Experimental studies on fluid pathophysiology in small intestinal obstruction in the rat. I. Effects of intraluminal hyperosmolality.

An experimental model is described which is intended to simulate and accentuate the movement of fluids across the intestinal mucosa resulting from simple small intestinal obstruction as well as to provide a means for measuring these fluid shifts. Working on the hypothesis that the increase in fluid in the obstructed small intestine is a consequence of increased osmolality resulting from enzymatic breakdown of the intestinal contents, a solution of high osmolality was introduced into an intestinal segment of known size and position. Under these conditions the intestinal mucosa functioned in the manner of a semipermeable membrane and permitted only fluids of low osmolality to enter the intestinal lumen, thus tending to normalize its hyperosmolal contents. The process of dilution followed a simple dilution curve. At the same time hemoconcentration and increased serum osmolality reflected the mobilization of fluids from the extravascular and vascular compartments. The transfer of fluids into the intestinal lumen continued throughout the test period, despite the fact that there was a linear increase in intraluminal pressure to a relatively high level, indicating increased smooth muscle tone probably due to the hyperosmolal provocation. The observed accumulation of fluid was well reproducible and associated with predictable effects on the vascular and extra-vascular compartments.