1. Accidental Hypothermia François Dufresne McGill Emergency Medicine May 2nd 2001

2. The Case of Tommy • 23h10 • Call from MD working in James Bay • Male, 27 y.o. Unresponsive. • Found in snow, cross-country skiing • Normal Airway. Breathing.  O2 sat. • Femoral pulse + (35)  BP. • GCS=3 TR = 28C. • IV. Monitor. Mask with 100% O2

3. The Case of Tommy… • Friend told MD: •  PMH.  Rx.  drugs.  EtOH • Major foot deformity • Looks like fell in ski and could not return home by himself… • MD has some questions for you…

4. The Case of Tommy… • Should he intubate? Are there risks to precipitate dysrythmias? • Cold myocardium prone to arythmias? • How should he rewarm the patient? • Danger of afterdrop? • He wants an ABG but should he ask for the blood to be warmed to normal T for analysis…or it doesn’t matter? Answer: You’ll call him back…

5. The Case of Tommy… • MD calls you back 30 minutes later • Pt in cardiac arrest : V.fib. Now 27C • 3 shocks • Epinephrine + re-shock • Having Amiodarone prepared… • How long should he do CPR and rescussitation? Answer ? Anything wrong ?

6. Introduction • Maritime / War litterature • Hannibal experience in 218 B.C

7. Hannibal against Rome

8. Introduction • EtOH  • Mental illness  • Homelessness  • Province of Quebec  Cold

9. Plan • Definitions • Physiology • Pathophysiology • Labs findings : ABG, ECG • Rewarming methods • Afterdrop • ACLS 2000 guidelines

10. Definitions • Primary VS Secondary • Primary • Normal thermoregulation • Overwhelming cold exposure • Secondary • Abnormal thermogenesis • Multiple causes

11. Definitions • Hypothermia : < 35C • Mild : 32-35C • Moderate : 28-32C • Severe : < 28C

12. Physiology: Heat production • Basal metabolism (Metabolic rate) • Heart / Liver • Anterior hypothalamus • Thyroid / Sympathetic • Preshivering muscle tone (2x) • Shivering (2-5x) • Posterior hypothalamus

13. Physiology: Heat dissipation • Radiation (55-65%) • Gradient between environement and exposed body area. • Conduction (2-3%) • Direct contact with cold substance • Convection (10-15%) • Wind… • Evaporation (20-35%)

14. Physiology… • Above 32C: • Vasoconstriction • Shivering • Basal metabolic rate • Below 32C: • No shivering • Below 24C: • No basal metabolic rate

15. Pathophysiology Cardiovascular • Initial tachycardia • Gradual bradycardia : HR 50% at 28C. • Not consistent ? • Hypoglycemia, intoxication, hypovolemia,…? • Refractory to atropine •  BP  CI • A.fib (T < 32C) • V.fib (T < 28C)

16. Pathophysiology… CNS • Cerebral metabolism  6% / 1C • Normal autoregulation until 25C • EEG flat at 19C Renal • Cold diuresis • Peripheral vasoconstriction • Failure to reabsorb Na+ and water.

17. Pathophysiology… Respiratory • CO2 production  50% at 30C • Decreased RR • ARDS possible Hematology • Hemostasis and coagulation impaired • Problems with CPB

18. Mild (> 32C) • Increase metabolic rate • Maximum shivering thermogenesis • Amnesia / dysarthria / ataxia • Loss of coordination • Tachycardic, tachypneic • Normal BP

19. Moderate (28– 32C) • Stupor • No shivering • Bradycardic / A.fib •  BP  RR • Pupils dilated (< 30C)

20. Severe (<28C ) • Coma • No corneal or oculocephalic reflexes •  BP • V.fib (Maximum risk: 22C) • Apnea • Asystole • Areflexia / fixed pupils • Flat EEG (19C)

21. Lab findings : ECG • Woman, 75 y.o • Found unconscious in her apartment

24. Osborn (J) Wave • Mr. John J. Osborn in the early ’50’s. • When T< 33C • 25%-30% of patients • Positive-negative deflection Osborn JJ: Experimental hypothermia: respiratory and blood pH changes in relation to cardiac function. Am J Physiol 1953; 175:389.

25. Osborne (J) Wave… • Amplitude proportionnal to degree of hypothermia • Usually V3-V6 • At junction of QRS and ST segment Osborn JJ: Experimental hypothermia: respiratory and blood pH changes in relation to cardiac function. Am J Physiol 1953; 175:389.

26. ECG in Hypothermia • Muscle tremors artifacts • Early changes • Bradycardia • T wave inversion • Prolonged PR, QRS and QT intervals • A.fib when T < 32C • V.fib when T < 28C

27. Lab findings : ABG • Man, 45 y.o,. • Rectal T= 30C. LOC Intubated. • Acid-base status? • Technician asks you if he should warm the blood before analysis… A) Don’t warm it : 30C B) Warm it to 37C C) heu…(30+37)/2….33.5C D) Both and I’ll pick the best one.

28. ABG in Hypothermia • 1st ABG (30C): • pH = 7.5 • pCO2 = 27 • 2nd ABG (37C): • pH = 7.4 • pCO2 = 40 • Which one do you pick? • Will you try to  RR or VT to  pCO2 ? • Everything’s perfect, I don’t touch the ventilator ? • The answer ? …. The Good One !!!

