Hydrochloric acid infusion for treatment of metabolic alkalosis associated with respiratory acidosis

Hypercapnia due to respiratory failure can be more severe when accompanied by coexistent metabolic alkalosis. We therefore tested the hypothesis that hydrochloric acid (HCl) infusion could improve Paco2 in 15 critically ill patients admitted with mixed respiratory acidosis and metabolic alkalosis, and a pH of between 7.35 and 7.45. HO was infused at a constant rate of 25 mmol/h until the bicarbonate concentration decreased <26 mmol/L, or until the pH decreased < 735 (initial pH > 7.40) or 730 (initial pH < 7.40). Administration of 170 ± 53 mmol of HCl decreased the bicarbonate concentration from 34 ± 3 to 25 ± 2 mmol/L (p < .001), the pH from 7.41 ± 0.03 to 733 ± 0.02 (p < .001), and the Paco2 from 54 ± 8 to 48 ± 8 torr (p < .001). Postinfusion Paco2 could be predicted accurately from the initial status of the patients (r = .95, p < .001) except in one patient with fixed hypercapnia. Paco2 increased from 77 ± 19 to 94 ± 24 torr (p < .001) and Pao2/Pao2 increased from 59 ± 17 to 66 ± 17% (p < .001). The effects of HCl were still present 12 h after the end of the infusion. No complications related to the acid infusion were noted. These results indicate that, even in the absence of alkalemia, active correction of metabolic alkalosis by HCl infusion can improve CO2 and oxygen exchange in critically ill patients with mixed respiratory acidosis and metabolic alkalosis.