Chapter Anesthesia Machine Malfunction

Edwin B. Liem

Samsun Lampotang

CASE SUMMARY

A patient is scheduled as the first case of the day for a hysterectomy. The patient has a history of asthma and is medicated with albuterol via a metered dose inhaler. Past surgeries were all without complications. The patient is in no apparent distress with clear breath sounds on auscultation.

The patient is taken to the operating room; initial vital signs are: heart rate 80 beats per minute, blood pressure 145/75 mmHg, and SpO₂100% on room air. After preoxygenation, general anesthesia is induced. Mask ventilation and endotracheal intubation proceed uneventfully. An Aestiva anesthesia machine (Datex-Ohmeda, Madison, WI) is being used. Positive-pressure ventilation is initiated using volume-controlled, pressurelimited, time-cycled ventilation, with a set tidal volume (VT) of 650 mL, a rate of 10 breaths per minute, and fresh gas flow rate at 2 L per minute of oxygen.

Approximately 5 minutes after initiation of positivepressure ventilation, monitored exhaled VT appears significantly decreased. Breath sounds are verified and appear to be equal bilaterally. The endotracheal tube cuff is checked, and there is no audible leak below 30 cm H₂O when positive pressure is applied. An attempt is made to (temporarily) compensate for the loss of VT by increasing the ventilator VT setting. However, the discrepancy between the set VT and the monitored exhaled VT continues to increase. The ventilator has an ascending bellows (ascending during expiration), and it is noted that bellows travel corresponds with the set VT (i.e., with a VT set to 650 mL, the bellows travel is visually observed to be ˜ 650 mL). Nevertheless, the monitored exhaled VT has now decreased to 300 to 400 mL with each breath. In addition, the bellows does not reach the top of the housing at the end of expiration. Fresh gas flow needs to be increased to compensate for this apparent leak.

The patient is temporarily disconnected from the anesthesia machine and ventilated with a self-inflating manual resuscitator, which achieves adequate VTs. Help is requested, and another anesthesia provider arrives. Now that another anesthesia provider is taking care of the patient, an attempt is made to troubleshoot the machine. The bag-ventilator selector is switched to manual (bag), and fresh gas flow is reduced to minimal. A positive-pressure leak test is performed by manually occluding the Y-piece of the breathing circuit, closing the adjustable pressurelimiting (APL) valve completely, and pressing the oxygen flush valve to increase the pressure to 30 cm H₂O. There does not appear to be a significant leak from the breathing circuit. The patient is reconnected, the selector knob is switched to the ventilator, and mechanical ventilation is restarted.

With the APL valve left completely closed from the previous maneuver, it is now noted that during each mechanical inspiratory breath, the manual bag surprisingly appears to slightly inflate with each mechanical breath. The manual bag continues to increase in size, and it appears that a leak is occurring from the mechanical ventilation circuit into the manual ventilation circuit. A looseness is noted on manipulation of the bag selector switch. Pushing the lever to its full mechanical stop seems to resolve the leak. The remainder of the surgery is completed without further issues, but it is decided not to use the anesthesia machine for subsequent cases.

When a service technician inspects the machine, there is a crack in an internal piece that anchors the bagventilator selector switch, as reported by others.¹ The effect of the crack appears to be such that when the bag-ventilator selector is switched from manual (bag) to mechanical ventilation, the bag-ventilator selector valve does not completely prevent gas flow to the manual ventilation circuit (i.e., the bag-ventilator selector valve acts as a three-way connector between the breathing circuit, mechanical ventilation, and manual ventilation sub-systems). A significant amount of gas loss is occurring during mechanical ventilation through the partially open bag-ventilator selector valve. Replacement of the part resolves the malfunction.

CASE DEBRIEFING

The case described highlights issues surrounding anesthesia machine complications. First and foremost, the leaky bag-ventilator selector switch can be detected by an anesthesia machine pre-use check—specifically at steps
12e and 12f of the 1993 U.S. Food and Drug Administration (FDA) pre-use check (see Table 56.1). This raises questions as to whether: (a) a correct pre-use check was actually performed before the case, and (b) the medical record documented that a pre-use check had been performed. It is possible that the anesthesia provider did perform a complete pre-use check, but performed or interpreted tests 12e and 12f incorrectly. Another possibility is that part of the anesthesia machine checkout was performed manually, but that it was incorrectly assumed that a “semi-automated” pre-use check would perform those checks the provider did not do, specifically 12e and 12f. Documentation of pre-use check performance is particularly relevant if other anesthesia providers or anesthesia technicians perform all or part of the pre-use check in an institution and raises the question of whether miscommunication between team members occurred.

