Acid-base alterations in heatstroke

Abstract

Objective: To analyze the acid-base balance during heatstroke. Design: Retrospective study. Setting: Heatstroke Center, Makkah, Saudi Arabia. Patients: Hundred nine consecutive heatstroke patients (mean age 55±12 years) with rectal temperature from 40 to 43.4°C following exposure to hot weather. Intervention: Arterial blood gases collected prospectively and analyzed using 95% confidence limits established by controlled experimental studies. Severity of heatstroke on admission assessed by Simplified Acute Physiology Score and Organ System Failure score. Results: Metabolic acidosis was the predominant acid-base change followed by respiratory alkalosis (81 and 55% of the patients, respectively). The prevalence of metabolic acidosis (but not respiratory alkalosis) was significantly associated with the degree of hyperthermia: 63, 95 and 100% at 41, 42 and 43°C, respectively (p<0.0001). Patients with metabolic acidosis had a large anion gap (24±5). Arterial partial pressure of oxygen (PaO₂), systolic blood pressure and Organ System Failure score were similar with or without metabolic acidosis. Although the acute physiology score was higher in patients with, than without, metabolic acidosis (15.7±3.7 vs 9.8±4.4, p<0.001), there was no significant difference in neurologic morbidity and mortality (7.9 vs 1.1%, 5.6 vs 0%, p=0.776 and 0.581, respectively). Conclusion: We conclude that metabolic acidosis is the predominant response in heatstroke.