Systemic hypothermia, but not regional gut hypothermia, improves survival from prolonged hemorrhagic shock in rats

Background. Extracorporeal blood perfusion of the gut or enterectomy can improve survival during hemorrhagic shock (HS), suggesting that the gut may be of primary importance in resuscitation. We hypothesized that cooling the gut alone could improve survival in a rat HS model and avoid potential deleterious effects of systemic hypothermia. Methods: Thirty-two Sprague-Dawley rats were anesthetized with halothane. The gut (small intestine, cecum, and colon) was exteriorized. The right atrial (T-RA), rectal, and gut (T-GUT) intraluminal temperatures were monitored. HS was induced by withdrawal of 2 mL of blood per 100 g body weight over 10 minutes. Mean arterial pressure was then maintained at 35 to 40 mm Hg to HS 90 min. From HS 20 min to resuscitation time 1 h, rats were randomized into four groups (n = 8 each): normothermia (T-RA and T-Gut similar to38.0degreesC), gut-25degreesC (T-RA similar to38degreesC, T-Gut similar to25degreesC, induced by rinsing the gut with cooled saline), gut-33degreesC (T-RA similar to38degreesC, T-GUT similar to33degreesC), and systemic hypothermia (T-RA similar to33degreesC, T-GUT similar to25degreesC). At HS 90 min, shed blood and Ringer's solution were infused to restore normotension. Survival, metabolism, and tissue damage were observed to 72 hours. Results: Blood pressure was not different between groups. Compared with the normothermia group, the systemic hypothermia group had lower base deficit and lactate, and needed less fluid during resuscitation for normotension (p < 0.05), but these values were not different in the gut hypothermia groups. In addition, there were no significant improvements in tissue protection induced by regional gut hypothermia, whereas the systemic hypothermia group had lower plasma potassium, lower ornithine carbamoyltransferase (marker of liver injury), and higher glucose levels after HS (all p < 0.05). All rats in the systemic hypothermia group survived to 72 hours, whereas there was only one survivor in the normothermia group, two in the gut-33degreesC group, and none in the gut-25degreesC group (all p < 0.05 vs. systemic hypothermia). Conclusion. Cooling the gut alone does not improve acute survival from HS, suggesting that early deaths are not secondary to gut ischemia. Mild systemic hypothermia allowed 100% survival from prolonged HS.