A prospective survey of veterinary anesthesia equipment in Alberta, Canada, using a standardized checkout procedure

Abstract

Background

In both human and veterinary medicine, it is recommended that an anesthetic machine checkout procedure (preuse check) be performed daily, with some items tested before each case, to confirm safe function and the check results recorded.

Objective

The objective of this prospective study was to evaluate anesthetic machines in private veterinary clinics in Alberta (Canada) using a standardized checkout procedure.

Animals and procedures

One-hundred consecutive anesthetic machines were assessed. For each item of the checkout procedure, a “pass,” “fail,” or “not applicable” score was awarded. “Not applicable” indicated an item that could not be evaluated.

Results

Few machines (10%) evaluated had a secondary oxygen supply, no machines had an oxygen supply pressure alarm, and leaks were identified in 31 and 17% of rebreathing and non-rebreathing systems, respectively. Thirty-nine percent of machines did not have a high-pressure circuit alarm, 86% of machines were attached to an active scavenging system, although it was improperly connected in 56% of cases, and only 2% of machines were accompanied by a checkout log.

Conclusion and clinical relevance

There was widespread variation in anesthetic machine standards and function, highlighting the value of performing a regular machine checkout procedure in creating a foundation for safe anesthetic practice.

Introduction

In human medicine, the Association of Anaesthetists of Great Britain and Ireland (AAGBI), and the American Society of Anesthesiology (ASA) recommend that an anesthetic equipment checkout procedure be performed daily, and some parts of the checkout procedure should be performed before each case. In veterinary medicine, the anesthetic equipment checkout procedure largely mirrors what has been traditionally described for human anesthetic practice (1); this includes maintaining a record confirming that the checkout procedure has been completed (1–3).

If anesthetic equipment is not checked properly, risk of patient morbidity and mortality increases (4). Completion of an anesthetic equipment checkout procedure is associated with a reduction in risk of anesthetic morbidity and mortality in humans [odds ratio (OR): 0.64, 95% confidence interval (CI): 0.43 to 0.95] (4).

Two surveys of veterinary anesthetic equipment have been reported. In a prospective survey by Scuffham et al (5), 91% of veterinary anesthetic equipment was faulty (n = 153 machines and breathing systems), and 88% of anesthetic machines had a leak in the rebreathing system, most often associated with the CO₂ absorbent canister (5). Furthermore, in a retrospective survey by Redondo et al (6), 73.6% of anesthetic machines (n = 1243) were faulty: problems were identified with the scavenging system, CO₂ canister, reservoir bag, adjustable pressure-limiting (APL) valve, and oxygen source. The authors described that most anesthetic machine problems noted in the study could have been identified by using a daily checkout procedure (6).

The goal of this prospective survey was to evaluate veterinary anesthetic equipment in Alberta (Canada) with the use of a standardized checkout procedure. A secondary objective was to evaluate the use of anesthetic machine checkout procedures in veterinary clinics in Alberta.

Materials and methods

A prospective survey of anesthetic machines in veterinary clinics in Alberta was performed, using a convenience sample of 100 consecutive machines by a trained service technician (MP) as part of a service contract with a private company. Machines were assessed using a checkout procedure (tests presented in Appendix; checkout document available from Pang, Daniel, 2022, “Anesthesia machine survey,” https://doi.org/10.7910/DVN/W2H02D Harvard Dataverse, V3) created from a combination of human and veterinary sources (1,2,7–11). An ethics application (#REB21-0189) submitted to the institutional Research Ethics and Compliance Office was reviewed, with a decision that consent was not necessary as no information identifying persons was to be collected. The machine service company approved data collection for this study but was not involved in the study design, data analysis, manuscript drafting, or decision to publish. A company employee (MP) contributed to designing and testing the machine checkout procedure, performed data collection, and contributed to writing. No identifying information about the veterinary clinics was collected, so authors analyzing the data (JM, DP) were unaware of machine or clinic location, type of clinic, or number of machines in each clinic. All veterinary clinics were located in Alberta, Canada. Data were collected over a period of approximately 20 wk, from February 2021 to July 2021.

Appendix.

List of items and descriptors in anesthetic machine checkout procedure.

