1. Prehospital Management of Hypothermia in the 21 st Century Bryan E. Bledsoe, DO, FACEP

6. Temperature Regulation u Humans are warm- blooded mammals who maintain a constant body temperature (euthermia).

7. Temperature Regulation u Temperature regulation is controlled by the hypothalamus in the base of the brain.

8. Temperature Regulation u The hypothalamus functions as a thermostat for the body. u Temperature receptors (thermoreceptors) are located in the skin, certain mucous membranes, and in the deeper tissues of the body.

9. Temperature Regulation u When an increase in body temperature is detected, the hypothalamus shuts off body mechanisms that generate heat (for example, shivering). u When a decrease in body temperature is detected, the hypothalamus shuts off body mechanisms designed to cool the body (for example, sweating).

10. Temperature Regulation u Body Temperature = Thermogenesis–Heat Loss

11. Temperature Regulation u Basal Metabolic Rate: l The metabolism that occurs when the body is completely at rest.

12. Temperature Regulation u Metabolic Rate: l The body continuously adjusts the metabolic rate in order to maintain a constant CORE temperature.

13. Temperature Regulation u Normal body temperature is approximately 37º C (98.6º F). u However, what is normal for an individual may vary somewhat.

14. Hypothermia u Definition of Hypothermia: l CLASSIC DEFINITION: A state of low body temperature, specifically a low CORE temperature (< 35º C or < 95º F). l ALTERNATIVE DEFINITION: It is best defined as the unintentional decrease of around 2º C (3.6º F) from the “normal” CORE temperature

15. Hypothermia u What is the CORE temperature? l The deep internal temperature of normothermic humans.

16. Hypothermia u How is the CORE temperature measured? l There is little variance in CORE temperature because of perfusion. l Esophageal and tympanic temperatures are essentially the same as the temperature of the pulmonary artery.

17. Hypothermia u In steady-state conditions, the rectal temperature is a good index of CORE temperature.

18. Hypothermia u Oral temperature is an excellent index of CORE temperature, provided the mouth is kept closed.

19. Hypothermia u The type of temperature measurement utilized is less important than using the same device and measurement site to detect trends. u Thermometer must be able to read low temperatures.

20. u Heat loss results from: l Conduction l Convection l Radiation l Evaporation l Respiration Hypothermia

21. u Conduction: l Heat loss occurs due to direct contact of the body with a cooler object. l Heat flows from higher temperature matter to lower temperature matter.

22. Hypothermia u Convection: l Heat loss occurs due to air currents passing over the body. l Heat must first be conducted to the air before convection can occur.

23. Hypothermia u Radiation: l Heat loss results from infrared rays. l All objects not at absolute zero will radiate heat to the atmosphere.

24. Hypothermia u Evaporation: l Heat loss occurs as water evaporates from the skin. l Heat loss occurs as water evaporates from the lungs during respiration.

25. Hypothermia u Respiration: l Respiration combines the heat loss mechanisms of convection, radiation, and evaporation. l Expired air is normally 98.6 degrees F. and 100% humidified.

26. Heat-conserving Mechanisms u Vasoconstriction of blood vessels in the skin. u Stimulated through activation of the sympathetic nervous system. u Causes pale, cool skin.

27. Heat-conserving Mechanisms u Piloerection is more commonly called “goose bumps” or “goose flesh.” u Evolutionary remnant. u Caused by sympathetic stimulation of arrector pili muscles.

28. Heat-conserving Mechanisms u Increased heat production: l Shivering l Activation of futile cycles (chemical thermogenesis) l Increased thyroxine release

29. Hypothermia u When the core temperature of the body drops below 95º F, an individual is considered to be hypothermic.

30. Hypothermia u Clinically, hypothermia results from: l Inadequate heat generation by the body (thermogenesis). l Excessive cold stress. l A combination of both.

31. Hypothermia u Normal Range: l 96-100º F u Mild Hypothermia: l 90-95º F u SevereHypothermia l < 90º F

32. Hypothermia u Predisposing Factors to Hypothermia: l Patient Age l Patient Health l Medications l Prolonged or Intense Exposure l Co-existing Weather Conditions

33. Hypothermia u Patient Age: l Pediatric and geriatric patients cannot tolerate cold environments and have less capacity for heat generation. l Older patients often become hypothermic in environments that seem only mildly cool to others.

34. Hypothermia u Patient Health: l Hypothyroidism (suppresses metabolic rate) l Malnutrition, hypoglycemia, Parkinson’s disease, fatigue, and other medical conditions can interfere with the body’s ability to combat cold exposure.

35. Hypothermia u Medications: l Some drugs interfere with the body’s heat- generating mechanisms. l These include: narcotics, alcohol, antihistamines, antipsychotics, antidepressants, and many others.

36. Hypothermia u Prolonged or Intense Exposure: l The length and severity of cold exposure have a direct effect on morbidity and mortality. l The Wind Chill Index (WCI) must be taken into consideration.

38. Hypothermia u Coexisting Weather Conditions: l High humidity, brisk winds, and accompanying rain can all magnify the effect of cold exposure on the body by accelerating heat loss from the skin.

39. Hypothermia u Degrees of Hypothermia: l Mild– Core temperature > 90 degrees F (32 degrees C) l Severe– Core temperature < 90 degrees F (32 degrees C)

40. Signs and Symptoms u MILD Hypothermia: l Lethargy l Shivering l Lack of Coordination l Pale, cold, dry skin l Early rise in blood pressure, heart, and respiratory rates.

