Accidental Hypothermia

1. Accidental Hypothermia Laura Klouda, MD

2. Intro • Definition • Unintentional drop in body temperature of about 2°C from “normal” (normal = 37.2-37.7°) • Contributing factors/stressors • Extremes of age • Nutritional status/dehydration • Pre-existing health conditions • Intoxicants/medications that potentially decrease thermostability • Exposure type • Fatigue and lack of sleep • Trauma • Wet clothing • Treatment depends on duration and severity of hypothermia and contributing factors/stressors

3. Nervous system effects • Shivering (more effective at producing heat than voluntary muscle contraction) • Memory loss • Impaired judgment • Decreased level of consciousness • Slurring of speech

4. Cardiovascular effects • Bradycardia • Due to slowed pace-maker cell depolarization refractory to atropine • Decreased cardiac output • EKG changes • Prolonged PR, QRS, and QTc • J (Osborn) waves • Dysrhythmias • All of these can be worsened during afterdrop • Afterdrop is a drop in core temp after the warming process has begun

5. Respiratory effects • Initially tachypnea • Bradypnea as hypothermia worsens • Thus CO2 retention and respiratory acidosis • Noncardiogenic pulmonary edema • Increased and thickened secretions

6. Renal effects • Decreased blood flow to kidneys  decreased glomerular filtration rate  results in build up of nitrogenous waste products • An initial large diuresis results in hemoconcentration. Then followed by oligo/anuria.

7. Effects on coagulation • Bleeding • Due to cold-induced hypercoagulability and thrombocytopenia • Appears similar to DIC (disseminated intravascular coagulation) • Hyperviscosity of blood due to hemoconcentration from diuresis and also from stiffening of red blood cells

8. Physical exam findings • HEENT • Mydriasis, decreased extraocular movements, facial edema and/or flushing, epistaxis and/or rhinorrhea • Cardiovascular • Initial tachycardia followed by bradycardia, dysrhythmia, jugular venous distension, hypotension • Respiratory • Initial tachypnea followed by bradypnea/apnea, increased adventitious lung sounds • GI/GU • Constipation, abdominal distension, emesis, polyuria to anuria • Neuro • Decreased LOC, ataxia, amnesia, initial hyperreflexia followed by areflexia, mood/personality changes • Skin/Musculoskeletal • Shivering, increased muscle tone, erythema, pallor, cyanosis, frostbite, edema

9. Pre-hospital management • Basic principles: • Rescue and remove from cold exposure • Physical exam • Remove wet clothing, stabilize injuries, cover wounds • Body temperature IV fluids if possible • Place bag under patient’s buttocks or in a compressor • Warm fluids by taping hand/feet warmers to fluid bag • Limit rewarming to: • Hot water bottles covered in stockings/mittens placed in patient’s axillae/groin/neck • Be cautious not to burn the patient • Heated insulation • Inhalation of heated humidified oxygen • Patient should remain horizontal • Insulate and wrap patient • Sleeping bags, clothing, tents, etc. • Transport to hospital • Only consider surface re-warming if medical care is unavailable • Body-body contact, warm objects, radiant heat

10. Pre-hospital life support • Avoid jostling or quick movements of comatose patients • They are extremely likely to go into ventricular fibrillation if jostled • Primary objective = prevent further heat loss • Never assume death when patient is still cold. “No one is dead until warm and dead” • IV glucose, naloxone, and flumazenil

11. Pre-hospital life support • Rescue breathing may be difficult due to stiffened muscles • Common problem is overventilation causing hypocapnic ventricular instability • Indications for intubation are the same as for a normothermic patient • Avoid overinflation of the cuff in freezing temperatures. The cuff will expand upon reaching warmer temps  can kink tube and/or damage trachea • Palpate/auscultate pulses for a full minute before deciding if patient requires chest compressions • Often bradycardic with low cardiac output • Unnecessary chest compressions can cause ventricular fibrillation • If cardiac monitor and defibrillator available: • Defibrillate if ventricular fibrillation or asystole • Pads generally don’t stick well to cold skin • May need tincture of benzoin

12. Emergency Department Care • IV/O2/Monitor • Warmed IV normal saline • Monitor vitals and confirm hypothermia • Doppler may be needed to obtain a pulse • Rectal thermometer inserted 15cm or esophageal temps are generally reliable • Thermal stabilization • Heat via conduction/convection/radiation/respiration • Maintain tissue oxygenation • CPR/rescue breathing • Determine 1° vs 2° hypothermia • Obtain labs: CBC, blood gas, CMP, INR, PTT, fibrinogen • Rewarm • Passive external, active external, and/or active core rewarming • Treat injuries, infections, underlying medical problems

13. Passive external rewarming • Ideal for mild hypothermia • Insulation with blankets, aluminized body covers, etc.

14. Active Rewarming • For moderate-severe hypothermia (T<32°C), passive warming failure, peripheral vasodilation, secondary hypothermia, endocrine insufficiency • External warming • Hot water bottles, forced circulated hot air e.g. Bair Hugger, heating blankets, etcapply to THORAX, not extremities • Core warming • Heated humidified oxygen, heated IV fluids, gastric/colonic/mediastinal/thoracic/peritoneal lavage with warm saline, extracorporeal blood rewarming

15. Medications in hypothermia • Medications are temperature dependent • Often ineffective during hypothermia then become toxic during warming • Poor GI absorbtiondo not give oral meds • Erratic intramuscular absorbtionavoid IM meds

16. Hypothermia summary • Symptoms often vague, wide variety of presenting symptoms • Pre-hospital treatment • Rescue • Remove wet clothing, stabilize injuries • Limit rewarming • Gentle handling, keep horizontal • Insulate • Transport to hospital • Emergency Dept Treatment • IV/O2/Monitor • Warmed IV normal saline • CPR/rescue breathing • Passive external, active external, and/or active core rewarming • Treat injuries, infections, underlying medical problems

17. Reference: • Auerbach, P.S. (1995), Wilderness Medicine, 3rd edition. Mosby.