Anesthetic Machine Checkout: Daily Verification and Troubleshooting

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Key Takeaways

• Daily anesthetic machine checkout is the primary defense against equipment-related morbidity and mortality, with a survey revealing significant deficiencies like a lack of secondary oxygen supplies and pressure alarms, and common leaks in rebreathing (31%) and non-rebreathing (17%) systems.
• The checkout procedure systematically verifies oxygen supply (cylinder/pipeline pressure, alarm function), high-pressure (50 psi integrity), and low-pressure systems (flowmeter to common gas outlet occlusion test) to localize potential failures.
• Breathing system integrity is critical, requiring verification of unidirectional valve function, positive pressure leak testing of the circuit to 20-30 cm H2O, and assessment of CO2 absorbent condition to prevent rebreathing and barotrauma.
• Vaporizer function necessitates checking agent levels, secure seating, and performing leak tests; filling should occur at the start of the day to allow for thermal equilibration and prevent transiently inaccurate agent concentrations.
• Scavenging system verification involves tracing the hose, confirming connections, and ensuring patency to prevent waste gas exposure or circuit pressure imbalances, with a survey indicating improper connections in 56% of active systems.
• Documentation via a checkout log is essential for accountability and trend analysis, with machines failing any test requiring immediate tagging and removal from service until corrected.

The daily anesthetic machine checkout is the single most reliable defense against equipment-related morbidity and mortality in veterinary anesthesia. This article provides a systematic, step-by-step procedure for verifying anesthetic machine function in veterinary practice, with specific attention to leak testing, breathing system integrity, and vaporizer performance. It is written for practicing veterinarians and veterinary technicians who perform or supervise anesthesia delivery across species.

The procedures described here establish a reproducible baseline for machine safety. A prospective survey of 100 anesthetic machines in private veterinary clinics in Alberta, Canada, found that only 10% had a secondary oxygen supply, no machines had an oxygen supply pressure alarm, and leaks were identified in 31% of rebreathing systems and 17% of non-rebreathing systems Marchiori et al., 2023. These findings demonstrate that equipment failure is not hypothetical, it is common, and a standardized checkout procedure is the primary defense.

This article covers the conceptual basis for each checkout step, the practical execution of the daily verification, and troubleshooting guidance for common failures. Advanced repair of internal machine components is excluded, the focus is on what a veterinary team can and should verify before every anesthetic event.

At a Glance

Principles of Machine Design and Failure Modes

An anesthetic machine consists of three functional divisions: the high-pressure system, the intermediate-pressure system, and the low-pressure system. The high-pressure system includes the cylinder, cylinder pressure gauge, and pressure-reducing valve. The intermediate-pressure system carries gas at approximately 50 psi from the regulator to the flowmeters. The low-pressure system begins at the flowmeter needle valves and includes the vaporizer and the common gas outlet.

Each division has characteriztic failure modes. High-pressure failures include empty cylinders, regulator malfunction, and obstructed cylinder outlets. Intermediate-pressure failures include hose disconnection, pressure gauge inaccuracy, and alarm failure. Low-pressure failures are the most clinically relevant because they are the most common and the most likely to go undetected. The Alberta survey found that 39% of machines lacked a high-pressure circuit alarm, meaning a loss of oxygen supply could occur without audible warning Marchiori et al., 2023.

The checkout procedure is designed to test each division in sequence, from the gas source to the patient connection. This order ensures that a failure at any point is localized before proceeding to the next component. The procedure described here follows the logic of the anesthesia machine checkout and troubleshooting approach used in veterinary teaching hospitals Mason, 1993.

Oxygen Supply Verification

Begin with the oxygen supply. Identify whether the machine is connected to a pipeline, a cylinder, or both. Pipeline systems require verification of line pressure, typically 50 psi, and confirmation that the pipeline hose is correctly attached to the oxygen inlet. Cylinder systems require verification of the cylinder pressure gauge and the cylinder contents.

