Increased inspired oxygen concentration as a factor in improved brain tissue oxygenation and tissue lactate levels after severe human head injury

Object. Early impairment of cerebral blood flow in patients with severe hea d injury correlates with poor brain tissue O-2 delivery and may be an impor tant cause of ischemic brain damage. The purpose of this study was to measu re cerebral tissue PO2, lactate, and glucose in patients after severe head injury to determine the effect of increased tissue O-2 achieved by increasi ng the fraction of inspired oxygen (FiO(2)). Methods. In addition to standard monitoring of intracranial pressure and ce rebral perfusion pressure, the authors continuously measured brain tissue P O2, PCO2, pH, and temperature in 22 patients with severe head injury. Micro dialysis was performed to analyze lactate and glucose levels. In one cohort of 12 patients, the PaO2 was increased to 441 +/- 88 mm Hg over a period o f 6 hours by raising the FiO(2) from 35 +/- 5% to 100% in two stages. The r esults were analyzed and compared with the findings in a control cohort of 12 patients who received standard respiratory therapy (mean PaO2 136.4 +/- 22.1 mm Hg). The mean brain PO2 levels increased in the O-2-treated patients up to 359 /- 39% of the baseline level during the 6-hour FiO(2) enhancement period, w hereas the mean dialysate lactate levels decreased by 40% (p < 0.05). Durin g this O-2 enhancement period, glucose levels in brain tissue demonstrated a heterogeneous course, None of the monitored parameters in the control coh ort showed significant variations during the entire observation period. Conclusions. Markedly elevated lactate levels in brain tissue are common af ter severe head injury. Increasing PaO2 to higher levels than necessary to saturate hemoglobin, as performed in the O-2-treated cohort, appears to imp rove the O-2 supply in brain tissue. During the early period after severe h ead injury, increased lactate levers in brain tissue were reduced by increa sing FiO(2). This may imply a shift to aerobic metabolism.