Accidental hypothermia

Background

Definition: Core Temp <35C (95F)

  • Accidental hypothermia (unintentional core cooling <35C) is associated with significant morbidity and mortality. Roughly 1500 persons die of accidental hypothermia in the US annually.[1] Despite the high mortality associated with pre-hospital arrest, well directed treatment can result in complete neurologic recovery in the hypothermic patient.[2]
  • 50% who die of hypothermia are >65 years old[3]
  • Risk of cardiac arrest increased w/ temp < 32C as stable cardiac rhythms can quickly degenerate into unstable rhythms. Hypothermic patient patient without a pulse must be managed differently due to physiology changes that occur at low temperatures.

Scenarios and Risk Factors

  • Avalanche victims
  • Homeless population
  • Intoxicated patients
  • Elderly patients -> particularly low income during winter months
  • Submersion injuries

Clinical Features

Swiss Hypothermia Staging System[4]

Classification Temperature Signs/Symptoms
I / Mild 32-35°C (90-95°F) Shivering, awake
II / Moderate 28-32°C (82-90°F) Shivering, depressed mental status
III / Severe 20-28°C (68-82°F) unconscious/severely depressed mental status, shivering ceases
IV / Profound <20°C (68°F) unobtainable VS

Differential Diagnosis

Impaired thermoregulation

Increased heat loss

Diagnosis

  • Use low-reading thermometer
    • Some standard thermometers record only to 34C
  • Check blood glucose as can be very high in DM or CVA or low when metabolized to keep warm
  • Potassium >10-12 mEq/L not compatible with life
  • Coagulopathy: clotting factor activity and platelet function significantly reduced at temp < 34C
    • blood is rewarmed for lab testing so results may be normal

ECG

Osborn wave.gif
  • Typical sequence is sinus brady > a fib with slow ventricular response > v-fib > asystole
  • Other ECG findings:
    • Osborn (J) wave
    • T-wave inversions
    • PR, QRS, QT prolongation
    • Muscle tremor artifact
    • AV block
    • PVCs

General Management

Handling

  • Handle pt gently
  • V-fib may be induced by rough handling of pt due to irritable myocardium (anecdotal)

O2

  • Hypothermia causes leftward shift of oxyhemoglobin dissociation curve
  • Intubation
  • Intubate gently
  • if RSI is given medications may act at a slower rate

IVF

  • Patients are also hypovolemic since Hypothermia > impaired renal concentrating ability > cold diuresis
  • Patients are prone to rhabdomyolysis and will need hydration
  • Intravascular volume is lost due to extravascular shift
  • NS preferred over LR as cold liver poorly metabolizes LR

CPR

  • Only perform if patient truly does not have a pulse (unnecessary CPR may lead to V-fib)
  • Spend 30-45s attempting to detect respiratory activity and pulse before starting CPR

Dysrhythmias

  • May occur spontaneously if temp <30C (86F)
  • Rewarming is treatment of choice
  • Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
  • Activity of antiarrhythmics is unpredictable in hypothermia
  • Hypothermic heart is relatively resistant to atropine, pacing, and countershock
  • Ventricular tachycardia or Ventricular fibrillation are most common
    • May be refractory to therapy until patient is rewarmed
    • Attempt defibrillation
    • Value of deferring repeat defibrillation until a target temperature is reached is uncertain[5]
    • Reasonable to perform further defibrillation attempts concurrent with rewarming[6]

Antibiotics

  • Give if suspect sepsis (e.g. hypothermia fails to correct w/ rewarming measures)

Thiamine

  • Consider if Wernicke disease is possible cause of hypothermia (e.g. alcoholic pt)

Hydrocortisone

  • Consider if pt has history of adrenal suppression or insufficiency
    • 100mg Hydrocortisone

Thyroxine

Rewarming

Recommendations on Rewarming Modality based on Temperature and Clinical picture

Stage of Hypothermia Rewarming modality
I/ Mild: 32-35C (90-95F) Passive external -> Warm environment and clothing, blankets
II/ Moderate: 28-32C (82-90F) Active External and minimally invasive active rewarming
III/ Severe: 20-28C (68-82F) Active internal -> intraperitoneal, bladder, intrathoracic lavage

Extracorporeal -> Dialysis, ECMO, Bypass

IV/ Profound: <20C (68F) Management as with Moderate and Severe +

modified ACLS

Passive

Perform in all patients with hypothermia who is able to generate intrinsic heat

  1. Removal from cold environment which includes removal of wet clothing
  2. Insulation with warm blankets and warming devices

Passive External

  • Prevent additional losses -> remove wet clothes
  • Heated room
  • Blankets - If patient still shivering, capable of rewarming 0.5C/hr

Active

Perform in patients with moderate to severe hypothermia or those who have failre response to passive rewarming

  • Rewarm trunk BEFORE the extremities otherwise you cause further hypotension ("core temperature afterdrop")
  • Afterdrop: warmed vasodilated peripheral tissue allows cooler blood in extremities to circulate back to core
  1. Warm water immersion
  2. Heating blankets
  3. Radiant heat
  4. Forced air - Bair hugger
  5. Warm humidified air via facemask or endotracheal tube

