Let's Talk About Weaners

I am a very mature medical professional

This is part three, I guess, of my series on mechanical ventilation, to the extent I’m that organized. We started with Fun with Balloons! and continued with Mr. Hamilton Takes Over.

We left our hypothetical patient freshly intubated, nicely sedated and paralyzed, on a mechanical ventilator. We haven’t specified why he’s on the ventilator in the first place; he might be in respiratory failure, he might have had a heart attack, he might just have become unconscious for other reasons so we intubated him for fear he might choke on his own barf¹. Whatever we tubed him for, our next priority needs to be weaning him off the ventilator as soon as practical, for two big reasons.

First, because the ventilator is not a healthy way to breathe; it bypasses the natural defenses of the nose and throat with an express train right down to the lungs². A vent patient can’t cough normally and much of the time won’t even try because he’s sedated. The mouth is a cesspit of germs and saliva which constantly wants to dribble down the airway. You can suction his lungs, you can brush his teeth, you can make sure the cuff at the base of the ETT is perfectly inflated at all times, but once a patient is tubed, ventilator-associated pneumonia is a question of when, not if. In the end, they all get nasty crap in their lungs.

Second, a patient on the ventilator is not exercising, and human bodies are interconnected sets of feedback systems. When you’re stuck in a bed not exercising, your body rapidly loses strength, and when there’s a machine breathing for you—well! I’ve seen patients on the vent get so puny that they needed ridiculous amounts of help from it to breathe on their own. There’s a rule of thumb that every day on the vent adds a week to your recovery time. Yeah.

So our job is to take that intubated patient, fix whatever went wrong to require a ventilator, and pull the tube back out. Quickly. A good intensivist³ will look at every vent patient, every morning, and say, “what’s keeping us from pulling the tube out?” In general, to be extubated, a patient needs to be hemodynamically stable—that is, not requiring drugs to keep their blood pressure up—to need relatively little oxygen⁴, to be able to follow commands such as “give me a thumbs up” or “wiggle your toes,” and to pass a brief test period breathing on their own through a ventilator.

That last one is known as a spontaneous breathing trial, or SBT⁵. When the patient is sedated, you need a full-support mode like PRVC that makes them breathe a set number of times per minute, receiving a given volume. Once they are off sedation and can breathe on their own, you put them in pressure support mode—we use settings of 8/5⁶, which is pretty well standard. 8/5 means the ventilator has a PEEP⁷ of five, and increases pressure by eight every time it senses the patient taking a breath. There is no set rate. In pressure support, you breathe on your own, and the vent watches to make sure you don’t stop. If you start breathing too slowly, it alarms, and if you stop entirely, a backup mode kicks in to make you restart.

A valid SBT lasts at least half an hour, usually no more than an hour and a half if we’re aiming for extubation; we can also flip patients we aren’t planning to extubate yet for whatever reason, just to give them some exercise. Assuming we mean to extubate them, we give them some time to breathe on their own. At the end of that time, we draw an ABG, and if that’s good, we’re probably okay to extubate⁸.

Extubation itself is quick and straightforward, but you customarily always do it with the nurse in the room to help. You prepare whatever oxygen, if any, they need to extubate to. You lay a towel on their chest to catch the tube. You suction their mouth, you suction down the tube. You loosen whatever apparatus is holding the tube in place. “Okay, sir/ma’am, I’m going to deflate this cuff, and if I hear a gurgle, I’m going to pull this tube. When I do, I need you to give me a big cough, you understand?” The last step is always to check for cuff leak; if you deflate the cuff and don’t hear air escaping, it might mean the vocal cords have become irritated from the tube and swollen shut around it. No leak? Reinflate, reattach the ETT holder, apologize to patient, talk to MD about a round of steroids. But you usually hear a leak unless they’ve been on the vent for a long time.

