The Effect of Deep Halothane Hypotension upon Labile Phosphates and upon Extra‐ and Intracellular Lactate and Pyruvate Concentrations in the Rat Brain

Nilsson, L. and B. K. Siesjö, The effect of deep halothane hypotension upon labile phosphates and upon extra‐ and intracellular lactate and pyruvate concentrations in the rat brain. Acta physiol. scand. 1971. 81. 508–516. A study was made of the energy metabolism of the rat brain during deliberate hypotension induced by 2 % halothane and partial airway obstruction. A reduction of the mean arterial blood pressure to 30 mm Hg led to moderate increases in the extra‐ and intracellular lactate and pyruvate concentrations and in the lactate/pyruvate ratios, and to moderate decreases in the phosphocreatine content. At the same blood pressure level, hyperventilation with reduction of the PaCO2 to about 20 mm Hg aggravated the metabolic changes, indicating a further reduction of the cerebral blood flow. Although hypercapnia with an increase in tile PaCO2 to about 85 mm Hg decreased the tissue lactate content markedly, the oxidative metabolism was not normalized. It is concluded that although halothane hypotension with a reduction of the mean arterial blood pressure to about 30 mm Hg leads to changes in the energy metabolism of the brain, the changes are so moderate that a critical degree of hypoxia probably can be excluded. This conclusion may be even more valid if the mean blood pressure is not allowed to fall to such low values, and if marked hyperventilation is avoided at very low blood pressures.