# Anesthesia Machine Safety Checks for Laboratory Animal Use


## Key Takeaways

- **Pre-use checks are critical for preventing anesthetic machine failure, which can lead to compromised data, personnel endangerment, and animal morbidity/mortality.** Essential checks include verifying oxygen supply pressure (50 psi for pipeline, adequate for cylinder), vaporizer fill level and function (no agent odor), breathing circuit integrity (holds pressure for 30 seconds), expiratory valve function (moves freely with manual ventilation), adjustable pressure-limiting valve operation (opens smoothly), carbon dioxide absorbent color (within manufacturer limits), oxygen analyzer calibration (21% room air, 100% flush), and waste anesthetic gas scavenging (negative pressure confirmed).

- **A systematic diagnostic sequence is paramount for troubleshooting equipment malfunctions during anesthesia.** This involves first confirming the problem is real and not an artifact (e.g., verifying monitoring device function), then disconnecting the patient to assess the machine independently, reverting to a manual mode with a known gas source, and finally replacing suspect components or the entire machine if the fault is not quickly localized.

- **Valve failure, particularly the expiratory valve, represents a subtle yet potentially fatal malfunction.** A malpositioned or stuck valve disc can cause complete mechanical obstruction, leading to rapid airway pressure increases despite an open adjustable pressure-limiting valve, or rebreathing of exhaled gas. Dynamic testing with manual ventilation and observation of valve disc movement under flow, in addition to static leak tests, is crucial for detection.

- **Species-specific considerations are vital for adapting anesthesia machine checks, especially for rodents and rabbits.** Non-rebreathing systems are often preferred for animals under 5 kg due to dead space concerns, requiring verification of fresh gas flow and expiratory limb integrity. For larger animals, ensuring the absorbent canister volume and breathing hose diameter match tidal volume is essential, and manual ventilation with a test lung of appropriate compliance confirms valve function.

- **Documentation of all checks, maintenance, and repairs is a regulatory requirement and supports quality assurance.** Logs should detail the date, machine identifier, operator, oxygen supply status, leak test results, absorbent changes, and any corrective actions. This record-keeping aids in identifying recurring equipment problems and demonstrates compliance with institutional standards and guidelines like the *Guide for the Care and Use of Laboratory Animals*.

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Anesthesia machine failure in a laboratory animal setting can compromise data integrity, endanger personnel, and cause preventable morbidity or mortality. This article provides a structured approach to pre-use and routine safety checks for anesthesia machines used with laboratory rodents, rabbits, and other small research animals. It is written for veterinary researchers, laboratory animal veterinarians, and technical staff who are responsible for anesthetic delivery systems in research facilities. The content focuses on the practical execution of checkout procedures, the interpretation of test results, and the troubleshooting of common equipment faults, with attention to the specific constraints of small animal circuits and high-throughput research schedules.

The clinical question addressed is straightforward but consequential: how does an operator verify that an anesthesia machine will deliver the intended gas mixture, at the intended pressure, without leaks, before an animal is connected to it? The answer requires familiarity with the machine's component architecture, the physical principles of gas flow and pressure, and the failure modes that occur in daily use. A methodical checklist, executed before every anesthetic episode and supplemented by periodic deeper inspections, is the standard of care in research animal programs. The [Guide for the Care and Use of Laboratory Animals](https://grants.nih.gov/grants/olaw/guide-for-the-care-and-use-of-laboratory-animals.pdf) identifies veterinary care and oversight of anesthetic procedures as core responsibilities of an institutional animal care and use program, and equipment verification is an implicit component of that duty.

