air changes.
• OR traffic is a direct contamination variable: Each door opening disrupts positive pressure and introduces unfiltered corridor air. Every unnecessary entry during an active procedure elevates contamination risk.
• Between-case disinfection must be standardized and documented: Assumptions about cleaning do not prevent SSI. Protocol-driven, documented disinfection between cases does.

OR location and spatial design

Flow design principles

The spatial relationship between the surgical prep area, OR, and recovery area determines how much contamination risk is introduced during patient transport.

Recommended flow pattern:

1. Patient anesthetized and clipped in the prep area
2. Patient transported directly to OR (minimal distance, minimal traffic zone transit)
3. Surgery performed in OR
4. Patient transferred directly to recovery
5. Staff exit and re-entry minimized throughout

DVM360 (2026) describes the design principle: traffic into and out of the OR should be minimized, and the arrangement of zones must allow ease of transportation between the prep area and OR without routing patients through high-traffic clinical corridors.

OR sizing

The OR must accommodate the largest anticipated procedure with full equipment and personnel complement. Undersized ORs force personnel proximity to the sterile field and limit the movement margins that prevent accidental sterile field contact.

Door configuration

Minimizing the number of OR doors reduces entry points for corridor air and contamination. NIH veterinary surgical suite design guidance specifies unidirectional patient flow from prep to OR and limited bidirectional access at the scrub room interface.

The scrub sink should be positioned such that the surgical team can move from scrub to OR without passing through non-surgical areas.

Ventilation and airflow standards

Positive pressure differential

Veterinary ORs should maintain positive pressure relative to all adjacent spaces. The NIH veterinary surgical suite design standard specifies 2.5 Pa positive pressure differential.

Positive pressure means air continuously flows outward from the OR into adjacent corridors. This prevents unfiltered corridor air from entering the OR when doors open.

Loss of positive pressure during active surgery, from HVAC failure, door propping, or excessive simultaneous door openings, allows contaminated corridor air to enter the sterile field zone.

Air changes per hour

ASHRAE Standard 170 (2021) specifies for operating rooms:

The 20 air changes per hour standard ensures rapid dilution and removal of airborne particles, bacteria shed from surgical team skin, and aerosols generated during surgery.

Airflow pattern: turbulent vs. laminar

Most veterinary ORs use turbulent mixed airflow, where supply air enters from ceiling diffusers and return air exits through low wall grilles. This creates a general dilution effect across the room.

Laminar airflow (LAF) systems deliver air in a unidirectional downward pattern over the surgical zone at defined velocities. They were designed to provide ultraclean air directly over the sterile field for implant procedures.

Current evidence on LAF:

A 2023 systematic review and meta-analysis of 10 randomized controlled trials covering over 1 million orthopedic patients found that LAF systems did not significantly reduce SSI rates compared to conventional turbulent ventilation. The pooled odds ratio was 1.70, indicating LAF was associated with higher, not lower, SSI risk in this analysis.

The evidence for LAF in veterinary settings specifically is limited. The safest current position is that well-maintained turbulent ventilation with HEPA filtration and positive pressure is the appropriate standard for veterinary ORs, and LAF installation is not supported by current evidence as a superior alternative.

HVAC maintenance requirements

• Filter inspection and replacement on manufacturer-scheduled intervals
• Positive pressure differential verified periodically
• Duct cleaning per facility maintenance schedule
• Any system service or malfunction requiring OR entry should be followed by reconfirmation of pressure differential before surgical use resumes

For environmental controls critical for implant surgery, including the specific airflow and contamination control requirements that elevate for orthopedic procedures with hardware, that guide covers the implant-specific environmental standards.

OR traffic management

Why traffic matters

Every OR door opening disrupts the positive pressure differential and introduces a pulse of unfiltered corridor air into the sterile environment. Personnel entering the OR shed skin cells and bacteria with every movement. Clothing contact near the sterile field carries contamination risk.

Research in human surgical settings has documented that SSI risk is 3.5 times higher when there are lapses in adherence to aseptic principles, including non-obvious events such as general movement and OR visitors.

Traffic standards

Before the first incision:

• All required supplies confirmed in the OR (eliminates the most common reason for during-surgery door openings)
• Only personnel with an active role in the case present
• OR doors closed; entry by non-essential personnel prevented

During active surgery:

• No additional personnel should enter without clinical necessity
• Any entry should use a single door; the second OR door should remain closed
• Personnel re-entering the OR after any exit should be reminded that OR attire does not substitute for scrub technique

Between cases:

• OR cleaned and disinfected before next case begins
• OR should not be used as a corridor between other clinical areas at any time

Personnel count and SSI risk

Studies in human orthopedic surgery consistently identify higher personnel counts during OR procedures as associated with elevated SSI rates. While direct veterinary data on this relationship is limited, the biological mechanism is identical: more people means more skin shedding, more movement, and more door openings.

For auditing OR standards compliance, including how traffic logs, door-opening counts, and personnel-in-OR records are used in compliance audits, that guide covers the monitoring and measurement of OR behavioral standards.

Surface disinfection protocols

Between-case disinfection

All horizontal surfaces in the OR must be disinfected between cases. This includes:

• OR table and table extensions
• Instrument tables and Mayo stand
• Overhead light handles (if touched by non-sterile personnel between cases)
• IV poles and any equipment that was contacted during the previous case
• Floors (mopped, not just swept)

Agent selection: A hospital-grade disinfectant with documented efficacy against veterinary-relevant pathogens, including Staphylococcus pseudintermedius and Clostridium spores for higher-contamination cases. Contact time must be observed; surfaces wiped and immediately dried have not received the agent's full disinfectant benefit.

Documentation: Between-case disinfection should be documented. Without documentation, there is no verifiable confirmation that cleaning occurred.

End-of-day terminal cleaning

Terminal cleaning at the end of the surgical day is more thorough than between-case cleaning:

• All horizontal and vertical surfaces
• Walls to approximately shoulder height
• Floor, including under equipment
• Inside of overhead light housing
• All equipment surfaces including monitor screens, cables, and IV poles

OR re-entry after contamination events

If a case produces significant biological contamination (abscess drainage, open GI work, or a dirty wound), terminal cleaning should follow rather than standard between-case cleaning before the next case.

For environmental controls within OR standards, including the specific airflow mechanisms, contamination dynamics, and the broader environmental asepsis framework that complements surface disinfection, that guide covers the environmental domain in full.

OR attire and behavioral standards

Scrub attire in the OR

All personnel present in the OR during active surgery should wear appropriate surgical attire:

• Scrub top and trousers (freshly laundered, not worn outside the facility)
• Surgical cap covering all hair
• Surgical mask covering nose and mouth
• Shoe covers if required by facility protocol

Non-scrubbed personnel (circulating nurses, anesthesiologists) maintain clean but not sterile status. They must not contact the sterile field.

Talking and mask discipline

Exhaled droplets contain bacteria. Masks significantly reduce but do not eliminate droplet dispersal. Unnecessary conversation during surgery, particularly when facing the sterile field without mask coverage, increases airborne contamination at the wound site.

Behavioral standards for OR attire and mask use should be included in staff training and reinforced during audits.

