Revisions to the official, government-sponsored anesthesia equipment checkout recommendations have been proposed and comments from all members of the anesthesia practice community are sought.
In 1987, the United States Food and Drug Administration (FDA) published Anesthesia Apparatus Checkout Recommendations, a checkout procedure by which anesthesiologists and anesthetists can determine whether an anesthesia gas machine is functioning properly and is ready for patient use. Studies of the checkout protocol have revealed that it is neither well understood nor used correctly by a majority of anesthesia practitioners. When challenged to check anesthesia machines intentionally configured with a variety of malfunctioning components, clinicians detected only 28.5% of the faults. (1) In March, 1991, the FDA reviewed the development of the checkout procedure and studies of its effectiveness at a meeting convened by the American Society of Anesthesiologists’ (ASA) Committee on Equipment and Facilities. Invited participants included representatives of the ASA, the ASA Committee on Equipment and Facilities, the Anesthesia Patient Safety Foundation (APSF), the American Association of Nurse Anesthetists (AANA), anesthesia machine manufacturers, and anesthesia equipment experts.
The result of that meeting and other subsequent work has led to a 1992 draft revision of the Anesthesia Apparatus Checkout Recommendations. Availability of this document was announced in the October 6, 1992, Federal Register. The FDA has requested that written comments on the draft document be sent by February 16, 1993 to the Dockets Management Branch (HFA-305), Food and Drug Administration, Room 1-23,12420 Parklawn Drive, Rockville, MD 20857. Comments should be identified with the docket number 86B-0058. The Federal Register article announcing availability of revised document merely describes the modifications that transformed the original 1987 Checkout Recommendations into the currently proposed 1992 draft. The Federal Register article does not include the entire document, which makes it impossible to provide meaningful comments. Thus, the complete draft of the 1992 Anesthesia Apparatus Checkout Recommendations is included in this issue of the APSF Newsletter so that anesthesia practitioners can review it. As recommended in a recent APSF Committee on Technology Position Paper, narrative comments describing the rationale for each specific step and for the revision process in general are included.
Many clinicians believe that existing protocols for anesthesia machine checkouts are too long and too complex. Those who revised the recommendations agreed that the average clinician should be able to check an anesthesia machine in 5 minutes or less. This is not possible with the 1987 Checkout Recommendations or with check procedures published by anesthesia machine manufacturers in the manuals for their anesthesia machines.
Contemporary anesthesia gas delivery machines are durable and dependable. They fail infrequently. They are armed with alarms and safety devices, which, coupled with the array of monitoring instruments used in contemporary anesthesia practice, make failure of most components in the anesthesia machine easily detectable before the safety of the anesthetized patient is jeopardized.
Safe Fail Safe?
For example, many checkout protocols include daily testing of the oxygen pressure failure safety mechanism (fail-safe), a durable device that arrests the flow of other gases when the oxygen supply pressure (pipeline or cylinder) decreases below a preset threshold, which prevents continued flow of a hypoxic gas mixture. Does the isolated failure of the fail-safe mechanism put the patient at immediate risk? I do not think so. Failure of the fail-safe mechanism does not affect the normal function of the anesthesia machine as long as the oxygen supply pressure is adequate. Even if the fail-safe mechanism malfunctions AND the oxygen supply pressure is simultaneous lost, the anesthesia provider is warned by several if not all of the following: (1) low oxygen-supply pressure alarm in anesthesia machine, (2) low oxygen-supply pressure alarm in mechanical ventilator, (3) failure of the mechanical ventilator to cycle properly, (4) report of low oxygen concentration in the breathing circuit by the oxygen analyzer (and an alarm if it is set), and (5) report of decreased oxyhemoglobin saturation by the pulse oximeter. Even in a ‘worst case” scenario, the anesthesiologist or anesthetist is warned of the developing hypoxic gas mixture, as first the inspired oxygen concentration and then the oxyhemoglobin saturation begin to decrease. This combination (a hypoxic gas mixture and oxyhemoglobin desaturation) indicates that the patient should be disconnected from the anesthesia machine.
