design and ergonomics of anesthesia machines
anesthesia machine safety features
ASA monitoring standards
In the recent past, it was easier to perform a preanesthetic checkout on an anesthesia machine. The machines were not as complicated, and the checkout did not differ much from one type of machine to another. There was a list that you could either commit to memory or attach to the machine as a guide, and you had to complete each step, similar to an airline pilot’s preflight checkout. (But as we said earlier, we anesthesia providers would be much more careful about machine checkout if not only the patient’s, but our lives depended on it, in the same way a pilot’s life depends on his or her machine.)
Things are much different now. Not only are there many more models of anesthesia machines, with different features, but some machines do an automated checkout. This makes things potentially confusing because an automated checkout may or may not check for everything that needs to be checked. As an example, the user manual for some machines will indicate that the user is to perform a low-pressure leak test, but other machines do not. It can certainly be difficult to remember what machine requires what test to be performed by the user instead of being done automatically by the machine. The manufacturers say the clinician needs to read the user manual, and certainly that is true, but few of us do or even know where to find one. In fact, there is now not a standard preanesthesia checkout for every machine because machines vary so much. In 2008, the American Society of Anesthesiologists (ASA) devised an overview1 of what should be checked, but not in the “step one, step two” manner of previous checklists.
Keep in mind that a failure to perform a complete preanesthetic machine checkout would not be looked upon favorably in a medicolegal situation if any untoward event led to patient injury related to an equipment malfunction. But besides that, it is of prime importance that we as caregivers strive to perform at the highest standards possible; clinical excellence is not to be hoped for but is to be expected.
STANDARD MACHINE CHECKOUT
So, what is part of a standard anesthesia machine checkout? Sadly, the only morning checkout many clinicians will perform is to simply see if the anesthesia circle circuit will hold positive pressure. In an emergency situation, that may indeed be all that you have time to do. If a patient may suffer because of a delay, a machine check of the most basic things is appropriate; this would include if the power is on, if a source of oxygen is attached, and if the circuit hold can positive pressure.
Table 13-1 provides a generic machine checkout list from the Food and Drug Administration that has been used for many years. It is still quite adaptable to many anesthesia machines. Even with machines that have an automated checkout system, this list can be referenced for things that may not be checked by the automatic system. For instance, an automated system will not tell you if you have suction, airway equipment, or a bag valve mask (BVM; “Ambu”) available.
Keep in mind that this checkout list is for a bellows ventilator, but nevertheless it can be modified for use with a piston-type ventilator anesthesia machine or for a bellows machine with an automated checkout. Some newer machines may not have an outlet from where to perform a low-pressure test. That is where you need to know what is in the user manual from the manufacturer and what it recommends in such a situation.
AUTOMATED MACHINE CHECKOUT
Whether it is called automated, automatic, or electronic, this kind of checkout is a mixed blessing in our opinion. Although it can check out the sophisticated electronics of modern anesthesia machines better than we can and will never miss a step, it may or may not be an inclusive checkout, depending on the type of machine. Even though we call it automated, many of the machines with an automated checkout still require a human operator during the process to open or close valves and so forth by following instructions on the interface screen. And still, it moves the operator one more step away from the process of machine checkout, and with that, removes the operator from thinking about and understanding how the machine works. It moves the anesthesia machine closer to the concept of a “black box,” something that the user is not supposed to know how it works. An anesthesia machine with automated checkout keeps track of how often the complete checkout was performed.
Because it is not possible to have a universal checkout for modern machines because of design and feature differences and the amount of automation in self-testing, the ASA’s “Recommendations for Pre-Anesthesia Checkout Procedures” is a useful guideline even though it is much less specific than the previous standard anesthesia machine checkout list.1 Steps in the list below marked with an asterisk (*) are done only in the morning or if the machine is moved from one location to another; the other steps are done between each case.
1. Verify that the auxiliary oxygen cylinder and self-inflating manual ventilation device are available and functioning.*
An electronic preanesthesia checkout cannot discern if there is a BVM (Ambu), which is your backup anesthesia machine, is there or not.