For the checklist aligned with OR standards, including the pre-incision time-out, OR preparation verification, and between-case documentation steps that operationalize these OR standards, that guide provides the structured verification tool.

SSI surveillance as an OR standard

Ongoing SSI surveillance is part of OR asepsis standards, not a separate activity. Tracking post-operative infection rates by case type, surgeon, and time period allows identification of:

• Increases in SSI rate that signal a breakdown in OR asepsis
• Clusters of SSI associated with a specific procedure, personnel, or time window
• Baseline rates for comparison after protocol changes

The AVMA Journal (2026) SSI definitions consensus notes that implementation of surveillance programs produces a "surveillance effect": the act of tracking SSI rates itself increases team compliance with asepsis protocols.

For aseptic technique that OR standards mandate, including the intraoperative technique standards that OR environmental standards are designed to support, that guide covers the technical component of what OR infrastructure protects.

Frequently asked questions

Does a veterinary clinic need a dedicated OR, or can procedures be performed in a general treatment area?

Elective and complex surgical procedures should be performed in a dedicated surgical suite with appropriate environmental controls. General treatment areas lack the traffic control, air handling, and surface disinfection protocols required to maintain the surgical asepsis standard. For minor procedures in lower-risk patients, a clean procedure room may be appropriate. For orthopedic, implant, and abdominal procedures, a dedicated OR is the standard of care.

How do we know if our OR is maintaining positive pressure?

A simple smoke test at the door threshold during and after door opening can demonstrate air movement direction. More precisely, a manometer measures the pressure differential between the OR and adjacent corridor. Confirming positive pressure at the time of HVAC installation and after any system modification is the minimum requirement.

Should we use laminar airflow in our veterinary OR?

Based on current evidence, turbulent mixed ventilation with HEPA filtration and maintained positive pressure differential is the appropriate standard for most veterinary ORs. The evidence that laminar airflow reduces SSI in orthopedic procedures is not supported by the most current meta-analytic data. Well-maintained turbulent HEPA-filtered ventilation represents current best practice.

How frequently should OR surface swabs be taken for environmental monitoring?

Quarterly is a reasonable baseline for active surgical practices. More frequent sampling is warranted after any SSI cluster, after facility renovation or construction near the OR, or after any HVAC system service. Surface swabs identify colonization patterns and can detect environmental contamination before it translates to clinical infection.

The OR is a system, not just a room. Its asepsis standard depends on design decisions made before the first patient arrived, maintenance decisions made between cases, behavioral decisions made during procedures, and surveillance decisions made after procedures. Every one of these components contributes to the SSI rate. None of them alone is sufficient.

Resources

The following sources were used as reference and background for this article:

• DVM360. A veterinary surgeon's take on designing an operating room. dvm360.com
• NIH Office of Research Facilities. Veterinary Surgical Suites, Part II. orf.od.nih.gov
• MEP Academy. How Operating Room HVAC Systems Work. mepacademy.com
• NIH/PMC. Laminar airflow ventilation systems in orthopaedic operating rooms do not prevent SSI. ncbi.nlm.nih.gov
• AdeoPets. How to Equip a Veterinary Surgery Suite. adeopets.com
• ASHRAE Standard 170 (2021). Referenced via envigilance.com

Environmental contamination is a distinct and often underappreciated SSI pathway. Even when surgical technique is flawless and instruments are sterile, an inadequately controlled OR environment can introduce bacteria into the operative field through airborne routes.

Understanding the mechanisms of environmental contamination allows veterinary surgical teams to design and maintain ORs that work with technique rather than against it.

What this covers: The mechanisms of environmental contamination in the veterinary OR, the airflow standards that mitigate them, and the practical protocols for surface disinfection, traffic management, and environmental monitoring.Scope: Applies to the OR environment itself: the air, surfaces, and behavioral factors outside the sterile field that influence contamination at the surgical site.Key distinction from technique: Technique errors contaminate the sterile field through direct contact. Environmental contamination acts through indirect routes: airborne particles, surface residue, and disrupted pressure differentials. Both pathways matter; both require active management.Evidence note: Research in human surgical settings consistently links OR traffic density, door-opening frequency, and personnel movement to elevated airborne bacterial counts. The biological mechanisms are species-independent and apply equally in veterinary ORs.

Key takeaways

• Human skin shedding is the dominant source of OR airborne contamination: Each person in the OR continuously sheds skin particles, many carrying bacteria. This is why personnel count and movement are direct contamination variables.
• Door openings disrupt positive pressure and introduce corridor air: Each door opening during active surgery introduces a pulse of unfiltered air from adjacent non-sterile areas.
• Air changes per hour determine how quickly contamination is removed: Rooms with fewer air changes per hour accumulate airborne bacteria faster than rooms with high air exchange rates.
• Surfaces are a secondary contamination reservoir between cases: Inadequate between-case disinfection allows bacteria from one case to colonize surfaces the next surgical team contacts.
• Environmental monitoring provides objective data rather than assumptions: Surface swabs and periodic air sampling confirm whether environmental controls are working.
• Temperature and humidity affect microbial survival: Controlled temperature and humidity reduce the viability of airborne bacteria and support antiseptic agent performance.

Sources of environmental contamination in the OR

1. Personnel skin shedding

The surgical team is the largest source of airborne contamination in the OR during active procedures.

Human skin continuously sheds squames (skin cells), and these squames frequently carry bacteria from the skin surface, including Staphylococcus aureus, coagulase-negative staphylococci, and Staphylococcus pseudintermedius in veterinary settings.

Factors that increase shedding rate:

• Movement: walking, reaching, and turning generate substantially more particles than standing still
• Talking without a mask: exhaled droplets directly contaminate the air over the sterile field
• Number of personnel: each additional person in the OR adds to the total shedding load

2. OR door openings

Each time an OR door opens:

• The positive pressure differential is momentarily disrupted
• A volume of unfiltered corridor air enters the OR
• Bacteria-laden air from adjacent clinical areas mixes with the filtered OR air

Research in human surgical settings demonstrates that OR door-opening frequency during active surgery correlates with elevated airborne bacterial counts. CDC and JCAHO guidelines in human healthcare explicitly address traffic pattern management in the surgical suite on this basis.

3. Patient-origin contamination

The patient's own microbiome contributes to OR contamination:

• Skin bacteria not eliminated during antiseptic prep remain viable on the prepared site
• During surgery, blood and tissue fluids can aerosolize with electrosurgery or powered instruments
• Patients with pre-existing skin infections or MRSP colonization carry higher contamination loads

4. Equipment and surface residue

Inadequately cleaned surfaces between cases can harbor bacteria from the previous procedure. Contact between personnel or instruments and these surfaces can reintroduce bacteria into the next sterile field.

Equipment that frequently harbors residual contamination if not specifically cleaned:

• Overhead surgical light handles
• IV pole surfaces
• Cable insulation and suction tube exteriors
• OR table adjustment mechanisms

Airflow: the primary environmental control

How OR ventilation works

OR ventilation systems serve two functions simultaneously:

1. Dilution: Introducing fresh filtered air to dilute and remove airborne particles
2. Pressure management: Maintaining positive pressure differential to prevent unfiltered air from entering

Both functions depend on air changes per hour (ACH): the number of times per hour the total room air volume is replaced.