Active Internal

  • Consider alone or along with active external warming in:
    • Cardiovascular instability / life-threatening dysrhythmias
    • Severe hypothermia
    • Moderate hypothermia which fails to respond to less aggressive measures
  1. Heated IV fluids: 38°C -42°C.
    • Two animal studies have showed 65°C IVF via central line warmed subjects faster without side effects, but this has not been tested in humans[7][8]
    • If central line is placed avoid irritating the heart
  2. GI tract lavage
  3. Bladder lavage
  4. Thoracic Lavage
  5. Peritoneal lavage
  6. Bypass/ECMO[9]/AV Dialysis

Bladder irrigationThis method can be used if large volumes (>10L) of warmed fluids are not available

  1. Insert temp sensing foley
  2. Instill 100-200cc warmed fluids
  3. Clamp Foley and wait for foley temp probe to begin to equilibrate 2-3 degrees celsius
  4. Drain bladder and repeat

Rewarming Rates

Various measures of rewarming cause different core body increases per hour[10]

  • IV fluids - no net change
  • Shivering - 1.5°C/hr
  • Warming Blanket - 2°C/hr
  • Peritoneal Lavage - 3°C/hr
  • Thoracic Lavage - 3-6°C/hr
  • Hemodialysis 3-4°C/hr
  • Cardiac Bypass 7-10°C/hr



Active External

  • Heated forced-air blanket -> Up to 1-2.5C/Hr rewarming
  • Warm water immersion -> Capable of 2-4C/Hr rewarming

Active Internal

Mode C/Hr Comments
Warm Humidified Air (intubated) 0.5-1.2 Low heat transport capacity
Warm IV fluids (47C) highly variable 1-3 Limited by tubing distance, requires large volumes but risk of volume overload
Intracavitary (peritoneal,bladder,thoracic) lavage variable 1-4 6-10L/Hr with fluid heated up to 45C
Open thoracotomy lavage Up to 8 (median 3) Highly invasive. 71% survival in 1 study

Management of the coding hypothermic patient

Risk of cardiac arrest increased w/ temp < 32C Rhythms can quickly degenerate into unstable rhythms Be careful when inserting guidewires, persistent shocks can degenerate fib into asystole Standard ACLS guidelines may not apply: Any organized rhythm should be assumed to be perfusing the patient adequately Starting CPR may precipitate fatal ventricular rhythms Modified vs. Standard ACLS: ERC recommends up to 3 defibrillations w/ epi held until temp > 30C then epi interval of 6 min until temp >35C AHA recommends 3 defibrillations and 3 rounds of epi with further dosing guided by clinical response Recent consensus suggest only one defib and dose of ACLS meds -> rewarm 5C -> one defib/meds -> etc.

Termination of CPR should be considered if

  • K > 12 mmol
  • Asystole persists beyond >32C
  • Lactate and pH have less consistent prognostic significance in hypothermia

Complications

  • Acid-base disorders
  • "Afterdrop"
    • Initial drop in temp and MAP as rewarming is started due to loss of vasoconstriction/AV shunting colder peripheral tissues
  • Aspiration pneumonia
  • Bleeding
    • Decreased platelet function and inhibition of coagulation cascade
  • Cold injuries
  • Dysrhythmias
  • Disseminated Intravascular Coagulation
  • Pancreatitis
  • Rhabdomyolysis
  • Thromboembolism
    • Secondary to hemoconcentration, increased blood viscosity, and poor circulation
  • Ineffective Drugs
    • Protein binding increases as body temperature drops, and most drugs become ineffective
    • Pharmacologic manipulation of the pulse and blood pressure generally should be avoided
    • Orally meds poorly absorbed because of decreased gastrointestinal motility
    • Intramuscular route avoided due to poor absorption from vasoconstricted sites

External Links

See Also

References

  1. ↑ Baumgartner EA, Belson M, Rubin C, Patel M. Hypothermia and other cold-related morbidity emergency department visits: United States, 1995-2004. Wilderness Environ Med 2008;19:233-237
  2. ↑ Friberg H, Rundgren. Submersion, accidental hypothermia,and cardiac arrest, mechanical chest compressions as a bridge to final treatment: a case report. Scand J Trauma Resusc Emerg Med. 2009; 17: 7
  3. ↑ 1. Centers for Disease Control and Prevention: Hypothermia-related deaths—United States, 2003–2004. MMWR Morb Mortal Wkly Rep 54: 173, 2005
  4. ↑ Brown et al., Accidental Hypothermia. N Engl J Med 2012; 367:1930-1938
  5. ↑ Hoek T. 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010. 122:5829-5861
  6. ↑ Hoek T. 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010. 122:5829-5861
  7. ↑ Fildes J, Sheaff C, and Barrett J. Very hot intravenous fluid in the treatment of hypothermia. J Trauma. 1993; 35(5):683-686.
  8. ↑ Sheaff CM, Fildes JJ, Keogh P, et al. Safety of 65 degrees C intravenous fluid for the treatment of hypothermia. Am J Surg. 1996; 172(1):52-55.
  9. ↑ Ginty C, et al. Extracorporeal membrane oxygenation rewarming in the ED: an opportunity for success. American Journal of Emergency Medicine. 2014 December 3 (ahead of print).
  10. ↑ Kempainen, R. R. and Brunette, D. D. The Evaluation and Management of Accidental Hypothermia. Respir.Care 2004;49(2):192-205
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