[Effect of normobaric hyperoxia on parameters of brain metabolism]

In the literature there is only little information about the influence of hyperoxia on cerebral metabolic parameters. The aim of our study was to examine the effect of increased inspiratory oxygen concentrations on parameters of brain metabolism in elective neurosurgical patients. Ten patients undergoing an elective craniotomy for brain tumour resection were included in the study. The inspiratory oxygen concentration was raised at intervals of 15 minutes from 0.4 to 0.6 to 1.0 before opening the skull under "relative steady state conditions". At five defined measuring points, a blood gas analysis and an analysis of lactate and glucose levels were performed from arterial and jugularvenous blood. The lactate oxygen index (LOI), the arterio-jugularvenous lactate difference (AJDL) and the oxygen content of the arterial (caO2) and jugularvenous (cjO2) blood were calculated. Under increasing levels of FiO2, one can see an increase in sjO2, of jugularvenous oxygen tension (pjO2) and in oxygen content (cjO2). The most important result is the significant decrease (10% from baseline) in jugularvenous lactate at FiO2 1.0, while arterial lactate did not change significantly nor did the following parameters: paCO2, pjCO2, LOI, modified LOI, arterial and jugularvenous glucose. Hyperoxia causes a possible shift to aerobic metabolic situation in the brain reflected by decreased jugularvenous lactate.