The Effect of Hypercapnia upon the Energy Metabolism of the Brain during Arterial Hypoxemia

Abstract

In order to evaluate whether hypercapnia affects the energy metabolism of the hypoxic brain, lightly anesthetized rats were maintained for 30 min at a PaO₂ of close to 28 mm Hg and a PaCO₂ of close to 65 mm Hg, and compared with normocapnic rats maintained either at a normal PaO₂ or at a PaO₂ of close to 28 mm Hg. The results showed that in the hypoxic rats the energy state of the tissue, as evaluated from the energy charge of the adenine nucleotide system, was unaffected by the added hypercapnia. The hypercapnia decreased the accumulation of lactate during hypoxemia and affected the tissue levels of carbohydrate substrates in a direction suggesting decreased metabolic flux. It is concluded that during hypoxemia, and in the absence of ischemia, carbon dioxide protects rather than disrupts the energy metabolism of the brain.

Key Words:

• Brain
• energy state
• hypercapnia
• hypoxemia