hypothermia or baby, it s cold outside

1. Hypothermiaor�Baby, it�s cold outside!� Margaret Stafford, MD Inpatient Service talk 2/9/07

3. Cases FH: y/o man with h/o alcoholism; tried to get into shelter but no beds available Found down outside by EMS with T=25� C Warmed in ED/ICU with blankets, warm saline, warm NG lavage, Bair hugger Awake and combative by 26� C Normal and conversant by ~32� C

4. Hypothermia: definition Core temperature (by rectal or foley) below 35� C Mild hypothermia: 32-35� C Moderate hypothermia: 28-32� C 21% mortality rate Severe hypothermia: <28� C ~50% mortality rate About 700 people in the U.S. die every year from primary accidental hypothermia

5. Causes of hypothermia Increased heat loss: environmental exposure, vasodilation (alcohol), burns, bad dermatitis, iatrogenic Decreased heat production: hypothyroidism, adrenal insufficiency, hypopituitarism, malnutrition/ hypoglycemia, impaired shivering, inactivity Impaired regulation: spinal cord injuries, neuropathy, Parkinson�s, MS, TCAs, sedatives, alcohol Other: sepsis, pancreatitis, trauma

6. Pathophysiology of accidental hypothermia Heat is generated by metabolism, mostly in heart and liver, and lost by skin and lungs Most significant types of heat loss in hypothermia are convective loss to cold air and conductive loss to cold water

7. Pathophysiology of accidental hypothermia Hypothermia leads to altered cell membrane function, enzyme dysfunction, and electrolyte imbalances, esp. hyperkalemia Body�s response: hypothalamus tries to increase heat production by shivering and increased thyroid and SNS activity. Vasoconstriction shunts blood from peripheral tissues CNS metabolism decreases linearly with core temperature

8. Risk factors for hypothermia In urban settings: alcohol or drug use, overdose, mental illness Wet clothing in cold or windy weather Alcohol is a peripheral vasodilator and exacerbates hypothermia

9. Clinical presentation Mild hypothermia: tachypnea, tachycardia, impaired judgement, shivering, cold diuresis Moderate hypothermia: bradycardia, decreased cardiac output, hypoventilation, loss of shivering, paradoxical undressing Severe hypothermia: pulmonary edema, coma, ventricular fibrillation, asystole, rigidity, apnea

10. Diagnosis/workup Need low-reading thermometer; measure rectal or bladder temp Pulse ox monitoring: place probes on ears or forehead (less vasocontriction in setting of hypothermia)

11. EKG changes Slowed impulse through potassium channels leads to prolongation of all intervals Decreased depolarization of pacemaker cells leads to bradycardia V-fib and asystole can begin spontaneously, esp in severe hypothermia Osborne wave: J point elevation representing distortion of repolarization Height of Osborne wave proportional to degree of hypothermia Most prominent in V2-V5

12. Osborne waves

13. Labs Electrolyte abnormalities: no consistent pattern Coagulation fails at low temps, but since labs are measured at room temp coags may be deceptively normal ABGs: machines warm blood to 37�C, so show higher O2 and CO2, lower pH than actual values Also should check for lactic acidosis, rhabdo (potential complications)

14. Treatment Important: avoid sudden sharp movements of patient (can induce vfib) Pre-hospital care: remove wet clothing and replace with dry coverings

15. Passive external rewarming For mild hypothermia only Remove wet/cold clothing, replace with blankets Allow patient�s shivering and metabolism, along with warm environment, to increase temperature Requires physiologic reserve

16. Active external rewarming For mod-severe hypothermia, or mild hypothermia which doesn�t respond to passive rewarming Warm blankets, heat packs, etc applied to skin If core and extremities warmed simultaneously, risk of core temperature afterdrop Cold, acidemic blood from extremities returns to circulation, plus peripheral vasodilation leads to hypotension

17. Active internal rewarming For severe hypothermia Least aggressive: warm IVF, warm NG and bladder lavage, warm humidified O2 (often adjunctive therapy) Pleural or peritoneal lavage with warm fluids Continuous arteriovenous rewarming Cardiopulmonary bypass

18. Management of arrhythmias To prevent: handle patient gently For vfib: bretylium if availble Initiate CPR If defibrillation and drugs unsuccessful, continue CPR and try again once patient 30-32� C �You�re not dead until you�re warm and dead� (unless chest is frozen)

19. Summary Urban areas have high-risk patients for hypothermia Use combinations of passive and active external rewarming and active internal rewarming Warm core before extremities Gentle patient handling to avoid arrhythmias

20. References Mechem, CC. Accidental hypothermia. In UpToDate, last updated May 2006. Li, J, and Decker, W. Hypothermia. In emedicine.com, last updated September 2006.