The influence of moderate hypothermia on cerebral cortex tissue oxygen tension.

The validity of mechanisms balancing oxygen transport and consumption in hypothermia are difficult to analyse because almost any parameter of the transport system is temperature dependent. Two types of experiments have been performed in the rat cerebral cortex to elucidate this problem: PO2 microelectrode study: 32-37 degrees C body temperature, spontaneous respiration. Measurements within the upper tissue layer of 200-500/microgram thickness (N = 15). PO2 surface electrode study: 26-37 degrees C body temperature, artificial respiration. Investigation of the arachnoidal and pial area (N = 46). Mean tissue PO2 (+/- SD) of neo- and archeocortex declined slightly from 27.8 +/- 14.4 mm Hg at 37 degrees C to 25.5 +/- 15.5 mm Hg at 32 degrees C (p less than 0.05, n = 15). Surface PO2 (sPO2) (+/- SD) in response to hypothermia showed a small decrease from 18.1 +/- 4.5 mm Hg (n = 186) at 37 degrees C to 14.7 +/- 4.3 mm Hg (n = 41) at 26 degrees C (p less than 0.05, N = 46). Despite different initial PO2 values at normothermia both groups of experiments are characterized by the same relatively small hypothermia induced PO2 decrease. Oxygen transport and consumption might be balanced under hypothermia and tissue hypoxia does not exist in the temperature range between 26 degrees and 37 degrees C.