Checklist Item	Description
Electrical Supply	Anesthetic machine is connected to the electrical supply and switched on (yes/no).
Oxygen Supply Test A	Confirm secondary oxygen source (cylinder) is available and functioning: Open cylinder valve and check adequate contents (approximately 50% full or 1000 psig/6895 kPa) and close cylinder valve.
Oxygen Supply Test B	Pipeline gas: Confirm gas pressure is between 40 and 60 psig (approximately 275 and 413 kPa).
Oxygen Supply Test C	Oxygen supply pressure alarm (to indicate pressure failure and/or low FiO2) present and functioning.
Vaporizer Test A	Vaporizers are adequately filled (i.e., at least three quarters full), and filling ports are closed.
Vaporizer Test B	Vaporizers are properly seated on back bar of the machine and secured.
Vaporizer Test C	Vaporizer dial turns smoothly throughout range.
Carbon Dioxide Absorbent	Absorbent use is recorded (by date of last absorbent change, or time in use).
Flowmeter Test	Confirm flow valve operates and that bobbin/ball moves smoothly throughout full range.
Oxygen Flush — Part A	Confirm function of oxygen flush: Gas flow is present when activated, and flow stops when control is released.
Oxygen Flush — Part B	Confirm line pressure does not drop during operation.
Leak Test A	Vaporizer: Turn on oxygen (~3 L/min) and occlude common gas outlet with vaporizer dial in on/off position. Flowmeter bobbin/ball should dip (confirms absence of significant leak between flowmeter and common gas outlet).
Leak Test B	Breathing system: Visually inspect system components to confirm correct assembly and that breathing system is free of obstruction.
Leak Test C	Do breathing systems connect securely? (yes/no).
Leak Test D	Rebreathing leak test: Occlude patient end of breathing system, close APL valve and pressurize system via oxygen flowmeter to 30 cmH2O. Turn off oxygen flow and observe pressure gauge, pressure should be maintained at 30 cmH2O for 10 s. Open APL valve and confirm that reservoir bag deflates (pressure gauge should return to zero). Uncover/unplug patient end. A leak of ≤ 200 mL/min is acceptable.
Leak Test E	Non-rebreathing system leak test: Occlude patient end of breathing system, close APL valve and pressurize system via oxygen flowmeter to 30 cmH2O. Turn off oxygen flow and observe pressure gauge, pressure should be maintained at 30 cmH2O for 10 s. Open APL valve and confirm that reservoir bag deflates (pressure gauge should return to zero). Uncover/unplug patient end. A leak of ≤ 200 mL/min is considered acceptable.
Leak Test F	Test inner limb of non-rebreathing system; with oxygen flowing at approximately 3 L/min occlude inner limb, flowmeter bobbin should dip (confirms absence of significant leak between common gas outlet and patient end of inner limb).
Two Bag Test A	Confirms whole rebreathing system patent and free of obstructions.
Two Bag Test B	Rebreathing system: Attach a reservoir bag to the patient end of the circle breathing system. Turn on oxygen to approximately 3 L/min, and manually ventilate. Observe unidirectional valve function during manual ventilation.
Two Bag Test C	APL valve in open position: Attach a reservoir bag to the patient end of the rebreathing system. Squeeze both reservoir bags and confirm APL valve function. Proper testing will demonstrate that pressure can be developed in the breathing system during both manual and mechanical ventilation and that pressure can be relieved during manual ventilation by opening the APL valve.
Two Bag — Part D	Is ventilator present? (yes/no).
Two Bag — Part E	Breathing systems should be protected with reservoir bag when not in use to prevent intrusion of foreign bodies.
High pressure circuit alarm — Part A	Is high pressure circuit alarm present? (yes/no).
High pressure circuit alarm — Part B	If high pressure alarm is present, is it adjustable? (yes/no).
Scavenge Test A1	Active scavenging: Confirm scavenging system is correctly connected to the machine.
Scavenge Test A2	Passive scavenging: Confirm charcoal canister is not obstructed, it is not overweight, and that its weight is recorded.
Scavenge Test B	Confirm that reservoir bag deflates at conclusion of leak test for both rebreathing and non-breathing system.
Scavenge — Part C	Is scavenging above minimal measurable flow [30 L/min (yes/no)].
Scavenge — Part D	Occlude patient end of non-rebreathing system and activate oxygen flush with APL valve open. Confirm that breathing system pressure gauge reading is below 10 cmH2O. This test confirms that scavenging flow is sufficient to limit pressure build up within the breathing system.
Scavenge — Part E	Occlude patient end of rebreathing system and activate oxygen flush with APL valve open. Confirm that breathing system pressure gauge reading is below 10 cmH2O. This test confirms that scavenging flow is sufficient to limit pressure buildup within the breathing system.
Log of Checkout Procedure	Is there a log of machine checkout procedure kept with the machine? (yes/no).
Machine Concerns	Did the clinic staff describe any problems with the machine before the checkout procedure was performed? (yes/no).

