Although any piece of machinery can malfunction due to mechanical failure or human error, rarely are the stakes higher than with anesthesia machines. According to statistics compiled by the American Society of Anesthesiologists, 2 percent of medical liability claims stem from accidents involving anesthesia apparatus; half of the adverse events that precipitate these claims result in death and another 30 percent of patients suffer brain damage.

The good news is that facilities can avoid almost all catastrophes like this and ensure patient safety with just a few simple checks at the start of the day and before each case. In the following article, I'll briefly describe my protocol for this. But before I do, let me offer three caveats. First, there are different types of anesthesia machines, so you may have to adjust the suggestions to your machine. Second, the protocol varies slightly from the process recommended by the FDA and the Walter Reed guidelines; I've made mine more specific and in some cases better, in my opinion. Finally, it should go without saying that you should always document every check you make, no matter which protocol you follow. At my facility, we use a checklist to note that we've pre-flighted each machine; every machine is numbered and the number is recorded on the checklist. If there is a problem, we can easily identify and isolate the machine for closer examination or servicing.

With that said, here's what we do when we check an anesthesia machine.

1. Check the emergency ventilation equipment.
Basically this means having an Ambu bag and mask available and testing to make sure that they work.

2. Check the machine's high-pressuresystem.
This part of the machine includes the filter and the unidirectional valve, the cylinder pressure gauges and the cylinder pressure regulator.

There are two steps involved here. First, check the pressure gauge on the tank containing the spare oxygen source. Do not proceed unless the pressure is at least 1000 psi. When full, most tanks are pressurized to 2000 psi.

Second, make sure that all of the hoses are connected to the wall sources for gas and that the pipeline gauges (distal to the regulator) read out at or near 50 psi. This is the pressure at which gas is delivered to the patient.

3. Check the intermediate and low-pressure systems.
There are quite a few components to this part of the check-out.

• First, be sure the flow control valves and vaporizers are turned off. Check the fill level of the vaporizers and also check to make sure the vaporizer's filler caps are tight.
• Activate the machine by turning on the main switch. Now turn the flow all the way on and off, examining the flowmeters to make sure the system operates smoothly.
• Next, create a hypoxic O₂/N₂O mixture to document that either the flow changes correctly or the alarm goes off. This is how you do it: First, turn on equal flow rates for each gas and make sure that the flowmeters are freely floating. Then, turn down the oxygen flow-the nitrous oxide flow should decrease automatically to ensure that the ratio of oxygen to nitrous oxide never falls below 30 percent. When the oxygen flow is off, no nitrous oxide should be able to flow even when the nitrous oxide valve is open.
• Test the scavenging system to make sure that it is properly connected to the pop-off (APL) valve and the ventilator relief valve. The only way to make sure that the scavenging system is correctly hooked up is to visually inspect the hoses connecting the APL (a.k.a "pop off" valve) to the scavenging system (or valve) on the anesthesia machine, which in turn needs to be attached to the wall plug for scavenging waste gases through a low-suction system. During this step of checkout, you should open the APL valve and the Y-piece; these will remain open during the next several steps.

Just a note here: The FDA guidelines suggest that during this phase of the check, you also should allow the scavenger reservoir bags to collapse, and check to see if the absorber pressure gauge reads near zero. Then activate the oxygen flush and allow the scavenger reservoir bag to fill completely, verifying that the gauge reads less than 10 cm of water (if your system works that way). Our system has a flowmeter that monitors the scavenging system suction, so we only need to inspect the flowmeter. I believe this test is a good idea, but it's too time-consuming to do every day. I suggest doing it periodically.

• Check the breathing system. This involves several steps.

Test out the oxygen monitor to make certain that the alarm works. Ensure that the monitor reads about 21 percent on room air. Remove the oxygen analyzer from its receptacle on the anesthesia circuit and wave the analyzer around in the room air. Since room air is 21 percent oxygen and the alarm should be set to go off at lower than about 30 percent, within 30 seconds or less, the low oxygen alarm should go off.

Check the breathing circuit. Most anesthesia providers do this by breathing into it themselves a couple of times and looking at the one-way inspiratory and expiratory valves on the circuit to make sure they have a functioning circuit. Perhaps it's not the most hygienic way to do this test but it works to ensure that the patient will be able to safely breathe through the circuit. The valves should appropriately open and close with the proper phase of the breathing cycle. These valves are very visible and readily inspected on all anesthesia machines. If the valves are stuck open or closed or if there is an obstruction to breathing through the circuit, test a new disposable circuit; if the problem persists, the entire machine should be inspected for malfunction. If the source of the malfunction cannot be readily identified, the machine should be isolated from use until it can be repaired.

