Intestinal obstruction: N2O

Nitrous oxide is 34 times more soluble than nitrogen. Therefore, nitrous dissolves into an air pocket much faster than nitrogen dissolves out leading to an expansion of the air pocket. This is bad in some cases: cases in which the air space is closed off, such as the following:

Clinical Scenarios in Which Nitrous Oxide is Dangerous: Bowel obstruction Air Embolism COPD – think of the blebs that will expand and possibly rupture Ear and Eye surgery in which air pockets may be introduced but cannot escape Pneumothorax or pneumocephalus

In a patient with an intestinal obstruction, there is air trapped within the bowel. Nitrous will diffuse from the blood and through the wall of the bowel into that air space. Nitrous will continue to diffuse into the air space until the partial pressure equals that of the blood. The air space will expand. Since the bowel is compliant, it will get larger as the air expands and make surgery more technically difficult – leading to unhappy surgeons. At some point, the bowel may rupture – leading to really unhappy surgeons. Thus, nitrous oxide is contraindicated in patients with an acute intestinal obstruction.

Although studies performed with nitrous oxide and intraluminal pressure have been in animal models (mongrel dogs), it would seem prudent to consider bowel obstruction as a relative contraindication to nitrous oxide anesthesia at inspired concentrations greater than 50%.

Eger-EI II, Saidman LJ: Hazards of nitrous oxide anesthesia in bowel obstruction and pneumothorax. Anesthesiology 1965; 26: 61–6.

Intraluminal pressures of 55 mmHg where detected in pigs administered 75% nitrous, which correlated with a 40% reduction of bowel perfusion without bowel rupture, which may be self limiting secondary to decreased perfusion.

Diffusion of xenon and nitrous oxide into the bowel during mechanical ileus. Reinelt H – Anesthesiology – 01-FEB-2002; 96(2): 512-3