Assuming a leak, you extubate with a quick, smooth pull, dumping the thing onto the towel, and suction vigorously before putting on oxygen. At some point in there you need to turn off the ventilator, which doesn’t know what extubation is and will probably be quite pissed. I have coworkers who like to quickly turn it off immediately before extubation, for fear of spreading circuit-cooties around the room. I’m jaded about that sort of thing and turn it off after suctioning while the nurse fusses with the nasal cannula. Then I use my stethoscope to listen for irritated noises in the lungs and throat. All that’s left after that is cleanup and documentation⁹. I might come back later to strip and clean the vent after an hour or so, once it’s clear that the patient is doing fine without it.

That’s how weaning and extubation work if everything goes smoothly¹⁰. And it often does go smoothly! But the cases which go smoothly get extubated and transfer out of the ICU after a day or two, leaving the problem cases behind. As a result, problem cases tend to accumulate over time … and they can sit and accumulate for now, where this Substack is concerned. Difficulties in weaning can be their own topic. Later.

1. Respiratory therapists, and perhaps hospitals in general, are terrified of vomit. It has to actually jump over the top of the trachea to reach the mouth, for crying out loud. Acid and food going down into your lungs is a quick ticket to pneumonia or, worse, ARDS. If you don’t know what ARDS is, it’s the thing that made Covid fatal. The lungs get massively inflamed and stiff and suddenly you can’t oxygenate any more.

2. Also bypassing the mucociliary escalator. Did you know that your trachea is lined with little hairs that continually wave to push your lung secretions up and out? Well, it doesn’t matter, because the tube goes right past them and contains no such hairs.

3. The doctor running the show in the ICU, generally a pulmonologist (at least at my hospital).

4. 40% or less. You can be extubated to higher amounts of oxygen—you can be extubated to bipap if need be—but really it’s not a good habit to get into and if a patient needs that much O there’s probably something wrong that needs fixing.

5. We will also use the slang “flipping,” as in, “okay, surgical’s given the green light, let’s wake him up, flip him, and pull the tube.” Or we say “put him in a wean.”

6. Read “eight over five.”

7. Positive end-expiratory pressure. Baseline pressure in the circuit, if you’ve forgotten.

8. There are other factors known as “weaning parameters,” such as a machine-calculated value known as Rapid Shallow Breathing Index (if you’re working like mad to keep your numbers normal, extubation won’t go well, you’ll just exhaust yourself), and vital capacity (patient takes a big breath and exhales hard). My hospital tends not to worry about those explicit values, in favor of simply looking at the patient. Is the patient breathing comfortably? Is their breathing fast? A rate of twenty-five is okay, they might just be anxious about the tube in their throat, but forty is not acceptable. Can they lift their head off the pillow in case they need to throw up? Things like that. We might lean on weaning parameters if we’re on the fence, but otherwise they’re just another RT school thing that doesn’t apply everywhere. That’s my opinion, anyway.

9. The vent will have a separate heater for its circuit, which also needs to be turned off. When I withdraw on terminal patients, I am ultra-paranoid and always turn the heater off first, before anything else. In the past, I’ve forgotten, and about five minutes later as the family was in there crying over their dying loved one the heater started beeping and fussing since it could tell there wasn’t air running through it anymore. I got to go back in, apologize, and turn it off before scurrying back out, feeling like just the world’s biggest asshole.

10. As it won’t fit anywhere else, I want to mention SIMV in this final footnote. SIMV, synchronized intermittent mandatory ventilation, is like ordinary PRVC/assist control/whatever you want to call the default mode depending on ventilator brand, except that it only guarantees the set volume for breaths initiated by the machine at its set rate. For breaths initiated by the patient, you may or may not enable pressure support to make sure they aren’t just taking pathetic guppy-gasps in between.

My wise coworker-sensei tells me SIMV is useful for a specific kind of brain-damaged patient who just wants to breathe fast and shallow all the time; the set breaths will deliver a full volume, while the in-between breaths don’t get pressure support so they don’t hyperventilate. That’s … a pretty niche use case. The rest of the time, yeah, SIMV is a solution in search of a problem. As my RT-school instructor put it, “are you resting the patient, or not?” If pressure support is enabled, it’s basically identical to ordinary set-rate modes; if not, you’re letting them do extra work to no benefit IMO. I’m mentioning it because it is a thing and some hospitals like it.

But it’s still kinda stupid.