## At a Glance

| Check | Frequency | Acceptable Result | Common Failure |
| --- | --- | --- | --- |
| Oxygen supply pressure | Before each use | Tank pressure adequate for procedure, pipeline pressure 50 psi | Empty tank, regulator failure |
| Vaporizer fill level and function | Before each use | Agent level visible, no agent odor | Overfill, leak, wick saturation |
| Breathing circuit integrity | Before each use | System holds pressure for 30 seconds | Loose connections, cracked hoses |
| Expiratory valve function | Before each use | Valve opens and closes with manual ventilation | Valve stuck closed or open |
| Adjustable pressure-limiting valve | Before each use | Opens and closes smoothly, pressure relief verified | Stuck closed causing barotrauma |
| Carbon dioxide absorbent color | Before each use | Color change within manufacturer limits | Exhausted absorbent, channeling |
| Oxygen analyzer calibration | Daily | Reads 21% in room air, 100% with oxygen flush | Sensor drift, dead battery |
| Waste anesthetic gas scavenging | Before each use | Negative pressure or active scavenging confirmed | Blocked tubing, disconnected interface |

## Principles of Machine Design Relevant to Safety Checks

Anesthesia machines for laboratory animals share a common architecture with clinical machines but differ in scale. The gas supply, flowmeter, vaporizer, and breathing circuit are arranged so that oxygen and carrier gases pass through the vaporizer where volatile anesthetic is added, then to the patient via the circuit. The circle system recirculates exhaled gas through a carbon dioxide absorbent, while non-rebreathing systems such as the Bain or Jackson-Rees design rely on high fresh gas flow to eliminate carbon dioxide. Each design has distinct leak points and pressure characteriztics that determine which checks are meaningful.

The physical principles governing these checks are simple. Gas flows from high to low pressure. A leak is any unintended path for gas to escape or room air to enter. Pressure within the circuit rises when inflow exceeds outflow. The operator's task is to create controlled pressure conditions and observe whether the system behaves predictably. This logic underlies the pressure leak test, the negative pressure check, and the functional assessment of valves. Training in these principles is essential, a study of veterinary students using interactive virtual reality to learn anesthesia machine operation found that structured feedback loops improved competency in performing safety checks such as the pressure check, suggesting that deliberate practice with immediate feedback is an effective instructional method for this skill set [interactive virtual reality training for anesthesia machine safety checks](https://pubmed.ncbi.nlm.nih.gov/39500503/).

## The Pre-Use Checkout Procedure

### Oxygen Supply and Flowmeter Verification

Begin with the oxygen source. For cylinder supply, confirm that the tank pressure is sufficient for the planned procedure and that a second cylinder is available for extended cases. Open the cylinder slowly and verify that the pressure regulator delivers oxygen at the machine's rated working pressure. For pipeline supply, confirm the line pressure reading on the machine's gauge. Close the cylinder or disconnect the pipeline and observe whether the pressure gauge holds steady, which verifies that the high-pressure system does not leak.

Turn on the oxygen flowmeter and set a flow appropriate for the circuit type. The flowmeter float should move freely without sticking. If the float bounces or fails to respond smoothly to valve adjustment, the flowmeter tube or valve requires service. Confirm that oxygen flows through the circuit by occluding the patient port and observing the flowmeter float drop, which indicates backpressure. This simple test verifies continuity from flowmeter to patient connection.

### Vaporizer Inspection

Check the vaporizer fill level against the sight glass. Fill with the correct agent only, using the keyed filler system to prevent cross-filling. Overfilling can cause liquid anesthetic to enter the circuit, producing dangerously high delivered concentrations. After filling, tighten the filler cap and wipe any spillage. Turn the vaporizer on and off while sniffing near the unit, a sweet odor indicates a leak that must be corrected before use. Vaporizers should be serviced and calibrated at intervals specified by the manufacturer, and the service date should be recorded on the unit.

### Breathing Circuit Integrity and Valve Function

The pressure leak test is the central check of circuit integrity. Occlude the patient end of the circuit, close the adjustable pressure-limiting valve, and fill the circuit with oxygen to a pressure of 20 to 30 cm H2O. Stop the flow and observe the pressure gauge for 30 seconds. A stable reading indicates an intact circuit. A falling pressure indicates a leak, which is localized by listening for hissing, feeling for gas flow at connections, or applying soapy water to suspected sites and watching for bubbles.

