Tuesday, February 19, 2008

The Michelin Man, The Balloon, and the Harpoon

You know how some folks get when they see a pile of bubble wrap? They are drawn to it like Odysseus was drawn to the Sirens, can't keep their hands off it....pop, pop, pop, pop, pop.....Such is the case with subcutaneous emphysema.

SQ emphysema is kinda cool, unless you are the one with the problem. Basically, it occurs when air escapes from some portion of the respiratory tract and instead of staying within the chest cavity, it works its way into the subcutaneous tissues. I see this most frequently with blunt trauma to the chest, which causes a tear in the lung or even part of the bronchial tree. The air can track along the chest wall, into the neck, and even down along the abdomen or up into the face. With each breath, more air can escape, and in some cases the patient starts to look like Bibendum.

So, what's the deal with bubble wrap? Well, pressing on the area of SQ emphysema yields a crunchy but soft sensation .... sort of like popping bubble wrap. It can be for some sort of irresistible; since we don't see it every day, all of the students or young staff in the area wants to see what it feels like. The technical name for this is popping sensation is crepitus, but that term covers a wide variety of other processes that generate a vibratory and auditory sensation under the skin. (Image from Learning Radiology)

As dramatic as SQ emphysema in a trauma patient sounds, in many cases it can be an indicator that the patient's respiratory status will be OK, at least for a short while, without an immediate chest tube insertion. This is because the air that is leaking is making it's way out of the chest cavity. When air leaks from the lung or bronchial tree into the chest, and the leak persists with each new breath, then we've got a problem. In that situation, the air that escapes has nowhere to go, and starts taking up so much space that the lung has no place to expand into.....more air leaks with each breath, taking up more space with more built-up pressure, making the lung collapse further, and so on, and so on, etc.

And so on, up to a point where the lung is completely collapsed, the pressure in that half of the chest cavity is pretty great, and it starts to push the heart aside. This then prevents the heart from filling with blood (remember, the return of blood to the heart occurs via a low pressure system). Voila! You now have a perfect recipe for a cause of rapid death in a trauma patient: a tension pneumothorax. It's sort of like an over-filled balloon that needs to be popped.

Treatment for a tension pneumothorax, or a patient with SQ emphysema who has an associated pneumothorax (most often the case) is pretty simple and one of the most gratifying procedures in a surgeon's toolbox: put in a chest tube. It can be done quickly, and can be a life-saving maneuver. In the case of a tension pneumothorax, the amount of pressure present can be surprising, and I have had my hair blown back on more than one occasion upon getting into the pleural cavity. You sort of feel like a whaler, throwing a harpoon to finally put down Moby Dick, with the exhilaration of the chase and the wind in your hair raising your heart rate more than a few beats per minute.

Now, I know that most of you will (fortunately) never get the opportunity to harpoon a tension pneumothorax or pop the bubble wrap of SQ emphysema. But, here's a little substitute if you'd like to live vicariously through the trauma team. Have fun!