Some generally accepted patient safety principles are illustrated. First of all, once it was apparent that an anesthesia machine failure was present, the correct first response is to disconnect the patient from the suspect machine and call for help while ventilating the patient with a self-inflating manual resuscitator. This assumes that the availability of a properly functioning manual resuscitator was verified during the pre-use check step 1, because these devices may also malfunction.² An attempt at debugging the anesthesia machine intraoperatively was only initiated after help had arrived and the patient was being properly ventilated and monitored. The patient remained the priority, and the anesthesia machine malfunction was not allowed to become a distraction.

▪ INTRODUCTION

During daily clinical activities, proper functioning of our equipment is expected—and often assumed. Failure or malfunctioning of the anesthesia equipment, like all things mechanical, is at some point inevitable. For example, in a study of 83,154 anesthetics, the frequency of anesthetic equipment problems was 0.23% during general anesthesia. The anesthesia machine was involved in one third and human error in one quarter of the problems.³ This chapter is divided into two general sections: the first section focuses on strategies for prevention of malfunctions; the second section discusses different approaches that can be used when confronted with intraoperative anesthesia machine malfunctions. By using these approaches, patient injury should, in many cases, be preventable.

What Type of Checklist Is Used to Prevent Malfunction?

▪ THE ANESTHESIA MACHINE PRE-USE CHECK

The importance of the anesthesia machine pre-use check from a patient safety perspective has been underscored by a study in a cohort comprising 869,483 patients.⁴ This comprehensive, large scale study found the following: (a) the performance of an equipment check with a protocol and a checklist, and (b) documentation of this check were individually associated with a significantly decreased risk in 24-hour postoperative severe morbidity and mortality. Earlier studies also support the value of the pre-use check in breaking the chain of events that may conspire to create a critical incident.⁵,⁶

Most equipment faults can be detected with a systematic assessment and pre-use check of the anesthesia equipment. Ideally, each component of the anesthesia machine and each safety device or alarm must be tested and its correct function verified before a patient is anesthetized. The FDA has, over the years, published recommendations for conducting a pre-use checkout of the anesthesia equipment. The latest version of the protocol was revised in 1993 and updated in 1997⁷ (Table 56.1). The protocol was universal at the time of publication in the sense that it was broadly applicable to any type or brand of anesthesia machine from that era, with slight local modifications of the protocol for specific types of equipment. It is recommended that the protocol be performed completely on a daily basis, usually for the first case of the day. If an anesthesia provider uses the same anesthesia machine for successive cases during the day, an abbreviated pre-use check can be performed before each subsequent anesthetic administration. In addition, the availability and proper function of back-up ventilation equipment must be verified before every case.

▪ FOOD AND DRUG ADMINISTRATION CHECKLIST

Many countries outside the United States use the FDA checklist, whereas other countries have developed their own checklists.⁸ The 1993 FDA pre-use check is currently being redesigned by the American Society of Anesthesiologists (ASA) Task Force on Revising the Pre-use Checkout.⁹ At the time of writing, the new guidelines had not been finalized and were unavailable for inclusion in this chapter.

Frequency of the Pre-Use Check

The FDA anesthesia apparatus checkout recommendations state that “This checkout, or a reasonable equivalent, should be conducted before administration of anesthesia”. This means that a pre-use check, whether a complete one or an abbreviated one where appropriate, should be performed before every single anesthetic.

How well is the FDA’s recommendation to check before every anesthetic heeded in actual clinical practice? Outright omission and infrequent or sporadic performance of the anesthesia machine pre-use check has been reported in the past⁶,¹⁰ and seems to persist to this day.¹¹ A 1981 paper suggested failure to perform a preanesthetic check in at least one third of anesthetics.⁶ March and Crowley¹⁰ quoted an FDA report that indicated that pre-use checkout practices were inconsistent, and use of the FDA (or similar) checklist was minimal. In an anonymous web survey conducted by Lampotang et al.¹¹ 20% of 244 respondents reported performing a pre-use check before every case and 52% every morning before the first case of the day. The survey also attempted to identify the reasons that the pre-use check might be improperly performed or entirely omitted.¹¹