The expiratory valve deserves specific attention. A case report of complete mechanical expiratory obstruction in an anesthetized dog describes a scenario in which the expiratory valve was malpositioned, causing undetectable end-tidal carbon dioxide and a rapid rise in airway pressure despite an open adjustable pressure-limiting valve [complete mechanical expiratory obstruction from expiratory valve malposition](https://pubmed.ncbi.nlm.nih.gov/40447501/). The problem was identified only after systematic troubleshooting that included confirming capnograph function, verifying endotracheal tube placement, and auscultating the lungs. This case illustrates that valve malfunction can mimic other complications and that a structured approach to diagnosis is required. In the laboratory setting, verify that the expiratory valve disc moves freely, seats properly, and does not stick in either position. The adjustable pressure-limiting valve should open with a quarter turn and produce an audible hiss when the circuit is pressurized.

### Carbon Dioxide Absorbent and Scavenging

Inspect the carbon dioxide absorbent for color change, channeling, or powdering. Exhausted absorbent must be replaced before use. The absorbent chamber should be packed firmly to prevent gas channeling, which creates preferential flow paths that reduce carbon dioxide removal efficiency. Confirm that the scavenging interface is connected and that the vacuum or passive disposal system is functioning. A disconnected scavenging line exposes personnel to waste anesthetic gases and should be corrected before any animal is anesthetized.

## Routine Maintenance and Documentation

Daily checks extend beyond the pre-use procedure. The oxygen analyzer should be calibrated against room air and 100% oxygen. The carbon dioxide absorbent should be changed according to the manufacturer's recommendations or when color change indicates exhaustion, whichever comes first. The machine exterior and vaporizer should be wiped clean, and any anesthetic spillage should be cleaned immediately. A log of daily checks, maintenance, and repairs provides a record that supports quality assurance and helps identify recurring equipment problems. The [NC3Rs resources on refinement of procedures](https://www.nc3rs.org.uk/) emphasize that attention to equipment reliability is part of the broader commitment to minimizing animal suffering and improving experimental quality.

## Troubleshooting Common Equipment Failures

Even a machine that passes routine checks can fail during an anesthetic episode. The most dangerous failures are those that develop silently, such as a progressive leak, a sticking valve, or a depleted carbon dioxide absorbent. A structured approach to troubleshooting reduces the time to diagnosis and limits patient risk.

### The Diagnostic Sequence

When an equipment-related problem is suspected, follow a fixed sequence. First, confirm that the problem is real and not an artifact. Verify the monitoring device itself, as a faulty capnograph or pulse oximeter probe can mimic equipment failure. Second, disconnect the patient from the breathing system and assess the machine independently. This step isolates the patient from the equipment and allows direct testing of circuit integrity. Third, revert to a manual mode of ventilation and a known gas source, such as an oxygen cylinder with an independent regulator, if available. Fourth, replace the suspect component or the entire machine if the fault cannot be localized quickly.

The sequence matters because it prevents wasted effort. A capnograph that reads zero despite adequate ventilation may reflect a sampling line blockage, a disconnected adapter, or a failed analyzer, not a breathing system fault. Confirming monitor function by exhaling into the sampling line, as described in a 2025 case report of complete expiratory obstruction in a dog, is a rapid and effective check [Complete mechanical expiratory obstruction as a result of expiratory](https://pubmed.ncbi.nlm.nih.gov/40447501/). In that case, the capnograph was exonerated before the breathing system was examined, and the fault was traced to a malpositioned expiratory valve that caused complete mechanical obstruction despite a prior leak test [Complete mechanical expiratory obstruction as a result of expiratory](https://pubmed.ncbi.nlm.nih.gov/40447501/). The case illustrates that a leak test alone does not guarantee valve function under dynamic conditions.

