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 4

This 32-yr-old male runner (1.73 m, 81 kg, BMI of 27) was participating in his third 56-km Two Oceans Marathon. He began the race at 7 h 00 min, and after almost 7 h of running, he collapsed unconscious approximately 1 km from the finish. He was carried across the finish line by fellow competitors, so that his race time was recorded as 6 h 52 min 10 s, his slowest time to date. He was taken immediately to the medical facility at the race finish. He was pale, cold, diaphoretic, and vomited intermittently. His mucous membranes were moist, and his skin turgor was normal to increased. His rectal temperature was 41.8°C, his level of consciousness fluctuated [Glasgow coma scale (GCS): 3-10/15], and he was tachypneic (respiratory rate in excess of 40breaths·min-1), with a sinus tachycardia (140bpm) and a systolic blood pressure of 90 mm Hg. Oxygen saturation measured by pulse oximetry on room air was approximately 90%. His serum sodium concentration was reduced (131.0 mmol·L-1), potassium (4.5 mmol·L-1) and chloride (100.1 mmol·L-1) concentrations were normal, and blood glucose concentration was increased (7.5 mmol·L-1). It was unusual to observe an individual presenting with symptoms of both exercise-associated heatstroke and hyponatremia.

The patient was placed in an ice water bath with his torso and pelvis submerged but the limbs out of the water. The bath contained 50% water and 50% ice, and although the water temperature was not measured, it was estimated to be between 5 and 10°C. To increase evaporative heat loss, the air movement produced by a large fan was directed at the patient. He was also given 100% oxygen by polymask (10-15 L·min-1) and IV saline (5%) was infused at a rate of 100 mL·h-1 to correct the hyponatremia. After 20 min, his rectal temperature had decreased to 40.8°C, his GCS score had improved to 12/15, his respiratory rate had decreased to 30 breaths·min-1, whereas his heart rate remained elevated at 139 bpm. Ice water immersion was continued for another 25 min, following which his rectal temperature was 40.1°C and his GCS score had improved to 14/15 but was still fluctuating. Other observations remained unchanged. Mild shivering was noted, and 2 mg of diazepam was administered intravenously to attenuate this response. As his temperature had fallen to approximately 40°C, it was considered safe to transfer him to the nearest hospital with the torso surrounded by ice packs. A second bolus of 2-mg diazepam was administered because of continuing shivering.

On admission to the hospital, approximately 2 h after his collapse, the patient was transferred to the intensive care unit, where active cooling using ice packs was continued because his rectal temperature was still 39.4°C. Blood investigations performed on admission showed elevated serum sodium, urea, and creatinine concentrations, but normal potassium concentrations ( Table 4 ). Hemoglobin concentration, hematocrit, red cell, and white cell counts were all elevated, whereas his platelet count was normal. His urine was of normal appearance but tested positive for blood (4+) and protein (2+) with a specific gravity of 1030. A 12-lead ECG showed a sinus tachycardia without other abnormalities. A central venous line was inserted for venous access; the infusion of hypertonic saline was discontinued. Two hours after admission, the patient was sedated and intubated because of combative behavior. Active cooling using ice packs was continued until his rectal temperature reached 37.4°C, almost 10 h after he had stopped running. At this point, cooling was stopped, but his body temperature continued to drop to 36.1°C before stabilizing at 37.0°C approximately 30 h after his collapse. Figure 3 shows his rectal temperature response to continuous active cooling. The remarkable observation is the extreme resistance to cooling of the runner when exposed to ice water for approximately 50 min and to ice packs for a further 9 h. Confirmation that this subject was profoundly resistant to cooling was provided by the cooling response of another runner of similar build, treated identically for hyperthermia on the same day in the same ice water bath. This 87-kg runner completed the race in 4 h 49 min, more than 2 h faster than case 4, and sought medical care for the treatment of malaise and vomiting. Although his rectal temperature was 41.1°C, he was fully conscious and, therefore, not experiencing heatstroke as classically defined. He was immersed in an ice bath in an identical manner as case 4. After 15 min, his rectal temperature was 39.8°C; 5 min later, he was removed from the water because he was shivering and uncomfortable. Ten minutes later, without further cooling, his rectal temperature was 38.7°C, and 1 h after he was first placed in the ice bath, his temperature was 38.0°C (Fig. 3).

Case 4's Change in Rectal Temperature With 10 h of Active External Cooling. Convective cooling using an ice water bath and fan was commenced minutes after his collapse (time point 0) and was continued for approximately 50 min. Case 4 was actively cooled using ice packs while being transported to the hospital (time point 1), and this mode of cooling was continued for a further 8 h from the time of admission (time point 2) until his rectal temperature reached 37.4°C (time point 10). The horizontal line represents a normal body temperature of 37.5°C. Also included are data from another hyperthermic runner who was treated identically and whose rectal temperature fell to 38°C within 60 min.

Case 4's further recovery was uneventful. He was extubated the following day, after which he remained fully conscious and was transferred to a general ward 2 d later where he made a rapid recovery. His signs and symptoms continued to improve and he was discharged on the morning of the fourth day at his own request, at which time he was asymptomatic. Case 4 subsequently experienced a period of mildly impaired short-term memory that lasted approximately 2 wk. This has resolved, and he now reports no residual sequelae.

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