1. Generalized
heat & cold injury

2. Physics of heat transfer I
Radiation (65% of the heat loss) – transfer of heat through electromagnetic (infrared) waves
Direct contact transfer: conduction (2% - solid bodies) and convection (10%, air and water)
These cease when body’s temperature is equal to surrounding

3. Physics of heat transfer II
Evaporation (heat loss through transformation of liquid to vapor) = 30% of heat loss
Ceases when humidity is 100%

4. convection

5. Systemic heat injury

6. Definitions
Heat exhaustion = acute injury caused by hyperthermia and dehydration
It occurs when the body cannot dissipate heat – external or internally produced
If thermoregulation fails it can progress to heatstroke
Heatstroke = extreme hyperthermia with CNS involvement

7. Heat exhaustion: signs & symptoms
Hyperthermia, usually not more than 41°
Fatigue, weakness, dizziness
Headache
Orthostatism
Tachycardia
Tachyarrhythmias that may not be amenable to cardioversion

8. Headstroke Any or all signs of heat exaustion
Critical feature is CNS dysfunction, in 80% of cases sudden (-> “stroke” term)
Delirium, hallucinations
Bizarre behaviour
Cerebellar dysfunction
Seizures
Coma, fixed and dilated pupils

9. Sweating
Classically, heatstroke patient don’t sweat (thermoregulation failure)
In practice, almost half of the patients do sweat, esp. in exertional hyperthermia

10. Treatment Remove the patient from hot environment ABC
Initiate cooling with any resources available
Transport with air conditioning or windows open

11. Cooling methods Temperature reduction Method 0.2° per minute
Ice bath immersion
0.08° per minute
Warm air and water spray
0.04° per minute
Rest covered with cool wet towels

12. No drugs!
No drugs significantly reduce core temperature in heat illness!
Antypiretics (Paracetamole, Optalgin, Aspirin can be positively dangerous!

13. Disposition and prognosis
All patients with heatstroke should be admitted to ICU
With rapid cooling, adequate rehydration and aggressive treatment of complications – survival rate in heatstroke approaches 90%

14. Systemic cold injury

15. Defenitions Accidental hypothermia = core temperature < 35°
Mild hypothermia: °
Moderate hypothermia: °
Severe hypothermia: < 28°
Low-reading thermometer should be used PO or PR
Bladder, esophageal or rectal probe are preferred in the ED setting

16. Risk factors for death Alcohol use Homelessness Psychiatric disease
Older age
Some medications (beta-blockers, clonidine, neuroleptics) impair the compensatory ability

17. Signs and symptoms: mild
Irritability, poor judgment, lassitude
Paradoxical undressing
Shivering
Dysarthria, ataxia (can mimic stroke!)
Hemodynamically stable

18. Signs and symptoms: moderate
Presents in stupor
At 31° loss of a shivering ability
At 30°: pulse slow, cardiac output reduced, risk for arrythmias
°: pupils dilated and minimally responsive – mimics brain death!

19. Signs and symptoms: severe
Rigidity
Apnea
No pulse
Areflexia
Unresponsive
Fixed pupils
Susceptible to VT/VF

20. Patient is not dead Until warm and dead!

21. First aid Rewarming is first priority Transportation is next
CPR is third!

22. First aid Gently place patient in protected environment
Remove wet clothes and replace with dry blankets
Initiate rewarming with heat packs or hot water bottles on groins, axillae, abdomen
In dire circumstance – skin-to-skin rewarming can be provided

23. Don’ts of first aid
Do not apply heat to arms and legs or give them a hot bath. This can cause "after drop" which can be fatal.
Do not massage or rub the victim, rough handling may cause cardiac arrest.
If patient is stuporous do not give them anything to drink.
Never give alcoholic beverages

24. Prevention of malignant dysrhytmias
Conscious patient can develop sudden VT
Any movement can be a trigger!
Victims of cold-water immersion appear to be at esp high risk of VT
Thus, avoid movement of severly hypothermic patients

25. Ventricular tachycardia/ fibrillation
VF in cold patient is a desperate event
Generally, defibrillation is ineffective
Attempt IV bretyllium, followed by CPR while starting active rewarming, defibrillate after rewarming

26. ED Hypothermia is a true emergency
Warmed, humidified oxygen, warmed blankets, heat lamps
Heated to 45°C IV saline (do not use Hartmann – lactate is not metabolized, hyperkalemia)
Single trial demonstrate more effcicacy of 65°C fluids
Saline (not dextrose, not blood broducts!) can be heated in microwave oven

27. Slow rewarming These methods produce rewarming of 0.3 – 0.9 grade/hour
Patient that :
Is not becoming colder
Is conscious
Has good perfusion
may not need more intensive rewarming

28. Moderate rewarming Rate of 3 grade/hour: Warmed gastric lavage
IV solution at 65°C
Peritoneal lavage at 45°C at 4 liter/ hour (recommended method in Alaska)

29. Rapid rewarming – single cases reported
Cardiopulmonary bypass (18 grade/hour)
Thoracic lavage (6 to 20 grade/hour at 500 mL/min to 2 L/min rate):
Two left-sided chest tubes, °C saline or even tap water
Warm-water immersion