Hypothermia

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Hypothermia

  1. 1. Hypothermia David Caro, MD University of Florida Emergency Medicine
  2. 2. Introduction  Definition  Etiology  Epidemiology  Physiology  Impact on organ systems
  3. 3. Introduction (cont’d)  Response of organ systems  Identification  Treatment modalities  Sequelae  Review
  4. 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. 5. Physiology – Heat Generation  Basal Metabolic Rate = 40-60 Kcal/m2  Movement, shivering can increase the BMR 2 to 5 x normal
  6. 6. Physiology: The physics of temperature 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. 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. 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. 9. Hypothermia – Morbidity/Mortality  Mild hypothermia – very little  Moderate – one study showed a mortality rate of 21% for moderate hypothermia
  10. 10. Clinical features  Mild: shivering, loss of fine motor control  Moderate: lethargy, confusion  Severe: pupillary dilation, coma, cardiovascular irritability and eventual collapse
  11. 11. Hypothermia Etiology Overview  Increase in heat loss  Decrease in heat production  Thermoregulatory failure
  12. 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. 13. Etiology Increased Heat Loss  Exposure (cont’d)  Sports  Altitude
  14. 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. 15. Etiology Decreased Heat Production  Acute Illness  Metabolic abnormalities  DKA  Hypoglycemia  Myxedema coma  Hypoadrenalism
  16. 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. 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. 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. 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
  20. 20. 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)
  21. 21. 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)
  22. 22. 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
  23. 23. 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
  24. 24. Organ System Response  Neurologic  Decline in mental status  Mild confusion  Delirium  Coma  Peripheral anesthesia  Ataxia
  25. 25. Impact on Organ Systems  Renal  Hypothermia impairs renal concentrating abilities  “Cold-induced diuresis”  Potential rhabdomyolysis → ATN
  26. 26. Impact on Organ Systems  Gastrointestinal  Pancreatitis ± pancreatic necrosis can develop due to HT
  27. 27. Impact on Organ Systems  Hematologic  Hemoconcentration  Increased blood viscosity  Decreased flow in capillaries  Potential for thrombosis  Potential for DIC
  28. 28. 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
  29. 29. Organ System Response  Musculoskeletal  Frostbite  Gangrene
  30. 30. 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
  31. 31. Frostbite  Grading  Second degree  progresses to blister formation, anesthesia, and deep color change
  32. 32. Frostbite  Third degree  involvesfull skin thickness and extends into the subcutaneous tissue  Subfascial pressure increases; compartment syndromes are common
  33. 33. 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.
  34. 34. 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.
  35. 35. Hypothermia Identification  Thermometry  Most thermometers’ lower temperature limit is 93oF  A special low-temperature-reading thermometer is necessary to read temperatures lower than 93
  36. 36. Evaluation  ABCDEs are the priority  Handle patients gently  Begin passive rewarming immediately  Cautious ACLS care (coming up)
  37. 37. Evaluation  History is essential  Environment/exposure  PMH  Medications  Exam – be complete!  Rectal temperature!  Vital signs
  38. 38. Evaluation  Head-to-toe secondary exam  Neuro exam important – especially cranial nerves (Wernicke’s)  CV exam  Extremities/nose/ears/other end- arterial places
  39. 39. Evaluation  Testing  Cardiac monitor, EKG  SaO2, ±ABG  Electrolytes, CBC  UA  If severe:  LFTS, PT/PTT, CK (rhabdo)
  40. 40. Treatment  General Rx for various degrees of hypothermia  Specific Rx for sequelae  CV  Respiratory  ATN/Rhabdo  Frostbite/gangrene
  41. 41. Treatment Modalities – Mild hypothermia  Warm room  Cover with dry, warm blankets  Radiant warming  Warmed p.o. fluids
  42. 42. Treatment Modalities – moderate hypothermia  ABCs – every patient  Airway, Breathing – warm, humidified air by ETT or NRBfm  Circulation – IV access; warmed crystalloid  All of the above  Bear Hugger
  43. 43. Treatment Modalities – Severe Hypothermia  All of the above  Invasive modalities  NG, foley lavage  Pleural, peritoneal lavage  Dialysis or Cardiac bypass
  44. 44. 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
  45. 45. 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)
  46. 46. Treatment modalities- Sequlae  Ventricular Fibrillation; MI  Renal Failure  DIC  Frostbite  Gangrene  Afterdrop
  47. 47. Afterdrop  Paradoxical drop in core temp during rewarming  Due to influx of cold blood from periphery  Can precipitate arrhythmias
  48. 48. 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)
  49. 49. Treatment of sequelae  Renal Failure  Rhabdomyolysis : force fluids; alkalinization  Cold-diuresis : fluids, watch electrolytes
  50. 50. 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.
  51. 51. Treatment of sequelae - Afterdrop  Try to avoid – aggressive rewarming  Expect arrhythmias, be prepared to treat
  52. 52. 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!
  53. 53. Text References  Ann Emerg Med 1993 Feb;22(2 Pt 2):370-7  Wilderness Medicine – Auerbach  Rosen’s Principles of Emergency Medicine

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