In contrast to the seemingly complex fail-safe mechanism, is the seemingly innocuous and simple scavenging system. Yet certain failures of the scavenging system can cause pulmonary barotrauma in just a few breaths! For example, anesthesia personnel have used adhesive tape to incorrectly mate a standard 22-mm breathing circuit hose to the 15-mm scavenging port. If the adhesive tape slips into the hose and obstructs its lumen, a closed circuit is created when mechanical ventilation is instituted. Gas flowing into the breathing system cannot escape, and airway pressures (both inspiratory and expiratory) quickly rise and may exceed 40 cm H20. (This scenario is demonstrated in the ASA/APSF Patient Safety Video 412.)
The 1992 FDA Anesthesia Apparatus Checkout Recommendations have retained or added checks of machine components that fail more frequently than other components (for example, breathing system), and those components that directly and quickly injure the patient when they fail (for example, scavenging system). Components that fail infrequently and that do not put the patient in immediate danger when they do fail are not included in the 1992 Checkout Recommendations but should be checked as part of routine periodic maintenance. In the paragraphs that follow, the specific rationale for each checkout step is discussed.
The introductory paragraph clearly states that the checkout procedure is valid only for anesthesia machines with an ascending (‘upright’) bellows ” of mechanical ventilator and a specific array of monitoring instruments. This configuration forms a web of safety systems that warn the clinician and protect the patient from injury in the event of an isolated component failure.
Clinicians using anesthesia machines that do not conform to this configuration or to current manufacturing and monitoring guidelines must critically analyze the specific failures that might go unrecognized and adapt the checkout procedure as indicated. For example, the 1992 Checkout Recommendations specify that a capnograph should be in use. The 1987 Checkout Recommendations stipulated that clinicians verify that the unidirectional valves are-competent by inhaling and exhaling into isolated limbs of the breathing system. While this is a sensitive test for detecting valve malfunction, many clinicians prefer not to share the breathing system with their patients. Incompetent unidirectional valves are readily detected with a capnograph, an instrument that reports minimum (‘inspired’) and maximum (‘expired’ or ‘endtidal’) concentrations of carbon dioxide and also traces a capnogram, a plot of the airway carbon dioxide concentration as a function of time. Characteristic changes in the shape of the capnogram accompany both incompetent inspiratory and expiratory valves. An incompetent inspiratory valve, however, may not be detected with a capnometer, an instrument that only reports the minimum and maximum concentrations of carbon dioxide during each respiratory cycle.
Steps Removed from the Checkout Recommendations:
Nitrous Oxide and Air Cylinder Gas Supply
Nitrous oxide and air are not life-sustaining gases. While the undetected loss of nitrous oxide may result in ‘light’ anesthesia and the potential for awareness and recall, once detected, intravenous or other inhaled anesthetic agents can be used to re-establish the appropriate anesthetic depth. Thus, while it may be reassuring to have reserve cylinders of nitrous oxide and air attached to the anesthesia machine, daily checks of their pressure is not thought to enhance safety.
Low Oxygen-Supply Pressure Alum
Contemporary anesthesia machines alarm when the oxygen supply pressure (from pipeline or cylinder) falls below a preset threshold, usually 25 to 30 psig. This alarm sounds each time the anesthesia machine is turned on and off, which pressurizes and depressurizes the alarm mechanism. The 1992 Checkout Recommendations do not include daily checks of this alarm mechanism. Isolated failure of the low oxygen-supply pressure alarm will not injure a patient. Failure of the alarm coupled with loss of oxygen supply pressure should similarly not injure the patient because the oxygen-pressure failure safety mechanism (fail-safe) will arrest the flow of other gases to prevent the patient from inspiring a hypoxic gas mixture. Mechanical ventilators that are powered by oxygen pressure should independently alarm when oxygen supply pressure is lost. Should this alarm in the ventilator also fail, instruments that monitor ventilation of the patient’s lungs, specifically the capnograph and spirometer, will immediately warn the clinician because loss of oxygen supply pressure to a mechanical ventilator results in apnea.
Oxygen Pressure-Failure Safety (fail-safe) Mechanism
This device arrests the flow of all gases except oxygen whenever the oxygen supply pressure falls below a preset threshold, typically 30 psig. This prevents the hypoxic gas mixture that would result from the continued flow of, for example, nitrous oxide without oxygen. As with the low oxygen supply pressure alarm, daily testing of the oxygen pressure-failure safety mechanism is not included in the 1992 Checkout Recommendations because its failure does not directly injure the patient, and multiple simultaneous failures are required before the patient is at risk of injury. Even if the oxygen pressure-failure safety mechanism failed along with the simultaneous loss of oxygen supply pressure during anesthesia with nitrous oxide, the low oxygen-supply pressure alarm will indicate loss of oxygen supply pressure. If this alarm failed, as noted in the previous section, the oxygen analyzer and the pulse oximeter will warn the clinician of the hypoxic gas mixture, regardless of its cause.
