Downloaded 493 times
More Related Content
Hypothermia
- 1. Hypothermia David Caro, MD University of Florida Emergency Medicine
- 2. Introduction Definition Etiology Epidemiology Physiology Impact on organ systems
- 3. Introduction (cont’d) Response of organ systems Identification Treatment modalities Sequelae Review
- 4. Physiology The hypothalamus is your temperature control center Core and peripheral receptors provide temperature information Various responses help maintain temperature homeostasis Cut heat loss; generate heat!
- 5. Physiology – Heat Generation Basal Metabolic Rate = 40-60 Kcal/m2 Movement, shivering can increase the BMR 2 to 5 x normal
- 6. Physiology: The physics oftemperature homeostasis 4 ways heat is lost Radiation (65%) Evaporation (25%) Convection (5-10%) Conduction (2-5%) (except in immersion; cold water conductivity 32 times that of air)
- 7. Physiology Our body responds to decreased temperature by attempting to: Decrease heat loss Vasoconstriction Behavior modification Increase heat production Shivering Am J Physiol 1997 Feb;272(2 Pt 2):R557-62
- 8. Hypothermia-Definition A core body temperature below 96.8oF Mild hypothermia = 92 – 96.8oF Moderate = 88 – 92oF Severe = < 88oF “They’re not dead until they’re warm and dead.” One case report of recovery after accidental 15.2oC (59.4F) hypothermia.
- 9. Hypothermia – Morbidity/Mortality Mild hypothermia – very little Moderate – one study showed a mortality rate of 21% for moderate hypothermia
- 10. Clinical features Mild: shivering, loss of fine motor control Moderate: lethargy, confusion Severe: pupillary dilation, coma, cardiovascular irritability and eventual collapse
- 11. Hypothermia Etiology Overview Increase in heat loss Decrease in heat production Thermoregulatory failure
- 12. Etiology Increased Heat Loss Exposure to ambient temperature drop Trauma Alcohol/drugs Cutaneous vasodilation, impaired shivering, decreased awareness of environment , Wernicke’s encephalopathy (Eur J Appl Physiol 1996;74(3):293-5. Also, Ann Neurol 1981 Oct; 10(4):384-7)
- 13. Etiology Increased Heat Loss Exposure (cont’d) Sports Altitude
- 14. Etiology Increased Heat Loss Exposure (cont’d) Immersion Significant risk begins in water colder than 25 C (72 F). The water temperature of Lake Huron is approximately 4.6 C (40 F) in May and is highest in August at 19 C (66 F). Hypothermia can occur rapidly during cold-water immersion (one hour or less when water temperature is below 45oF). Core temp drops 0.3C in 20 min when immersed in 22C (Am J Phys Med Rehabil 1999 Jan-Feb; 78(1):33-8.
- 15. Etiology Decreased Heat Production Acute Illness Metabolic abnormalities DKA Hypoglycemia Myxedema coma Hypoadrenalism
- 16. Etiology Impaired Thermoregulation Sepsis ↓ lymphocyte activation ↓ IL-1,2,6 (Anesthesiology 1998 Nov; 89(5):1133-40. J Neurotrauma 1999 Mar; 16(3): 225-32) CVA Autonomic dysfunction
- 17. Impact on Organ Systems Respiratory Altitude will decrease pO2 Temperature of inspired air decreased Airwarmed + humidified by oral/nasal mucosa prior to hitting lower airways Expired air rich in warm water – heat lost
- 18. Impact on organ systems Hemoglobin increasingly binds O2 as temperature drops (oxyhemoglobin dissociation curve) Hypoxia may occur due to decrease offloading of oxygen (Cardiovasc Surg 1999 Jun;7(4):425-31
- 19. Organ System Response Acid-base balance 11/18 with decompensated metabolic acidosis (Coll Antropol 1999 Dec;23(2):683-90 Most texts recommend not correcting for temperature when evaluating ABGs
- 21. Impact on Organ Systems Cardiac Repolarization becomes abnormal with decreasing temperature Osborn Wave – lead V3 or V4 Increasing cardiac irritability with decreasing temperature QT prolongation (0.45-0.688 vs. 0.343-0.444; Coll Antropol 1999 Dec; 23(2):683-90)
- 22. Osborn Wave 86% of hypothermic patients (Acad Emerg Med 1999 Nov; 6(11):1121-6) Voltage gradient due to action potential notch in epicardium; epicardium activated later, which manifests as notching or J-point elevation (Circulation 1996 Jan 15;93(2):372-9)
- 24. Impact on Organ systems Cardiac Mild: Tachycardia, hypertension, increased CO Moderate: Bradycardia, Arrhythmias Severe: Arrhythmias, hypotension, decreased cardiac output Below 30C, ventricular fibrillation risk increases
- 25. Impact on Organ Systems Neurologic Decreasing metabolic activity of neurons; therefore, decreased O2 requirement Linear decrease in CNS function as temperature decreases Neuron function stops below 20C
- 26. Organ System Response Neurologic Decline in mental status Mild confusion Delirium Coma Peripheral anesthesia Ataxia
- 27. Impact on Organ Systems Renal Hypothermia impairs renal concentrating abilities “Cold-induced diuresis” Potential rhabdomyolysis → ATN
- 28. Impact on Organ Systems Gastrointestinal Pancreatitis ± pancreatic necrosis can develop due to HT
- 29. Impact on Organ Systems Hematologic Hemoconcentration Increased blood viscosity Decreased flow in capillaries Potential for thrombosis Potential for DIC
- 30. Impact on Organ Systems Musculoskeletal Temperature extremes can cause crystallization of blood in capillaries of extremities Cutaneous vasoconstriction occurs in response to lower ambient temperature
- 31. Organ System Response Musculoskeletal Frostbite Gangrene
- 32. Frostbite Grade as burns 1st degree Erythema, edema, burning Swelling for ten days or more Desquamation Parathesias, aching, and necrosis of the pressure points of the foot Increased sensitivity to cold, hyperhydrosis
- 33. Frostbite Grading Second degree progresses to blister formation, anesthesia, and deep color change
- 34. Frostbite Third degree involvesfull skin thickness and extends into the subcutaneous tissue Subfascial pressure increases; compartment syndromes are common
- 35. Frostbite 4th degree Destruction of entire thickness Cyanotic, insensitive; hemorrhagic blister formation. Severe pain on rewarming Dry gangrene can progress quickly with mummification. The line of demarcation becomes obvious at 20-36 days and extends into the bone in 60 or more days.
