Oxygen in tissues during deep hypothermia

Abstract

An oxygen electrode and a thermistor were placed in the brain stem, leg muscle, or abdomen of a rat cooled to 17—15 C. When the rat was thereafter kept at 16∘the electrode usually showed a steady current. At 13—11∘ the apparent Po2 of tissue in most instances diminished during 2—3 hr unless artificial breathing was given. Forced breathing of air or oxygen ordinarily raised the Po2; of nitrogen usually, but not always, lowered the Po2. When the apparent Po2 was not thus raised or lowered, the flow of blood to the one tissue being examined, but not necessarily to all tissues, was evidently inadequate. The heart could be stopped reversibly by further cooling to 9—5∘; brain Po2 diminished only gradually at that low temperature. Survival was assured by a Po2 that was high and steady, but often occurred also after a diminishing or zero Po2. In the hypothermic rat, either pulmonary ventilation or systemic blood flow or an unidentified factor could limit the rat's survival. Submitted on October 26, 1960