ASHRAE Standard 170 (2021) specifies a minimum of 20 total ACH during occupied surgical conditions, with a minimum of 4 outdoor air changes. This rate ensures that contamination introduced by personnel activity or door openings is continuously diluted and removed.

The role of HEPA filtration

HEPA filtration captures particles at 99.97% efficiency for particles 0.3 microns and larger. Bacteria range from approximately 0.5 to 5 microns in diameter.

HEPA filtration ensures that recirculated air returns to the OR at a contamination level below the threshold for clinical significance.

HEPA filtration requirements for veterinary ORs:

• Primary air supply must pass through HEPA filtration
• Filter maintenance must follow manufacturer intervals; clogged filters reduce efficiency and airflow rate
• Return air grilles must be positioned to maximize airflow across the entire OR rather than short-circuiting from supply to return

Positive pressure: mechanism and maintenance

Positive pressure in the OR means the air pressure inside the room exceeds adjacent spaces by a defined differential. This continuous outward airflow prevents corridor air from entering the OR when doors open or seal integrity is imperfect.

NIH veterinary surgical suite guidance: 2.5 Pa positive pressure relative to adjacent spaces.

Conditions that compromise positive pressure:

• Propped OR doors during surgery
• Simultaneous opening of multiple doors
• HVAC system malfunction or filter clogging reducing airflow rate
• Construction or renovation creating gaps in the OR envelope

Temperature and humidity control

Extremely low humidity also increases electrostatic activity, which attracts particles to surfaces and personnel.

Traffic management as environmental control

The contamination arithmetic

Every person in the OR is a contamination source. Every door opening is a contamination event. The relationship is cumulative, not linear.

A procedure with 3 personnel and 2 door openings produces a fundamentally different contamination environment than the same procedure with 7 personnel and 12 door openings, even if individual technique is identical.

Traffic protocol standards

Pre-procedure supply confirmation:

Confirming all required supplies are in the OR before the first incision is the most effective single intervention for reducing during-surgery door openings. Door openings during surgery most commonly occur to retrieve forgotten items.

Personnel limit:

Only personnel with an active procedural role should be present during surgery. Observers without an active role and non-essential staff should not be in the OR during active surgery.

Door discipline:

When entry is necessary during active surgery, it should occur through a single door and be performed quickly with minimum door-open duration. The door should never be propped open during a procedure.

For OR standards that include environmental controls, including the physical infrastructure, traffic management policies, and between-case disinfection standards that implement environmental asepsis at the facility level, that guide covers the full OR standards framework.

Surface disinfection: the environmental reset between cases

What surfaces harbor bacteria

After any surgical case, the following surfaces should be considered contaminated and must be disinfected before the next case:

• OR table surface and edges
• Instrument tables and Mayo stand
• Any equipment or surface contacted by non-sterile personnel during the case
• Floor within the OR
• Overhead light handles if adjusted by ungloved personnel

Disinfection agent requirements

The disinfectant must:

• Have documented bactericidal activity against Staphylococcus species (including MRSP-equivalent strains)
• Be approved for use on the specific surface material being cleaned
• Have an observed contact time (surface must remain visibly wet for the specified duration)

Wiping a surface and immediately drying it defeats the disinfectant's mechanism. Contact time is non-negotiable.

Between-case vs. terminal cleaning

Between-case cleaning targets horizontal surfaces, the OR table, and floor. It resets surface contamination level before the next case.

Terminal cleaning (end of surgical day) includes all horizontal and vertical surfaces, walls, equipment exteriors, light housings, cable surfaces, and floor. It is more thorough and longer in duration.

After cases involving significant biological contamination (abscess drainage, contaminated wounds, open GI work), terminal cleaning standards should be applied before the next surgical case.

For environmental breaks in asepsis, including the specific break categories that arise from environmental failures and how to respond to each, that guide covers the break taxonomy for the environmental domain.

Environmental monitoring

Why monitoring matters

Environmental asepsis is frequently managed by assumption: the assumption that the HVAC system is running correctly, that cleaning was performed correctly, and that surface contamination is within acceptable limits. Environmental monitoring replaces assumption with data.

Monitoring methods

Surface swabs:

Swabs of high-contact surfaces taken after cleaning and before the first case of the day provide a baseline contamination measure. Periodic sampling (quarterly baseline; more frequent after any SSI cluster) detects trends before they manifest as clinical infections.

Air sampling:

Settle plates (open Petri dishes exposed during surgery) provide a simple measure of airborne particle deposition. Volumetric air samplers provide colony-forming unit counts per cubic meter and baseline reference data.

Positive pressure verification:

Simple smoke pencil testing at door thresholds during occupied conditions confirms pressure direction. Manometer measurement provides precise differential data.

Acting on monitoring data

Monitoring data is only useful if it triggers a response when findings exceed threshold. Clinics should define what surface contamination levels constitute acceptable versus requiring investigation, and what that investigation entails.

Environmental monitoring data should feed directly into the broader surgical asepsis quality system. The connection between OR environmental performance and surgical outcomes is what makes monitoring clinically meaningful rather than a bureaucratic exercise.

For the surgical asepsis that depends on environment, including how the five domains of surgical asepsis integrate and how environmental controls relate to patient preparation, instrument sterilization, and intraoperative technique, that guide covers the full surgical asepsis framework.

The environmental standard requirements are not uniform across procedure types. Orthopedic and implant procedures create a substantially more demanding environmental asepsis context, because contamination that might not cause SSI in a soft tissue procedure can directly cause implant failure in an orthopedic one.

For environmental control critical for implant surgery, including the elevated environmental asepsis requirements for procedures involving orthopedic hardware where a single contamination event can lead to implant failure, that guide covers the implant-specific environmental demands.

Frequently asked questions

How much does OR personnel count actually affect SSI rate?

Human surgical data consistently demonstrates that higher intraoperative personnel counts correlate with elevated SSI rates, primarily through the airborne contamination mechanism. While direct veterinary data is limited, the mechanism is biologically identical. Every additional non-essential person in the OR during surgery represents a quantifiable contamination risk.

Can we use a portable air purifier in the OR instead of a dedicated HVAC system?

Portable HEPA recirculators can supplement room air filtration but are not equivalent to a properly designed HVAC system. They do not provide positive pressure relative to adjacent spaces, do not deliver the required air changes per hour, and do not provide the directional airflow pattern that protects the sterile field. For dedicated surgical suites, a properly designed HVAC system is the required standard.

How often should OR HVAC filters be changed?

Per manufacturer specifications. As general guidance, pre-filters in high-use veterinary ORs typically require inspection monthly and replacement every 3 months. HEPA filters have longer service intervals but should be replaced on schedule regardless of appearance. Filter replacement schedules should be part of the facility maintenance log and reviewed during compliance audits.

Does keeping the OR cold help prevent infection?

Lower temperatures within the acceptable OR range (68 to 75 degrees F) reduce some aspects of microbial activity. However, patient hypothermia is itself a significant SSI risk factor. Patient warming during surgery should be maintained to prevent hypothermia-related immune suppression, which is a more significant SSI risk than the modest contamination reduction from cooler OR temperatures.

