Chest tubes

Think about what keeps lungs from collapsing normally...

You don't want to have a seal on the collection side of that system, well, at least at the collection chamber. You want any drainage coming from the patient to make it's way into the collection chamber. You could put a one-way valve on the tube coming from the patient going to the collection chamber... but suction from the wall going to the collection canister is what sets up the negative pressure in the device itself. I was looking at some images on google and remember that the devices such as the Pleur-evac do exactly the same thing as the "old" suction bottle system, just in a more convenient package...

This image pretty much describes how the whole system works... The water seal is exactly that... a way to seal the collection side from the suction side and it works both ways.

The collection chamber is kind of like a vacuum chamber. There is negative pressure in the collection chamber du to the suction from the wall. So when air comes into the collection chamber from the chest tube, it then passes through the water seal which prevents it from being able to go back into the pleural space. The water level of the suction control chamber controls the negative pressure by keeping the suction from the wall from acting full force on the pleural space. I don't know how to explain it exactly, but more water allows for more negative pressure. So by increasing the water level, the pressure rises. Decrease the water level and the pressure decreases.

Chest tubes, pneumothorax, and tension pneumos made clear

This little tutorial started out with a few sample NCLEX questions someone posted. I answered this one....

1. Place the client in Trendelenburg position.

2. Hold the insertion site open with a Kelly clamp.

3. Obtain sterile Vaseline gauze to cover the opening.

4. Cover the opening with the cleanest material available.>>

As always in NCLEX-land (and in real life), you're looking for the answer that keeps the patient safest. I know you'd rather cover that hole with something sterile, but what is a greater immediate danger to this unfortunate fellow, an infection (which may not even develop) or a great honking pneumothorax, (which certainly will)?

And while we're at it, let's talk about how you know whether to clamp or not to clamp a chest tube that has been disconnected from its drainage device (but is still in the pleural space). To understand this, let's look at the differences between a tension pneumo and a pneumo that isn't a tension pneumo .

Respiratory mechanics first ! When you breathe in, you're not actually pulling air into your lungs with your muscles. You're actually making a suction inside your chest with them (I know this may seem like a distinction without a difference, but stay with me), and the air enters the lungs thru the route provided for it to do so-- your trachea, via your nose or mouth (or trach tube, if you aren't so lucky).

Your lungs are covered with a slippery membrane called the visceral pleura. The inside of your chest wall has one too, the parietal pleura. They allow the lungs to slip around with chest wall motion, like you can slip two wet glass plates around that are stuck together. Like the two glass plates, they're hard to pry apart due to the surface tension of the wet between them, and that's why the lungs fill the chest cavity and stay there. But just as you can easily pop those glass plates apart if you get a teeny bit of air between them, you can pop the bond between the two pleural layers with air, and if you do, the natural elasticity of the lung will cause it to collapse down to about the size of a goodish grapefruit.

How does the air get in the pleural space where it doesn't belong? Well, you can do it two ways. One is to play rough with the bad boys (or have surgery, which is, after all, only expensive trauma) and have a sharp object puncture your chest wall and admit air into the pleural space. How does it get in there? Well, you make suction in your chest when you breathe in, and now air has TWO routes to get inside your chest-- down the trachea into the lungs, and thru the hole in the chest wall into the pleural space. This is called a pneumothorax, air in the chest that is outside of the lung. The lung will tend to collapse because the surface tension between the wet layers is now interrupted (remember how the pieces of wet glass can be separated by introducing air between them?) and the lungs are naturally elastic.

The other way to get air into your pleural space is from having blebs/bullae on your lung surfaces, and pop one (or more). Then air gets out of your lungs thru the hole(s) and disrupts that pleural side-to-side thing, and there you go again, a pneumothorax. This, however, is called a TENSION pneumothorax, because that air increases with every exhalation (the lung now having two routes to exhale air out of, the trachea and the hole in the lung itself). This allows the lung to collapse on that side, and soon enough pressure (tension) will develop in that half of the chest to push the chest contents over to the other side, compromising blood flow and air exchange in the other lung & heart when it does so. (This is when you see the "tracheal shift.") This is also a bad thing.

