Sunday, February 19, 2006


Most of the patients that I deal with are quite pleasant. There are occasional exceptions, of course. Those folks that are a bit cranky often mention a lack of coffee (or breakfast, or whatever) as the reason for their irritability, having followed the pre-op instructions to not eat or drink after midnight.

So why DO we ask you to be NPO? (As this Wikipedia blurb notes, NPO is an abbreviation for the Latin nil per os, meaning nothing by mouth.)

Well, it's like this. When we induce general anesthesia, i.e., put you to sleep, you become instantly and profoundly unconscious. It's not like regular sleep, in which you continue to move, breathe, have reflexes, etc. No, general anesthesia creates a state in which you don't breathe, or have reflexes--and, most importantly, pretty much all muscle tone is lost. This includes the muscle tone to your stomach and esophagus. When that all relaxes, it's pretty easy for anything in your stomach to flow back up toward your mouth. Between your stomach and your mouth is your larynx, or the entrance to your lungs. Since it has lost muscle tone too, and you no longer have any reflexes like coughing, your stomach contents can also flow into your lungs. Small amounts generally don't have much effect, but if you have a lot of stuff in your stomach, or if it's very acidic, it's like pouring hydrochloric acid into your lungs.

Needless to say, your lungs don't like it.

People have died from aspiration pneumonitis. It's not a way I'd want to go.

But what about people who have unplanned procedures, you say--like a car wreck or something? Obviously, they didn't skip breakfast planning to get T-boned in their SUV later.

There are some things we can do as anesthesia providers to minimize the risk of aspiration, and/or to minimize the damage if aspiration does occur. Those types of things are utilized in patients who are at higher risk for aspiration. (Would you like a list? Here's a few: emergency surgeries are at the top, of course, but anyone whose stomach doesn't empty as well as is should, or has higher pressure on or in their stomach, can be at increased risk. Diabetes causes delayed gastric emptying, as does late pregnancy. Obese people have more pressure on their stomach than thin people because of the weight of their adipose tissue, and are at higher risk of aspiration than their thin counterparts. People who have fundamental problems with the connection between their stomach and esophagus--like say, hiatal hernia--are also at increased risk. These are just a few that we worry about.)

Anyway, like I said, there are things that we can do to minimize the risk of aspiration in our patients. But the very best way to keep your stomach contents from going in your lungs during induction of anesthesia is to have nothing in your stomach! And, I might mention, NPO means nothing by mouth. Even chewing gum and smoking cigarettes can stimulate your stomach to start secreting acid as a reflex.

Of course, I can understand when people don't know not to chew gum and so forth, because the pre-op nurses usually just say "don't eat or drink after midnight." But I had one woman tell me she'd had breakfast that morning--thankfully, she was honest--because she said she "just couldn't do that [not eating or drinking] thing." We had to tell her that we "just couldn't do" her surgery, either.

Most patients try really hard to follow the directions they're given. I think some would try harder if they knew the reason why we ask some of the things that we do. When it comes to NPO status, now you know!


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