Environmental asepsis is the component of infection control that operates before the first instrument is touched and continues after the final suture is placed. The surgical team that understands airflow mechanics, controls OR traffic deliberately, monitors surface disinfection systematically, and verifies environmental conditions rather than assuming them is the team that gives its technique the environmental foundation it requires.

Resources

The following sources were used as reference and background for this article:

• MEP Academy. How Operating Room HVAC Systems Work. mepacademy.com
• NIH Office of Research Facilities. Veterinary Surgical Suites, Part II. orf.od.nih.gov
• ASHRAE Standard 170 (2021). Referenced via envigilance.com
• NIH/PMC. Laminar airflow ventilation systems in orthopaedic operating rooms: systematic review and meta-analysis. ncbi.nlm.nih.gov
• APSF. Recommendations for OR Ventilation. apsf.org
• Veterinary Practice. Infection control in the surgical environment. veterinary-practice.com

Orthopedic surgery in dogs carries higher SSI rates than most other surgical categories. The combination of complex anatomy, prolonged procedure times, tissue trauma from bone work, and the frequent use of implants creates a surgical environment where asepsis must be applied with particular rigor.

What this covers: The asepsis protocol for orthopedic surgery in dogs, including pre-operative preparation, intraoperative standards, and post-operative wound management. Both implant and non-implant orthopedic procedures are addressed, with specific attention to where requirements differ.Evidence base: TPLO SSI retrospective cohorts; veterinary orthopedic surgical site infection incidence data; intraoperative bacterial contamination survey (Vet Surg, Andrade et al., 2016); MRSP colonization as SSI risk factor.SSI rate context: SSI rates in veterinary orthopedic surgery range from approximately 3% to 18%, with the highest rates in procedures involving implants and joints (TPLO: 0.8 to 14.3%; arthrodesis: up to 25%). These rates are substantially higher than for clean soft tissue procedures (1 to 5%).

Key takeaways

• Orthopedic SSI rates are higher than soft tissue SSI rates across all procedure types.
• MRSP colonization is a documented significant risk factor for orthopedic SSI.
• Prolonged procedure time increases SSI risk; minimize through efficient technique.
• Bone work (saw, drill) generates aerosolized contamination near the sterile field.
• Implant procedures require enhanced asepsis; non-implant procedures meet standard.
• Intraoperative lavage is standard for all orthopedic procedures before closure.

Why orthopedic surgery carries elevated SSI risk

Several procedure-specific factors elevate SSI risk for canine orthopedic surgery beyond the baseline for clean soft tissue procedures:

1. Prolonged procedure time

Longer procedures increase SSI risk through cumulative contamination exposure, personnel fatigue leading to technique lapses, and extended anesthesia duration which may impair immune function. SSI risk increases with each additional hour of surgical time.

2. Bone and soft tissue trauma

Oscillating saws, drills, and osteotomes create significant local tissue trauma. Devitalized tissue is more susceptible to bacterial colonization. Thermal damage from bone cutting can further reduce local tissue viability and host defense.

3. Periosteal and soft tissue dissection

Extensive tissue dissection creates dead space. Blood and tissue fluid accumulation in dead space provides a culture medium for bacteria. Minimizing dead space through careful tissue handling and closure is part of the aseptic technique in orthopedic surgery.

4. Implant presence

When metal implants are used, the minimum infective dose required to establish infection drops dramatically. Implants provide an abiotic surface for biofilm formation that bypasses host immune defense. This is why implant procedures require a higher asepsis standard than non-implant procedures.

5. MRSP colonization

S. pseudintermedius, including MRSP strains, is commensal on canine skin and the most common cause of orthopedic SSI. MRSP colonization of the patient is a documented independent risk factor for SSI (OR 9.0 in one orthopedic cohort study).

Pre-operative asepsis: orthopedic-specific requirements

Patient preparation

Clipping:

Clip immediately before surgery. Clip margins should be generous: for extremity procedures, clip from the body wall to the distal limb. For stifle procedures (TPLO, cruciate repair), this typically means the entire limb from the groin to the paw.

A study by Andrade et al. (Vet Surg, 2016) surveyed intraoperative bacterial contamination in dogs undergoing elective orthopedic surgery, confirming that contamination is common and multifactorial. Generous clip margins reduce the zone of potential surface contamination adjacent to the incision.

Skin antisepsis:

Minimum three-pass centrifugal scrub with CHG-alcohol or PVI-alcohol combination. For limb procedures, the scrub extends to the entire clipped area.

Limb hanging:

After skin antisepsis, the limb is suspended (hung) for sterile draping to allow circumferential draping. The hanging apparatus should not contaminate the prepped site. The foot is typically covered with a sterile cohesive bandage or towel before suspension to reduce contamination from paw surfaces.

Pre-operative MRSP consideration:

For high-risk patients (previous MRSP positive culture, recent antimicrobial treatment, chronic skin disease, prior SSI at same site), pre-operative MRSP screening allows scheduling adjustments, decolonization where protocols exist, and enhanced intraoperative asepsis.

Surgical team preparation

Standard surgical hand antisepsis applies. Double gloving is recommended for all implant orthopedic procedures.

Orthopedic instrument sets:

Confirm all instruments are sterile before case start. Orthopedic instrument sets are often complex with many components; each must have chemical indicator confirmation and pack integrity verification before being opened onto the sterile field.

Intraoperative asepsis: orthopedic-specific requirements

Sterile field management

Draping for limb procedures:

Circumferential draping of the limb is standard for most extremity orthopedic procedures. This requires:

• Limb hanging in a sterile loop or stockinette suspended from an IV stand
• Initial circumferential draping with impervious drape material
• Sterile stockinette or cohesive bandage over the distal limb
• Final draping to isolate the surgical site within the sterile field

Once placed, drapes must not be repositioned. Any draped area contaminated during patient positioning must have a new sterile drape applied.

Powered instrument management:

Oscillating saws and drills generate bone and tissue debris that contaminates the surrounding sterile field. Management strategies:

• Use irrigation during bone cutting to reduce heat generation and debris dispersion
• Use sterile drapes positioned to capture contaminated material where possible
• Surgical team members not directly holding the powered instrument should step back during cutting to reduce contamination exposure

Implant insertion:

The moment of implant insertion into bone is the highest-risk moment for contamination in orthopedic surgery. The implant transitions from the sterile field into the bone canal, and any contamination of the implant surface at this moment cannot be subsequently corrected.

Implant handling standards:

• Grasped only with sterile instruments, never bare gloved hands unless using sterile technique
• Not resting on any surface below sterile field level
• Not touched by non-sterile personnel or instruments at any point

OR traffic:

Enforce strict traffic control throughout. Orthopedic procedures are often long (1 to 3+ hours). The temptation to allow additional personnel entry during extended procedures must be resisted. Each entry increases airborne contamination cumulatively across the procedure duration.

For aseptic technique applied during orthopedic procedures, including the sterile field rules, instrument handling, and personnel behavior standards that govern the intraoperative phase of all surgical procedures, that guide covers the intraoperative technique framework.

Intraoperative lavage

Wound lavage before closure is standard for all orthopedic procedures, both implant and non-implant.

