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

Disclosures

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

In This Article

Case 1

An active 34-yr-old man (1.8 m, 85 kg, BMI of 26) who had no known medical conditions took part in his fourth Argus Cycle Tour. Although he was reportedly not as fit as normal and slightly overweight, he had completed a 21.1-km footrace 1 wk before the Cycle Tour and was about to run another such race a week later. For the weeks preceding and on the morning of the race, he used a supplement (Dymetadrine Xtreme), of which the primary ingredients are 300 mg of ephedra and 100 mg of caffeine percapsule. He started the race at 8 h 53 min and collapsed after approximately 4 h of cycling, having covered an estimated 80 km. While being transported to the hospital, paramedics attempted to resuscitate him. He was also intubated and manually ventilated but was apparently not actively cooled. Unfortunately, we could not source any further details of the management he received in the 1-h period between his collapse and his admission to the hospital, and there was no record of his rectal temperature before hospitalization.

On arrival at the hospital at 14 h 00 min, approximately 1 h after collapsing, he was unconscious, cyanosed, very hot (rectal temperature of 42°C), hypotensive (systolic blood pressure of 90 mm Hg), and with a tachycardia (120 bpm). Immediate emergency management included manual ventilation, cooling (sheet, ice water, and a fan), and intravenous (IV) fluids. Blood test results on admission to the hospital are presented in Table 4 . Blood gas analysis indicated metabolic acidosis with partial respiratory compensation. Serum sodium and potassium concentrations were within the normal ranges. Serum urea and creatinine concentrations were markedly elevated. Hemoglobin concentration, hematocrit, red cell, and platelet counts were normal, but white cell count was elevated. His urine was reportedly "dark" and positive for protein and blood, suggestive of myoglobinuria. A chest x-ray was normal, as was a cerebral computed tomography (CT) scan. The initial diagnosis was coma secondary to hyperthermia. By that evening, he had developed generalized seizures. The following morning, his rectal temperature was normal but he was still unconscious. He was oliguric, despite continued fluid replacement and inotropic support, and his serum creatinine concentration continued to rise. A second chest x-ray again showed no abnormalities, but repeat blood tests revealed, in addition to acute renal failure, signs of liver damage, myocardial damage, and disseminated intravascular coagulation (DIC). In addition, during the morning after his collapse, an ECG showed ST segment depression suggesting developing myocardial ischemia. Despite continued multisystem support, he developed bradycardia that progressed to asystole. He was pronounced dead at 13h00min, approximately 24 h after his collapse. The final diagnosis was exertional heatstroke progressing to multisystem failure including encephalopathy, acute circulatory collapse, myocardial failure, respiratory failure, acute renal failure, liver damage, and DIC.

Autopsy revealed that the heart weighted 470 g with normal coronary arteries. There was widespread subendocardial hemorrhage over the left ventricular surface. The lungs had pronounced congestion and mild edema. The brain appeared macroscopically normal. The liver was enlarged, fatty, and markedly congested with signs that individual cells had undergone apoptosis or necrosis. The adrenal glands were congested with signs of acute hemorrhage; the kidneys displayed acute tubular necrosis, had numerous casts, and stained positive for hemoglobin/myoglobin(Fig. 1). A sample of the vastus lateralis muscle showed widespread necrosis of individual fibers and groups of fibers as indicated by the swollen and fragmented musclesubstance (Fig. 2). Finally, there were diffuse hemorrhages in the lungs, heart, and the submucosa of the trachea. The pathologist concluded that an exact cause of death could not be determined from autopsy alone, but observed that heatstroke, possibly secondary to exertion, was a likely diagnosis.

Cross-sections of the Kidneys of Case 1 Were Stained With the Okajima Stain That Stains Hemoglobin and Myoglobin as orange. The kidneys were histologically positive for the presence of tubular necrosis with (A) multiple orange-brown casts (×100) and (B) myoglobin casts (×100).

Longitudinal Sections of the Lower Limb Skeletal Muscle of Case 1 Were Stained With Hemotoxylin and Eosin, Which Stained the Cell Cytoplasm pink and the Nuclei purple. Histological examination showed (A) swollen and severely fragmented fibers (×200) and (B) fiber thickness variation and the presence of necrotic fibers (×100).

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