TABLE 56.1 Anesthesia Apparatus Checkout Recommendations, 1993

EMERGENCY VENTILATION EQUIPMENT
	1.	Verify back-up ventilation equipment is available and functioning.^a
HIGH PRESSURE SYSTEM
	2.	Check oxygen cylinder supply.^a Open O₂ cylinder and verify at least half full (˜1,000 ψ). Close cylinder.
	3.	Check central pipeline supplies.^a Check that hoses are connected and pipeline gauges read approximately 50 ψ.
LOW PRESSURE SYSTEM
	4.	Check initial status of low pressure system.^a Close flow control valves and turn vaporizers off. Check fill level and tighten vaporizers’ filler caps.
	5.	Perform leak check of machine low pressure system.^a Verify that the machine master switch and flow control valves are OFF. Attach “Suction Bulb” to common fresh gas outlet. Squeeze bulb repeatedly until fully collapsed. Verify bulb stays fully collapsed for at least 10 s. Open one vaporizer at a time and repeat “c” and “d” as above. Remove suction bulb, and reconnect fresh gas hose.
	6.	Turn on machine master switch and all other necessary electric equipment.^a
	7.	Test flowmeters.^a Adjust flow of all gases through their full range, checking for smooth operation of floats and undamaged flowtubes. Attempt to create a hypoxic O₂/N₂O mixture and verify correct changes in flow and/or alarm.
SCAVENGING SYSTEM
	8.	Adjust and check scavenging system.^a Ensure proper connections between the scavenging system and both APL (pop-off) valve and ventilator relief valve. Adjust waste gas vacuum (if possible). Fully open APL valve and occlude Y-piece. With minimum O₂ flow, allow scavenger reservoir bag to collapse completely and verify that absorber pressure gauge reads approximately zero. With the O₂ flush activated, allow the scavenger reservoir bag to distend fully, and then verify that absorber pressure gauge reads <10 cm H₂O.
BREATHING SYSTEM
	9.	Calibrate O₂ monitor.^a Ensure monitor reads 21% in room air. Verify low O₂ alarm is enabled and functioning. Reinstall sensor in circuit and flush breathing system with O₂. Verify that monitor now reads >90%.
	10.	Check initial status of breathing system. Set selector switch to “Bag” mode. Check that breathing circuit is complete, undamaged, and unobstructed. Verify that CO₂ absorbent is adequate. Install breathing circuit accessory equipment (e.g., humidifier, PEEP valve) to be used during the case.
	11.	Perform leak check of the breathing system. Set all gas flows to zero (or minimum). Close APL (pop-off) valve and occlude Y-piece. Pressurize breathing system to approximately 30 cm H₂O with O₂ flush. Ensure that pressure remains fixed for at least 10 s. Open APL (pop-off) valve and ensure that pressure decreases.
MANUAL AND AUTOMATIC VENTILATION SYSTEMS
	12.	Test ventilation systems and unidirectional valves. Place a second breathing bag on Y-piece. Set appropriate ventilator parameters for next patient. Switch to automatic ventilation (ventilator) mode. Fill bellows and breathing bag with O₂ flush and then turn ventilator ON. Set O₂ flow to minimum, other gas flows to zero. Verify that during inspiration bellows delivers appropriate tidal volume and that during expiration bellows fills completely. Set fresh gas flow to approximately 5 L/min. Verify that the ventilator bellows and simulated lungs fill and empty appropriately without sustained pressure at end expiration. Check for proper action of unidirectional valves. Exercise breathing circuit accessories to ensure proper function. Turn ventilator OFF and switch to manual ventilation (bag/APL) mode. Ventilate manually and assure inflation and deflation of artificial lungs and appropriate feel of system resistance and compliance. Remove second breathing bag from Y-piece.
MONITORS
	13.	Check, calibrate and/or set alarm limits of all monitors—capnometer, pulse oximeter, oxygen analyzer, respiratory volume monitor (spirometer), pressure monitor with high and low airway alarms.
FINAL POSITION
	14.	Check final status of machine. Check if vaporizers are OFF. Check if actuator feed limit (AFL) valve is open. Check if selector switch is set to “Bag”. Check if all flowmeters are set to zero. Check if patient suction level is adequate. Check if breathing system is ready to use.
This checkout, or a reasonable equivalent, should be conducted before administration of anesthesia. These recommendations are only valid for an anesthesia system that conforms to current and relevant standards and includes an ascending bellows ventilator and at least the following monitors: Capnograph, pulse oximeter, oxygen analyzer, respiratory volume monitor (spirometer), and breathing system pressure monitor with high and low pressure alarms. This is a guideline which users are encouraged to modify to accommodate differences in equipment design and variations in local clinical practice. Such local modifications should have appropriate peer review. Users should refer to the operator’s manual for the manufacturer’s specific procedures and precautions, especially the manufacturer’s low pressure leak test (step 5).
^aIf an anesthesia provider uses the same machine in successive cases, these steps need not be repeated or may be abbreviated after the initial checkout.
APL, adjustable pressure limiting; PEEP, positive end-expiratory pressure.
U.S. Food and Drug Administration. Center for Devices and Radiological Health. Anesthesia apparatus checkout recommendations, 1993. (Updated May 12, 1997). Available at: http://www.fda.gov/cdrh/humfac/anesckot.html. Accessed September 21, 2006.

