Critical Care Conference -

Severe Hypothermia

Mark Byrne, MDDept of Emergency Medicine

Boston Medical CenterSeptember 10, 2008

Definition

• Degrees of hypothermia

Mild 90° - 95° F

Moderate 82° - 90° F

Severe <82° F

Mild hypothermia

• Mild hypothermia (90° - 95° F)– “Excitation” phase

• Shivering (max ~95°F)• Tachypnea (hyper-ventilation)• Tachycardia

– Early CNS depression (92°F)• Ataxia/Dysarthria• Impaired judgement/Apathy

Moderate hypothermia

• Moderate hypothermia (82° - 90° F)– “Slowing” phase

• Hypo-ventilation• Bradycardia• Loss of shivering (88°F)

– Further CNS depression• Hyporeflexia• Lethargy/Stupor (90°F)• Dilated pupils (86°F)

Moderate hypothermia

• Moderate hypothermia (82° - 90° F)– Cardiac arrhythmias (87-88°F)

• Sinus bradycardia• Atrial fibrillation (slow)

Severe hypothermia

• Severe hypothermia (<82° F)– Cardiopulmonary failure

• Hypotension• Pulmonary edema• Apnea• Ventricular fibrillation (82°F)

– Profound CNS depression• Areflexia• Dilated, unreactive pupils (80°F)• Coma

Trivia

• What temperature goal is used with therapeutic hypothermia?

• 90-93°F

Definition

• Degrees of hypothermia

Mild 90° - 95° F

Moderate 82° - 90° F

Severe <82° F

Cardiac arrhythmias

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

Cardiac arrhythmias

• Sinus bradycardia– NOT responsive to atropine or pacing

• Slow atrial fibrillation (i.e. without RVR)

• Resolve spontaneously with rewarming

Cardiac arrhythmias

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

Cardiac arrhythmias

• Ventricular fibrillation– Lidocaine ineffective in severe hypothermia– Prophylactic Bretyllium (from animal studies)– May be refractory until rewarmed (86-90°F)

• Trial of defibrillation• If unsuccessful, CPR and aggressive rewarming

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

Trivia

• What is “paradoxical undressing”?

• “Profoundly hypothermic victims sometimes rip off their clothes prior to death.”

Treatment

• Passive rewarming

• Active external rewarming

• Active internal (core) rewarming

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 --> peripheral vasodilation• May cause precipitous hypotension

Passive rewarming

• Supportive care– Remove wet clothing– Cover with blankets– Room temp 75° F

• Body self-corrects– Shivering 1.5°C/hr– Increased metabolic rate

• Reserved for early “excitation” phase

Active external rewarming

• Warm blankets

• Heat lamps

• Forced warm air (“Bair Hugger”) 1°C/hr

• Used in mild hypothermia

Active core rewarming

• Non-invasive– Warm, humidified oxygen 41°C 0.5°C/hr– Warmed IV crystalloid 42°C 0.3°C/L

• Only significant with large volumes

– Used in mild hypothermia

Active core rewarming

• Mildy invasive– Bladder irrigation– Gastric lavage 42°C 1.5°C/hr

• 250mL NS aliquots q10-15min

– Used in mild-moderate hypothermia

Active core rewarming

• Moderately invasive– Peritoneal irrigation 42°C 1-2°C/hr

• 1-2L NS aliquots q20-30mins

– Pleural irrigation 42°C 3°C/hr• 500mL/min* NS infusions

– Reserved for – CV instability

– Profound CNS dysfunction

– Temp <30°C(86°F)

Active core rewarming

• Most invasive– Hemodialysis 2-3°C/hr– Cardiopulmonary bypass >9°C/hr

– Reserved for cardiac arrest

New therapies

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

“No one is dead until they are warm and dead.”

Resuscitation

• Contraindications– Pulseless– Apneic– Fixed, dilated pupils

Resuscitation

• Contraindications– Pulseless– Apneic– Fixed, dilated pupils

– Chest wall frozen making CPR impossible– Nose or mouth blocked with ice

X

Resuscitation

• Neuroprotection from hypothermia may allow recovery despite prolonged arrest

• Endpoint of resuscitation is temperature of at least 90°F

Trivia

• What is the lowest temperature from which someone has been successfully resuscitated?

• Recovery has been documented with temps as low as 61°F in an adult and 57°F in a child.

Summary

• “No one’s dead until they’re 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

Thank You