Steps Retained in or Added to the 1992 Checkout Recommendations:
1. Verify Backup Ventilation Equipment is Available & Functioning
Though rare, certain malfunctions (for example, contaminated oxygen supply, loss of oxygen supply pressure, total obstruction of the breathing system) render the anesthesia machine inoperable. When this happens, a patient must be quickly disconnected from the anesthesia machine and the patient’s lungs ventilated by using backup ventilation equipment. Therefore, the 1992 Checkout Recommendations begin with a check of the backup ventilation equipment. Example systems include self-inflating resuscitation bags, or Mapleson-type circuits with separate oxygen cylinder.
2. Check Oxygen Cylinder Supply
The length of time an anesthesia machine can operate on the reserve oxygen cylinder depends on the volume of compressed oxygen in the cylinder and on the rate of use. The volume of oxygen in the reserve cylinder is directly proportional to its pressure, a W oxygen cylinder having 625 liters and a pressure of approximately 2200 psi. The 1992 Checkout Recommendations suggest that at least one reserve oxygen cylinder be at least half full, in other words, have a pressure of at least 1000 psi, which will enable the anesthesia machine to function for 10 minutes to over an hour, depending on rate of use. Because many anesthesia ventilators are powered totally or in part by oxygen, a low flow of oxygen and either spontaneous ventilation or manual (“bag’) ventilation will prolong the time the anesthesia machine can operate with a reserve oxygen cylinder.
3. Check Central Pipeline Supplies
Normal operating pressure for pipeline gases is 45 to 55 psi. A lower pressure suggests that a pipeline hose is not properly connected, that the hose is kinked, that the hose or connector is defective, or that the pipeline system itself has a problem. A higher than normal pressure also suggests that the primary problem is the pipeline system, not the anesthesia machine.
4. Check Initial Status of Low Pressure System
This check is a preparatory step in setting certain controls (that is, flow control valves, vaporizer concentration knob) and sensors (that is, sensor for oxygen analyzer) for subsequent steps in the checkout procedure. The vaporizers are checked and, if necessary, filled at this point as well.
5. Perform Leak Check of Machine Low Pressure System
The low pressure system of the anesthesia machine comprises all components between the flow control valves and the common gas outlet and includes the flow meter tubes, vaporizers, connecting manifolds, and, if present, a common gas outlet check valve. The concentration of volatile anesthetic in the fresh gas mixture may be significantly decreased with small leaks, for example 100 ml/min, in the low pressure system of the anesthesia machine, which may result in consciousness and recall. In certain situations, leaks in the low pressure system may also lead to the patient’s inspiring a hypoxic gas mixture, even though a nonhypoxic fresh gas flow ratio has been set.
A variety of check procedures have been proposed for detecting leaks in the low pressure system of the anesthesia machine. A positive pressure leak check (occluding the Y-piece of the breathing circuit, pressurizing it to 20 cm H20, and observing the canister pressure gauge for loss of pressure) will not detect a leak in an anesthesia machine with a common outlet check valve, because positive pressure in the breathing system cannot be transmitted back into the low pressure system. The negative pressure leak check (attach suction bulb to common gas outlet, squeeze to develop negative pressure, and observe to see if bulb remains collapsed) detects leaks in the low pressure system on all makes and models of anesthesia machines and is sensitive enough to detect the small leaks (100 ml/min) that can disrupt the proper function of the low pressure system. When done correctly, both positive and negative pressure leak checks require the use of a bulb attachment to the anesthesia machine. Accordingly, so that a single, highly sensitive check procedure could be recommended for all anesthesia machines, the 1992 Checkout Recommendations suggest using the negative pressure leak check for the low
6. Turn On Machine Master Switch
This enables subsequent checks to be performed.
7. Test Flowmeters
This step verifies that gas is flowing into the anesthesia machine; that the flow control valves and flow meters are functioning; and that the ‘hypoxic guard’ mechanism either prevents the clinician from setting a hypoxic oxygen-nitrous oxide fresh gas flow ratio or alarms when such a flow ratio is set.