Open the cylinder valve slowly and listen for the audible oxygen pressure alarm. If the alarm does not sound when the cylinder is opened with the flowmeter closed, the alarm is nonfunctional. The Alberta survey found that no machines in the study had an oxygen supply pressure alarm, which means this failure mode is widespread and underappreciated Marchiori et al., 2023.

Record the cylinder pressure. A full E-cylinder contains approximately 660 L of oxygen at 1900 psi. The duration of flow can be estimated by dividing the cylinder contents in liters by the fresh gas flow rate in liters per minute. This calculation should be performed before each case to ensure adequate reserve for the planned procedure duration.

High-Pressure and Intermediate-Pressure System Testing

With the oxygen cylinder closed and the machine unplugged from the pipeline, open the oxygen flowmeter briefly to vent any residual pressure. Close the flowmeter. The high-pressure system is now isolated. Attach a pressure gauge to the common gas outlet or use the machine's built-in pressure manometer if present.

Open the cylinder valve fully. The pressure gauge should read approximately 50 psi. If the pressure rises slowly or fails to reach 50 psi, suspect a partially open cylinder valve, a faulty regulator, or an obstruction in the high-pressure hose. Close the cylinder valve and observe the pressure gauge for 1 minute. A drop in pressure indicates a leak in the high-pressure or intermediate-pressure system.

The oxygen pressure failure alarm, where present, should be tested by closing the cylinder valve and opening the flowmeter. The alarm should sound within a few seconds as the intermediate pressure falls below the alarm threshold. If the alarm does not sound, the machine should be removed from service until the alarm is repaired.

Low-Pressure System and Leak Testing

The low-pressure system is the most common site of undetected leaks. The test procedure differs depending on whether the machine has a vaporizer mounted on the back bar or a vaporizer that is integral to the flowmeter assembly.

For machines with a back-bar vaporizer, occlude the common gas outlet and fill the low-pressure system with oxygen to a pressure of 30 to 50 cm H2O using the oxygen flowmeter at 1 L/min. When the pressure reaches the target, close the flowmeter and observe the pressure for 30 seconds. A pressure drop of more than 10 cm H2O indicates a leak. Common sites include the vaporizer fill port, the vaporizer mounting gasket, and the flowmeter tubes.

For machines with an integral vaporizer, the same test is performed with the vaporizer in the on position and again with the vaporizer off. A leak that appears only when the vaporizer is on localizes the problem to the vaporizer itself. A leak that appears in both positions implicates the flowmeter assembly or the common gas outlet connection.

The Alberta survey identified leaks in 31% of rebreathing systems and 17% of non-rebreathing systems Marchiori et al., 2023. These leaks are clinically significant because they can result in inadequate delivered oxygen concentration, environmental contamination with inhalant anesthetics, and underestimation of delivered agent concentration.

Breathing System Integrity and Circuit Verification

The breathing system connects the machine to the patient and is the most frequently manipulated portion of the anesthetic delivery apparatus. Its integrity determines whether delivered gas reaches the patient and whether exhaled carbon dioxide is eliminated. A systematic approach to circuit verification prevents the majority of intraoperative ventilation failures.

Rebreathing System Assessment

For circle rebreathing systems, verify the unidirectional valves move freely and seat properly. Remove the dome of each valve and inspect for debris, moisture, or soda lime dust that may prevent full excursion. The inspiratory and expiratory valves must open with a gentle breath and close completely when flow ceases. A valve that sticks open permits rebreathing of carbon dioxide, a valve that sticks closed creates dangerous resistance to breathing.

Test the adjustable pressure limiting (APL) valve by occluding the patient port, closing the APL valve, and pressurizing the circuit to 20 to 30 cm H₂O using the oxygen flush. The circuit should hold pressure for at least 10 seconds without decay. Then open the APL valve fully and confirm the pressure returns to zero promptly. A valve that fails to vent traps gas and can produce barotrauma, a valve that leaks during the pressure hold indicates incomplete closure.