244 surveys were filled with 138 US respondents. The average age was 38.7 years, with an average of 7.5 years providing anesthesia. Responders included 56 anesthesiologists, 47 certified registered nurse anesthetists (CRNAs), 46 residents, 11 anesthesiology assistants, and 49 nonanesthesia providers (anesthesia technicians/biomedical engineers). 182 responders had anesthesia technicians or biomedical engineers at their institution, with 163 indicating that the anesthesia technicians or biomedical engineers did not perform the pre-use check for the anesthesia providers.

Seventy-one responders (29%) rated their competence in performing the 1993 FDA pre-use check as Poor (do not know what, how or why of each step), 81 (33%) as “Satisfactory” (know what to do), 64 (26%) as “Good” (know what to do and how to do each step), and 28 (12%) as “Excellent” (know what, how and why of each step). The frequency of performing the pre-use check was:

Every case: n = 48
Every morning/first case of the day only: 128
Never: 12
Someone else does it for me: 21
Last time was in residency: 1

The most often cited reasons for not performing a pre-use check were:

Insufficient time: 75
Takes too long to perform: 73
I do not know how to perform a proper pre-use check: 42
My anesthesia machine has an automated pre-use check and does it for me: 37
Production pressure from surgeon: 33
Was never taught during residency training: 23
Production pressure from administration: 15
1993 FDA pre-use check is obsolete and does not apply to my local environment: 12
Do not have knowledge to adapt 1993 FDA pre-use check to local conditions: 11

Participants responded that they would perform a preuse check before every case if it took at most 4.9 minutes on average to perform.

The preliminary results clearly indicate that the pre-use check continues to present an opportunity for improvement. The number of responders who indicated that they did not know or have not been taught in residency training how to properly perform a pre-use check gives cause for concern and action, and offers no defense in the event of an otherwise preventable equipment malfunction.

Performance of the Pre-Use Check

When the anesthesia machine pre-use check is actually performed, current evidence seems to indicate that it is performed poorly, both in terms of fault detection rate and procedural criteria.¹²,¹³,¹⁴

In the study by Buffington et al.¹² 190 participants were informed before the exercise that faults were present; however, 13 (7.3%) detected none of five planted faults, three of which would have administered a hypoxic gas mixture. Only six subjects (3.4%) found all five faults. The average number of detected faults was 2.2 ± 1.2 (44%). Practitioners with 10 years’ experience did better than those with less years of practice. Buffington et al. recommended that “Greater emphasis should be placed on aggressive system checking in education programs and in daily clinical practice”.¹²

A 1996 paper reported that 40.9% of 22 anesthesia providers missed more than 50% of planted faults when using the 1993 FDA Anesthesia Apparatus Checkout Recommendations.¹⁴ Both nurse and physician anesthesia providers had poor scores on questions related to gas supply in a Swiss study on the anesthesia machine pre-use check.¹⁵

A simulator-based study was performed in Canada to investigate how thoroughly anesthesiologists check their machinery and equipment before use and determine what influence seniority, age, and type of practice may have on checking practices.¹⁶ One hundred and twenty anesthesiologists were videotaped during a simulated anesthesia session. Each participant was scored by an assessor according to the number of items checked before the induction of anesthesia. A checklist of 20 items derived from well publicized, international standards was used. Participants were grouped according to their type of practice. Overall, mean scores were low. The ideal score was 20. There were no differences among university anesthesiologists (mean score 10.1), community anesthesiologists (7.5), and anesthesia residents (9.0). Each of these groups scored, on average, better than medical students (3.6 ± 3.7) (p < 0.05). Neither age nor number of years in practice correlated with the score. The authors concluded that the equipment-checking practices of anesthesiologists require considerable improvement when compared with national and international standards.

