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Exertion-induced heat exhaustion is a potentially lethal condition. The earliest signs include unsteady gait and confusion. Recording of rectal temperature is essential. Skin colour, blood pressure and heart rate are not reliable diagnostic signs. The mainstays of therapy are rapid rehydration and cooling. Prompt diagnosis and rapid effective therapy will minimise the risk of death.
BACKGROUND: This paper presents a further analysis of biochemical data collected during a 1 year prospective study of 106 cases of heat exhaustion at a deep underground metalliferous mine. RESULTS: Multiple regression analysis results indicate that the haemoglobin, serum creatinine and plasma lactate concentrations are statistically significant predictors of the anion gap. Together, they explain 65% of the variance in the anion gap (R(2) = 0.650). Spearman's rho correlation results also confirm that haemoglobin, creatinine and lactate are each statistically significantly correlated with the anion gap (P < 0.001). CONCLUSIONS: These results indicate that dehydration and lactate are important determinants of the metabolic acidosis previously observed in occupational heat exhaustion. It is likely that dehydration in these workers has resulted in poor muscle perfusion, anaerobic conditions and elevated lactate. This constitutes Type A lactic acidosis. Creatine kinase is not a statistically significant predictor of the anion gap in multiple regression (P = 0.956). Furthermore, the Spearman's rho correlation coefficient for creatine kinase versus the anion gap is weak (r(s) = 0.175) and is not statistically significant (P = 0.073). These results suggest that there was no rhabdomyolysis contributing to the metabolic acidosis.
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During the years 1978 to 1984, only 197 (0.14%) of 144 950 starters in a 14-km road race had suffered from heat exhaustion; of these, only three (1.5%) required admission to hospital. The effectiveness of treatment in medical centres was indicated by the fact that the mean time taken for the body temperature to fall to 38 degrees C was 31 +/- 12 minutes in all heat-exhaustion casualties, and 49 +/- 14 minutes in 41 subjects who had rectal temperatures of 42 degrees C and higher. When disaster teams from metropolitan hospitals were introduced in 1983, it became apparent that skilled staff members, despite their lack of experience in the resuscitation of combative heat casualties, could carry out the established procedures and protocols effectively and efficiently.
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This investigation focuses on the hormonal response to electrolyte changes and water loss in patients suffering from heat exhaustion, hospitalized in Muna during Hajj seasons. The concentrations of cortisol, aldosterone, renin (PRA), vasopressin (ADH) parathyroid hormone (PTH), adrenocorticotrophic hormone (ACTH) and growth hormone (GH) were determined in venous blood samples drawn from the patients upon admission, during, and after treatment. Highly elevated PRA mean values (396.77 +/- 88.58-462.18 +/- 106.95 ng.ml-1.h-1) were recorded, with no statistically significant difference between the readings. A similar trend was seen for cortisol (42.92 +/- 4.30-60.20 +/- 11.90 ug/dl). Vasopressin (ADH) showed a highly elevated value upon admission (42.48 +/- 18.82 pg/ml), which decreased to 23.66 +/- 8.27 pg/ml during treatment, and declined further to 7.67, ranging between 4.04 and 11.30 pg/ml, thereafter. Statistically speaking, however, there was no significant difference between these readings. PTH concentration, on the other hand, increased from an initial value of 143.31 +/- 47.64 to 245.90 +/- 107.34 pmol/l after treatment, but again there was no significant difference between the values. ACTH concentrations showed no detectable values throughout this study. The GH concentration was within normal throughout, ranging from 4.42 +/- 0.87 to 5.19 +/- 1.78 ng/ml. Aldosterone concentration was significantly reduced in the patients upon admission, with an initial value of 187.93 +/- 21.41 pg/ml (p < 0.05 as compared to normal mean value). During and after treatment, aldosterone values were still significantly lower than normal mean (152.63 +/- 13.47, p < 0.05; 145.2 +/- 17.55, p < 0.01, respectively), thereby shedding some light on the possible etiology of persistent metabolic acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)
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METHOD: We examined the thermoregulatory and hemodynamic responses of 12 miniswine (31 +/- 3.9 kg) during 25-30 min of treadmill exercise (5.4 km.h-1, 5% grade) under cool (10 degrees C), moderate (20 degrees C) and warm (30 degrees C) ambient temperature (Ta) conditions. RESULTS: Within 15-20 min of exercise at Ta = 30 degrees C, the miniswine demonstrated significant hyperventilation, hypersalivation, and unsteady gait. Exercise-heat endurance time (T) at Ta = 30 degrees C decreased by 35% and 40% in comparison to T at Ta = 20 degrees C and 10 degrees C, respectively. This resulted from a significant rise in heat strain (S)-defined as the rate of change in rectal temperature. Averaged throughout exercise, S increased from 0.04 +/- 0.01 degree C.min-1 and 0.05 +/- 0.02 degree C.min-1 at Ta = 10 degrees C and 20 degrees C, respectively, to 0.10 +/- 0.03 degree C.min-1 at Ta = 30 degrees C. Due to the comparatively large storage capacity of the porcine spleen relative to humans, splenectomized miniswine were used. This permitted calculation of percentage changes in plasma volume (% delta PVc) from hematocrit (HCT) and hemoglobin (HGB) without the confounding effects of splenic red cells released into the circulation during exercise. Independent of Ta, pre-exercise PVc decreased 3%-5% (p < or = 0.05) within the first 10 min of exercise, but increased 5%-9% (p < or = 0.05) by 10 min post-exercise. CONCLUSION: We conclude that the poor thermoregulatory ability of miniswine manifested in insignificant sweating and restricted evaporative cooling, may make them an appropriate model for acute exertional heat exhaustion in humans working in hot, humid conditions and/or wearing impermeable protective clothing. Further, evaluation of plasma volume changes from HCT and HGB in a miniswine model should consider the merit of a splenectomized design.
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