Thermoregulation 2015 WMA

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2 1 Structure: Temperature sensors Endocrine system Muscles Skin Function: Maintain body core at 37 C Problem: Too little heat Too much heat

3 2 Normal Body Compensation Heat Response: Vasodilation Sweat Cold Response: Shivering Vasoconstriction Cold diuresis You can watch these mechanisms work, but they are not under your direct control.

4 3 Compensation Factors Voluntary Efforts: Clothing and shelter Eating and drinking Fitness and morphology: Larger muscle mass generates more heat. Long and thin people lose heat more quickly. Fit people generate heat more easily. Acclimatized people dissipate heat more easily.

5 4 Impaired Compensation Immobilized by injury, unable to generate heat Multiple trauma, volume shock Illness that impairs circulation, metabolism, sweat production, or temperature sense Drugs that inhibit temperature regulation: cocaine, methamphetamine, diuretics, behavioral medications, pseudoephedrine. Extremes of age Sunburn

6 5 Transfer of Heat Energy Conduction: by direct contact Convection: by wind or moving water Radiation: by long-wave energy Evaporation: by water absorbing energy as it evaporates from skin Respiration:

7 6 Mild Hypothermia Mechanism: Heat loss exceeds heat production Onset can be acute (sudden) or sub-acute Signs and Symptoms: Altered mental status (mild to moderate mental status changes) Significant shivering Shell/core effect (peripheral vasoconstriction) Core temp C

8 7 Mild Hypothermia Acute: Rapid onset, minutes to hours (cold water) Usually not dehydrated or calorie depleted Spontaneous rewarming is usually possible Low Risk High Risk

9 8 Mild Hypothermia Sub-Acute: Slow onset, hours to days Dehydrated and calorie depleted Will not rewarm spontaneously Low Risk? High Risk

10 9 Mild Hypothermia Treatment: FOOD / CALORIES! Warm, sweet fluids Trap heat with proper clothing/shelter Insulate from ground and weather Remove wet clothing to reduce evaporation Consider adding hot water bottles, etc. Exercise only after improvement in mental status is noted.

11 10 Rewarming Methods Gordon G. Giesbrecht, PhD

12 11 Calories and Fluid Sugar Carbs / Proteins Fat Tinder Sticks Logs

13 12 Hypothermia Prevention Don t be lazy; correct cold response! Stay hydrated and well fed. Keep insulation dry and clean. Dress for the conditions. Protect the patient! Early recognition = easy cure

14 13 Severe Hypothermia Signs and Symptoms: Significantly altered mental status (V, P, or U) No shivering Core temperature < 32 C VS may be undetectable Cardiac irritability Dehydration, metabolic derangement Low Risk High Risk

15 14 Severe Hypothermia Evacuation: Package with added heat source to minimize continued heat loss Urgent but gentle evacuation to hospital maintained in horizontal position PPV with heated and humidified O2, 6/min Warmed IV if available No chest compressions if it will delay transport

16 15 Severe Hypothermia Wilderness Perspective No Chance of Survival: Obvious lethal injury The chest is frozen The core temperature is below 10 C Submerged underwater more than one hour Airway packed with snow in prolonged avalanche burial

17 16 Hypothermia Package A hypo-wrap can be used to help prevent hypothermia. Adding heat to the package in the form of hot water bottles or a forced air warming device will be useful if it does not delay evacuation.

18 19 Heat Related Illness Heat Exhaustion Heat Stroke Exertional Hyponatremia

19 20 Heat Exhaustion Mechanism: Fatigue from exertion or intolerance to heat May include volume depletion if fluid has not been available Signs and Symptoms: Awake, normal mental status, subdued Near normal core temperature Might be sweating; might have normal vital sign pattern normal or early compensated volume shock depending on fluid status

20 21 Heat Exhaustion Treatment: Reduce exercise and heat exposure IV or PO fluids and food or electrolytes if s/sx of volume depletion. Evacuate if not improving Low Risk High Risk

21 22 Heat Stroke Mechanism: High heat challenge, environmental and/or metabolic Inadequate cooling Signs and Symptoms: Significant mental status changes, seizures Hot, dry or sweating. Temp > 40.5 C Potential vital sign pattern for volume shock Skin may be red, or pale with shell/core

22 23 Heat Stroke Emergency Treatment: Immediate and aggressive cooling! Low Risk High Risk

23 Rate of Temperature Change Cooling Rates from 42 o C to 39 o C 1. Ice water immersion 2 C 2. Cold water immersion 3. Half the body submersed at 1.3 C 4. Cold water immersion 14 C 5. Water, gauze sheet and fan 6. Fan with water 83min 6 30min 5 17min min 2 1 Hand cooling device and ice to major arteries were even slower Data from Casa DJ, et al.current Sports Medicine Reports : Cooling Method

24 24 Heat Stroke Continued Care (post recovery): IV or PO hydration for normal urine output Food as tolerated Protect from heat challenge Evacuate to hospital, emergent if abnormal mental status or abnormal urine output

25 25 Hyponatremia Mechanisms: Excessive fluid intake (overhydration) Possibly some loss of electrolytes through sweat Signs and Symptoms: Altered mental status (slow mentation, tremors, seizures) Nausea, headache, weakness Near normal urine output Core temperature normal

26 26 Hyponatremia Treatment: Rest Fluid restriction unless there is evidence of volume depletion Evacuate if not improving Low Risk? High Risk

27 27 Heat Related Illness Wilderness Perspective High Risk Problem: VS do not return to normal Persistent altered mental status Decreased urine output Urine color becomes red or brown You cannot prevent exposure to heat The patient is getting worse

28 28 Prevention of Heat Illness Drink in response to thirst. Replace fluid and electrolytes. Beware if not acclimatized! Beware of impaired compensation due to medications, illness and injury.