- 36. Trenchfoot Caused by prolonged exposure of the feet to cool, wet conditions. The skin is initially reddened with numbness, tingling pain, and itching then becomes pale and mottled and finally dark purple, grey or blue. If circulation is impaired for more than 6 hours there will be permanent damage to tissue. If circulation is impaired for more than 24 hours the victim may lose the entire foot.
- 37. Hypothermia Identification Thermometry Most thermometers’ lower temperature limit is 93oF A special low-temperature-reading thermometer is necessary to read temperatures lower than 93
- 38. Evaluation ABCDEs are the priority Handle patients gently Begin passive rewarming immediately Cautious ACLS care (coming up)
- 39. Evaluation History is essential Environment/exposure PMH Medications Exam – be complete! Rectal temperature! Vital signs
- 40. Evaluation Head-to-toe secondary exam Neuro exam important – especially cranial nerves (Wernicke’s) CV exam Extremities/nose/ears/other end- arterial places
- 41. Evaluation Testing Cardiac monitor, EKG SaO2, ±ABG Electrolytes, CBC UA If severe: LFTS, PT/PTT, CK (rhabdo)
- 42. Treatment General Rx for various degrees of hypothermia Specific Rx for sequelae CV Respiratory ATN/Rhabdo Frostbite/gangrene
- 43. Treatment Modalities – Mildhypothermia Warm room Cover with dry, warm blankets Radiant warming Warmed p.o. fluids
- 44. Treatment Modalities – moderatehypothermia ABCs – every patient Airway, Breathing – warm, humidified air by ETT or NRBfm Circulation – IV access; warmed crystalloid All of the above Bear Hugger
- 45. Treatment Modalities – SevereHypothermia All of the above Invasive modalities NG, foley lavage Pleural, peritoneal lavage Dialysis or Cardiac bypass
- 46. Treatment Modalities How effective are they? Reflective Foil – 0.3C/hr Ann Emerg Med 2000 Apr; 35(40):337-45 Warmed IVF – 1.0C/hr J Clin Anesth 1998 Aug;10(5):380-5. Warm IVF, Warm/humdified oxygen, blankets – 1.4 C/hr Ann Emerg Med 1996 Apr;27(4):479-84 Bear-Hugger – 0.7C/hr Ann Emerg Med 2000 Apr; 35(40):337-45; IVF/humidified O2/BH – 2.4C/hr Ann Emerg Med 1996 Apr 27(4):479-84
- 47. Treatment Ideas Aviat Space Environ Med 1992 Dec;63(12):1070-6 Total immersion in 42C bath – 10.2C/hr Blankets – 0.2C/hr J Appl Physiol 1998 Nov;85(5):867-8 Subatmospheric pressure to limbs while applying warm-water blanket increased rewarming 10-fold over WWB alone (13.6C/hr vs. 1.4C/hr)
- 48. Treatment modalities- Sequlae Ventricular Fibrillation; MI Renal Failure DIC Frostbite Gangrene Afterdrop
- 49. Afterdrop Paradoxical drop in core temp during rewarming Due to influx of cold blood from periphery Can precipitate arrhythmias
- 50. Treatment of sequelae Ventricular fibrillation Cold heart very irritable Will not respond to multiple rounds of drugs Shock – 3 times, then wait until warm Bretylium your drug of choice (ACLS Guidelines)
- 51. Treatment of sequelae Renal Failure Rhabdomyolysis : force fluids; alkalinization Cold-diuresis : fluids, watch electrolytes
- 52. Treatment of sequelae Frostbite Narcotics! Warm water immersion – warm, wet heat is best. Do NOT warm then allow to refreeze. Better to keep frozen until definitive care is available.
- 53. Treatment of sequelae- Afterdrop Try to avoid – aggressive rewarming Expect arrhythmias, be prepared to treat
- 54. Hypothermia Summary Physiology plays a HUGE role Etiology Treatment History is key Rectal temp with low-reading thermometer Treat temperature aggressively, but handle patient gently Watch for afterdrop!
- 55. Text References Ann Emerg Med 1993 Feb;22(2 Pt 2):370-7 Wilderness Medicine – Auerbach Rosen’s Principles of Emergency Medicine