Lactic acid kinetics in respiratory alkalosis

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Abstract
To evaluate the impact of respiratory alkalosis on the elimination of intravenously infused lactate. Prospective, randomized, crossover study. Medical ICU of a university hospital. Eight patients treated by ventilatory support for neurologic or neuromuscular diseases. Patients were investigated on two occasions: during normoventilation (pH7.42±0.1, Pco241 ± 2torr[5.5 ± 0.2kPa])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. 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 β 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). 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.

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