Inspect the soda lime canister for channeling, desiccation, or exhaustion. The indicator color change provides a guide, but color alone is insufficient. Exhausted absorbent permits carbon dioxide accumulation and hypercapnia. Replace absorbent when the indicator color change is visible across the canister or when the patient-side capnograph shows an elevated inspired carbon dioxide level. The interval between changes depends on fresh gas flow rate, patient size, and case duration.

Non-Rebreathing System Assessment

Non-rebreathing systems such as the Bain, Magill, and Lack circuits have no unidirectional valves and no carbon dioxide absorbent. Their integrity depends on the inner gas delivery tube and the outer expiratory limb. Test the Bain circuit specifically by occluding the patient end, delivering oxygen through the fresh gas inlet, and observing the reservoir bag. With the inner tube intact, gas flows through the inner tube and the bag fills. If the inner tube is disconnected or torn, gas exits through the outer limb and the bag fails to fill properly.

For all non-rebreathing systems, verify that the expiratory limb and scavenging interface are patent and that the reservoir bag is the correct size for the patient. The fresh gas flow requirements for non-rebreathing systems are substantially higher than for circle systems, typically two to three times minute ventilation. This higher flow increases the importance of a functioning scavenging interface, since waste gas production is correspondingly greater.

Scavenging System Verification

The scavenging system collects waste anesthetic gases from the APL valve and ventilator relief valve and conveys them to an active vacuum or passive disposal route. A scavenging system that is disconnected, obstructed, or incorrectly assembled creates either positive pressure in the circuit or a route for waste gas to enter the room.

Trace the scavenging hose from the machine to its termination point. Confirm that the hose is connected at both ends and that the interface valve operates freely. For active scavenging systems, verify that vacuum is present by listening for airflow or using a flow indicator. For passive systems, confirm the exhaust hose leads to a non-recirculating vent and is not kinked or blocked.

The Alberta survey found that 86% of machines were attached to an active scavenging system, but the system was improperly connected in 56% of cases. This finding underscores the need for a deliberate, visual check of the scavenging pathway instead of an assumption that connection implies function. A scavenging system that is connected but assembled incorrectly can create negative pressure that siphons gas from the circuit or positive pressure that impedes exhalation.

Vaporizer Function and Filling

Vaporizer verification begins with the fill port and sight glass. Confirm that the vaporizer contains sufficient agent for the planned procedure and that the agent matches the vaporizer calibration. A vaporizer filled with the wrong agent delivers an unpredictable concentration and can produce profound overdose or underdose. The filling key system prevents this error on most modern vaporizers, but older units may accept a range of bottles.

Check the vaporizer for leaks by pressurizing the machine with the vaporizer in the off position and then turning the vaporizer on while observing the pressure gauge. A drop in pressure indicates a leak in the vaporizer itself or in its mounting. The concentration dial should turn smoothly through its full range and return to zero when released. A dial that sticks or fails to zero may deliver agent when the vaporizer appears to be off.

Temperature compensation is automatic on modern vaporizers, but the unit must be allowed to stabilize after filling. Filling a cold vaporizer with room-temperature agent or filling immediately before use can produce transiently inaccurate concentrations. Fill the vaporizer at the start of the day and allow 10 to 15 minutes for thermal equilibration before the first case.

Vaporizer output can be verified with an agent analyzer placed between the common gas outlet and the breathing system. This device measures the actual delivered concentration and detects calibration drift. An agent analyzer is particularly valuable for machines used infrequently or after vaporizer service. The cost of the analyzer is justified by the risk of undetected vaporizer malfunction, which can cause unintended deep anesthesia or awareness.

Ventilator Verification

Mechanical ventilators used with rebreathing systems require a separate checkout sequence. Verify that the ventilator hose connects the ventilator to the circuit and that the ventilator bellows or piston moves through its full excursion when the ventilator is cycled manually. The bellows should fill completely during the expiratory phase and empty fully during inspiration. A bellows that fails to fill indicates a leak in the ventilator circuit or insufficient driving gas pressure.