Install any breathing circuit accessories, such as a humidifier, which will be used during the case.

Do a leak check of the breathing system. Set the gas flow down to zero, and close the APL valve and the Y-piece. Flush in oxygen to pressurize the breathing system to about 30 cm of H₂0, leaving it pressurized for about 15 seconds. Open the APL valve to ensure that the pressure decreases normally. Note that many anesthesia providers do not perform this leak check test on a routine basis.

4. Check the ventilation systems.
To check the ventilator, remove the breathing bag from the anesthesia machine (this is the disposable bag that is changed between cases along with the anesthesia circuit). After connecting the breathing circuit to the anesthesia machine, connect the bag to the end of the circuit that will be connected to the patient (via a mask or by the endotracheal breathing tube). On the anesthesia machine, flip the switch/valve (this may not be necessary on some newer machines, which do the switch automatically) from manual mode to ventilator mode. Turn the ventilator on, and push the oxygen flush button to fill the circuit and breathing bag with oxygen. Turn the oxygen flow to about 5L/min. This will simulate the machine ventilating a patient's lungs by pushing air into and out of the breathing bag.

Next, check to make sure that the inspiratory and expiratory valves are moving appropriately, as you did when testing the breathing circuit. Check that the ventilator is in fact delivering the tidal volume that is set and is delivering the breathing rate that was set on the machine. While the ventilator is filling the bag during an inspiratory phase, squeeze the bag tightly with both hands to simulate an obstruction/restriction to air flow-an alarm should promptly sound. Then, remove the bag from the circuit but allow the ventilator to continue to run.

Within less than 30 seconds, another alarm should sound indicating that there is a disconnection in the anesthesia circuit, because the machine will not detect any air returning from the bag. When done, replace the breathing bag in its proper location on the anesthesia machine.

On some machines, it may be necessary to check the "flow rate" of the ventilator to ensure that it's in the medium range. This is the flow rate with which the ventilator drives air into the patient. Also, some machines have a high-pressure relief dial, a sort of "pop-off" valve, for the ventilator. Make sure that this is set at a reasonably high value to avoid loss of ventilation in patients with high airway pressures.

5. Check the monitors.
Breathe into the capnometer and check to make sure that it's reading some carbon dioxide.

Also check the pulse oximeter, the spirometer, and the oxygen analyzer.

Test the pulse oximeter by putting it on your own finger and seeing that it detects your pulse and gives a proper reading of the oxygenation in your blood.

Check the spirometer (a dial which shows how much volume the patient is breathing with each breath) while breathing into the circuit or while testing the ventilator, as described above.

If you did the low-oxygen alarm test properly, you've already checked the oxygen analyzer. No additional test is needed.

Finally, you should always check your suction. The suction system may or may not be attached to the anesthesia machine. It consists of a hose plugged into the wall that provides suction from the room. This hose is then attached to a suction system that usually consists of a clear disposable bucket to which a disposable length of tubing is attached. A "suction tip" is attached to the tubing. The suction tip is placed into the patient's mouth during the case.

When you are done with your check, make sure the vaporizers are off, the APL valve is open, and the flowmeters are set to zero.

Re-checks between cases
After the initial complete morning check, there are certain re-checks that are necessary between each case. First, after you replace the disposable breathing circuit, check the breathing circuit for leaks and obstructions. Secondly, make sure the vaporizers are turned off and adequately filled with anesthetic agent. Finally, change the suction system between cases and check to be sure that it's correctly hooked up and working.

You are now ready to do the next case, safely and with almost no fear of anesthesia machine malfunction.

The Case for Agent Analyzers

Neither the Food and Drug Administration nor the Walter Reed US Army Medical Center guidelines for anesthesia machine checkout mention agent analyzers, the instruments that determine whether the correct anesthetic agent is in the vaporizer and whether the amount of gas being delivered is the same as indicated on the dial. Because of their price tag (around $5,000), many facilities don't use them. I believe this is a mistake. Although rare, there are real situations in which the vaporizer dial could mislead the physician. For example, if the vaporizer were accidentally inverted as the reservoir was filled (the anesthesia provider would never be able to tell that from a checkout of the machine), the paper lining at the bottom of the reservoir's basin would become super-saturated with the anesthetic. When the dial was set for the agent to be delivered, the vaporizer would make the assumption that no such super-saturation occurred. The resulting anesthetic concentration would be much higher than what is on the vaporizer dial, potentially resulting in overdose and death.

Jeffrey Katz, MD, is the director of the VA Pain Center, Lakeside Division, and an instructor in the Department of Anesthesiology at Northwestern University Medical School Chicago, Ill.