“Automated” Pre-Use Checks

Newer models of anesthesia machines (e.g., models made by Draeger [Draeger Medical, Telford, PA] such as the Julian, Fabius GS, Apollo, and Narkomed 6000, and models made by GE Healthcare [GE Healthcare, Chalfont St. Giles, UK] such as anesthesia delivery unit [ADU], Avance and Aisys, among others) often feature “automated” preuse checks that guide users through a model-specific pre-use check. In addition to automating certain parts of the pre-use check, they also offer reminders to help users remember each step of the pre-use check. However, the proper term is semi-automated pre-use checks, because they only perform a portion of the recommended check automatically, with the user still having to manually perform or validate the remainder (e.g., the first step in the 1993 FDA pre-use check : verifying that back-up ventilation equipment is available and functioning).

Despite their potential convenience and usefulness, a few words of caution are needed. The automated sections are only part of the more comprehensive preuse check and not a substitute for a full pre-use check. A common misconception is that anesthesia machines with “automated” pre-use checks absolve users of the need to perform a pre-use check, as evidenced by the number of times (37) the checkbox, “my anesthesia machine has an automated pre-use check and does it for me”, was selected by 244 survey responders as a reason for not performing a pre-use check.¹¹ Furthermore, the effectiveness of a semi-automated pre-use check depends on the actual implementations and the logic and usability of the user interface. Because it is based on the communication between the different teams designing and implementing the pre-use check, the pre-use check is only as good as the knowledge programmed into it. The pre-use check may be omitting instructions that could lead users to incorrectly perform the pre-use check such that, for example, a loose vaporizer filler cap would be missed. Anesthesia providers need to realize that, without an understanding of the anesthesia machine components and functions on their part, the outcome of the semi-automated pre-use check could be misleading and result in incorrect conclusions.

▪ TRANSPARENT REALITY SIMULATION

Following the example set by aviation, simulation is gaining acceptance as a teaching and training tool in medicine. Lack of instruction and poor understanding of the anesthesia machine pre-use check may be contributory factors for poor compliance and suboptimal fault detection rates that have potential consequences for patient safety in light of the study by Arbous et al.⁴ that links performance and documentation of the pre-use check to a reduced risk of 24-hour, severe postoperative morbidity and mortality. This lack of instructional materials related to the pre-use check was identified and addressed by the U.S. Anesthesia Patient Safety Foundation (APSF), which funded the development of a web-disseminated transparent reality
simulation of the anesthesia machine pre-use check at the University of Florida (UF).

This type of simulation presents a simplified, interactive, graphical mental model of the internal workings of the entire anesthesia machine. The designs emphasize concepts and relationships (rather than dimensional accuracy). Nonetheless, users can adjust numerous controls and observe, in real time, the essential effects of their interventions on gas pressures, flows, compositions, and volumes. Gas “molecules” can be made visible or invisible and color-coded.¹⁷,¹⁸ The term, transparent reality, has been coined to describe this type of simulation modality, where the emphasis is placed on making the internal, and usually invisible, functions and processes of a system visible and understandable.¹⁹ Users can appreciate the essential effects of their correct (and incorrect) actions and interpretations during the simulated pre-use check.

A web survey of users of the APSF/UF pre-use check simulation was conducted.²⁰ Preliminary results indicate that this type of simulation may be effective.²¹ Ninetyone percent of users who responded to a survey on the simulation believe that it will cause them to perform the pre-use check more accurately, in the sense of detecting more faults. Seventy-seven percent indicated that the simulation will cause them to perform the pre-use check more regularly. Sixty-four percent indicated that the simulation will cause them to perform the pre-use check more rapidly.

Given the patient safety consequences of not performing a pre-use check before every anesthetic established by Arbous et al.,⁴ we hope that the responses of the survey concerning the effectiveness of the APSF/UF anesthesia machine pre-use check simulation will prove to be true. We purposely described first in this chapter the prevention of anesthesia machine complications because we wanted to emphasize that, just like in patients, “prevention is better than cure”. The next section will describe how to manage anesthesia machine malfunctions if they occur intraoperatively in spite of our best efforts.

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