Each item of the checkout procedure was assessed and scored as “pass,” “fail,” or “not applicable;” the latter was awarded if an item could not be evaluated (for example, if the anesthetic machine did not have an oxygen flush, oxygen flush function could not be evaluated). As the checkout procedure had not previously been used, a small pilot study was performed to confirm that it could be applied to anesthetic equipment typically encountered in clinics, and that the descriptions were clear and could be applied consistently. Fifteen machines that were included in the pilot study were not included in the final results.

Analysis

Descriptive statistics were applied to data, using commercial software for data management and calculations [Microsoft Excel 2016 MSO (16.0.7127.1021) 32 bit].

Each item of the checkout procedure that could be assessed for each machine was summed to generate the denominator. If an item of the checkout procedure was identified as non-applicable for a particular machine, then this item was not included in the denominator during data analysis. The numerator (pass or fail) and denominator were used to calculate a percentage of machines that passed or failed each checkout procedure item. To facilitate presentation of results, items from the checkout procedure were grouped as follows: machine specifications, oxygen supply and vaporizers, leak tests, 2 bag tests, waste gas scavenge system, and administrative observations. All data supporting the results are available in a repository: Pang, Daniel, 2022, “Anesthesia machine survey,” https://doi.org/10.7910/DVN/W2H02D Harvard Dataverse, V3.

Results

Twenty-nine clinics were visited with a median of 3 machines (range: 1 to 12 machines) tested per clinic (data provided by MP).

Machine specifications

None of the anesthetic machines in the current study required electricity to function, so none could be included for this item of the checkout procedure, i.e., they were all classified as non-applicable.

Approximately 2/3 of machines tested had a high-pressure circuit alarm, and most of these alarms were adjustable (Table 1). Almost all machines evaluated had carbon dioxide (CO₂) absorbent (Table 1). Of these machines, > 3/4 had an accompanying record documenting that the absorbent had been changed (Table 1). The CO₂ absorbent item from the checkout procedure was not included for 11 machines, as a CO₂ absorbent canister was not attached to the machine.

Table 1.

Machine specifications.

Item on checkout sheet	Description	Percentage of applicable machines that passed the checkout procedure
Electrical supplya	Anesthetic machine is connected to the electrical supply and switched on.	n/a
High pressure circuit alarm — Part A	High pressure circuit alarm present? (yes/no).	61% (61/100)
High pressure circuit alarm — Part B	High pressure circuit alarm is present, is it adjustable? (yes/no).	91.8% (56/61)
CO2 Absorbentb	Absorbent (yes/no).	82% (73/89)

^aNone of the anesthetic machines in the current study required electricity to run.

^bThe CO₂ absorbent item from the checkout procedure was not included for 11 machines, as they did not have a CO₂ absorbent canister attached to the machine.

n/a — Not available.

The accuracy of documenting absorbent use was difficult to determine. The number of days since CO₂ absorbent change was determined in approximately 2/3 of machines based on the date recorded and labeled on the canister (Table 2). The interval between absorbent changes varied between < 1 d to > 2 y (1067 d). The interval since the last recorded change was > 90 d in approximately 10% of machines (Table 2). The number of days could not be determined in 32 machines because there was no rebreathing system (n = 11), the date was mistakenly not recorded during the checkout procedure (n = 3), a “due date” was written instead of date changed (n = 2), or no date was written at all (n = 16).

Table 2.

Time since CO₂ absorbent was changed as indicated by label on canister.

