Centrally and locally mediated thermoregulatory responses alter subcutaneous oxygen tension

Mild perianesthetic hypothermia decreases resistance to infections. Decreased resistance likely results in part from direct immune inhibition. However, decreased tissue oxygen partial pressure also decreases resistance to infection by impairing oxidative killing by neutrophils and collagen deposition. Thermoregulatory vasoconstriction decreases skin blood flow and may also decrease subcutaneous tissue oxygen tension. Accordingly, we determined the influence of centrally and locally mediated thermoregulatory vasomotion on subcutaneous oxygen tension. We also compared subcutaneous oxygen tension to other potential markers of tissue perfusion: laser Doppler flowmetry and transcutaneous oxygen tension. Arterial oxygen tension was maintained near 325 mm Hg in five volunteers. Control subcutaneous oxygen tension values were recorded after 1 hour of euthermia (no sweating or vasoconstriction). Volunteers were then cooled with a circulating-water mattress positioned under the trunk and legs. After 1.5 hours of cooling sufficient to produce shivering, the right upper arm was covered for 1 hour with a small circulating water blanket set to 40 degrees C while systemic cooling continued. The volunteers were then systematically warmed to produce sweating, and the right arm was locally cooled. There was no correlation among laser Doppler flowmetry, transcutaneous oxygen tension, and subcutaneous oxygen tension. Systemic cooling significantly decreased subcutaneous oxygen tension, but subcutaneous oxygen tension in the right arm returned to control values during local heating. Systemic warming significantly increased subcutaneous oxygen tension, and 1 hour of local cooling failed to fully reverse the increase. These data indicate that thermoregulatory vasoconstriction significantly decreases tissue oxygen availability. Decreased subcutaneous oxygen tension may be one mechanism by which mild perianesthetic hypothermia facilitates development of surgical wound infections.