So: now both of these fine folks have bought themselves chest tubes. The guy with the chest wall trauma has had his trauma hole sewed up, so when he takes a deep breath air enters his trachea only. He has a water seal on his chest tube so he can't pull air into his chest thru the tube-- the water seal acts like the bend in your sink drain and prevents continuity of the inside and outside places. The suction on the chest tube setup has done its job of removing the air from the pleural space where it didn't belong--it was seen bubbling out thru the water seal and then couldn't get back in. (When all the air is gone from his pleural space, there will be no more airleak in the water seal compartment.) Now, if he disconnects his Pleurevac (or other copyrighted device), he can again take a deep breath and pull air thru the open tube into his pleural space, where it doesn't belong, collapse his lung, and start all over again. THEREFORE, when this guy disconnects his tube, you clamp it IMMEDIATELY, to prevent air from entering the pleural space. He should ALWAYS have those two big old chest tube clamps taped to his Pleurevac (so they go with him to xray and all), just in case he does this.

However, the other guy, with the ruptured blebs and the intact chest wall? Well, his chest tube is pulling air out of the pleural space, but more is still getting in there since he still has a hole in his lung. The idea of the CT is to pull it out faster than he can put it in, and allow the hole to heal up, at which point he will no longer collect air in his pleural space and be all better. Meanwhile, though, you see air bubbling in the waterseal chamber, showing you that there is still air being pulled out of his pleural space. He has an air leak.” What happens to him if his chest tube gets disconnected?

Well, remember, he still puts air into his pleural space, because there's still a hole in his lung. You put a tube in there to take it out, remember? OK, so what happens if you clamp his tube? Bingo, air reaccumulates in the pleural space all over again, his lung collapses, and things go to hell in a handbasket. This guy NEVER should have clamps at his bedside, because some fool may be tempted to clamp his tube before his airleak seals, and he'll get in trouble all over again. If he pulls his tubing setup apart, have him breathe slowly and shallowly (to minimize the air leaving the hole in his lung and getting trapped in his pleural space) while you quick-like-a-bunny hook him up again to a shiny new sterile setup. But do NOT clamp his tube while your assistant gets it set up for you.

What I don't understand is before air goes down the tube to the water seal it hits the collection chamber first, since the tube going to the collection chamber is not submerged in 2cm of water and therefore not a one way valve mechanism what keeps air from going up that first tube and to the patient? It can't be because there is drainage coming out because then we wouldn't have use of a water seal.

Think of the drainage compartment as just an enlargement of the drainage tube. That's really all it is. The exit through the waterseal comes from the drainage compartment which is one with the drainage tube. Does that help?

And... In the suction chamber, how does the amount of water control the pressure? What's the physics there

It's not actually pressure, it's suction (negative pressure). Think of it as suction, and that will help you understand. To understand how the suction control chamber works is really a lot easier than you think.

It's built such that if the suction being applied to it exceeds the cmH20 you put into it (or dial into it, if yours doesn't use actual water), say, 20cmH20, then it allows room air to enter it to break the suction and thus prevent it from exceeding -20cmH20. Think of it as a straw that's 20cm deep into the water in the suction control chamber. If the suction in the chamber exceeds 20cmH20, it will pull all the water out of the bottom part of the straw, and then the chamber will be delivering -20cmH20 suction, no more, and no less.

This is why you can set the wall suction at anything you like, so long as it's enough to keep air bubbling in the suction control chamber, because that tells you that the suction being applied to the patient is -20cmH20.

If it's not bubbling, then there isn't -20cmH20 of suction in the system, and it surely isn't reaching the patient at -20cmH20. If it were, it would have pulled the water down that straw.

If the wall suction is at anything at all > -20cmH20, the device pops open/allows room-pressure air to enter the control chamber and maintain it at the desired -20cmH20, which does reach the patient.

Hope that helps some.