In this book, we will discuss different types of anesthesia equipment. When we say “anesthesia equipment,” we mean the anesthesia machine itself, as well as the major monitoring devices. The trend is currently to have both machine and monitors integrated in an “anesthesia delivery system” or “anesthesia work station.” Regardless of how the equipment is packaged, it is still useful to think of the components as separate entities in order to understand them. So in this book, when we talk about the “anesthesia machine,” we mean the device that delivers oxygen and other gases, delivers inhalational anesthetics, and ventilates the patient. When we talk about “monitors,” we generally mean the devices that measure physiologic, chemical, and pharmacologic information.
We will begin by reviewing what is found on a generic, modern anesthesia machine. It will be analogous to talking about airplanes; all airplanes fly, but there is a wide variety of designs, incorporating different engines, wings, and so forth, but all airplanes have things such as engines and wings. This is also how it is for anesthesia machines. They all do the same thing, but there are differences in how the same thing is done and differences in how machines are designed and function.
Purpose of an Anesthesia Machine
What is the main purpose of an anesthesia machine? This is a question we often ask medical students doing an anesthesia rotation. Naturally, many of them say something like “to deliver anesthesia gas to a patient.” In our minds, that ability is not the main purpose of an anesthesia machine.
The main purpose of an anesthesia machine is to deliver oxygen to a patient. See the list below. Everything else is secondary. Everything about an anesthesia machine is built around the purpose of delivering oxygen to a patient. All the fail-safe systems of a machine concern the prevention of the delivery of a hypoxic mixture, not the delivery of anesthetic agents.
Okay, so what is the second most important function of an anesthesia machine? The students will then answer “to deliver anesthesia gas to a patient.” But again they are wrong. After oxygenation, the next most important function or purpose of an anesthesia machine is to provide a means of positive-pressure ventilation. If we must ensure the patient receives oxygen, we must also have a means of being able to force oxygen into a patient because apnea is a major effect of anesthetics. Merely delivering oxygen to an apneic patient’s mouth will not help too much.
Okay, so now comes the anesthesia delivery part, right? Yes, the third main function of an anesthesia machine is to deliver inhalational anesthetic agents to a patient. You should remember these functions in their order of importance as we go along.