### Troubleshooting Table

The table below lists common failures, their typical causes, and the diagnostic steps that confirm each one. Use it as a decision aid during an episode, not as a substitute for direct inspection.

| Observed Problem | Likely Causes | Diagnostic Steps | Immediate Action |
| --- | --- | --- | --- |
| No capnograph waveform | Sampling line disconnect or kink, water trap occlusion, analyzer failure, esophageal intubation | Check sampling line patency, exhale through adapter, confirm ET tube position | Reconnect or replace sampling line, verify tube placement |
| Rising airway pressure | Expiratory valve stuck closed, APL valve closed, soda lime exhaustion, circuit obstruction, bronchospasm | Observe valve movement during ventilation, open APL valve, palpate circuit for resistance | Switch to manual ventilation, open APL valve, replace circuit if needed |
| Falling oxygen flow despite unchanged flowmeter setting | Downstream leak, loose connection, cracked manifold | Pressure test the system, listen for hissing, apply leak detection solution | Tighten connections, isolate and replace faulty component |
| Inability to deliver positive pressure | APL valve open, large leak, disconnected hose, empty oxygen cylinder | Close APL valve, pressure test, check cylinder pressure | Close valve, repair leak, change cylinder |
| Rebreathing of carbon dioxide | Exhausted absorbent, incompetent one-way valve, incorrect circuit assembly | Check absorbent color, observe valve disc movement, capnograph trace showing rebreathing | Replace absorbent, replace valve, reassemble circuit |
| Anesthetic agent odor in room | Leaking vaporizer O-ring, loose filler cap, scavenging failure | Sniff test at connections, check scavenging flow, pressure test vaporizer | Tighten or replace O-ring, close filler cap, repair scavenging |

### Valve Failure as a Special Case

One-way valve failure deserves particular attention because it can be subtle and rapidly fatal. Inspiratory and expiratory valve discs should move freely with each breath. A disc that sticks in the open position allows rebreathing of exhaled gas. A disc that sticks closed produces complete obstruction, as in the reported dog where the expiratory valve was malpositioned [Complete mechanical expiratory obstruction as a result of expiratory](https://pubmed.ncbi.nlm.nih.gov/40447501/). The pressure manometer showed a rapid increase despite an open adjustable pressure-limiting valve, which is a classic sign of downstream obstruction. When this pattern appears, stop ventilation, disconnect the circuit, and inspect both valve assemblies before proceeding.

## Species-Specific Considerations in Checkout Procedures

The same machine may serve multiple species in a laboratory setting, and the checkout procedure must be adapted to the smallest and largest animal expected. A circuit that passes a leak test at 30 cm H2O may still deliver excessive resistance for a mouse or a neonatal rat. The tidal volume of a mouse is approximately 0.15 mL, and the internal volume of a standard circle system far exceeds this, making rebreathing of dead space gas a significant concern. For this reason, non-rebreathing systems such as the Bain or Ayre's T-piece are preferred for animals under approximately 5 kg, and the checkout procedure must confirm the integrity of the fresh gas flow line and the expiratory limb separately.

For larger laboratory animals such as rabbits, ferrets, and non-human primates, a circle system is appropriate, but the absorbent canister volume and the breathing hose diameter must match the patient's tidal volume. A rabbit with a tidal volume of 15 to 20 mL will not generate enough flow to move the valves of a large circle system reliably. The pre-use check should include a manual ventilation test with a test lung of appropriate compliance to confirm that the valves open and close with the expected pressure changes.

The oxygen flow rate during the check differs by species. For rodents, flow rates of 0.5 to 1 L/min are typical, and the flowmeter must be accurate at these low settings. A flowmeter calibrated for 0 to 15 L/min may be imprecise below 1 L/min, so a separate low-flow flowmeter or a precision vaporizer with an integrated flow control should be used. Verify the flowmeter reading against a known standard, such as a calibrated rotameter or a timed collection of gas into a water displacement device, at least quarterly.

## Documentation and Quality Assurance

Documentation of machine checks serves two purposes: it satisfies institutional oversight requirements and it creates a record that can be reviewed when a problem occurs. The [Guide for the Care and Use of Laboratory Animals](https://grants.nih.gov/grants/olaw/guide-for-the-care-and-use-of-laboratory-animals.pdf) requires that anesthetic equipment be maintained in a manner consistent with the institution's animal care and use program [Guide for the Care and Use of Laboratory Animals,](https://grants.nih.gov/grants/olaw/guide-for-the-care-and-use-of-laboratory-animals.pdf). A written log of daily checks, leak test results, absorbent changes, and vaporizer servicing provides that evidence.