Anesthetic machines with date recorded for absorbent change	Machines with CO2 absorbent changed 30 d or less at the time of checkout procedure	Machines with CO2 absorbent changed between 31 and 60 d at the time of checkout procedure	Machines with CO2 absorbent changed between 61 and 90 d at the time of checkout procedure	Machines with CO2 absorbent changed > 91 d at the time of checkout procedure
76.4% (68/89)a	69.1% (47/68)	16.1% (11/68)	2.9% (2/68)	11.7% (8/68)

^aThe number of days could not be determined in 32 machines because there was no rebreathing system (n = 11), the date was mistakenly not recorded during the checkout procedure (n = 3), a “due date” was written instead of date changed (n = 2), or no date was written at all (n = 16).

Oxygen supply and vaporizers

Almost all anesthetic machines had vaporizers that were adequately filled with closed filling ports and all anesthetic machines had proper vaporizer fixation (Table 3). Most vaporizer dials turned smoothly throughout the range (Table 3).

Table 3.

Oxygen supply and vaporizers tests.

Item on checkout sheet	Description	Percentage of applicable machines that passed the checkout procedure
Vaporizer Test A	Vaporizers are adequately filled, and filling ports are closed.	99% (99/100)
Vaporizer Test B	Vaporizers are properly seated on back bar and secured.	100% (100/100)
Vaporizer Test C	Vaporizer dial turns smoothly throughout the range.	97% (97/100)
Oxygen Supply Test A	Secondary source of oxygen present.	10% (10/100)
Oxygen Supply Test Ba	Pipeline gas is between 40 to 60 psig.	85.9% (67/78)
Oxygen Supply Test C	Oxygen supply pressure alarm is present and functioning.	0% (0/100)
Oxygen Flush — Part Ab	Oxygen flush functional.	92% (81/88)
Oxygen Flush — Part Bc	Line pressure does not drop during operation of oxygen flush.	87.5% (7/8)
Flowmeter Test	Flow valve operates and that bobbin moves smoothly throughout full range.	86% (86/100)

^aPipeline pressure item (Oxygen Supply Test B) of the checkout procedure could not be assessed for 22 machines, as they did not have pipeline oxygen (n = 2), or pipeline pressure could not be assessed as a pressure gauge was not fitted on the machine (n = 20).

^bThe oxygen flush item (Oxygen Flush Test A) was not included for 12 machines, as oxygen flush was not present.

^cIt could not be confirmed in most machines (92/100) that line pressure did not drop when oxygen flush was activated because most machines did not have a line pressure gauge on the machine or within sight.

Few machines had a secondary source of oxygen (Table 3). More than three-quarters of machines tested had appropriate pipeline oxygen pressure (Table 3). Pipeline pressure item (oxygen supply test B) of the checkout procedure could not be assessed for 22 machines, as they did not have pipeline oxygen (n = 2), or pipeline pressure could not be assessed as a pressure gauge was not fitted on the machine (n = 20). No machines had an oxygen supply pressure alarm (Table 3).

Most machines had an oxygen flush, and of those machines, the majority were functional (Table 3). The oxygen flush item (oxygen flush test A) was not included for 12 machines, as oxygen flush was not present. It could not be confirmed in most machines (92/100) whether the oxygen line pressure dropped when oxygen flush was activated because most machines did not have a line pressure gauge on the machine or within sight (Table 3). Of the 8 machines with a line pressure gauge, 7 did not have line pressure drop during operation of the oxygen flush (Table 3).

Most machines had a flowmeter with an operational flow valve and bobbin (Table 3).

Leak tests

More than 3/4 of machines passed the vaporizer leak test (Test A, Table 4). Of the 14 machines that failed this test, 8 machines failed because the flowmeter bobbin did not dip when the common gas outlet was occluded. In most machines, the breathing systems were correctly assembled and free of obstruction (Test B, Table 4). Almost all machines tested had securely connected breathing system components (Test C, Table 4).

Table 4.

Leak tests.

Item on checkout sheet	Description	Percentage of applicable machines that passed the checkout procedure
Leak Test A	Vaporizer: Turn on oxygen (~3 L/min) and occlude common gas outlet with vaporizer dial in on/off position, flowmeter bobbin should dip.	86% (86/100)
Leak Test B	Breathing systems correctly assembled and free of obstruction.	91% (91/100)
Leak Test C	Breathing systems connected securely.	99% (99/100)
Leak Test Da	Rebreathing system leak test passed.	69% (60/87)
Leak Test Eb	Non-rebreathing system leak test passed.	83% (78/94)
Leak Test Fc	Inner limb of non-rebreathing system leak test passed.	96.2% (75/78)

^aRebreathing system leak tests could not be performed for 11 machines as a rebreathing system was not present. For 2 machines, a rebreathing system was present but could not be tested for a leak as a pressure gauge was not present.

