Biochemical mechanisms in anaesthesia

Anaesthesia and pyruvate dehydrogenase deficiency

A ten-month-old infant with pyruvate dehydrogenase deficiency received anaesthesia on two occasions, once for a laparotomy and once for a tracheostomy. During both anaesthetics (different techniques) she developed an increase in arterial lactate levels and a metabolic acidosis. Pyruvate dehydrogenase deficiency results in the inability to metabolize pyruvate with resultant accumulation of pyruvate and lactate. Inhibition of gluconeogenesis, which may be produced by halothane and thiopentone, will also increase lactate levels. Other causes of increased lactate levels are hypocarbia and high carbohydrate intake. In this patient hypocarbia may have produced increased lactate levels and increased the metabolic acidosis. Recommendations include avoidance of halogenated anaesthetics, avoidance of lactate containing solutions, maintenance of normocarbia, and stress-free anaesthesia.

Effects of halothane on the incorporation of [14C]-serine into phospholipid in the guinea-pig ileum

1 The effects of halothane on the incorporation of L-[3-14C]-serine into phospholipid were studied in the resting, innervated longitudinal muscle preparation of the guinea-pig ileum. 2 The anaesthetic, at clinical concentrations, caused a dose-dependent, partial inhibition of incorporation. The effect was rapid and reversible, and did not show characteristics of competitive inhibition. 3 The incorporation was reduced by a decrease in the Ca2+ concentration of the Krebs incubation buffer. Part of the activity persisted in the absence of added Ca2+ and this was most susceptible to inhibition by halothane. Sensitivity to external Ca2+ was not influenced at the halothane concentrations studied. 4 Evidence in support of the 14C-incorporation being due to L-[3-14C]-serine-phospholipid base-exchange activity included: (a) the rapid appearance of radioactivity in phosphatidylserine; (b) the kinetics of this incorporation in relation to that in phosphatidylethanolamine; (c) its dependence on Ca2+, and (d) its sensitivity to 2,4-dinitrophenol and its sensitivity to temperature. 5 It is concluded that this preparation makes it possible for a membrane-bound lipid-dependent activity (L-serine-phospholipid base-exchange) to be studied in conditions of cellular integrity under which the normal functional effects of lipophilic drugs can be simultaneously tested. 6 A rapid gas-chromatographic assay for halothane from an aqueous medium is also described.