Exaggerated compensatory response to acute respiratory alkalosis in panic disorder is induced by increased lactic acid production.

BACKGROUND: In acute respiratory alkalosis, the severity of alkalaemia is ameliorated by a decrease in plasma [HCO(3)(-)] of 0.2 mEq/L for each 1 mmHg decrease in PaCO(2). Although hyperventilation in panic disorder patients is frequently encountered in outpatients, the drop in plasma [HCO(3)(-)] sometimes surpasses the expectation calculated from the above formula. The quantitative relationship between reduced PaCO(2) and plasma [HCO(3)(-)] in acute respiratory alkalosis has not been studied in panic disorder patients. Our objective was to provide reference data for the compensatory metabolic changes in acute respiratory alkalosis in panic disorder patients.

METHODS: In 34 panic disorder patients with hyperventilation attacks, we measured arterial pH, PaCO(2), plasma [HCO(3)(-)] and lactate on arrival at the emergency room.

RESULTS: For each decrease of 1 mmHg in PaCO(2), plasma [HCO(3)(-)] decreased by 0.41 mEq/L. During hypocapnia, panic disorder patients exhibited larger increases in serum lactate levels (mean +/- SD; 2.59 +/- 1.50 mmol/L, range; 0.78-7.78 mmol/L) than previously reported in non-panic disorder subjects. Plasma lactate accumulation was correlated with PaCO(2) (P < 0.001).

CONCLUSIONS: These results suggest that the compensatory metabolic response to acute respiratory alkalosis is exaggerated by increased lactic acid production in panic disorder patients. Here, we call attention to the diagnosis of acid-base derangements by means of plasma [HCO(3)(-)] and lactate concentration in panic disorder patients.