Hypothermia

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Background

Definition: Core Temperature <35C (95F)

  • Unintentional hypothermia (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 with temperature <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.

Causes of hypothermia

  • Increased heat loss
    • Environmental exposure
      • Avalanche victims
      • Homeless population
      • Elderly patients → particularly low income during winter months
      • Submersion injuries
    • Induced vasodilation
      • Drugs
      • Alcohol
  • Decreased heat production
    • Endocrine
      • Hypopituitarism
      • Hypothyroidism
      • Hypoadrenalism
      • Hypoglycemia
    • Neuromuscular inefficiency
      • Extremes of age
      • Impaired shivering
    • Other
      • Sepsis
      • Trauma

Clinical Features

Swiss Hypothermia Staging System[4]

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

Differential Diagnosis

Cold injuries

Evaluation

  • Use low-reading thermometer
    • Some standard thermometers record only to 34C
    • Measure core temperature with esophageal probe if intubated (most accurate)
  • 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 temperature < 34C
    • Blood is rewarmed for lab testing so results may appear normal

ECG

Osborn wave.gif
  • Typical sequence is sinus bradycardia → atrial fibrillation with slow ventricular response → ventricular fibrillation → asystole
  • Other ECG findings:

General Management

Handling

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

O2

  • Hypothermiacauses 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 temperature <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[5]

Antibiotics

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

Thiamine

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

Hydrocortisone

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

Thyroxine

Rewarming

Recommendations on Rewarming Modality based on Temperature and Clinical picture

Stage of Hypothermia Recommended rewarming modality
I/ Mild: 32-35C (90-95F) Passive external
II/ Moderate: 28-32C (82-90F) Active external
III/ Severe: 20-28C (68-82F) Active internal
IV/ Profound: <20C (68F) As severe + modified ACLS

Passive External

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

Active External

  • 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
  • Options:
    • Warm water immersion (Capable of 2-4C/Hr rewarming)
    • Heating blankets
    • Radiant heat
    • Forced air - e.g. Bair hugger (Up to 1-2.5C/Hr rewarming)
    • Warm humidified air via facemask or endotracheal tube

Active Internal

Options:

  • Heated IV fluids: 38-42°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[6][7]
    • If central line is placed, avoid irritating the heart
  • GI tract lavage
    • Can cause fluid and electrolyte fluctuations, also risk of pulmonary aspiration
  • Bladder lavage
    • Small surface area available for heat exchange
  • Thoracic lavage
  • Peritoneal lavage
  • Bypass/ECMO[8]/AV Dialysis

Rewarming Rates

Mode °C/Hr Comments
Passive External
Shivering[9] 1.5
Warming Blanket[9] 2
Active External
Warm IV fluids (47C) 1-3 Highly variable; Limited by tubing distance, requires large volumes with risk of volume overload
Forced air (Bair hugger) 1-2.5
Warm water immersion 2-4
Active Internal
Warm Humidified Air (intubated) 0.5-1.2 Low heat transport capacity
Peritoneal Lavage[9] 3
Thoracic Lavage[9] 3-6
Hemodialysis[9] 3-4
Open thoracotomy lavage Up to 8 (median 3) Highly invasive. 71% survival in 1 study
Cardiac Bypass[9] 7-10

Management of the coding hypothermic patient

  • 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 with [[epi] held until temperature >30C, then epinephrine interval of 6 min until temperature >35C
    • AHA recommends 3 defibrillations and 3 rounds of epinephrine with further dosing guided by clinical response
    • Recent consensus suggest only one defibrillation and round of ACLS meds → rewarm 5C → one defib/meds → Repeat

Termination of CPR

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

Disposition

Complications

  • Acid-base disorders
  • "Afterdrop"
    • Initial drop in temperature 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
    • Oral 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. Hypothermiaand 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. ↑ 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. ↑ 5.0 5.1 Hoek T. 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010. 122:5829-5861
  6. ↑ Fildes J, Sheaff C, and Barrett J. Very hot intravenous fluid in the treatment of hypothermia. J Trauma. 1993; 35(5):683-686.
  7. ↑ 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.
  8. ↑ 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).
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 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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