Underwater seal drainage?

[Ezekiel20]

Can anyone help me to understand this concept?

This is apparently the standard treatment for (tension) pneumothorax.

In tension pneumo there is a build-up of pressure in the pleural space, so you insert an intercostal cathether and hook it up to the underwater seal drainage.

However, I have trouble getting my head around how this device works. What is the purpose of having the other end of the drain under water?

I've done a few searches but haven't seen a satisfactory explanation.


Thanks in advance,

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[boilerbeast]

I'm not totally sure if this is right, but one of the advantages of the water seal is that it lets you to see if there is still an air leak. You have the patient cough or take a deep breath and if you see bubbles in the fluid seal, you know that there's still air in the pleural space and the pneumo hasn't yet totally resolved.

 

[Ezekiel20]

Thanks it kind of makes sense, but I still can't understand what drains the air, because it's not like draining a pleural effusion where gravity does the job.

I was hoping someone could explain the physics of how it works, but I think I'll leave it for now.. lots of other, more important things to be learnt.. 🙂

The below link has some good info on this, for anyone interested:

http://www.anaesthesiauk.com/article.aspx?articleid=245

 

[surfej]

Pleuravac can be either connected to suction or to water seal... how the suction works is obvious, but the water seal is less so. As I understand it, when a patient with a pneumothorax has a tube to water seal, there is a high pressure situation in the pleural space (the "leaking air) and by connecting the tube to a water seal it creates a one way valve. Ie. the air can leave the pleural space and exit through the water seal (low pressure escape), but air cannot reenter.

 

[RockShox]

The response above is correct. When there is air in the thorax the pressure inside is greater than the pressure of room air outside. So the air blows out the tube through the water and out...(just like when you blow through a straw.) Then when the air pressure in the thorax becomes negative to air pressure it instead becomes a sucking tube...however in order for air to come in it first must push all of the water in container up the tube in to the thorax. (you know this is true because when you suck on a straw air bubbles do not get sucked into the water and up the straw unless the entire soda is gone.) However, the difference between the air pressure outside and the negative pressure in does not generate enough potential to do this. So a water rises a little in the tube but not very much at all. You now have a pretty simple one-way valve.