The effect of combined hypocapnia and hypoxemia upon the energy metabolism of the brain.

To evaluate whether hypocapnia affects the energy metabolism of the hypoxic brain, lightly anesthetized rats were maintained for 30 min at a of close to 30 mm Hg (1 mm Hg = 133 N/m2) and at 's of close to 35, 25, and 18 mm Hg, and compared with normoxic rats maintained at equivalent . The results showed that in hypoxic rats the energy state of the tissue, as evaluated from the adenylate contents and energy charge of the adenine nucleotide system, was adversely affected by exposures to of 18 mm Hg. The hypocapnia increased the accumulation of lactate during hypoxemia without altering the lactate/pyruvate ratio. Examination of the tissue levels of carbohydrate substrates, cerebral venous , derived intracellular pH, and cytoplasmic NAD+/NADH ratios did not indicate that the increased tissue lactate accumulation was due to a further defect in tissue oxygenation. It is concluded that hypocapnia during hypoxemia is potentially detrimental.