Metabolic Acidosis during Anhepatic Phase

A patient with end-stage liver disease caused by viral hepatitis underwent orthotopic liver transplantation. Blood gas analysis performed late in the anhepatic phase (see Chapter 56 ), after earlier administration of bicarbonate revealed pHa = 7.10, PaCO₂ = 28 mm Hg, BE = -18 mEq/L, bicarbonate = 8.6, PaO₂ = 260 mm Hg, and Na⁺ = 153 mEq/L— indicating a severe metabolic acidosis with a moderate respiratory alkalosis. The patient was treated with 500 mL (150 mEq, 18 g) of 0.3 M solution of trishydroxymethylaminomethane (THAM) by infusion over 20 minutes. Repeat blood gas analysis showed pHa = 7.09, PaCO₂ = 30 mm Hg, BE = -18 mEq/L, bicarbonate = 9.0, PaO₂ = 251 mm Hg, and Na⁺ = 154 mEq/L. A second dose of THAM was administered by infusion. After transplantation, blood gas analysis showed pHa = 7.30, PaCO₂ = 33 mm Hg, BE = -9 mEq/L, bicarbonate = 16, PaO₂ = 283 mm Hg, and Na⁺ = 149 mEq/L—indicating a marked metabolic acidosis with a mild respiratory alkalosis typical of a partially compensated metabolic disturbance.

The metabolic acidosis during the anhepatic phase demonstrated the importance of the liver in metabolizing lactate to bicarbonate. The high sodium militated against repeat administration of sodium bicarbonate. In this case, THAM was used to minimize sodium administration while controlling the metabolic acidosis. On reperfusion (phase 3), the new liver started to function, and there was improvement in the metabolic acidosis.