Test the ventilator relief valve, which vents excess gas to the scavenging system during the expiratory phase. Occlude the patient port and cycle the ventilator. The circuit pressure should rise to the peak inspiratory pressure setting and then return to the set positive end-expiratory pressure (PEEP) or zero during expiration. A relief valve that fails to open produces progressive pressure buildup, a valve that leaks during inspiration reduces delivered tidal volume.

The ventilator pressure limit alarm must be tested before each use. Set the alarm to a value below the expected peak pressure, occlude the patient port, and cycle the ventilator. The alarm should sound when the pressure limit is reached and the ventilator should cycle to expiration. A ventilator that fails to alarm or fails to cycle on pressure limit can deliver excessive pressure to the patient.

Documentation and Daily Log

The checkout procedure has value only when its results are recorded. The Alberta survey found that only 2% of machines were accompanied by a checkout log. A written log creates accountability, documents trends in machine performance, and provides a record for quality assurance review. The log should include the date, the machine identifier, the name of the person performing the check, and the result of each test item.

A machine that fails any portion of the checkout should be tagged and removed from service until the fault is corrected. The tag should state the nature of the fault and the date it was identified. A backup machine or alternative anesthetic delivery method should be available for cases scheduled during the repair period. The American Animal Hospital Association anesthesia guidelines emphasize that equipment verification is part of the preanesthetic preparation for every patient.

The checklist format should match the machine configuration. A machine with an integrated ventilator, a specific vaporizer type, or a unique scavenging interface requires a checklist that addresses those components. A generic checklist that does not match the equipment invites skipped items or false assumptions about what has been verified. The checklist should be reviewed whenever the machine configuration changes, such as after the addition of a new vaporizer or ventilator.

The time required for a complete checkout is approximately 5 to 10 minutes for an experienced user. This investment is small relative to the cost of an equipment failure during anesthesia. The checkout is not a substitute for vigilance during the case, but it reduces the probability that a machine fault will be the cause of an anesthetic complication.

Recognized Complications and Early Detection

The most consequential machine failures are those that develop gradually during a case instead of at initial checkout. A vaporizer that drifts out of calibration delivers a lower or higher agent concentration than the dial setting, and the first clinical sign is often an unexpected depth of anesthesia relative to the vaporizer setting. Early detection depends on comparing the dial setting against an independent measure, such as an agent analyzer or a second vaporizer used as a reference. When an agent analyzer is unavailable, a rising or falling trend in end-tidal agent concentration that does not match dial changes should prompt immediate investigation.

Fresh gas flow errors produce a different signature. A flowmeter that reads falsely high because of a cracked tube or debris in the needle valve delivers more oxygen than intended, which can silently distend the breathing system and, in a rebreathing circuit, produce barotrauma if the adjustable pressure limiting (APL) valve is closed. The discriminating check is the low-pressure leak test performed with the flowmeter at the intended setting, not at maximum flow. A system that holds pressure at 20 cm H2O with a low fresh gas flow but leaks at higher flows points to a flowmeter fault instead of a circuit fault.

Carbon dioxide absorbent exhaustion is detected by inspired carbon dioxide, not by color change alone. The pH-sensitive dye in soda lime is an unreliable indicator under low humidity and in the presence of certain agents, and the color change lags behind functional exhaustion. Capnography showing inspired carbon dioxide above 5 mm Hg, or a rising baseline, mandates absorbent replacement regardless of color. The same capnography trace can reveal a stuck inspiratory or expiratory unidirectional valve, which produces rebreathing and a characteriztic elevation of the inspired carbon dioxide baseline with a normal fresh gas flow.

Common Errors and Corrective Action

Less experienced clinicians frequently omit the negative pressure leak test because it requires removing the breathing system and attaching a test bulb or syringe directly to the common gas outlet. The omission is consequential because the test is the only routine check that detects leaks in the vaporizer and flowmeter internal pathways. Corrective action is to perform the test daily, before the first case, and to record the result in the checkout log.