2. Verify whether patient suction is adequate to clear a patient airway.*
Suction might very well be the thing that is forgotten the most during a room setup; the buckets and controls are probably behind the machine and hard to get to, the tubing may not be long enough, and so forth. Also, is the suction strong enough? Some things we still have to do ourselves instead of having the automated checkout do it.
It is possible, as one of the authors embarrassingly discovered while he was a resident, to do an anesthesia circuit pressure check with the oxygen flush button with the electric power to the machine turned off. The flush button works when electric power is off, but the rest of the pneumatic system does not.
4. Verify availability of required monitors and check the alarms.
Have you ever been setting up your room and not noticed there were no electrocardiographic leads until the patient was in the room? Again, an automated machine checkout will not tell you something like that. As far as alarms, did the last clinician turn off the alarms? Are they set where you want them? Are you doing an adult, pediatric, or neonatal case?
5. Verify that pressure is adequate on the spare oxygen cylinder mounted on the anesthesia machine.*
This may or may not be part of an automated anesthesia machine checkout; some machines may prompt the user to open the cylinder to check pressure, but others may not.
6. Verify that piped gas pressures are equal to or greater than 50 psig.*
We always assume there is enough pipeline pressure, but assumption can be a bad thing.
7. Verify that vaporizers are adequately filled, and if applicable, that filler ports are tightly closed.*
Desflurane vaporizers will indicate if filling is necessary, but in general, common vaporizers do not. That is up to you; it is the same with closing up vaporizers after filling.
8. Verify that there are no leaks in the gas supply lines between the flowmeters and the common gas outlet.*
This may be done by your machine or not. If not, how to perform this varies from machine to machine, so instruction from a manufacturer’s representative, biomedical technician, colleague, or user manual is necessary. An old-fashioned negative leak test may be needed (see step 4 in Table 13-1). In addition, leaks from unclosed vaporizers will not be detected unless that vaporizer was turned on.
9. Test scavenging system function.*
Whether the machine has an open or closed interface, the scavenger system needs to be checked. Is the scavenger attached to vacuum? Is the vacuum hose unobstructed? Unfortunately, some machine designs make it difficult to adjust scavenger suction. The flowmeter for an open interface system may be in the back of the machine, not visible from the usual user’s position.
Some oxygen sensors require the user to calibrate the sensor to room air; other designs are self-calibrating.
11. Verify that carbon dioxide absorbent is not exhausted.
Absorbent status, whether it is good, exhausted, or even present, is not checked automatically. If you some in on Monday morning and the anesthesia machine was left on all weekend, think about changing the absorbent even if it does not look exhausted; it may be desiccated (more on that in the carbon dioxide absorber Chapter 9). Also, do you trust the person who refilled the canister? The absorber is a common place for leaks.
12. Perform breathing system pressure and leak testing.
This is part of many automated checkouts. The circuit is also checked for its compliance automatically on some machines, so the circuit should be the way you intend to use it, whether partially or completely extended. The machine will have greater accuracy in set versus delivered tidal volume because the circuit’s compliance will be factored into volume delivery.
13. Verify that gas flows properly through breathing circuit during both inspiration and exhalation.
This can be done by breathing through the circuit or using a spare reservoir bag or a specialty reservoir. Leak testing will not necessarily detect an obstruction to ventilation. This can be a concern with coaxial circle circuits because the inspired limb is not clearly seen.
14. Document completion of checkout procedures.
Documentation may be done automatically by the machine. Most machines keep a log of checks, and this information can be retrieved if needed. Many anesthetic written or automated records also have a check box indicating that the anesthesia machine was checked out properly.
15. Confirm the ventilator settings and evaluate readiness to deliver anesthesia care.
You do not want to turn on the ventilator for a pediatric patient, having not changed the tidal volume setting for the adult you just anesthetized. Some call this step an “anesthetic time-out,” making sure that you are ready to deliver a safe anesthetic, with not only a proper anesthesia machine and monitoring setup but also to ensure you are prepared for airway management, medication delivery, line setups, and so forth.