Saline lavage:

Copious pulsatile or syringe-pressure saline irrigation removes:

• Loose bone fragments (sequestra)
• Blood clots and debris that would otherwise remain in dead space
• Free-floating bacteria that accumulated during surgery

Volume: typically 500 mL to 1 L for a single joint procedure; more for larger procedures.

Antiseptic lavage:

For higher-risk procedures (implant placement, MRSP-positive patient, prolonged procedure), antiseptic lavage before closure addresses residual bacterial contamination that saline alone cannot eliminate. Non-antibiotic antiseptic lavage options targeting biofilm-forming organisms have been used in veterinary orthopedic settings to reduce bacteria, biofilm, and resistant organisms before suturing.

This is a non-antibiotic contamination control step aligned with antimicrobial stewardship principles.

For asepsis requirements when implants are involved, including the enhanced asepsis protocol and the clinical rationale for each enhancement in the context of implant-associated infection risk, that guide covers implant-specific asepsis.

Procedure-specific asepsis notes

TPLO (tibial plateau leveling osteotomy)

TPLO is the highest-volume and highest-SSI-rate procedure in veterinary small animal orthopedic surgery. Key asepsis considerations:

• Entire limb prep from groin to paw
• Prolonged procedure time warrants strict OR traffic management
• Bone work with oscillating saw generates significant local contamination
• MRSP risk is the primary driver of treatment-resistant SSI in TPLO patients
• Implant presence (plate and screws) elevates the consequence of any contamination event

For TPLO-specific asepsis protocols, including the procedure-specific application of enhanced orthopedic asepsis to TPLO, that guide covers TPLO asepsis in detail.

Fracture stabilization

Trauma patients presenting for fracture repair often have wound contamination from the injury. Wound classification should be assessed before surgery:

• Closed fracture: generally Class I (clean); standard asepsis applies
• Open fracture: Class III (contaminated) or higher; enhanced protocols apply; antimicrobial therapy (not prophylaxis) indicated

Arthroscopy

Arthroscopic procedures have lower SSI rates than open orthopedic procedures. However, fluid distension media must be sterile, instruments must be sterile (high-level disinfection is not sufficient for instruments entering joint space), and skin antisepsis applies to all portal sites.

Joint replacement

Where performed, hip and elbow total joint replacement represents the highest-consequence orthopedic implant procedure. Full implant asepsis protocol, MRSP screening, and antiseptic lavage are all indicated.

For asepsis standards applied to orthopedic cases, including the five-domain surgical asepsis framework and how it applies across the full range of surgical procedures, that guide covers the broader surgical asepsis standard.

Post-operative wound management

Wound monitoring is more intensive after orthopedic surgery than after routine soft tissue procedures, reflecting the higher SSI rate and the greater treatment difficulty when infection does occur.

Monitoring schedule:

• Wound check at 48 to 72 hours post-operatively
• Suture/staple removal at 14 days
• Follow-up radiographs at defined intervals for bone healing assessment

What to monitor:

• Incision: redness, swelling, discharge, dehiscence
• Systemic signs: fever, lethargy, reduced appetite
• Limb use: sudden worsening of weight-bearing may indicate deep SSI

Early SSI (within 30 days): typically reflects intraoperative contamination.Late SSI (30 days to 12 months): may reflect biofilm maturation, licking-related contamination, or hematogenous seeding.

Any suspicion of SSI in an orthopedic patient warrants prompt veterinary assessment, bacterial culture, and sensitivity testing before antibiotic selection.

For breaks in asepsis during orthopedic procedures, including the specific break categories that are most common and consequential in orthopedic settings, that guide covers the break identification and response framework.

Frequently asked questions

Do all canine orthopedic procedures require implants?

No. Many orthopedic procedures are performed without permanent implants: cruciate ligament extracapsular repair, femoral head and neck excision, arthrotomy for joint exploration or fragment removal. Non-implant procedures carry lower SSI risk and do not require all of the implant-specific enhancements. They still require the full standard orthopedic asepsis protocol described above.

How does procedure duration affect SSI risk?

Longer procedures accumulate more contamination events, increase OR traffic needs, and may involve personnel fatigue affecting technique compliance. SSI risk increases measurably with each additional hour of surgical time. Efficient surgical technique that minimizes unnecessary tissue handling and procedure duration is itself an asepsis-related quality variable.

Is post-operative antimicrobial prophylaxis required for orthopedic procedures?

Current evidence and stewardship guidelines in both human and veterinary medicine recommend limiting prophylaxis to the perioperative period (within 60 minutes of incision; discontinued within 24 hours). Extended post-operative antimicrobial courses do not reduce SSI rates and contribute to resistance development. The goal is optimizing intraoperative asepsis and prophylaxis timing, not extending post-operative antibiotic coverage.

Orthopedic surgery in dogs demands asepsis that accounts for longer procedures, more tissue trauma, the specific risks of implants and biofilm, and the prevalence of MRSP as the dominant SSI pathogen. None of these factors are addressed by antibiotics alone. All of them are addressed by rigorous asepsis applied across every phase of the perioperative period.

Resources

The following sources were used as reference and background for this article:

• NIH/PMC. Surgical site infection after 769 Tibial Plateau Leveling Osteotomies. pmc.ncbi.nlm.nih.gov
• DVM360. Improving Infection Rates After TPLO. dvm360.com
• Veterinary Practice News. Old and New Thoughts on Infection Control. veterinarypracticenews.com
• Wiley Online Library. Surgeon and Patient Preparation to Minimize Surgical Site Complications in CCL Surgery. onlinelibrary.wiley.com
• Springer Nature. Antimicrobial prophylaxis is sufficient for acceptable SSI rate in clean orthopaedic and neurosurgeries in dogs. link.springer.com

Instrument sterilization is the most consequential single process in veterinary surgical infection control. A contaminated instrument delivers bacteria directly into deep tissue, bypassing the skin barrier entirely.

Getting this step right requires a complete protocol: from cleaning through packaging, sterilization cycle selection, validation, and storage. Failure at any point in this chain produces an instrument that is not sterile, regardless of how well every other step was performed.

What this covers: The complete instrument sterilization protocol for veterinary clinics, from post-use cleaning through validated sterilization, packaging, storage, and shelf-life management.Scope: Applies to all surgical and invasive instruments in small animal veterinary practice. Some elements (HLD protocols) apply to semi-critical items such as endoscopes that cannot be autoclaved.Evidence base: Research Animal Care and Safety shelf-life standards; Wayne State IACUC autoclave monitoring and sterile pack storage standards; VetSurgeryOnline sterilization packaging standards; Veterinary Teaching Hospital Naples shelf-life comparative study (PMC12197567).Critical principle: Sterilization failure is not always visible. A pack that passed all chemical indicators may still have failed to achieve sterility if cycle parameters were not met. Biological indicator testing is the only confirmation of functional sterilization efficacy.

