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

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.

Sodium salicylate has no effect on cerebrospinal fluid [H+] in dogs with normal acid-base balance.

The experiments described here were designed to investigate the possibility that central stimulation of respiration by salicylates may be due to changes in [H+] of cerebral fluids. Two groups (n = 6 in each) of anesthetized, paralyzed, and mechanically ventilated dogs were studied for 6 hr. Renal pedicles were ligated to maintain blood salicylate level constant. Group II received 150 mg/kg Na salicylate intravenously at 0 hr after samples had been obtained. Group I (control) received equal volume of half-normal saline. Mean plasma salicylate levels were 18.9, 18.4, and 19.6 mg % at 0.5, 3, and 6 hr after administration of Na salicylate. Respective cisternal cerebrospinal fluid (CSF) levels were 3.2, 4.8, and 5.9 mg %. Salicylate-induced hyperthermia was prevented by peritoneal cold dialysis, and a rise in PaCO2 was prevented by increasing ventilation. During the 6 hr of relatively normal systemic acid-base balance, cisternal CSF mean PCO2 values were 45.3, 43.6, and 49.3 mm Hg at 0, 3, and 6 hr in the control group; in group II, respective values were 46.9, 45.7, and 47.7 mm Hg. Cisternal CSF [H+] were 44.4, 45.2, and 50.5 nEq/L in group I at 0, 3, and 6 hr. Respective values in group II were 45.0, 47.5, and 50.6 nEq/L. These values were similar and statistically insignificant from those in group I. In both groups cisternal CSF [HCO3-] fell about 2 and CSF lactate concentration rose about 1 mEq/L at 6 hr.(ABSTRACT TRUNCATED AT 250 WORDS)