The log should record the date, the machine identifier, the person performing the check, the oxygen cylinder pressure or pipeline supply status, the leak test result, the absorbent color and last change date, and any corrective actions taken. A separate maintenance log should track vaporizer calibration, flowmeter accuracy, and replacement of hoses, valves, and seals. These records are reviewed during institutional inspections and can identify recurring failure patterns that warrant equipment replacement.

Training in machine checks is a component of competency assessment for veterinary personnel. A 2024 study of veterinary students using interactive virtual reality to learn anesthesia machine operation found that the virtual reality approach was well accepted and produced similar training times to real machines, though virtual reality exam scores were lower, possibly due to increased cognitive load [Interactive Virtual Reality with Educational Feedback Loops to Train](https://pubmed.ncbi.nlm.nih.gov/39500503/). The study supports the use of simulation-based training as a supplement to hands-on practice, particularly for rare events such as complete valve obstruction that may not occur during routine training [Interactive Virtual Reality with Educational Feedback Loops to Train](https://pubmed.ncbi.nlm.nih.gov/39500503/). Institutions should incorporate both real machine practice and simulation into their training programs.

## When to Remove a Machine from Service

A machine should be removed from service immediately if any of the following conditions are present: a leak that cannot be localized and repaired, a vaporizer that delivers an inconsistent agent concentration, a flowmeter that is inaccurate at the required flow range, a one-way valve that sticks or fails to seat, or an absorbent canister that cannot be sealed. These conditions compromise patient safety and cannot be managed by adjustment during anesthesia.

The decision to repair versus replace a machine depends on the age of the equipment, the availability of parts, and the cost of repair relative to replacement. Older machines with proprietary parts may be uneconomical to repair. Institutions should maintain a spare machine or a backup vaporizer so that a failed unit can be removed without delaying scheduled procedures. The backup equipment must be checked with the same rigor as the primary machine, and the check should be documented in the same log.

The [NC3Rs](https://www.nc3rs.org.uk/) emphasizes refinement of procedures to minimize animal suffering, and reliable anesthetic equipment is a prerequisite for refinement [NC3Rs Resources on Replacement, Reduction and Refinement](https://www.nc3rs.org.uk/). A machine that fails during an experiment also risks the animal's welfare but also compromises the scientific validity of the data. Routine checks, prompt troubleshooting, and clear documentation are the practical means by which refinement is achieved in the anesthetic setting.

## Recognized Failure Modes and Early Detection

The most dangerous failures are those that present as normal function during a cursory check. A circle breathing system that passes a static leak test can still fail dynamically. Complete expiratory obstruction from a malpositioned expiratory valve has been documented in an anesthetized dog, where the system had been leak-tested before connection and the capnograph initially read zero despite manual ventilation. The discriminating findings were a rapid rise in airway pressure despite an open adjustable pressure-limiting valve, and the absence of an expiratory waveform while the anesthetist confirmed correct endotracheal tube placement and capnograph function by exhaling into the sampling adaptor. The case resolved only when a second machine was substituted. The lesson is that a pressure check verifies integrity at rest, not valve motion under flow. Every pre-use check must include manual ventilation with observation of both the reservoir bag and the one-way valves during inspiration and expiration, plus a capnograph trace that returns to zero between breaths.

Fresh gas flow errors are detected by cross-checking the flowmeter against the vaporizer setting and the calculated minute ventilation. A vaporizer that is tilted during transport can deliver a liquid bolus of agent, the early sign is an unexpectedly deep plane of anesthesia within minutes of connection. Detect this by verifying vaporizer orientation before mounting, and by monitoring end-tidal agent concentration where a gas analyzer is available. Carbon dioxide absorbent exhaustion presents as a rising inspired carbon dioxide fraction, rebreathing, or tachypnea in a spontaneously breathing animal. The discriminating check is the color change indicator, but color indicators can fail or be obscured. Palpate the canister for heat, which is present during active absorption and absent when exhausted. Replace absorbent when the indicator shows change or at the interval specified by the institutional standard operating procedure.

