Heatstroke During Endurance Exercise: Is There Evidence for Excessive Endothermy?

Dale E. Rae; Gideon J. Knobel; Theresa Mann; Jeroen Swart; Ross Tucker; Timothy D. Noakes


Med Sci Sports Exerc. 2008;40(7):1193-1204. 

In This Article

Case 2

This 40-yr-old man, who was a keen recreational cyclist and who had no history of medical problems, participated in his sixth Argus Cycle Tour. He started the race at 9 h 48 min and completed the 109 km in 5 h 1 min 13 s. Shortly after finishing the race, he vomited, collapsed, and was found to be apneic. He was taken immediately to the medical facility at the race finish where resuscitation was attempted. He was given 50 mg of midazolam and 50 mg of tramadol hydrochloride, intubated, and placed on 100% oxygen. There is no evidence that he was actively cooled either at the medical facility at the race finish or while being transported to the hospital, and there are no records showing that his rectal temperature was measured before admission to the hospital.

On arrival at the hospital at 16 h 50 min, approximately 2 h after his collapse, he was comatose, his rectal temperature was 41.2°C, his blood pressure was 120/80 mm Hg, his heart rate was 170 bpm, and his blood glucose concentration was 8 mmol·L-1. The attending physician noted that he had reduced air entry with crepitations on the right side of the chest. Emergency treatment included ventilation, IV fluids, cooling (fan and sponging), and administration of adenosine with repeated cardioversion, which failed to correct his tachyarrhythmia. Blood gas analysis ( Table 4 ) showed an elevated PO2 with respiratory compensation for a mild metabolic acidosis. Serum sodium concentration was normal, but serum potassium, urea, and creatinine concentrations were elevated above the normal ranges indicating compromised renal function. Alternatively, raised serum potassium and creatinine concentrations may indicate heat-related rhabdomyolysis, heatstroke, or dehydration, or all three. Blood myoglobin and troponin T concentrations and creatine kinase-myocardial band (CK-MB) activities were all markedly elevated indicating muscle damage. Hemoglobin concentration, hematocrit, red cell, white cell, and platelet counts were all within the normal ranges. The initial diagnosis was heatstroke complicated by dehydration, renal failure, myocardial infarction, refractory supraventricular tachycardia, probable pneumonia, and coma of uncertain cause (possibly hypoxic ischemic encephalopathy). A CT scan was normal, ruling out a cerebral bleed. However, the chest x-ray showed increasing opacity in the right midzone. Aggressive IV fluid therapy was continued to counter the progressively falling central venous pressure (2 cm H2O). As a result, the patient received a total of 8 L of IV saline for approximately 9.5 h. Despite this, he remained anuric. By 22 h 00 min, he was bleeding from all access sites and from his pharynx, nostrils, and rectum, indicating DIC. Approximately 7 h after his collapse, his rectal temperature was normal (38°C). Assisted ventilation became increasingly more difficult, requiring high concentrations of oxygen and increasing pressure. He developed adult respiratory distress syndrome, and the persistent hypotension was treated with an adrenaline infusion. At 2 h 00 min, approximately 11 h after his collapse, his core temperature was 37°C. He was given plasma and blood transfusions and was ventilated with 100% oxygen. At 2 h 30 min, he developed cardiac arrest from which he could not be resuscitated. The final diagnosis was heatstroke complicated by dehydration and renal failure, encephalopathy, myocardial infarction, probable aspiration pneumonitis, adult respiratory distress syndrome, and DIC. No autopsy was performed.


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