Accidental hypothermia

Background

Whid chill chart

Definition: Core Temperature <35°C (95°F)

  • Unintentional hypothermia (core cooling <35°C) 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 <32°C, as stable cardiac rhythms can quickly degenerate into unstable rhythms. Hypothermic patient without a pulse must be managed differently due to physiology changes that occur at low temperatures. Defibrillation and many medications may be ineffective until the core temperature is above 30.0°C. If defibrillation is warranted but unsuccessful, active rewarming should be initiated while CPR is continued.

Causes

Clinical Features

Medical students learning about the effects of hypothermia on the body.
Man being rewarmed after spending five-minutes in near freezing water.

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

Associated Problems

  • Cold injuries
  • Cardiac dysfunction
    • Dysrhythmias
      • May occur spontaneously if temperature <30°C (86°F)
    • Afterdrop: Initial drop in temperature and MAP as rewarming is started due to loss of vasoconstriction/AV shunting colder peripheral tissues
  • Coagulopathy
  • 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
  • Other

Differential Diagnosis

Cold injuries

Evaluation

  • Use low-reading thermometer
    • Some standard thermometers record only to 34°C
    • 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 < 34°C
    • Blood is rewarmed for lab testing so results may appear normal
  • If ABG is rewarmed before analysis, results will be different from patient's actual acid/base state

ECG

Osborn wave.gif
Atrial fibrillation and Osborn J waves in a person with hypothermia.
  • Typical sequence is sinus bradycardia → atrial fibrillation with slow ventricular response → ventricular fibrillation → asystole
  • Other ECG findings:
    • Osborn (J) wave - Size of wave correlates with degree of hypothermia. No prognostic value.
    • Muscle tremor artifact
    • T-wave inversions
    • PR, QRS, QT prolongation
    • ST segment elevation or depression
    • AV block
    • PVCs

General Management

Basic Measures

  • Handling
    • Handle patient gently
    • V-fib may be induced by rough handling of patient due to irritable myocardium (anecdotal)
  • Oxygen therapy
    • 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 causes impaired renal concentrating ability, in turn causing cold diuresis
    • Patients are prone to rhabdomyolysis and will need hydration
    • Intravascular volume is lost due to extravascular shift
    • Normal saline preferred over Lactated Ringers, as cold liver poorly metabolizes LR

Dysrhythmias

  • Rewarming is treatment of choice
  • Most dysrhythmias (e.g. sinus brady, a-fib/flutter) require no other therapy
  • If the patient requires central venous access, femoral is recommended to avoid irritating the myocardium
  • 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]

Medications for Unexplained Hypothermia in Specific Patient Populations

  • 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
  • Levothyroxine
  • Hyperglycemia
    • Hyperglycemia common in hypothermia:
      • Stimulates catecholamine induced glycogenolysis
      • Inhibits insulin release and uptake by cell membranes
    • Rebound hypoglycemia during rewarming can occur if clinicians too aggressively deliver exogenous insulin

Rewarming

Recommendations on Rewarming Modality based on Temperature and Clinical picture

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

Passive External

  • Prevent additional heat loss → Remove wet clothes
  • Heated room
  • Blankets - If patient still shivering, capable of rewarming 0.5°C/hr
  • Hypothermia cap

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 2-4°C/Hr rewarming)
    • Heating blankets
    • Radiant heat
    • Forced air - e.g. Bair hugger or Arctic Sun (Up to 1-2.5°C/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 (47°C) 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

Cardiac Arrest

  • 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
  • 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 >30°C, then epinephrine interval of 6 min until temperature >35°C
    • 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 5°C → one defib/meds → Repeat

Termination of CPR

  • Should be considered if:
  • Lactate and pH have less consistent prognostic significance in hypothermia

Disposition

  • ICU for severe cases

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
  10. Schaller M, Fischer AP, Perret CH. Hyperkalemia: A Prognostic Factor During Acute Severe Hypothermia. JAMA. 1990;264(14):1842–1845. doi:10.1001/jama.1990.03450140064035
  11. Paal P, Gordon L, Strapazzon G, et al. Accidental hypothermia-an update : The content of this review is endorsed by the International Commission for Mountain Emergency Medicine (ICAR MEDCOM). Scand J Trauma Resusc Emerg Med. 2016;24(1):111. Published 2016 Sep 15. doi:10.1186/s13049-016-0303-7