## Common Operator Errors and Corrective Actions

Less experienced clinicians and students most often err in the order of the checkout, skipping the oxygen supply check and moving directly to the breathing circuit. The corrective action is a fixed sequence that begins at the source and ends at the patient end of the circuit. A second common error is performing the pressure check with the adjustable pressure-limiting valve closed and then forgetting to reopen it, which produces barotrauma on the first manual breath. The corrective action is to make valve position part of the final visual sweep before connecting the patient.

Students also tend to trust a single observation instead of a confirming one. A capnograph reading of zero is attributed to patient apnea instead of to a disconnected sampling line or a leak at the endotracheal tube cuff. The corrective action is to test the sampling line by occluding it and observing the waveform, and to auscultate the lungs during a manual breath. Training tools that incorporate feedback loops, such as interactive virtual reality, have been shown to be acceptable and useful for teaching anesthesia machine operation, though they may increase cognitive load and produce lower examination scores than oral and practical assessments. Virtual reality training times were similar to real machine training times, and prior virtual reality experience was not required. Computer glitches and cybersickness were noted as drawbacks. These findings support the use of simulation as a supplement to, not a replacement for, supervised practice on the actual machine.

## Limitations of the Evidence and Areas of Expert Disagreement

The published evidence on anesthesia machine safety checks in laboratory animals is thin. Most guidance is extrapolated from human anesthesia practice or from clinical veterinary case reports, and the laboratory animal literature contains few systematic evaluations of checkout protocols. Expert opinion differs on how frequently the full checkout should be repeated during a long surgical day. Some institutional programs require a full check before every case, while others accept a reduced check between cases on the same machine. The National Research Council guidance for laboratory animal care emphasizes the institutional responsibility to maintain equipment and train personnel, but it does not prescribe a specific checkout interval. Institutions should adopt a written standard that specifies the full check, the between-case check, and the daily check, and should document compliance.

There is also disagreement about the value of routine replacement of consumables. Some programs replace carbon dioxide absorbent on a fixed schedule regardless of indicator status, while others rely on the indicator and clinical signs. The latter approach is defensible when the indicator is verified against a known standard, but it requires that personnel be trained to recognize the transition reliably.

## Escalation, Referral, and Reporting

Remove a machine from service when a fault cannot be corrected within the diagnostic sequence, when a safety check fails twice after adjustment, or when any component shows visible damage, corrosion, or unexplained contamination. Tag the machine clearly and notify the institutional veterinary staff or the designated equipment manager. Do not return a machine to service until it has been inspected and cleared by a qualified individual, which may be a service engineer for vaporizer calibration or internal valve repair.

Referral to a specialist is warranted when the fault involves the vaporizer output, the oxygen proportioning system, or the scavenging interface, because these require calibrated test equipment. Laboratory animal veterinarians should be consulted when a species-specific adaptation, such as a non-rebreathing circuit for a small rodent, is implicated in a failure. Regulatory reporting is required when a failure causes or contributes to an animal death, an unplanned recovery, or a prolonged anesthetic event that compromises welfare. The institutional animal care and use committee and the attending veterinarian must be informed, and the event should be documented in the animal's record and in the equipment log. Where institutional policy or national standards apply, such as those published by the World Organization for Animal Health for laboratory animal welfare, the reporting pathway should follow the designated institutional official.

| Observation | Likely cause | Discriminating check |
| --- | --- | --- |
| No capnograph waveform, normal airway pressure | Sampling line leak or disconnection | Occlude sampling line, observe waveform return |
| Rising airway pressure with open APL valve | Expiratory valve obstruction | Ventilate manually, watch valve disc excursion |
| Inspired CO2 above zero | Absorbent exhaustion | Palpate canister for heat, check indicator color |
| Unexpectedly deep plane of anesthesia | Vaporizer tilt or overfill | Verify orientation, check agent concentration |
| Reservoir bag does not refill | Fresh gas flow too low or inlet leak | Increase flow, listen for leak at connections |
| Flowmeter float does not settle | Damaged tube or static charge | Compare with second flowmeter, replace tube |