A second common error is pressurising the breathing system with the APL valve fully closed and the oxygen flush held, then interpreting a slow pressure drop as a leak when the system has simply not reached equilibrium. The correct technique is to pressurise to 30 cm H2O, close the APL valve, stop the flush, and observe for 30 seconds. A drop of less than 5 cm H2O is acceptable for a rebreathing system. For non-rebreathing systems, the acceptable leak threshold is lower, and the manufacturer's specification for the specific circuit should be consulted.

Students often confuse the high-pressure system test with the low-pressure test. The high-pressure test verifies the oxygen supply from the cylinder or pipeline to the machine's pressure regulators, while the low-pressure test verifies everything downstream of the flowmeter. Performing only one of the two leaves a gap in coverage. The corrective action is to follow a written checklist that sequences the tests in order, from oxygen supply through to scavenging, and to initial each step.

Limitations of the Evidence and Areas of Expert Disagreement

The evidence base for veterinary anesthesia machine checkout is limited. A prospective survey of 100 anesthetic machines in private veterinary clinics in Alberta, Canada, found that only 10% had a secondary oxygen supply, no machines had an oxygen supply pressure alarm, and leaks were present in 31% of rebreathing and 17% of non-rebreathing systems A prospective survey of veterinary anesthesia equipment in Alberta, Canada. The same survey found that only 2% of machines were accompanied by a checkout log. These figures describe one Canadian province and may not generalize to other regions or practice types, but they indicate that routine checkout is not yet a universal standard.

Expert opinion differs on the frequency of full checkout. Some authorities recommend a complete checkout daily and a shorter verification before each case, while others argue that a full checkout before every case is warranted in high-volume or multi-user practices. The American Animal Hospital Association anesthesia guidelines for dogs and cats emphasize the importance of equipment verification as part of anesthetic planning but do not prescribe a single universal protocol AAHA anesthesia and monitoring guidelines for dogs and cats. Practices should adopt a written protocol appropriate to their caseload and equipment, and review it whenever a new machine or circuit is introduced.

Escalation and Reporting

Most findings at checkout are correctable in practice. A leaking breathing bag, a cracked absorber canister, or a loose connection can be replaced or tightened immediately. A vaporizer that fails calibration, a flowmeter that leaks, or a pressure regulator that drifts out of specification requires manufacturer service or replacement. These items are not field-repairable, and continued use of a known faulty vaporizer or flowmeter is unsafe.

A machine that fails checkout should be tagged and removed from service until repaired. The tag should state the date, the failed test, and the name of the person who identified the fault. A machine that passes checkout after repair should be re-tested in full before return to service.

Regulatory reporting is rarely required for equipment failure in companion animal practice, but jurisdictions differ. In production animal practice, equipment used for anesthesia or euthanasia may fall under food safety or welfare inspection frameworks, and the relevant regional authority should be consulted WOAH terrestrial animal health standards. Where a machine failure has contributed to a patient death or serious injury, the practice should review the incident internally and consider whether the equipment manufacturer should be notified, particularly if the failure suggests a design or manufacturing defect.

Frequently Asked Questions

How Often Should I Perform a Full Checkout Versus a Pre-Case Check?

The daily checkout covers the complete machine, including oxygen supply reserves, pressure systems, breathing circuits, scavenging, and vaporizers. A pre-case check is shorter and focuses on items that can change between patients or fail suddenly: oxygen cylinder pressure, fresh gas flow accuracy, circuit integrity, one-way valve function, and scavenging connection. A prospective survey of veterinary anesthesia equipment in Alberta found that only 2% of machines had a checkout log, yet leaks were present in 31% of rebreathing systems, which supports the value of daily verification as a foundation for safe practice. Document the daily check and repeat the pre-case check before every anesthetic episode.

What Is the Minimum Acceptable Checkout When Time or Equipment Is Limited?

When a full checkout is impossible, prioritize patient safety over completeness. Verify an adequate oxygen supply, confirm the oxygen pressure alarm functions if present, perform a low-pressure leak test, and assess the breathing circuit for obvious leaks or disconnections. The AAHA anesthesia and monitoring guidelines for dogs and cats emphasize that anesthetic safety depends on preparation and monitoring. If a machine fails any critical check, do not use it until the fault is corrected. A machine with an unidentified leak can cause hypoventilation, waste gas exposure, or awareness under anesthesia. Record the limitation and escalate to the responsible clinician or service provider.

