Reevaluation of the linkage between acute hemorrhagic shock and bacterial translocation in the rat

The present study was undertaken to determine the conditions under which acute periods of hemorrhagic shock induce bacterial translocation. Rats (at least six per group) were anesthetized intraperitoneally with the barbiturate, pentobarbital (50 or 65 mg/kg), or the inhalation anesthetic methoxyflurane. Following anesthesia, the femoral artery was catheterized, from which blood was withdrawn to maintain a mean arterial blood pressure of 30 mmHg for 30, 60, or 90 min, followed by reinfusion of shed blood. Instrumented, but nonshocked animals served as controls. Rats were sacrificed at 0, 2, or 24 hr postshock, and quantitative bacterial cultures of the mesenteric lymph node complex (MLN), liver, and spleen were made. Within groups, the effects of heparinization were also determined. In pentobarbital- treated animals, regardless of the extent of heparinization, consistent translocation to both MLN and distant organs occurred when shock was prolonged for 90 min, and assessment of translocation was made 24 hr after reinfusion of shed blood. Furthermore, a mortality rate of ~30% was found in rats subjected to this protocol. The magnitude of translocation was less consistent, and did not differ from that in sham shock controls, under other conditions of shock and evaluation. In rats anesthetized with methoxyflurane, no mortality occurred, and no statistical significance between the incidence or degree of translocation in shocked animals vs. sham shock controls could be demonstrated, regardless of the shock protocol. In additional studies, effects of these anesthetics on intestinal morphology and superior mesenteric arterial (SMA) flow in the context of hemorrhagic shock were assessed. Compared to methoxyflurane counterparts, histologic aberrations were found in the ileum of pentobarbital-treated animals following shock and resuscitation, and SMA flow was profoundly inhibited during shock and resuscitation. Thus, we conclude that acute periods of hemorrhagic shock in rats of 90 min duration or less do not enhance bacterial translocation, regardless of the time of sacrifice after resuscitation. The finding of translocation in pentobarbital-treated animals is most likely due to the adverse effects of this anesthetic on the splanchnic circulation and the resultant vascular compromise to the intestinal mucosa.