## Frequently Asked Questions

### How Should I Prioritize Machine Checks When Budget or Time Constraints Are Severe?

When resources are limited, prioritize checks that prevent immediate patient harm. The pressure leak test, oxygen supply verification, and vaporizer fill level inspection are non-negotiable. These detect the most common catastrophic failures, including disconnections, empty oxygen tanks, and depleted agent. Valve function assessment, particularly the expiratory valve, should follow, since a malpositioned valve can cause complete expiratory obstruction and rapid pressure increases. Carbon dioxide absorbent color inspection and scavenging verification rank next. If time permits only a subset, document which checks were deferred and flag the machine for full checkout before the next use. Institutional policies may define minimum requirements, and the [Guide for the Care and Use of Laboratory Animals](https://grants.nih.gov/grants/olaw/guide-for-the-care-and-use-of-laboratory-animals.pdf) describes the veterinary team's responsibility to maintain safe anesthesia delivery.

### What Is the Minimum Acceptable Checkout When Using a Portable or Field Anesthesia Machine?

Portable machines require the same functional verification as stationary units, adapted to their design. Confirm the oxygen source pressure and flowmeter accuracy, since portable regulators drift more frequently. Perform a pressure leak test on the circuit, recognizing that some portable systems use non-rebreathing circuits with higher acceptable leak rates. Verify the vaporizer is upright, filled, and locked in place before transport. Check all connections, as vibration during movement loosens fittings. Test the scavenging interface if present, or confirm the room ventilation plan. For field use, carry a spare oxygen cylinder and a backup manual ventilation bag. Document the checkout in the same format used for stationary machines. The [NC3Rs resources on refinement](https://www.nc3rs.org.uk/) emphasize that procedure quality, including equipment reliability, directly affects animal welfare.

### How Do I Perform a Safety Check on a Machine Used Exclusively for Rodents?

Rodent anesthesia typically uses non-rebreathing circuits, often with a coaxial Mapleson design or a simple T-piece. The pressure leak test differs because these circuits are intentionally open. Instead, verify fresh gas flow with a calibrated flowmeter and confirm the circuit delivers gas to the patient port. Occlude the patient port and confirm the pressure relief valve opens at the expected threshold. Check the vaporizer output, ideally with an agent analyzer, since low flow rates used in rodents amplify vaporizer inaccuracies. Inspect the scavenging system, as waste gas exposure is a significant occupational concern in rodent facilities. Verify the induction chamber seals properly. The [MSD Veterinary Manual](https://www.msdvetmanual.com/) provides species-specific guidance on anesthetic equipment and techniques for small laboratory animals.

### What Records Should I Keep for Each Machine Checkout?

Record the date, time, machine identifier, and the name of the person performing the check. List each test performed and the result, including measured values such as leak rate in mL per minute or pressure decay over 30 seconds. Note any corrective action taken, including parts replaced or repairs performed. Record the vaporizer fill level and the lot number of any agent added. Document absorbent color and the date of last change. Keep these records in a logbook attached to the machine or in an electronic system accessible to all users. Retention periods may be set by institutional policy or accrediting bodies. The [AVMA practice resources](https://www.avma.org/resources-tools) offer guidance on medical record keeping standards that can be adapted to equipment logs.

### How Should I Explain a Machine Failure or Downtime to a Supervisor or IACUC?

Describe the failure in operational terms, also the symptom. State which check failed, the measured value, and the suspected cause. Explain the immediate action taken, such as removing the machine from service or substituting a backup unit. Estimate the timeline for repair based on parts availability and service contracts. If animal procedures were delayed or rescheduled, state this clearly. For reportable events, such as an animal injury or death attributable to equipment failure, follow institutional incident reporting requirements. The [Guide for the Care and Use of Laboratory Animals](https://grants.nih.gov/grants/olaw/guide-for-the-care-and-use-of-laboratory-animals.pdf) requires that veterinary care programs maintain equipment in safe working order, and the [WOAH terrestrial animal health standards](https://www.woah.org/en/what-we-do/standards/codes-and-manuals/terrestrial-code-online-access/) address veterinary service quality more broadly.

