Changes in intramucosal pH and gut blood flow during whole body heating in a porcine model

Heat stroke is a syndrome which reduces systemic vascular resistance and cardiac collapse. The gut plays an important role in shock. In hyperthermia, many of the same symptoms as heat stroke may be present, including inhibition of splanchnic vasoconstriction and endotoxemia. Furthermore, both conditions result in shock, in which the gut plays an important role. Detection of insufficient oxygenation of gut tissue, which sustains an earlier and more severe hypoxia, can warn of impending shock and can be performed by monitoring intramucosal pH (pHim). This index is very sensitive to tissue hypoxia and ischemia. In the present study both pHim, using tonometry, and gut blood flow during whole body heating (WBH) in pigs were measured. WBH was achieved by circulating warm water through a vinyl sheet covering the animal. Central venous pressure was maintained by fluid infusion. Body temperature was measured using a thermometer probe inserted into the right jugular vein. Mean arterial pressure, cardiac output and gut blood flow were also measured. pHim was evaluated using a tonometer placed into the midileum lumen. During WBH, cardiac index and mean arterial pressure increased, however systemic vascular resistance decreased. Gut blood flow was either maintained at the normal rate or increased. Intraarterial pH did not change significantly, however pHim significantly decreased from 7.30 at the beginning of WBH to approximately 7.05 after the body temperature reached 42.5 degrees C. These findings suggest that there was reduced oxygen delivery to the tips of the small intestinal villi during regional ischemia following WBH. In conclusion, insufficient tissue oxygen delivery as detected by a reduction in inramucosal pH is an important index in whole body heating.