Key takeaways

• Cleaning must precede sterilization: Bioburden (blood, tissue, protein residue) on an instrument surface protects bacteria from sterilizing agents. An unclean instrument cannot be reliably sterilized.
• Pack integrity must be confirmed before use: Every pack should be inspected for tears, moisture, seal failure, and expired sterilization date before being opened onto the sterile field.
• Chemical indicators confirm exposure; biological indicators confirm sterility: These are not interchangeable functions. Biological indicator (spore test) results are the only confirmation that an autoclave cycle achieved functional sterility.
• Biological indicators should be run weekly: In active veterinary surgical practices, weekly spore testing is the minimum. Any failed test requires immediate removal of all potentially affected packs from use.
• Sterility is event-related, not only time-related: Current evidence supports the concept that a sterile pack remains sterile until an event compromises it (moisture, tear, seal failure). However, maximum shelf-life limits based on packaging type provide a practical safety boundary.
• Overloading the autoclave is a common sterilization failure cause: Poor steam penetration from excessive pack density results in incomplete sterilization of items at the center of the load.

Phase 1: Post-use instrument cleaning

Cleaning is not optional and cannot be skipped in favor of sterilization. Bioburden on instrument surfaces shields bacteria from sterilizing agents, reducing efficacy regardless of autoclave cycle duration or temperature.

Manual cleaning

1. Rinse instruments immediately after use with tepid water to prevent blood and tissue from drying
2. Open hinged instruments (scissors, forceps) fully during cleaning
3. Use a soft brush and enzymatic detergent to clean all surfaces, joints, and box locks
4. Pay particular attention to serrations, grooves, and lumens (hollow instruments)
5. Rinse thoroughly with water after detergent cleaning
6. Inspect for residual debris under magnification if needed

Enzymatic detergents: Preferred over general detergents because they break down protein, fat, and carbohydrate bioburden. Follow manufacturer concentration and contact time instructions.

Ultrasonic cleaning

Ultrasonic cleaners use cavitation (pressure waves in liquid) to remove debris from surfaces and crevices that brushes cannot reach effectively.

• Fill with appropriate enzymatic cleaning solution at correct concentration
• Load instruments so they are fully submerged and not touching each other
• Run appropriate cycle (typically 5 to 15 minutes)
• Rinse thoroughly after ultrasonic cleaning
• Do not use ultrasonic cleaning for instruments with rubber components, cemented parts, or chromium plating if manufacturer contraindicates

Ultrasonic cleaning is particularly valuable for complex instruments (needle holders, tissue forceps with intricate box locks) where manual cleaning leaves residual debris.

Inspection after cleaning

After cleaning, inspect each instrument for:

• Visible debris (failure requiring recleaning)
• Corrosion or pitting (indicates instrument deterioration; may compromise sterilization efficacy)
• Functional integrity (scissors cutting, forceps closing correctly, box locks functioning)
• Alignment (jaws meeting evenly in forceps)

Damaged instruments should be removed from service. Corrosion can harbor bacteria in surface irregularities that cleaning and sterilization cannot fully address.

Phase 2: Packaging

Packaging maintains sterility from the autoclave to the moment of use. The packaging material must allow sterilizing agent penetration during the cycle while maintaining a microbial barrier afterward.

Packaging options

Event-related sterility (current standard): A 2024 veterinary hospital shelf-life study (PMC12197567) at the Veterinary Teaching Hospital of Naples confirmed that sterility is primarily event-related rather than strictly time-related: packs remain sterile until an event compromises the packaging (moisture exposure, tear, loss of seal integrity, handling damage).

Practical policy: Despite event-related sterility evidence, maximum shelf-life limits based on packaging type (cloth: 6 months; peel packs: 1 year in controlled storage) provide a safety boundary for quality assurance purposes. Expired packs should be re-sterilized before use.

Labeling

Every pack must be labeled before sterilization:

• Contents
• Sterilization date
• Clinician or technician initials (optional but supports accountability)
• Expiry date based on packaging type

Pack density and loading

This is one of the most common sterilization failure points in veterinary practice.

• Packs must be arranged to allow steam circulation between them
• Do not pack the autoclave chamber tightly; leave visible space between packs
• Heavier items on the bottom, lighter on top
• Porous items (textiles) at the top; metal instruments below
• Open hinged instruments during sterilization to allow steam penetration into joints

Phase 3: Sterilization method selection

Steam sterilization (autoclave): primary method

Indications: Metal instruments, textiles, most reusable surgical supplies. Unsuitable for heat-sensitive items.

Parameters:

Most common autoclave errors:

• Overloading (poor steam penetration)
• Packs wrapped too tightly (steam cannot penetrate)
• Instruments not opened during sterilization
• Water reservoir empty or using non-distilled water (mineral buildup on instruments)
• Failure to allow adequate drying time before removing packs (wet packs lose sterile barrier function)

Chemical sterilization (liquid sterilants)

Indications: Heat-sensitive instruments that cannot be autoclaved (flexible endoscopes, fiber-optic cables, some cameras).

• Glutaraldehyde 2%: 6 to 10 hours for sterilization (versus 20 to 30 minutes for HLD)
• 7.5% hydrogen peroxide: 6 hours at 20°C
• Items must be fully immersed, rinsed thoroughly after processing, and used immediately or transferred to the sterile field aseptically

Dry heat and ethylene oxide

Dry heat: appropriate for oils, powders, and instruments that corrode with moisture. Long cycle times (60 to 120 minutes at 160 to 170°C).

Ethylene oxide (EtO): for complex heat-sensitive devices. Requires specialized equipment and mandatory aeration period (12 to 24 hours). Not routinely available in most general veterinary practices.

For autoclave validation, including biological indicator protocols, mechanical monitoring standards, and what to do when a validation cycle fails, that guide covers the autoclave monitoring process in full.

Phase 4: Sterilization validation

Three-level monitoring system

Level 1: Mechanical indicators:

Temperature, pressure, and time readouts from the autoclave cycle. Modern autoclaves print cycle records automatically. File all records; review periodically.

Mechanical monitoring confirms the autoclave ran a cycle. It does not confirm the cycle achieved sterility.

Level 2: Chemical indicators:

• External indicators (Class 1): on the outside of packs; confirm the pack was in the autoclave
• Internal indicators (Class 4 to 6): inside the pack; confirm the sterilizing agent penetrated the pack interior
• Class 5 and 6 integrating indicators: most closely approximate a sterility confirmation

Chemical indicators confirm exposure to sterilization conditions. They do not confirm that sufficient conditions were met for actual microbial kill.

Level 3: Biological indicators (spore tests):

Contain Geobacillus stearothermophilus spores (the most heat-resistant relevant organism). If the autoclave cycle kills these spores, it confirms the cycle achieved the required sterility standard.

Biological indicators are the only method that confirms functional sterilization efficacy.

Frequency: Weekly minimum for active veterinary surgical practices; after any autoclave service or malfunction; after any cycle where parameters were outside normal range.

For sterilization vs. asepsis distinction, including how instrument sterilization relates to the aseptic technique that preserves sterility after the pack is opened, that guide covers the broader relationship between sterilization and asepsis.

Phase 5: Storage

Sterilized packs must be stored in conditions that protect packaging integrity.

Storage requirements:

• Clean, dry, enclosed storage area (closed cabinets preferred over open shelves)
• Protected from moisture: do not store below water pipes, in high-humidity areas, or in locations where water exposure is possible
• Protected from physical damage: do not stack heavy items on peel packs
• First-in, first-out (FIFO) rotation: older packs used before newer ones
• Packs inspected immediately before use: check integrity, seal, moisture, and expiry

Shelf-life standards by packaging type:

These represent maximum limits; any pack whose packaging is compromised before these dates should be treated as non-sterile and re-processed.

