Character of the Gaseous Distension in Mechanical Obstruction of the Small Intestine

Summary

The average percentage composition of the different gases is as follows: (a) Nitrogen 70%; (b) carbon dioxide, 6–12%, approached that found in blood gases; (c) oxygen, 10–12%, with a decided drop after the 72 hour period; (d) combustible gases (methane and hydrogen), a very low percentage in only a few experiments; (e) hydrogen sulphide, 1–14%, with a marked increase after death; (f) volatile basic group (ammonia, methyl amine, etc.) 0.5–4.0%, with an increase with longer duration of the obstruction.

In a quantitative determination of the origin of gases occurring in small bowel obstruction, about 68% of the gas was estimated to have arisen from swallowed air. The amount formed within the body was 32%, of this about 70% originated from diffusion from the blood into the bowel lumen, and the remaining 30% arose from decomposition of food material.

McIver 1 and his associates have shown that gaseous distension of the stomach after abdominal operations is largely due to swallowed air. In mechanical obstructions of the gut, McIver 2 believes that decomposition of intestinal contents is probably the most important source of the gaseous distension. Wangensteen and Rea 3 by excluding the swallowing of air by transecting the esophagus in the dog have indicated that swallowed air is probably the chief source of gaseous distension in mechanical obstructions of the small intestine as well.

In this study the nature of the gases present in the distended intestine was subjected to chemical analysis. Determinations were made in a group of dogs with terminal ileal obstructions, the gut being divided a few centimeters proximal to the ileo-cecal sphincter; in a similar group of dogs in which a preliminary esophagostomy had been made, and in a third group with closed intestinal loops.

The gases of the obstructed intestine were analyzed with the employment of the U. S. Bureau of Mines apparatus.∗ The gas sample was drawn over mercury into specially made gas tubes while the animals were under ether. In some analyses, brine was used in the gas apparatus instead of mercury, and this accounts for the lack of the estimation of the volatile basic group in some of the experiments.

The composition of the gas appearing in all groups (Tables I, II, and III) was different in some respects than the composition occurring in other conditions reported in the literature. Nitrogen tended to come into equilibrium with the blood and surrounding tissue, decreasing to about four-fifths of an atmosphere. In the early hours of obstruction the oxygen content was found to be quite high (10 to 12%), but after the 72 hour period its value fell to a uniformly low figure. Even in early obstruction, the carbon dioxide showed a decided approach to that found in the blood. Apparently this was due to its high diffusion rate. The average percentage of these gases agrees quite favorably with other conditions previously reported.