### Can I Use a Machine with a Known Minor Defect While Awaiting Repair?

Only if the defect does not affect delivered anesthesia or patient safety. A cracked vaporizer sight glass, a sticking flowmeter float, or a leaking circuit connector removes the machine from service immediately. A worn but functional oxygen hose or a slightly stiff adjustable pressure-limiting valve may be acceptable temporarily, provided the defect is documented, the machine is flagged, and the user confirms function with each pre-use check. Never bypass a failed safety device, such as a disabled oxygen failure alarm. If the defect could worsen during a procedure, do not use the machine. The case of a dog anesthetized with a circle system that had passed a leak test yet still caused complete expiratory obstruction from a malpositioned valve illustrates that even minor component issues can become life-threatening, so a low threshold for removing equipment from service is prudent.

## Related Clinical & Scientific Guides

* [Refining IACUC Protocols to Minimize Animal Pain and Distress](/knowledge/veterinary-medicine/laboratory-animal-science/refining-iacuc-protocols-minimize-animal-pain-distress)
* [Health Monitoring Programs for Laboratory Animal Facilities](/knowledge/veterinary-medicine/laboratory-animal-science/health-monitoring-programs-for-laboratory-animal-facilities)
* [Anesthetic Risk Assessment in Laboratory Animals: Preoperative Evaluation](/knowledge/veterinary-medicine/laboratory-animal-science/anesthetic-risk-assessment-in-laboratory-animals-preoperative-evaluation)


## References and Further Reading

- [Interactive Virtual Reality with Educational Feedback Loops to Train and Assess Veterinary Students on the Use of Anesthetic Machine.](https://pubmed.ncbi.nlm.nih.gov/39500503/). 2024.
- [Potential adverse ultrasound-related biological effects: a critical review.](https://pubmed.ncbi.nlm.nih.gov/21866043/). 2011.
- [The use of combined inhalation anesthesia in laboratory animal surgery.](https://pubmed.ncbi.nlm.nih.gov/22413207/). 1966.
- [Optic chiasmatic potential by endoscopically implanted skull base microinvasive biosensor: a brain-machine interface approach for anterior visual pathway assessment.](https://pubmed.ncbi.nlm.nih.gov/35547770/). 2022.
- [Complete mechanical expiratory obstruction as a result of expiratory valve malposition in an anesthetized dog.](https://pubmed.ncbi.nlm.nih.gov/40447501/). 2025.
- [Guide for the Care and Use of Laboratory Animals, 8th Edition](https://grants.nih.gov/grants/olaw/guide-for-the-care-and-use-of-laboratory-animals.pdf). National Academies Press, 2011.
- [NC3Rs Resources on Replacement, Reduction and Refinement](https://www.nc3rs.org.uk/). NC3Rs.
- [MSD Veterinary Manual, Professional Edition](https://www.msdvetmanual.com/). MSD Veterinary Manual.
- [American Veterinary Medical Association Practice Resources](https://www.avma.org/resources-tools). American Veterinary Medical Association.

## Related Articles

- [Anesthesia for Laboratory Rabbits: Protocols and Monitoring](/knowledge/veterinary-medicine/laboratory-animal-science/anesthesia-for-laboratory-rabbits-protocols-and-monitoring)
- [Anesthesia Monitoring Parameters for Laboratory Animals](/knowledge/veterinary-medicine/laboratory-animal-science/anesthesia-monitoring-parameters-for-laboratory-animals)
- [Anesthesia Equipment for Small Laboratory Animals: Setup and Maintenance](/knowledge/veterinary-medicine/laboratory-animal-science/anesthesia-equipment-for-small-laboratory-animals-setup-and-maintenance)
- [Anesthetic Considerations for Pregnant Laboratory Animals](/knowledge/veterinary-medicine/laboratory-animal-science/anesthetic-considerations-for-pregnant-laboratory-animals)
- [Anesthesia Monitoring for Laboratory Rats: Parameters and Equipment](/knowledge/veterinary-medicine/laboratory-animal-science/anesthesia-monitoring-for-laboratory-rats-parameters-and-equipment)

> This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.