29. ABG in Hypothermia……the rationale • pH of water at any given T defines neutrality • H2O  H+ + OH- • As T , less free H+ and OH- are generated and pH of neutrality . • As T , CO2 content is the same but pCO2 . Delaney KA and al. Assessment of Acid-Base Disturbances in Hypothermia and their physiologic consequences. Ann Emerg Med, Jan 1989; 18:72-82.

31. So… • 1st ABG (30C): • pH = 7.5 • pCO2 = 27 • 2nd ABG (37C): • pH = 7.4 • pCO2 = 40

32. ABG in Hypothermia……the rationale • ABG machines usually warms blood to 37C. • So use the UNCORRECTED ABG for normal T . Delaney KA and al. Assessment of Acid-Base Disturbances in Hypothermia and their physiologic consequences. Ann Emerg Med, Jan 1989; 18:72-82.

33. Rewarming methods :Passive rewarming • Endogenous heat production • Shivering, metabolic rate, TSH, sympathetic,… • Involves decreasing heat loss • Remove from cold environnement • Remove wet clothes • Provide blanket

34. Passive rewarming… • O2 consumption can > 90% • CO2 production can by 65% • Possible anaerobic metabolism Rewarming rate : 0.5C - 2.0C /h • Method of choice for mild hypothermia • Adjunt for moderate hypothermia

35. Rewarming methods :Active external rewarming • Heat to body surfaces • Heating blankets (fluid filled) • Air blankets • Radiant warmers • Immersion in hot bath • Water bottles / Heating pads • Less effective than internal rewarming if vasoconstricted +++

36. Active external rewarming… • Concern about afterdrop. • Rewarming rates : 1C – 2.5C / h • Circulatory problem may be  by applying devices to trunk only. • Very few prospective controlled study comparing methods.

37. Forced Air Blankets • ED patients • Moderate to severe hypothermia (< 32C) • Exclusion criteria • Cardiac arrest • Hypothalamic lesions • 16 patients • Randomized to passive insulation with cotton blanket or forcedair blanket @ 43C . Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

38. Forced Air Blanket… • All patients: warm iv fluids @ 38C • Warm O2 (40C) • End point: T = 35C • Looked at: • Rates of rewarming • Skin damage by blankets Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

39. Forced Air Blanket… Results • No afterdrop in both groups • No skin erythema/damage • Rewarming rates (p=0.01) • Forced-Air: 2.4C / h • Regularblanket: 1.4C / h Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

40. Forced air Mark T. Steele and al. Forced Air Speeds Rewarming in Accidental Hypothermia, Ann Emerg Med, April 1996; 27:479-484.

41. Electrical heating blanket • Carbon fiber-resistive blanket VS Passive rewarming • 8 patients • Induced-hypothermia (33C) • Skin thermal flux transducer • CO2 concentration production through mask • Compared: • rates of rewarming • core heat content Greif R and al, Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: a randomized controlled trial. Ann Emerg Med. April 2000; 35: 337-345.

42. Electrical heating Results • Core heat content >> electrical heating • Rates  1.5C/h > with electical heating • No afterdrop both groups Greif R and al, Resistive heating is more effective than metallic-foil insulation in an experimental model of accidental hypothermia: a randomized controlled trial. Ann Emerg Med. April 2000; 35: 337-345.

43. Rewarming methods :Active internal (core) rewarming • Warm iv fluids • Warm, humid oxygen • Peritoneal lavage • Gastric / Esophageal lavage • Bladder / Rectal lavage • Pleural / Mediastinal lavage • Microwaves (Diathermy) • Extracorporeal circulatory rewarming

44. Warm iv fluids • Up to 45C shown to be safe • 65C fluid studied in dogs • Journal of Trauma 1993 (8 dogs) • American Journal of Surgery 1996 (10 dogs) • Through IVC • Safe. No Complications • 2.9C/h compared to 1.25C/h (J Trauma) • 3.7C/h compared to 1.75C/h (Am J Surg)

45. Warm iv fluids… • Saline…Not RL • Long tubulure = lost of heat • Can use microwave for saline (No D5W) • Annals of EM, 1984 and 1985 • 1L of NS to 39C : 2 minutes at high power. • No microwave rewarming for PRBC • Hemolysis • Hemoglobinuria • Transfusion reaction

46. Warm, humidified O2 • 42C-46C • Prevent heat loss • Negligible heat gain • Very important in management of hypothermic patient: • Up to 30% of heat production lost through airway.

47. Gastric/Oesophageal/ Bladder/Rectal lavage • Not shown to be better than external rewarming. • Limited surface area • Limited heat exchange • Limited utility (!) • Recommend as last resort when other modalities not available.

48. Peritoneal lavage • Fluid at 40-45C • Up to 12 L/h • KCl free • Hepatic rewarming • Renal support when dialysate is used • 2C-4C / h • C.I. • Abdominal trauma • Acute abdomen • Free intra-abdominal air

49. Peritoneal lavage… • Almost all studies before 1980 • Almost all animal studies • Critical Care Medicine 1988 • 11 dogs • Comparing peritoneal/pleural lavage and heated aerosol inhalation • Peritoneal and pleural lavage equivalent •  6C/h/m2 • Heated inhalation alone : little heat gain

50. Pleural lavageClosed-thoracic lavageContinuous thoracic cavity lavage • Two large (38F) ipsilateral chest tubes • 1: 2nd or 3rd anterior intercostal space, midclavicular. • 2: 5th or 6th intercostal space, posterior axillary line. • NS or tap water @ 42C • Rewarms heart + greater vessels Hall KN and al. Closed thoracic cavity lavage in the treatment of severe hypothermia in human beings. Ann Emerg Med, Feb 1990;19:204-206.