LACTIC-ACID KINETICS IN RESPIRATORY ALKALOSIS

Objective: To evaluate the impact of respiratory alkalosis on the elimination of intravenously infused lactate. Design: Prospective, randomized, crossover study. Setting: Medical ICU of a university hospital. Patients: Eight patients treated by ventilatory support for neurologic or neuromuscular diseases. Interventions: Patients were investigated on two occasions: during normoventilation (pH 7.42 +/- 0.1, PCO2 41 +/- 2 torr [5.5 +/- 0.2 kPa]) and during respiratory alkalosis (pH 7.59 +/- 0.1, PCO2 27 +/- 2 torr [3.6 +/- 0.2 kPa]) induced by controlled hyperventilation. To evaluate lactate elimination kinetics, 1 mmol/kg body weight of L-lactic acid was infused over 5 mins. Measurements and Main Results: Arterial lactate concentrations and blood gas values were determined before and repeatedly after the infusion. Lactate elimination variables were calculated from the plasma curve by using a two-compartment model. Respiratory alkalosis increased plasma lactate from 1.56 +/- 0.1 to 2.49 +/- 0.2 mmol/L (p < .001). The lactate elimination half-life increased from 4.57 +/- 0.2 mins at pH 7.42, to 9.96 +/- 1.1 mins during pH 7.59 (p < .01), and beta-half-life increased from 12.2 +/- 1.9 to 44.1 +/- 1 mins (p < .01). Whole-body clearance decreased 40% from 24.2 +/- 2.9 to 14.3 +/- 2.0 mL/kg body weight.min (p < .01). Conclusions: Respiratory alkalosis increases the basal concentration of plasma lactate and decreases clearance of infused lactic acid. These findings provide further evidence of the adverse effects of alkalosis.