41. Signs and Symptoms u SEVERE Hypothermia: l No shivering l Heart rhythm problems l Cardiac arrest l Loss of voluntary muscle control l Low blood pressure l Undetectable pulse and respirations

42. Prevention u Preventive Measures: l Warm dress l Plenty of rest l Adequate diet l Limit Exposure

43. Treatment u Treatment for Hypothermia: 1. Remove wet garments 2. Protect against further heat loss and wind chill. 3. Maintain patient in horizontal position.

44. Treatment u Treatment for Hypothermia: 4. Avoid rough handling. 5. Monitor the core temperature. 6. Monitor the cardiac rhythm.

45. Treatment u ECG changes seen in hypothermia: l Prolongation of first the PR interval, then the QRS, then the QTc interval. l J waves (also called Osborne waves) can occur at any temperature < 32.3º C (90º F). l Most frequently seen in Leads II and V 6. l The size of the J waves increase with temperature depression.

46. “J” or Osborne Waves

49. Rewarming u Methods of Rewarming: l Active External Rewarming l Active Internal Rewarming

50. Rewarming u Active Rewarming of MILD Hypothermia: l Active external methods: u Warm blankets u Heat packs u Warm water immersion (with caution) l Active internal methods: u Warmed IV fluids

51. Rewarming u Active Rewarming of SEVERE Hypothermia: l Active external methods: u Warm blankets u Heat packs u Warm water immersion (with caution) l Active internal methods: u Warmed IV fluids u Warmed, humidified oxygen

52. Rewarming u Rewarming of the SEVERE hypothermia patient is best carried out in the Emergency Department using a pre-defined protocol, unless travel time exceeds 15 minutes. u Most patients who die during active rewarming die from ventricular fibrillation.

53. Rewarming u Application of external heat in the prehospital setting is usually not effective and not recommended because: l More heat transferrence is required than generally possible in the prehospital setting. l Application of external heat may cause “rewarming shock.”

54. Rewarming u Rewarming Shock: l Occurs due to peripheral reflex vasodilation. l Causes the return of cooled blood and metabolic acids from the extremities. l May cause a paradoxical afterdrop in the core temperature further worsening hypothermia.

55. Rewarming u Rewarming Shock: l Can be prevented in the prehospital setting by using warmed IV fluids during active rewarming.

56. Rewarming u Portable IV fluid heaters are available in the United States and Canada. u Devices fit in-line and are powered by DC power sources.

57. Rewarming u The device is single- use and remains with the patient in the hospital (both the ED and on the floor).

58. Rewarming u The HOT IV is powered from a Physio-Control battery or from a DC converter plugged in to an AC outlet.

59. Issues in Hypothermia u Benefits of IV Fluid Warming: l Maintains euthermia l Increases patient comfort l Prevents shivering

60. Issues in Hypothermia u Benefits of IV Fluid Warming: l Prevents cold-induced dysrhythmias l Decreases hemorrhage in abdominal trauma patients l Decreases the incidence of infectious complications in abdominal trauma patients

61. Issues in Hypothermia u Benefits of IV Fluid Warming: l Allows active internal rewarming to begin in the prehospital setting. l Less labor-intensive, freeing emergency personnel to manage other, more pressing care needs.

62. Cardiac Arrest u Other Clinical Concerns: l Resuscitation of cardiac arrest due to hypothermia is only successful when the patient is being re-warmed. l The hypothermic cardiac arrest patient is not DEAD until he is WARM and DEAD!

63. Survival from Hypothermia u 48.2º F (9º C)- Lowest reported survivor from therapeutic exposure. u 59.2º F (15.2º C) – Lowest reported infant survival from accidental exposure. u 60.8º F (16º C) – Lowest reported adult survival from accidental exposure.

64. Survival from Hypothermia u 64.4º F (18º C) – Asystole. u 66.2º F (19º C) – Flat EEG. u 71.6º F (22º C) – Maximum risk for ventricular fibrillation. u 77º F (25º C) – Cerebral blood flow decreased by 66%. u 78.8º F (26º C) – No reflexes or response to painful stimuli.

66. Issues in Hypothermia u Other Clinical Concerns: l Hypothermia is common, even in persons with minor trauma. l Hypothermia can worsen infectious complications of abdominal trauma. l Hypothermic trauma patients suffer increased blood loss compared to their normothermic cohorts.

67. Issues in Hypothermia u Considerations in Emergency Care: “Most traditional methods of maintaining trauma patient temperature during prehospital transport appear to be inadequate.” From: Watts DD, Roche M, et al. The utility of traditional prehospital interventions in maintaining thermostasis. Prehosp Emerg Care 1999;3(2)115-122

68. Issues in Hypothermia u Considerations in Emergency Care: “Based upon our findings, accidental hypothermia poses a relevant problem in the prehospital treatment of trauma patients. It is not limited to a special season of the year.” From: Helm M, Lampl L, Hauke J, Bock KH. Accidental hypothermia in trauma patients. Is it relevant to preclinical emergency treatment? Anaesthesist 1995;44(2):101-107

69. Issues in Hypothermia u Considerations in Emergency Care: “Thus, hypothermia is common in patients undergoing a laparotomy for trauma. Hypothermic patients with similar injury severity have greater blood loss.” From: Bernabei AF, Levision MA, Bender JS. The effects of hypothermia and injury severity on blood loss during trauma laparotomy. J Trauma 1992;33(6):835- 839

72. Temperature Regulation u For more detailed information on temperature regulation and hypothermia, see the March 2003 issue of JEMS magazine.