Value of lactic acidosis in the assessment of the severity of acute cyanide poisoning

Objective: To test the hypothesis that plasma lactate concentrations could be of confirmatory value in patients with histories consistent with acute pure cyanide poisoning because immediate laboratory confirmation of suspected cyanide poisoning is rarely possible and because clinicians must rapidly decide whether to administer specific antidotes, which may have severe side effects. Design: Retrospective clinical study. Setting: An intensive care unit in a university-affiliated teaching hospital. Patients: All acute cyanide-poisoned patients admitted to our intensive care unit, excluding fire victims, from 1988 to 1999. Interventions: None. Measurements and Main Results: Eleven patients were studied. Before antidotal treatment, the median plasma lactate concentration was 168 mg/dL, the median blood cyanide concentration was 4.2 mg/L. Using Spearman's test, there was a significant correlation between plasma lactate and blood cyanide concentrations (r = .74, p = .017). Before antidotal treatment, plasma lactate concentration correlated positively with anion gap and inversely with systolic blood pressure, spontaneous respiratory rate, and arterial pH. During the course of cyanide poisonings, a plasma lactate concentration of greater than or equal to72 mg/d/L (B mmol/L) was sensitive (94%) and moderately specific (70%) for a toxic blood cyanide concentration (greater than or equal to1.0 mg/L). The specificity was substantially improved in patients not receiving catecholamines (85%). Conclusions. The immediate and serial measurement of plasma lactate concentrations is useful in assessing the severity of cyanide poisoning.