Acid-base alterations in heatstroke

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 degreesC 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 Scare 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 degreesC, respectively (F, < 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 vs 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.