A “fail-safe” is a system or device that limits damage or harm. For instance, on locomotives, there is a “dead man’s switch” that the engineer must push every couple of minutes or the train will stop. This is a “fail-safe” in that if the engineer is incapacitated, unconscious, or dead, the train will stop automatically. Another fail-safe is the activation bar on walk-behind lawn mowers. The bar, on the handle of the mower, must be pushed in for the mower blade to spin. If you let go of the bar, the blade stops. Failsafe was also a great movie from the 1960s with Henry Fonda. You should watch it. George Clooney remade it in 2000, and it is pretty good, too.
You will find that virtually all fail-safes, whether in anesthesia or in other disciplines or circumstances, are not 100% foolproof. They can be intentionally or unintentionally circumvented, or they may malfunction in such a way that the event the fail-safe was supposed to prevent occurs anyway.
Let’s use the lawn mower as an example. We said the mower has an activation bar that must be pushed in along the mower handle for the cutting blade to spin. You’re mowing the lawn, but you are so tired of how the blade stops every time your hand shifts or you lose your grip. So you decide to tie the activation bar down to the handle, so when you let go to wipe your brow or adjust your iPod, the blade keeps going. You don’t have to grip the handle as tightly now because your hands were getting tired. You push the mower down a small slope and lose your footing; your foot slips in front of you as you fall backward. Where is your foot going to end up? It’s going to end up under the mower, where it will meet a sharp, spinning, hardened steel blade that unfortunately is going to lop off a good part of your foot. If you hadn’t tied the blade activation bar down, when you lost your footing and lost your grip on the mower handle, the blade would have stopped quickly enough that you would still have all your toes.
When we discuss fail-safes on an anesthesia machine, it is usually in reference to preventing the delivery of a hypoxic mixture of gas to the patient. These devices usually have something to do with preventing giving the patient too much nitrous oxide versus too little oxygen. They do a good job, but we will discuss later that hypoxic mixtures can still be given to a patient despite these built-in fail-safes on anesthesia machines. Fail-safes are found in various places on the anesthesia machine, and we will go over the location and function of each one. Some of them we discuss ...