^bIn 6 machines, the non-rebreathing system leak test was not included for the following reasons: machine did not have non-rebreathing system (n = 1), machine did not have a pressure gauge (n = 2), there was a modified Jackson-Rees system on the anesthetic machine (n = 3).

^cThe inner limb test (Test F) could not be included in 22 machines for the following reasons: breathing circuit tubing was manufactured in such a way that inner limb could not be tested (n = 18), no non-rebreathing system on anesthetic machine (n = 1), modified Jackson-Rees system on anesthetic machine (n = 3).

Approximately one-third of rebreathing systems tested had a leak (Test D, Table 4). Rebreathing system leak tests could not be performed for 11 machines, as a rebreathing system was not present. For 2 machines, a rebreathing system was present but could not be leak tested as a pressure gauge was not present.

One fifth of non-rebreathing systems tested had a leak (Test E, Table 4). In 6 machines, the non-rebreathing system leak test was not included for the following reasons: machine did not have non-rebreathing system (n = 1), machine did not have a pressure gauge (n = 2), or there was a modified Jackson-Rees system on the anesthetic machine (n = 3).

Almost all machines had a functional inner limb of the non-rebreathing breathing system (Test F, Table 4). The inner limb test (Test F) could not be included in 22 machines for the following reasons: breathing system tubing was manufactured in such a way that inner limb could not be tested (n = 18), no non-rebreathing system on anesthetic machine (n = 1), modified Jackson-Rees system on anesthetic machine (n = 3).

Two bag tests of rebreathing system

The 2-bag test items of the checkout procedure were not included for machines without a rebreathing system (n = 11). All rebreathing systems passed the 2-bag test (Table 5). Very few machines had a ventilator present, and no machines had a reservoir bag attached to the patient end of the rebreathing system when not in use (Table 5).

Table 5.

Two bag tests of the rebreathing system.

Item on checkout sheet	Description	Percentage of applicable machines that passed the checkout procedure
Two Bag Test A	Rebreathing system is patent.	100% (89/89)
Two Bag Test B	Unidirectional valve function during manual ventilation.	100% (89/89)
Two Bag Test C	APL valve functions.	100% (89/89)
Two Bag — Part D	Ventilator present.	14.6% (13/89)
Two Bag — Part E	Breathing system protected with reservoir bag when not in use.	0% (0/89)

Two bag test items of the checkout procedure were not included in machines without a rebreathing system (n = 11).

Waste gas scavenge system

Most anesthetic machines had active scavenging (Table 6). Just under half of the machines with active scavenging did not have the scavenging system correctly assembled or properly attached to the machine (Test A1, Table 6). More than 3/4 of machines with passive scavenging had an inappropriate set up (charcoal canister overweight or not weighed) (Test A2, Table 6). In all machines, the reservoir bag deflated at conclusion of leak test (Test B, Table 6).

Table 6.

Waste gas scavenging tests.

Item on checkout sheet	Description	Percentage of applicable machines that passed the checkout procedure
Active Scavenge System	Active scavenge in use.	86% (86/100)
Passive Scavenge System	Passive scavenge in use.	14% (14/100)
Scavenge System Test A1	Active scavenging: Correctly connected to the machine and functional.	55.8% (48/86)
Scavenge System Test A2	Passive scavenging: Confirm appropriate use of charcoal canister.	21.4% (3/14)
Scavenge Test B	Reservoir bag deflates at conclusion of leak test.	100% (100/100)
Scavenge — Part Ca	Active scavenging (> 30 L/min).	79.1% (68/86)
Scavenge — Part Db	Occlude patient end of non-rebreathing system and activate oxygen flush with APL valve open; breathing system pressure gauge reading is below 10 cmH2O.	48% (36/75)
Scavenge — Part Ec	Occlude patient end of rebreathing system and activate oxygen flush with APL valve open; breathing system pressure gauge reading is below 10 cmH2O.	67.9% (55/81)

^aThis test did not apply to machines connected to a passive scavenging system (n = 14).

