5. Heat Exchange Heat stress : environment and host condition that tend to increase body temperature Heat strain : physiological and psychological consequence of heat stress Body heat exchange Convection Radiation Conduction Evaporation
13. High Sweating Rate Water loss Vs Water replacement 0.3-1 L/hr in most activity Dehydration ↓ evaporative and convective heat loss ↑ body temperature 0.2 °C per % BW loss ↑ cardiovascular strain ↑ HR 5 bpm per % BW loss ↓ core temp that can be tolerated ↑ risk of heat injury
20. Heat Stress Index used to demonstrate environmental heat stress Wet Bulb Glove Temperature index (WBGT) Threshold limit values (TLVs) Corrected effective temperatures (CET) Thermal work limit (TWL) Heat Index Relative Humidity Air Temperatures
21. • Wet Bulb (WB temperature) • Wet Bulb Natural evaporation of Natural evaporation of water/sweat water/sweat • Black Globe (GT temperature) • Black Globe The radiant heat load The radiant heat load • Shaded Dry Bulb • Shaded Dry Bulb (DB temperature) The actual air temperature The Wet Bulb Glove Temperature (WBGT) 0.2 GT+0.1DB+0.7WB
22. WBGT WBGT greater than 33oC …increase the incidence of heat injury and heatstroke Wet-bulb temperature is the most significant variable in WBGT equation Emphasize the important of humidity in heat injury
23. Heat Index Measurement of how hot it actually feels when relative humidity is combined with air temperature If there is exposure to direct sunlight, heat index should be adjusted by adding 0.9oC
30. Heat Strain Index Core Temperature Heart Rate Physiological Strain Index (PSI) Heat Strain Index (HSI) Cumulative Heat Strain Index (CHSI) Predicted 4-h sweat rate index (P4SR)
31. Core Temperature Esophageal temperature Most accurate Response rapidly and quantitatively to changes in core temp Rectal temperature Most practical Typically higher ~ 0.4 °C Oral temperature Tympanic and ear canal temperature NOT RECOMMENDED
32. Physiological Strain Index (PSI) PSI = 5(Tret-Tre0).(39.5-Tre0) -1+ 5(HRt-HR0).(180-HR0) -1 Moran et al. Am J Physiol Regulatory Integrative Comp Physiol 275:129-134, 1998.
33. Core Temperature Response during Heat Stress Compensated Heat Stress (CHS) Uncompensated Heat Stress(UCHS)
36. Heat Acclimatization Progressive heat exposure and physical work Two weeks duration Minimum exposure 2 hours/day Reduction in physiological strain 50, 80% in week 1 and 2 Adequate water replacement during and after acclimatization period
45. Myths about Heat Stress Real men don’t drink water Don’t drink unless you’re thirsty Training decreases need for water You can get a lot of cooling from a damp cloth on forehead, neck or wrists Sport drinks are better than water Salt counteract dehydration Women are more vulnerable to heat than men
54. Prickly Heat (Heat Rash) Lichen tropicus, miliariarubra Itching is predominated Pruriticmaculopapular rash over clothed areas Acute inflammation of sweat ducts caused by blockage of sweat pores by macerated stratum corneum Ducts become dilated and ruptured
55. Prickly Heat (Heat Rash) Rx with antihistamine Prevented by wearing clean, light and loose clothing and avoid sweat generating situations
56. Heat Edema Mild swelling and tightness of hands and feet Appear within first few days of exposure to hot environment Cutaneous vasodilatation and orthostatic pooling of interstitial fluid in the extremities Aldosterone and ADH effects Mild edema , rarely on the ankle Usually resolves in a few days Diuretics are not effective
58. Heat Syncope Cumulative effect of peripheral vasodilatation, decreased vasomotor tone and relative volume depletion Most common in non-acclimatized person during early stage of heat exposure Removal from heat source, oral or IV rehydration, rest Most patients recover with fluid
59. Heat Cramps Painful, involuntary, spasmodic contraction of skeletal muscles…calves >> thighs, shoulders Usually occur in individuals who are sweat liberally and replace fluid loss with water or hypotonic solution Rest in cool environment, fluid and salt replacement orally or IV
60. HeatTetany Hyperventilation resulting in respiratory alkalosis, paresthesia, carpo-pedal spasm Usually associated with short period of intense heat stress Removal from heat Decreasing RR
61. Heat Exhaustion Nonspecific symptoms..dizziness, fatigue, light-headedness, nausea, vomiting, myalgia Clinical Syncope, orthostatic hypotension Sinus tachycardia, tachypnea Diaphoresis and hyperthermia Core temp..variable from normal to 40oC Mental status remains normal Combination of salt and water deletion Treated by rest, volume and electrolyte replacement
62. Heat stroke Elevated body temperature (core temperature > 40 oC) and CNS dysfunction (delirium, convulsion or coma) Catatrophic medical emergency resulting from a failure of thermoregulatory mechanism Extreme elevation of body temperature Multi-organ dysfunction
73. Prevention Attention to environmental conditions Acclimatization for workers, military and others Adequate hydration Work schedules for those who need to work under adverse conditions Social service care for elderly and the chronically ill
84. ภาพโดย : พ.อ.ถนอม สุภาพร Airtemp oC Relative Humidity Heat Index Chart: Modified from US National Weather Service Source: Walker JS and Barnes SB. Heat Emergency in Emergency Medicine: A Comprehensive Study Guide for the American College of Emergency Physicians 5th Edition, edited by Tintinalli. McGraw-Hill 2000: page 1237 Add 0.9oC if under direct sunlight
94. Cooling Rapid reduction of core temperature to 38oC is primary goal of treatment Antipyretics are not effective Physical cooling techniques Technique of choice is Evaporative Cooling Cooling efforts should be discontinued when rectal temperature reaches 38oC to avoid “overshoot hypothermia”
95.
96. Applied Essential Devices for Proper Cooling Technique in PMK Cont Temp monitors(rectal, skin) Water sprays Electric fans A warm-air blower
