CEREBRAL LACTATE-OXYGEN INDEX IN ACUTE BRAIN INJURY WITH ACUTE ANEMIA- ASSESSMENT OF FALSE VERSUS TRUE ISCHEMIA

Objective: To evaluate the occurrence of global cerebral ischemia in a cute brain trauma with acute anemia by combined measurements of cerebr al hemodynamics, oxygenation, and lactate production. Design: Prospect ive, intervention study. Setting: Neuroscience intensive care unit of a university hospital. Patients: Adults (n = 22) with severe acute bra in trauma (Glasgow Coma Scores ranging from 4 to 8), undergoing freque nt serial measurements of total hemoglobin content, jugular oxyhemoglo bin saturation, arteriojugular oxygen content difference, arteriojugul ar lactate concentration difference, lactate-oxygen index, and cerebra l blood flow, along with other routine procedures. Measurements and Ma in Results: Acute anemia (disclosed by a total hemoglobin content of < 11 g/dL in at least three measurements) was found in 19 (86%) of 22 pa tients. In 211 serial multivariate physiologic observations, only one (0.4%) disclosed abnormally negative arteriojugular lactate difference consistent with global cerebral ischemia. However, in 18 (8.5%) studi es in seven (31.8%) patients, acute anemia resulted in markedly decrea sed values of arteriojugular oxygen content difference. The latter, in turn, yielded abnormally high values of lactate-oxygen index despite normal cerebral lactate production (arteriojugular lactate difference) and oxygenation (jugular oxyhemoglobin saturation). Conclusions: In a cute brain injury with acute anemia, global cerebral ischemia is a rar e finding. However, false cerebral ischemia may be frequently found, i f assessed by the lactate-oxygen index, because the denominator of the index (the arteriojugular oxygen content difference) frequently decre ases as a function of decreasing hemoglobin, thus yielding false calcu lated ischemic high values for lactate-oxygen index despite normal cer ebral oxygenation and lactate production.