^bThe test could not be performed in 1/4 of all machines for the following reasons: no oxygen flush (n = 12), oxygen flush was not attached to the non-rebreathing system (n = 8), no pressure gauge (n = 2), machine did not have non-rebreathing system (n = 1). In 2 machines, the results of the test were not recorded.

^cThe test could not be performed in 19 machines for the following reasons: no oxygen flush (n = 5), no pressure gauge (n = 2), machine did not have rebreathing system (n = 4), machine did not have both oxygen flush and rebreathing system (n = 7). In 1 machine, the result of the test was not recorded.

Approximately 25% of machines with active scavenging did not have acceptable minimal measurable flow (Test C, Table 6). This test did not apply to machines connected to a passive scavenging system (n = 14).

Less than half of anesthetic machines passed the scavenging function tests with the non-rebreathing system attached (Test D, Table 6). The test could not be performed in 1/4 of all machines for the following reasons: no oxygen flush (n = 12), oxygen flush was not attached to the non-rebreathing system (n = 8), no pressure gauge (n = 2), or machine did not have non-rebreathing system (n = 1). In 2 machines, the results of the test were unintentionally not recorded.

Approximately 2/3 of anesthetic machines passed the scavenging function tests with the rebreathing system attached (Test E, Table 6). The test could not be performed in 18 machines for the following reasons: no oxygen flush (n = 5), no pressure gauge (n = 2), machine did not have rebreathing system (n = 4), machine did not have both oxygen flush and rebreathing system (n = 7). In 1 machine, the result of the test was unintentionally not recorded.

Administrative observations

Very few anesthetic machines had a record of a checkout procedure kept with the machine (Table 7). Very few machines were identified as having a pre-existing concern before or during machine service (Table 7).

Table 7.

Administrative observations of the checkout procedure.

Category on checkout sheet	Description	Percentage
Log of checkout procedure	Log of checkout procedure kept with machine.	2% (2/100)
Machine problems identified	Clinic staff voluntarily declare equipment problems.	4% (4/100)

Discussion

The main findings of the current study were that

1. few machines evaluated had a secondary oxygen supply;

2. no machines had an oxygen supply pressure alarm;

3. approximately 1/3 of machines had a leak identified in the rebreathing system;

4. approximately 40% of machines did not have a high-pressure circuit alarm;

5. about 1/2 of non-rebreathing systems and 1/3 of rebreathing systems had pressure build up within the system during the scavenging test; and

6. very few clinics maintained a record of machine checkout (pre-use check) procedures or reported a concern with their anesthetic machine(s) before or during the service visit.

Hypoxemia is an uncommon but potentially devastating complication during general anesthesia (12–14). Only short periods of hypoxemia can be tolerated before cardiopulmonary collapse occurs. During general anesthesia, cardiopulmonary changes secondary to drug effects, disease, procedure, and body position increase the risk of hypoxemia. For these reasons, an inspired concentration of oxygen exceeding that of ambient air is normally provided to anesthetized patients. It is widely recommended that a secondary (backup) supply of oxygen be available in the event that the primary system is drained or there is mechanical failure in oxygen supply (15,16). A secondary oxygen supply was available for only 10% of machines in this study. The reasons underlying this low rate are unknown.

Given the risks associated with failure of oxygen supply, oxygen supply pressure alarms are routinely fitted to human anesthesia machines (17,18). However, this study suggests their use in veterinary anesthesia is rare, as no machines had an oxygen supply pressure alarm fitted. Relying on oxygen pressure gauges to monitor supply is helpful but these gauges can malfunction, and the supply of oxygen is not typically monitored and recorded on anesthesia monitoring charts (19). In most cases, the first indications of oxygen supply failure are non-specific physiologic changes (tachycardia, hyperpnea) or a reduction in oxygen saturation of arterial hemoglobin. In both instances, hypoxemia is already present, reducing the time available to correct the situation before morbidity/mortality occur. Ideally, a 2-stage oxygen failure alarm system would be used, with an alarm at the oxygen supply manifold (when present) and a second alarm at the anesthetic machine. This latter should be powered by the oxygen supply, without reliance on a battery (e.g., Ritchie whistle).