Phase 6: Pack inspection and opening

Before any pack is opened onto the sterile field:

1. Confirm chemical indicator has changed (internal indicator visible through pouch or confirmed after opening)
2. Confirm pack integrity (no tears, punctures, moisture, or seal failure)
3. Confirm expiry date has not been exceeded
4. Open using sterile technique: The circulating nurse peels the outer wrapper back without contacting the sterile contents; contents are dropped or transferred to the sterile field without the non-sterile outer packaging touching the sterile surface

Any pack with a failed chemical indicator, compromised integrity, or uncertain sterility status is treated as non-sterile. Do not use; reprocess.

Failed sterilization cycle: response protocol

When a biological indicator test returns positive (indicating the cycle failed to kill spores):

1. Take the autoclave out of service immediately
2. Remove all packs sterilized since the last successful biological indicator from clinical use
3. Do not use instruments from those packs until the autoclave is repaired and re-validated
4. Have the autoclave serviced and repaired
5. Run a new biological indicator test before returning the autoclave to service
6. Flag all cases performed using instruments from potentially non-sterile packs for enhanced post-operative SSI monitoring
7. Document the incident and all corrective actions taken

For how instrument sterilization supports surgical asepsis, including how sterilized instruments are then managed through the aseptic technique chain to maintain sterility through wound closure, that guide covers the downstream asepsis steps.

Frequently asked questions

Can I re-sterilize an instrument that was opened but not used?

Yes, provided the instrument was not contaminated. If the instrument was opened onto a sterile field but not used and not contaminated, it should be reprocessed (cleaned, packaged, and re-sterilized) before the next use. The sterilization status of an opened pack cannot be assumed unless the instrument's cleanliness can be confirmed.

How do I know if the autoclave is working correctly between biological indicator tests?

Mechanical monitoring (cycle records showing correct temperature, pressure, and time) and chemical indicators inside packs provide interim monitoring. However, these do not confirm sterility. If there is any reason to suspect autoclave performance (unusual cycle times, abnormal pressure or temperature readings, unusual steam release), run a biological indicator test before continuing use.

Is it safe to use flash sterilization (unwrapped steam sterilization) for instruments needed urgently?

Flash sterilization (now more properly called "immediate-use steam sterilization" or IUSS) produces an unwrapped sterile instrument that must be transferred aseptically and used immediately. It is not a substitute for wrapped sterilization in routine surgical practice because it lacks the packaging sterility barrier and documented shelf life. Its use should be limited to emergency situations where standard sterilization cannot be used, and it should be documented as a deviation from standard protocol.

For quality control measures for sterilization, including how instrument sterilization monitoring fits within the broader quality control framework for veterinary surgical asepsis, that guide covers the quality assurance context.

Instrument sterilization is a chain with no acceptable weak links. Cleaning that leaves bioburden prevents sterilization. Packaging that blocks steam prevents sterilization. Overloading prevents sterilization. Failure to validate means sterilization failure goes undetected. Each link in this chain must hold for the instrument that reaches the surgical wound to be safe.

Resources

The following sources were used as reference and background for this article:

• University of Illinois RACS. Expiration and Shelf-Life Interpretation Standards for Materials Used in Animal Research. animalcare.illinois.edu
• Wayne State IACUC. Autoclave Monitoring and Sterile Pack Storage Standards. research.wayne.edu
• VetSurgeryOnline. Sterilization Packaging. vetsurgeryonline.com
• NIH/PMC. A Shelf-Life Assessment of Sterilized Surgical Instruments at a Veterinary Teaching Hospital. ncbi.nlm.nih.gov
• Today's Veterinary Nurse. Keys to Successful High-Level Disinfection and Sterilization Processes. todaysveterinarynurse.com

Feline soft tissue surgery follows the same asepsis principles as canine soft tissue surgery but requires adjustments at several points. Cats differ physiologically, anatomically, and in their response to certain antiseptic agents. These differences are clinically significant.

What this covers: The perioperative asepsis protocol for soft tissue surgery in cats, including feline-specific patient preparation requirements, antiseptic agent constraints, wound class application to common feline procedures, intraoperative technique, and post-operative wound management.Scope: Applies to all cats undergoing soft tissue surgical procedures, from elective ovariohysterectomy to emergency GI surgery, abscess drainage, and urinary tract procedures.Key feline differences from dogs: Cats are more sensitive to chlorhexidine at high concentrations; cats self-groom and may ingest residual antiseptic post-operatively; feline skin is more delicate than canine skin; stress-related immune suppression is a clinically relevant factor in feline SSI risk.

Key takeaways

• Core asepsis principles are identical to canine; the adjustments are agent-specific and anatomical.
• CHG is safe for cats at correct dilutions; concentrated CHG on wounds or cavities is not.
• Cats self-groom; any residual antiseptic on accessible skin creates ingestion risk.
• Feline skin is more delicate; clipping pressure must be reduced to prevent abrasions.
• Stress-related immunosuppression in cats can elevate SSI risk; minimize stress pre-operatively.
• Ovariohysterectomy (OHH) is the highest-volume feline soft tissue procedure; asepsis is standard.
• Post-operative wound protection (E-collar) is essential; cats can access more wound locations than dogs.

Feline-specific patient risk factors

In addition to the standard SSI risk factors (wound class, procedure duration, concurrent disease), cats present specific considerations:

Retroviral infection

FIV (feline immunodeficiency virus) and FeLV (feline leukemia virus) cause varying degrees of immunosuppression. Retroviral-positive cats undergoing surgery have potentially impaired wound immune defense.

Pre-operative retroviral status should be known before elective surgery. For retroviral-positive cats, enhanced post-operative monitoring is appropriate, and any elevation in wound class (unplanned contamination) warrants more aggressive management.

Stress and corticosteroid-driven immunosuppression

Cats under stress (hospitalization, handling, fear) produce elevated endogenous corticosteroids. Chronic corticosteroid elevation impairs neutrophil function and wound immune defense.

Minimizing pre-operative stress through:

• Reduced hospitalization time before elective surgery
• Feline-friendly handling protocols
• Anxiolytic pre-medication where appropriate

contributes to SSI prevention through immune function preservation.

Urethral obstruction patients

Male cats presenting for perineal urethrostomy or cystotomy after urethral obstruction have often had urinary catheters in place and may have concurrent urinary tract infection. These patients should be classified as Class II or III depending on urine culture results, and therapeutic antimicrobials rather than prophylaxis may be indicated.

Pre-operative preparation: feline-specific protocol

Clipping

Feline skin is more delicate than canine skin. Clipper pressure must be reduced to prevent abrasions that could compromise skin barrier function.

