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Adjustable Pressure Limit Valve Failure During Intraoperative Care: A Case Report

D’Mello, Ajay J. MD*,†; Raman, Vidya T. MD*,†; Tobias, Joseph D. MD*,†

doi: 10.1213/XAA.0000000000001045
Case Reports
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One of the many safety features of modern day anesthesia machines is the adjustable pressure limiting (APL) valve. This device regulates pressure within the anesthesia circuit during manual ventilation with the anesthesia bag. We report an unusual case where a crack in the APL valve allowed release of pressure from within the circuit resulting in ineffective bag-valve-mask ventilation of an infant. The appropriate steps to prevent such issues are reviewed, and an algorithm to quickly identify such intraoperative problems is presented.

From the *Department of Anesthesiology & Pain Medicine, Nationwide Children’s Hospital, Columbus, Ohio

Department of Anesthesiology & Pain Medicine, The Ohio State University College of Medicine, Columbus, Ohio.

Accepted for publication April 30, 2019.

Funding: None.

The authors declare no conflicts of interest.

Address correspondence to Ajay J. D’Mello, MD, Department of Anesthesiology & Pain Medicine, Nationwide Children’s Hospital, 700 Children’s Dr, Columbus, OH 43205. Address e-mail to ajay.dmello@nationwidechildrens.org.

Modern anesthesia machines are designed with a number of features that are intended to avoid potential complications during the delivery of anesthetic care including delivery of a hypoxic gas mixture or high airway pressures. During manual ventilation, the adjustable pressure limiting (APL) valve allows control of the maximum pressure that can occur within the anesthesia circle breathing system. The valve uses a spring-loaded device to control pressure within the circuit such that the degree of spring compression exerts a proportional force on a sealing diaphragm within the valve. With the valve partially closed, manual ventilation is possible via an anesthesia mask or airway device. During manual ventilation, pressure within the system is the result of the degree of valve closure, the fresh gas flow, and the force generated by compression of the anesthesia bag. When the pressure within the circle system and hence the patient’s airway exceeds this compressive force (high pressure level) of the APL valve, the valve or diaphragm opens and pressure is vented to the scavenging system.

Although modern day anesthesia machines with their safety features have arguably increased the safety of the delivery of anesthesia, the safe conduct of anesthetic care begins with a thorough, scripted check of the anesthesia machine.1 A closed claim study of gas delivery equipment reported that 35% of claims were judged as preventable by a preanesthesia machine check.2 Hence, the anesthesia providers who are ultimately responsible for the proper functioning of equipment used to provide patient care are advised to perform a standardized preanesthesia checkout procedure that is appropriate for the type of anesthesia machine and practice setting.3 We present an unusual source for a leak within the anesthesia circuit, a cracked APL valve. The leak resulted in problems during bag-valve-mask ventilation of an infant. The appropriate steps to prevent such issues are reviewed, and an algorithm to quickly identify such intraoperative problems is presented.

Written consent has been obtained from the patient’s parents for submission of this clinical case report for potential publication.

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CASE REPORT

Figure 1.

Figure 1.

Figure 2.

Figure 2.

Institutional review board approval is not required for presentation of single case reports at Nationwide Children’s Hospital (Columbus, OH). A 3-month-old, former 24-week premature infant was scheduled for an elective ventriculoperitoneal shunt placement. Medical history was significant for bronchopulmonary dysplasia, retinopathy of prematurity, intraventricular hemorrhage, and obstructive hydrocephalus. In preparation for the case, a preanesthesia checkout was performed on the Datex Ohmeda Aestiva 5 anesthesia machine (Datex-Ohmeda, Inc, Madison, WI). The infant was positioned on the operating room table, and routine American Society of Anesthesiologists (ASA) monitors were placed. Anesthesia was induced with the intravenous administration of fentanyl and propofol. Bag-valve-mask ventilation was provided. Neuromuscular blockade was provided by the administration of rocuronium, and the trachea was intubated with a 3.5 Microcuff endotracheal tube (ETT; Haylard, Alpharetta, GA). During positive pressure ventilation through the ETT with a fresh gas flow at 8 L/min, there was inadequate chest rise, poor air entry on chest auscultation, and lack of consistent capnography. The ETT was removed, and ventilation was attempted through an anesthesia mask. Ventilation was ineffective, and there appeared to be a large leak in the anesthesia breathing circuit with inadequate filling of the anesthesia bag despite a good seal with the facemask. The source of the air leak was identified by visual examination of the breathing circuit and anesthesia machine during which dislodgement of the plastic cover of the APL valve from its housing was noted (Figure 1). A crack was also noted on the plastic cover of the APL valve (Figure 2). Bag-valve-mask ventilation was provided by an Ambu bag (Ambu Inc, Columbia, MD), while the APL valve was replaced. A pressure check after resituating the plastic cover revealed that the anesthesia circuit could be pressurized. This was followed by intubation of the patient’s trachea and effective positive pressure ventilation with visual evidence of chest rise, capnography, and chest auscultation. The case proceeded uneventfully, after which the machine in question was removed from service and repaired.