How Does the Checkout Differ for Non-Rebreathing Circuits in Small Patients?

Non-rebreathing circuits have higher fresh gas flow requirements and less internal volume, so leak detection thresholds differ. The low-pressure system must still hold pressure, but circuit compliance and gas compression become more significant in small patients. Check the circuit for cracks at connection points, ensure the reservoir bag is appropriate for the patient size, and verify that the adjustable pressure limiting valve opens and closes fully. In avian and exotic patients, the circuit dead space and resistance matter more than in dogs and cats. The MSD Veterinary Manual notes that anesthetic equipment must be matched to the species and patient size. A leak that is trivial in a 30 kg dog can be clinically important in a 500 g bird.

What Should I Do When a Machine Fails the Daily Checkout?

Stop using the machine immediately and tag it clearly so another team member does not inadvertently use it. Isolate the fault to a specific system: oxygen supply, high-pressure, intermediate-pressure, low-pressure, breathing circuit, scavenging, or vaporizer. Simple faults such as a loose connection, cracked hose, or empty cylinder can be corrected in the practice. More complex faults, particularly vaporizer output inaccuracy or internal regulator failure, require service by a qualified technician. The AVMA practice resources advise practices to maintain equipment in good working order as part of professional standards. Document the failure, the corrective action taken, and the date the machine is returned to service.

How Should I Document Checkout Results and Who Should Review Them?

Record the date, machine identifier, person performing the check, and the result for each component. Use a standardized form or log that includes oxygen supply, pressure alarms, leak test results, circuit integrity, scavenging function, and vaporizer status. The survey of veterinary anesthesia equipment in Alberta found that only 2% of machines had a checkout log, which suggests that documentation is a widespread weakness in practice. The responsible veterinarian or practice manager should review logs periodically to identify recurring faults and plan maintenance. A written record also provides a defense if equipment function is questioned after an adverse event. Keep logs for at least the interval recommended by local professional standards.

How Do I Explain a Machine Fault to a Client Whose Procedure Must Be Rescheduled?

Be direct and factual without alarming the client unnecessarily. State that the anesthetic equipment failed a routine safety check, that the procedure cannot proceed safely until the fault is corrected, and that rescheduling protects their animal from anesthetic risk. Avoid technical jargon and do not speculate about the cause if you have not confirmed it. The WSAVA Global Pain Council guidelines emphasize that professional communication supports patient welfare and client trust. Offer the earliest available appointment and explain that the delay is a precaution, not a reflection of the animal's condition. If the client asks whether the fault could have harmed their pet, explain that the check is designed to prevent that harm.

Related Clinical & Scientific Guides

• Anesthetic Machine Leak Testing and Pressure Checks: A Step-by-Step Protocol
• Anesthetic Depth Assessment: Reflexes, Eye Position, and Ventilation
• Anesthesia for Patients with Obesity: Challenges and Solutions

References and Further Reading

• A prospective survey of veterinary anesthesia equipment in Alberta, Canada, using a standardized checkout procedure.. 2023.
• Anesthesia machine checkout and troubleshooting.. 1993.
• AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats. AAHA.
• WSAVA Global Pain Council Guidelines. WSAVA.
• MSD Veterinary Manual, Professional Edition. MSD Veterinary Manual.
• American Veterinary Medical Association Practice Resources. American Veterinary Medical Association.
• WOAH Terrestrial Animal Health Code. WOAH.

Related Articles

• Anesthetic Machine Failure Modes and Salvage Protocols
• Anesthesia Machine Safety Features and Backup Systems
• Anesthetic Circuit Disconnection and Leak Detection
• Avian Anesthesia: Monitoring and Troubleshooting in Pet Birds
• Anesthetic Complications in Cats: Recognition and Salvage

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.