8. Calibrate 02 Monitor
A contaminated oxygen supply (for example, oxygen-nitrous oxide pipeline cross, non-oxygen gas in oxygen pipeline or cylinder) can only be diagnosed by a functioning and calibrated oxygen analyzer. Other malfunctions within the anesthesia machine, as well as a very low rate of fresh gas flow, may also lead to hypoxic gas. Therefore, the oxygen analyzer should be calibrated at 21% and checked at high oxygen concentrations daily. (Do not recalibrate the analyzer at a high oxygen concentration because greater accuracy is needed at low concentrations.)
9. Check Initial Status of Breathing System
This is a preparatory step in which the clinician assembles and visually checks the breathing system, carbon dioxide absorbent, and any other breathing circuit accessories (for example, PEEP valve, humidifier system) required for the next case. It is important to add breathing circuit accessories before completing the checkout procedure. If the accessory has a fault (for example, a leak in the humidifier circuit), it will not be detected if attached to the anesthesia machine after the machine checkout is complete.
10. Perform Leak Check of the Breathing System
This is the traditional leak check of the breathing system in which the clinician occludes the Y-piece, pressurizes the breathing system with an oxygen flush, and observes the canister pressure to ensure that the breathing system holds pressure (that is, is leak free).
11. Check Adjustable Pressure-Limiting Valve and Scavenging System
Following the leak check of the breathing system, most clinicians depressurize the circuit by removing their finger from the Y-piece. The 1992 Checkout Recommendations, however, suggest that, instead, the Y-piece should be kept occluded; the adjustable pressure-limiting (APL), or ‘pop-off’, valve be opened; and the pressure be allowed to dissipate through this valve into the scavenging system. Though rare, should the APL fad to open properly, gas cannot escape from the breathing system, which creates a closed system and, thus, potential for excessive inspiratory and expiratory airway pressures and resultant barotrauma.
The latter half of this step is checking the scavenging system. Like the malfunctioning APL valve, an obstruction in the scavenging system can also create a closed system and increase airway pressures, which may result in cardiovascular compromise and barotrauma. Similarly, malfunction of the negative pressure relief mechanism in an active (that is, vacuum) scavenging system can transmit negative pressure back to the patient, which may cause negative pressure pulmonary edema. To detect this malfunction, the APL valve is opened fully to a properly connected and set scavenging system. Breathing system pressure should not increase or decrease significantly when the oxygen flow is minimal or when the oxygen flush valve is kept open. A malfunction in the scavenging system is indicated by either excessively high or subatmospheric pressure.
12. Test Ventilator Systems and Unidirectional Valves
By attaching a second breathing bag to the Y-piece to simulate a patient’s lungs, proper cycling of the mechanical ventilator and proper flow of gas through the breathing system, including proper function of the unidirectional valves, are checked. If the ventilator bellows progressively collapses during this step, suspect a leak in the ventilator hose, or other problem with the bellows assembly. Make sure the second breathing bag (simulated lungs) is supported by holding the Y-piece. Squeezing the bag during this check allows gas to escape through the ventilator pressure relief valve, and the ventilator bellows will not ascend to its baseline position, which creates the appearance of a ventilator hose leak when actually there is none. Flow of gas through the breathing system is also checked in the “bag’ mode.
13. Check, Calibrate, and/or Set Alarm Limits of all Monitors
The intent of the Checkout Recommendations is to verify that the anesthesia machine is functioning correctly. Because of the large variety of different makes and models of monitoring instruments currently used in anesthesia practice, specific recommendations for checking each monitoring instrument is beyond the scope of this document. Nonetheless, properly functioning monitoring instruments is a prerequisite for the 1992 Checkout Recommendations to be valid. Checks of the monitoring instruments and any necessary calibration should be conducted daily or according to manufacturers’ specifications.
14. Check Final Status of Machine
The user sets the controls of the anesthesia machine so that it is ready for clinical use.
Dr. Good is from the Department of Anesthesiology, University of Florida, Gainesville. Address correspondence to: Editorial Office, Department of Anesthesiology, University of Florida College of Medicine, Gainesville, FL 32610-0254.
1. March MG, Crowley JJ. An evaluation of anesthesiologists’ present checkout methods and the validity of the FDA checklist, Anesthesiology 1991;75:724-729