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DISCUSSION

Patient- or machine-related issues may result in difficulties with bag-valve-mask ventilation. While the anesthesia provider may focus on patient-related issues during a “cannot ventilate” scenario, the potential for machine or equipment failure must also be considered.3 As illustrated by our case, a leak anywhere along the anesthesia circle system may result in inadequate ventilation. To prevent physiologic compromise or deterioration, rapid intervention is required especially in neonates and infants. To that end, as was the case with our patient, an alternative means of providing bag-valve-mask ventilation should be present in all anesthetizing locations.4 Use of an Ambu bag allowed us to rapidly reestablish oxygenation and ventilation, while the source of the machine problem was identified. A suggested algorithm is outlined in the Table.

Table.

Table.

Although most commonly related to replaceable connections or components of the plastic circle system, problems may occur in the internal components of the machine itself. Common sites of leaks of dislodgement include the sites where the disposable anesthesia circle system is attached to the anesthesia machine, the attachment site for capnography, and holes or defects with the plastic anesthesia tubing. However, as illustrated by our case, damage or faculty function of the anesthesia machine may also be the cause. If the leak is not readily apparent by running the circle system, the circuit can be pressurized by occluding the distal end of the circle system. This not only demonstrates that there is a leak and the problem is within the circle system by demonstrating failure to maintain pressure with a minimal fresh gas flow, but may also result in an audible clue to identify the site of the problem.

Although infrequent, anesthesia machine equipment-related problems remain a common cause of critical incidents during anesthetic care.1,5 The anesthesia care provider is ultimately responsible for ensuring that anesthesia equipment is safe and ready for use. The most recent ASA Pre-Anesthesia Checkout Procedures describes 15 items to be completed daily, before the start of the first case, and a subset of 8 items to be repeated before every anesthetic.4

A number of case reports have reported that automated self-tests of the machine may miss leaks in the anesthesia systems.6–9 Review of the literature indicates that most anesthesia machine problems are related to the disposable breathing system.10,11 Cleaning of the breathing system and change of the circuit between cases may predispose to errors despite routine checkouts at the start of the day.12,13

Our case illustrates an unusual site of an anesthesia machine breathing circuit leak, a cracked APL valve. Our investigation demonstrated that a crack in the plastic cover of the APL system allowed it to be dislodged from the spring and diaphragm system as the system was pressurized during manual ventilation after tracheal intubation. This potential site of a circuit leak was not identified by standard preanesthesia machine checkout procedure because the circuit leak in this particular case developed after dislodgement of the defective plastic cover of the APL during induction of general anesthesia. We suggest a visual examination of the APL valve and other components of the anesthesia breathing system for cracks or damage as part of the recommended essential steps in a preanesthesia checkout procedure or when a significant leak is noted during patient care to help identify the source of the breathing system leak. The anesthesia provider should not hesitate to reach for the backup self-inflating manual ventilation device (item 1 on daily checklist of the Pre-Anesthesia Checkout Procedures) to rescue the patient in the event of a large circuit leak that results in an inability to ventilate.

Whenever a safety issue or malfunction is noted in the anesthesia machine, we would suggest that it be reported to the in-house technical support team for complete investigation. Additional reporting including to the manufacturer or the appropriate federal agency should depend on the results of the investigation. In our case, because this was related to a cracked knob related to inadvertent collision with another device, no outside reporting was deemed necessary.

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DISCLOSURES

Name: Ajay J. D’Mello, MD.

Contribution: This author helped the design, draft, and revise the manuscript.

Name: Vidya T. Raman, MD.

Contribution: This author helped the design, draft, and revise the manuscript.

Name: Joseph D. Tobias, MD.

Contribution: This author helped the design, draft, and revise the manuscript.

This manuscript was handled by: Mark C. Phillips, MD.

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REFERENCES

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