Sunday, July 03, 2005

When "Free Air" Isn't "Free"

One of the bits of medical lingo that confuses patients is the expression "free air," or pneumoperitoneum (isn't all air, by definition, free?). It refers to the idea that air normally contained within the confines of the GI tract has been liberated, and is "free" within the abdominal cavity. It can generally be seen on plain x-rays as air below the diaphragm, and may be due to perforated ulcer, perforated diverticulitis, and obviously after abdominal surgery. In the unoperated patient, it generally will require a trip to the room with no windows.

Patients, being people, sometimes don't make it easy on us to figure out what's going on (why can't they just read the textbooks?). Such is the case with a 30ish-year-old man I met the other evening. He had terrible abdominal pain, a fever, and an elevated white blood cell count. He also had chronic terrible abdominal pain, end stage renal failure requiring peritoneal dialysis, a history of pulmonary emboli, and was admitted to the hospital a week earlier with an upper GI hemorrhage and over-anticoagulation. His vascular options for dialysis are pretty much shot, so all the stops were pulled out to avoid an operation (which would eliminate peritoneal dialysis as an option) ---- lots of vitamin K and FFP as well as very aggressive endoscopic therapy for his bleeding....which, mercifully, stopped.

None too healthy, he was still here with pneumonia and a few other problems when his pain worsened, he developed fevers and chills, and his abdomen became suddenly much more tender; his dialysate is quite cloudy. Now, a CT in this gentleman can be confusing --- some free air and a lot of fluid will be expected due to peritoneal dialysis.

What we see initially is a striking amount of air(arrows) surrounding the pancreas and splenic hilum in the lesser sac, outside the "free" abdominal cavity. The stomach (square mark) and spleen (circle mark) can be seen in this view.




Another view shows how the stomach abuts the free air, concerning for a perforation of the posterior wall of the stomach.



However, the colon also abuts the free air near the tail of the pancreas (arrow; colon has white contrast within it) --- and could also be a source for the process.

Finally, a large amount of fluid is present within the abdomen due to peritoneal dialysis (arrows), and the result of renal failure can be seen in the shrunken kidneys (circles). There is no free air outside the confines of the lesser sac.

Once again, the abdomen is like a box of chocolates; you never know what you're going to get. By all rights, this patient should have a perforated posterior gastric wall in the area of known ulceration, where aggressive endoscopic therapy had been delivered. Instead, the splenic flexure of the colon was perforated, and I got to "deal with poop," as one of the surglings is fond of saying. This was likely an ischemic process at a watershed area, but could also be related to NSAIDs (which also contributed mightily to his ulcers) or diverticular disease. Unfortunately, his peritoneal dialysis access is gone for now, and we'll have to find another way to get his blood spun.