For ovariohysterectomy:

• Midline approach: clip from mid-sternum to pubis, with lateral extension to include bilateral flank
• Flank approach: clip the relevant flank from last rib to hindlimb; generous dorsal and ventral margins

For other soft tissue procedures:

• Clip area extends minimum 5 cm beyond anticipated incision in all directions
• Use a fine blade appropriate for feline coat
• Immediate pre-operative clipping; do not clip the night before

Skin antisepsis

Agent selection:

Chlorhexidine gluconate (CHG) is appropriate for feline surgical skin antisepsis at the correct concentrations:

• Surgical scrub: 2% CHG in 70% ethyl or isopropyl alcohol
• Final solution: 2% CHG-alcohol combination applied and allowed to dry fully

CHG safety constraints for cats:

• Do not use near ear canals: Ototoxic
• Do not use concentrated CHG on wound or cavity contact surfaces: Tissue toxic at surgical concentrations
• Wound irrigation if needed: 0.05% CHG maximum (1 mL CHG 5% to 99 mL sterile water)
• Post-operative grooming risk: Residual CHG on accessible skin creates ingestion exposure; E-collar use post-operatively is particularly important

Povidone-iodine is appropriate for ophthalmic surgical preparation and as an alternative for general sites where CHG is contraindicated.

Application technique:

Three-pass minimum centrifugal scrub (incision center outward; never reversing direction). Contact time: minimum 2 minutes for CHG combinations, 5 minutes for PVI. Full evaporation before draping.

For skin antisepsis preparation for cats, including the complete feline skin antisepsis protocol with the evidence from the 2024 circular vs. linear scrub study, that guide covers the cat-specific preparation protocol in full detail.

Wound classification for common feline soft tissue procedures

Intraoperative asepsis: feline considerations

Sterile field maintenance

Standard sterile field principles apply throughout. Feline patients are smaller than most dogs, which creates:

• Smaller operative field requiring precise draping
• Less dead space in most procedures, simplifying closure
• Different scale instruments: fine tissue forceps, smaller needle drivers, and smaller sutures

These differences do not change the asepsis standard. Every principle of sterile field management applies regardless of patient size.

Tissue handling

Atraumatic tissue handling is particularly important in cats. Feline tissue, especially bowel, mesentery, and subcutaneous fat, is more fragile than the equivalent canine tissue. Excessive trauma increases devitalized tissue at the wound, which increases SSI risk.

Fine instruments, adequate lighting, and a planned approach to tissue layers reduce unnecessary trauma and support faster wound healing.

GI tract procedures in cats

Cats present with intestinal foreign bodies, intussusception, and intestinal lymphoma among other conditions requiring GI surgery. The same tract-isolation and glove-change protocols that apply in dogs apply in cats:

• Isolate the intestinal segment with clamps or tapes before opening
• Instrument change and double-glove change after bowel closure
• Copious lavage before abdominal closure

Intestinal anastomosis in cats: The smaller feline intestinal lumen makes anastomosis technically more demanding. Reduced tissue handling requires sharp technique and fine instruments. Any spillage should be addressed with immediate copious lavage.

Pyometra surgery

Pyometra in cats requires surgical intervention in most cases. Uterine integrity determines wound class:

• Intact (closed pyometra, no rupture): Class II; controlled tract entry under antibiotic coverage
• Ruptured: Class III or IV; therapeutic antibiotics; copious lavage; drain placement may be indicated

Intraoperative culture of the uterine exudate guides post-operative antimicrobial selection.

For core aseptic technique, including the intraoperative sterile field maintenance, instrument handling, and personnel behavior standards that apply across all feline surgical procedures, that guide covers the intraoperative technique framework.

Post-operative wound protection in cats

E-collar or recovery suit use is mandatory after all feline surgical procedures where the cat can access the wound. Cats can access wounds that dogs cannot: notably the dorsal thorax, flank, and many proximal limb sites.

Why this matters more in cats than in some dogs:

• Cats are persistent and motivated groomers
• Cat tongues are barbed and more abrasive than dog tongues
• Cats often access wounds that owners believe are inaccessible
• The ingestion risk from residual antiseptic is eliminated by E-collar use

The E-collar should extend a minimum of 2 to 3 cm past the nose tip. Cats are particularly adept at working around shorter cones.

For asepsis during soft tissue surgery in dogs for comparison, including the canine soft tissue asepsis protocol with wound classification table and tract-specific considerations, that guide covers the canine equivalent in detail.

Frequently asked questions

Is the asepsis protocol for feline OHH different from canine spay?

The core protocol is the same: immediate pre-operative clipping, three-pass centrifugal antiseptic scrub, sterile gown and gloves, sterile draping, sterile instruments. The differences are agent-specific (CHG dilution requirements for cats) and anatomical (flank vs. midline approach options in cats). For a healthy young cat undergoing elective OHH, asepsis requirements are identical in principle to a dog.

Can CHG be used for wound irrigation in cats post-operatively?

Only at 0.05% concentration or below. Concentrated CHG is tissue-toxic. The 0.05% dilution (1 mL CHG 5% to 99 mL sterile water or saline) is within the safe range. Higher concentrations should not be applied to open wounds or body cavities in cats.

Should feline soft tissue cases be scheduled before or after canine cases?

Where possible, feline cases benefit from early scheduling in the surgical day to minimize stress from hospital sounds and smells. From an asepsis standpoint, scheduling contaminated cases (any species) last protects the OR environment for subsequent clean cases.

Is urinary catheterization pre- or intra-operatively relevant to SSI risk?

Yes. Pre-operative urethral catheterization carries SSI risk if performed without aseptic technique. Intra-operative catheterization (e.g., for cystotomy) should be performed using sterile catheter technique, and the catheter site should be kept out of the sterile field. Post-operative urinary catheters are a documented SSI risk factor in cats and should be removed as soon as clinically appropriate.

For surgical asepsis standards that provide the complete five-domain perioperative asepsis framework underlying these procedure-specific guidelines, that guide covers the full surgical asepsis standard.

Consistent execution of the feline soft tissue asepsis protocol requires recognizing which error categories are most likely in this specific clinical context, including CHG concentration errors, clipping micro-abrasion from excessive pressure, and insufficient E-collar use post-operatively.

For common errors specific to feline soft tissue procedures, including the error categories most frequently encountered in small animal surgery with particular relevance to feline cases, that guide covers the error taxonomy.

Feline soft tissue surgery demands the same asepsis standard as canine surgery, applied with awareness of the differences in agent sensitivity, tissue fragility, stress-related immune effects, and post-operative grooming behavior. Getting the CHG concentration right, using appropriately fine instruments, minimizing pre-operative stress, and enforcing E-collar use post-operatively are the feline-specific variables on top of the standard asepsis protocol that every cat patient undergoing soft tissue surgery deserves.

Resources

The following sources were used as reference and background for this article:

• NIH/PMC. Incidence of SSI in dogs undergoing soft tissue surgery: risk factors and economic impact. pmc.ncbi.nlm.nih.gov
• NIH/PMC. Effectiveness of two scrub methods with different chlorhexidine combinations for surgical field antisepsis in cats. pmc.ncbi.nlm.nih.gov
• ATDove. Surgical Site Infection. atdove.org
• The Veterinary Nurse. Surgical site infections: preparation, technique and perioperative prevention. theveterinarynurse.com
• ABCD Cats and Vets. Guideline for Disinfectant Choice in Feline Veterinary Hospitals. abcdcatsvets.org