The “nitrogen wash-out”

Baby had a small pneumothorax.  Symptomatic with sustained tachypnea and difficulty maintaining oxygen saturation.  I expected a chest tube insertion, but the doc wrote for a ‘nitrogen wash-out’ under oxyhood instead.  What. is. that? 

So, let’s think for a minute.  Pneumothorax is a bubble of air outside the lungs, where it shouldn’t be. Right? And that air, theoretically, is the same composition of room air. Room air is 21% oxygen, %78 nitrogen, and traces of carbon dioxide, argon, and so forth.  In short, the pneumo is mostly nitrogen.

The oxyhood creates an environment of highly concentrated oxygen for the baby to breath.  Delivering 100% oxygen into the (non-sealed) hood creates an environment of roughly 83% oxygen (according to the meter).  As the baby breathes that, the oxygen content of the lungs increases.  This makes a concentration gradient for the nitrogen, in which the nitrogen diffuses across the lung membrane into the lungs, basically sucking the pneumo out of the pleural space and into the lung.  In theory it closes the pneumo as the nitrogen is removed and the oxygen is gradually reabsorbed by the body.  Cool, no?

Well, as evidenced by chest xrays, it worked.  Within about 12 hours the pneumo had shrunk so much we could barely see it. No chest tube required.  Within 8 hours we were off IV fluids, on full gavage feeds, and weaning the oxyhood to a lower concentration of oxygen without any compromise in the baby’s oxygen saturation.  The baby was still tachypneic, but tolerating the wean based on oxygen saturation and easy respirations. According to the doc, the tachypnea would take longer to resolve (though I don’t know why)… explanations of that would be welcome.

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