The effects of systemic hypotension on postnatal intestinal hemodynamics and oxygenation.

This study investigated the effect of acute systemic hypotension, induced by pericardial tamponade, on intestinal hemodynamics and oxygenation in 3- and 35-d-old swine. To delineate intrinsic versus systemic responses, the effects of tamponade were compared with those noted after isolated pressure reduction to an innervated in vivo gut loop, achieved by local arterial constriction. Younger subjects demonstrated 16 and 58% increases in vascular resistance during constriction and tamponade, respectively, whereas older subjects exhibited an increase in resistance (27%) only during tamponade. Intestinal oxygen uptake decreased approximately 30% during both constriction and tamponade in the younger group, despite the greater effect of tamponade on gut perfusion. Older subjects exhibited no change in gut oxygenation during either perturbation. In a separate series of experiments, vasopressin, phenylephrine, and angiotensin II, each an element of the systemic pressor response, were infused into in vitro gut loops from 3- and 35-d-old swine. Vasopressin caused sustained vasoconstriction in both age groups; however, phenylephrine and angiotensin II caused greater sustained increases in intestinal vascular resistance in 3- than in 35-d-old intestine. We conclude that systemic hypotension compromises intestinal perfusion to a greater extent in younger subjects, although this effect is not associated with overwhelming tissue hypoxia. The pronounced rise in gut vascular resistance in 3-d-old intestine may reflect the additive effects of intrinsic and systemic vasoactive forces engaged during acute systemic hypotension.