Breathing system leaks are potentially detrimental to the patient, as a lower gas flow is delivered than intended. In addition, leaks contribute to workplace pollution with anesthetic agent, which can cause negative short-term effects, such as headache, fatigue, nausea, drowsiness, impaired motor coordination, and judgement (20,21). The ASA, AAGBI, and Association of Veterinary Anaesthetists guidelines recommend leak testing before each use and after any component of the breathing system is changed (tubing, reservoir bag) (1–3). In the current study, 2 machines with rebreathing systems, and 2 machines with non-rebreathing systems, did not have a pressure gauge, so that a leak test could not be properly performed. Scuffham et al (5) reported that 88% (29/33) of rebreathing systems tested had a leak and 20% (1/5) of non-rebreathing systems tested had a leak. The lower incidence of leaks identified in the current study may reflect changes in equipment or practice over time or the sample populations studied. The long-term health effects of chronic anesthetic gas exposure on personnel remain unclear, but current federal regulations require controls to minimize exposure to waste anesthetic gases (22,23). Exposure should always be minimized through good practice, including regular machine leak testing and use of functioning waste gas scavenging systems.

The inadvertent buildup of pressure in a breathing system is a well-recognized cause of morbidity and mortality in veterinary anesthesia (24). One of the most common sources of pressure increase is unintended closure of the APL valve (25,26). Although an equipment checkout procedure, when properly performed, will prevent an APL valve from being closed unintentionally at the start of an anesthetic procedure, a valve may still be left closed during a case. In the current study, ~40% of machines did not have a functioning high pressure circuit alarm. The use of a high-pressure circuit alarm is a simple, effective, and inexpensive method to identify pressure buildup early before pressure rises to levels leading to cardiovascular collapse are reached. Hofmeister et al (25) noted a significant decrease in the number of incidents of an unintentionally closed APL valve after implementing a checklist that included the operating room be checked by an anesthesia technician before patient transfer. Importantly, however, use of a checklist did not prevent all occurrences of closed APL valves. This emphasizes the value of a high circuit pressure alarm.

A further source of pressure buildup in anesthetic machines is inadequate scavenging. This was identified in approximately 1/2 of the non-breathing systems and in approximately 1/3 of the rebreathing systems. Redondo et al (6) reported that 37.9% of 1243 anesthetic machines evaluated had a faulty scavenging system, similar to the findings of the current study. Effectiveness of a scavenging system in removing waste gases is compromised if there is a leak in the system (4,25); this underlines the importance of regularly performing an equipment checkout procedure.

Checkout procedures are recommended in both human and veterinary anesthesia (6,7,27). A physical document of the checkout procedure attached to the machine promotes consistent practice, as well as accountability for the safety of the patient prior to anesthesia (1). When a checkout procedure is not performed before anesthesia, there is an increased risk of patient morbidity and mortality (3,4,28)

In the present study, very few clinics appeared aware of problems present in their anesthesia machines at the time of servicing. However, it was beyond the scope of this study to interview staff members; a necessary step in confirming this result and a limitation of this study. Importantly, all problems identified in the current study were identified with a standard equipment checkout procedure, highlighting the value of this practice. This finding is reflected in both the veterinary and human literature (4,6). The current study was limited to anesthetic machines in Alberta and further research is needed to quantify the use of equipment faults and checkout procedures in other Canadian provinces. This study was not designed to assess staff proficiency in performing anesthetic machine checks or use of anesthetic equipment and therefore cannot comment on either of these areas.

The findings of this study suggest room for improvement in the care and maintenance of anesthesia equipment. It is likely that a multipronged approach is required, including education, support, and regulation. Education is necessary for users to understand the risks associated with anesthetic equipment, such as the value of using pressure-limited or quick-release APL valves; however, education alone is unlikely to be effective in raising standards. Support could be provided through easily accessible tools to facilitate machine checks, such as printed or electronic copies of a checkout procedure. For example, a laminated checkout procedure could be attached to each anesthesia machine. A freely available “how to” video could be created, with a link distributed by equipment suppliers or embedded in a checkout procedure. Ultimately, regulatory oversight, as already performed by provincial bodies, could include a requirement for a checkout procedure log to be kept.

The results of this study highlight the prevalence of numerous faults in anesthesia machines, many of which have the potential to compromise patient safety or increase personnel exposure to waste anesthetic gas. The low apparent incidence of performing an anesthetic equipment checkout procedure indicates a need for further education, support, and potentially mandated equipment requirements. CVJ