Cerebrospinal fluid ions in metabolic acidosis in dogs: effects of acetazolamide.

Abstract

We hypothesized that, during isosmotic isonatremic HCl acidosis with maintained isocapnia in cisternal cerebrospinal fluid (CSF), acetazolamide, by inhibiting carbonic anhydrase (CA) in the central nervous system (CNS), should produce an isonatric hyperchloric metabolic acidosis in CSF. Blood and CSF ions and acid-base variables were measured in two groups of anesthetized and paralyzed dogs with bilateral ligation of renal pedicles during 5 h of HCl acidosis (plasma [HCO3-] = 11 meq/l). Mechanical ventilation was regulated such that arterial PCO2 dropped and CSF Pco2 remained relatively constant. In group I (control group, n = 6), CSF [Na+] remained unchanged, [HCO3-] and strong ions difference (SID) fell, respectively, 6.1 and 5 meq/l, and [Cl-] rose 3.5 meq/l after 5 h of acidosis. In acetazolamide-treated animals, (group II, n = 7), CSF [Na+] remained unchanged, [HCO3-], and SID fell 11 and 7.1 meq/l, respectively, and [Cl-] rose 7.1 meq/l. We conclude that during HCl acidosis inhibition of CNS CA by acetazolamide induces an isonatric hyperchloric metabolic acidosis in CSF, which is more severe than that observed in controls.