Critical Care Conference Severe Hypothermia

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Critical Care Conference -Severe Hypothermia

• Mark Byrne, MD
• Dept of Emergency Medicine
• Boston Medical Center
• September 10, 2008

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Definition

• Degrees of hypothermia

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Mild hypothermia

• Mild hypothermia (90 - 95 F)
• Excitation phase
• Shivering (max 95F)
• Tachypnea (hyper-ventilation)
• Tachycardia
• Early CNS depression (92F)
• Ataxia/Dysarthria
• Impaired judgement/Apathy

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Moderate hypothermia

• Moderate hypothermia (82 - 90 F)
• Slowing phase
• Hypo-ventilation
• Bradycardia
• Loss of shivering (88F)
• Further CNS depression
• Hyporeflexia
• Lethargy/Stupor (90F)
• Dilated pupils (86F)

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Moderate hypothermia

• Moderate hypothermia (82 - 90 F)
• Cardiac arrhythmias (87-88F)
• Sinus bradycardia
• Atrial fibrillation (slow)

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Severe hypothermia

• Severe hypothermia (lt82 F)
• Cardiopulmonary failure
• Hypotension
• Pulmonary edema
• Apnea
• Ventricular fibrillation (82F)
• Profound CNS depression
• Areflexia
• Dilated, unreactive pupils (80F)
• Coma

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Trivia

• What temperature goal is used with therapeutic
  hypothermia?
• 90-93F

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Definition

• Degrees of hypothermia

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Cardiac arrhythmias

• EKG changes
• Prolongation of all intervals
• Osborn (J waves)

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Cardiac arrhythmias

• Sinus bradycardia
• NOT responsive to atropine or pacing
• Slow atrial fibrillation (i.e. without RVR)
• Resolve spontaneously with rewarming

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Cardiac arrhythmias

• Hypothermic myocardium irritable
• Handle patients gently!
• Rough movement may precipitate Vfib
• Femoral central lines preferably

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Cardiac arrhythmias

• Ventricular fibrillation
• Lidocaine ineffective in severe hypothermia
• Prophylactic Bretyllium (from animal studies)
• May be refractory until rewarmed (86-90F)
• Trial of defibrillation
• If unsuccessful, CPR and aggressive rewarming

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Coagulation disorders

• Bleeding diasthesis
• Coagulation enzymes non-functional
• Manifests as a clinical phenemona
• Lab values may be deceptively normal
• PT/PTT performed at 98.6 F
• Giving clotting factors ineffective

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Trivia

• What is paradoxical undressing?
• Profoundly hypothermic victims sometimes rip off
  their clothes prior to death.

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Treatment

• Passive rewarming
• Active external rewarming
• Active internal (core) rewarming

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Principles of rewarming

• Extremities and trunk should NOT be warmed
  simultaneously
• Core temp afterdrop
• Cold, acidemic blood thaws in extremities
• Returns to core causing drop in temp pH
• Rewarming shock
• Warming extremities --gt peripheral vasodilation
• May cause precipitous hypotension

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Passive rewarming

• Supportive care
• Remove wet clothing
• Cover with blankets
• Room temp 75 F
• Body self-corrects
• Shivering 1.5C/hr
• Increased metabolic rate
• Reserved for early excitation phase

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Active external rewarming

• Warm blankets
• Heat lamps
• Forced warm air (Bair Hugger) 1C/hr
• Used in mild hypothermia

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Active core rewarming

• Non-invasive
• Warm, humidified oxygen 41C 0.5C/hr
• Warmed IV crystalloid 42C 0.3C/L
• Only significant with large volumes
• Used in mild hypothermia

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Active core rewarming

• Mildy invasive
• Bladder irrigation
• Gastric lavage 42C 1.5C/hr
• 250mL NS aliquots q10-15min
• Used in mild-moderate hypothermia

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Active core rewarming

• Moderately invasive
• Peritoneal irrigation 42C 1-2C/hr
• 1-2L NS aliquots q20-30mins
• Pleural irrigation 42C 3C/hr
• 500mL/min NS infusions
• Reserved for CV instability
• Profound CNS dysfunction
• Temp lt30C(86F)

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Active core rewarming

• Most invasive
• Hemodialysis 2-3C/hr
• Cardiopulmonary bypass gt9C/hr
• Reserved for cardiac arrest

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New therapies

• Endovascular warming
• Catheter advanced into IVC
• Balloon circulates warmed fluids

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• No one is dead until they are warm and dead.

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Resuscitation

• Contraindications
• Pulseless
• Apneic
• Fixed, dilated pupils

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Resuscitation

• Contraindications
• Pulseless
• Apneic
• Fixed, dilated pupils
• Chest wall frozen making CPR impossible
• Nose or mouth blocked with ice

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Resuscitation

• Neuroprotection from hypothermia may allow
  recovery despite prolonged arrest
• Endpoint of resuscitation is temperature of at
  least 90F

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Trivia

• What is the lowest temperature from which someone
  has been successfully resuscitated?
• Recovery has been documented with temps as low as
  61F in an adult and 57F in a child.

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Summary

• No ones dead until theyre warm and dead
• Sinus brady, Afib resolve with rewarming
• Vfib may be refractory to defib, meds
• Handle severely hypothermic patients gently!
• Bair hugger, warmed O2 IVF minimal effect
• Cavity lavage for CV or CNS instability
• CPB reserved for cardiac arrest
• Endovascular warming is a new option

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Thank You