JAMA Insights 

Extracorporeal Life Support in Accidental Hypothermia

Konrad Mendrala, Paweł Podsiadło, Tomasz Darocha

JAMA Published Online: October 8, 2025

doi: 10.1001/jama.2025.14593

Definition, Classification, and Temperature Measurement

Accidental hypothermia is defined as an unintentional core temperature of less than 35 °C (95 °F).¹ Although commonly associated with exposure to extreme cold in outdoor settings, hypothermia can occur in any climate or season and is particularly prevalent among urban populations, commonly affecting older, frail individuals with multiple comorbidities (often indoors), people experiencing homelessness, and those under the influence of alcohol or other psychoactive substances.¹

Accidental hypothermia is classified as mild (35-32 °C), moderate (32-28 °C), or severe (<28 °C) based on core temperature. Obtaining an accurate core temperature measurement is important to assess the risk of hypothermic cardiac arrest and guide treatment, including extracorporeal life support (ECLS) rewarming. Esophageal temperature measurement is the most accurate method to determine core temperature in routine clinical practice and is performed with a probe placed in the lower third of the esophagus. Peripheral measurements, including skin temperature and readings from common infrared ear thermometers, are less accurate. Specialized epitympanic thermistors may be reliable, but require that the external auditory canal is clear and the probe tip creates a secure seal. Bladder and rectal temperatures change more slowly than esophageal temperatures during rewarming and cooling, making them less useful for guiding dynamic therapeutic decisions.

In the prehospital setting, accurate temperature measurement is often not possible, so clinical staging scales that estimate core temperature based on clinical signs may be helpful. The revised Swiss system identifies the risk of hypothermic cardiac arrest based on the Alert, Verbal, Pain, and Unresponsive (AVPU) scale and vital signs and ranges from stage 1 (low risk of hypothermic cardiac arrest) in an alert patient to stage 4 (hypothermic cardiac arrest) in an unconscious patient with no detectable vital signs.¹

ECLS Indications: Hypothermic Cardiac Arrest

The risk of hypothermic cardiac arrest increases substantially in patients with a core temperature below 28 °C. Recommendations from the International Commission for Mountain Emergency Medicine and European Resuscitation Council advise transfer to ECLS centers for young, healthy patients with core temperature lower than 28 °C and for older patients or those with comorbidities with core temperature lower than 30 °C due to the high risk of cardiac arrest.¹ In severe hypothermia, the myocardium is highly irritable and susceptible to fatal arrhythmias, which can lead to cardiac arrest during rescue efforts, known as rescue collapse. Rescue collapse often occurs when a patient is moved suddenly into a nonhorizontal position, reducing preload, and is associated with double the risk of death compared with similar patients with hypothermia who maintain spontaneous circulation during rescue and transport (relative risk, 2.0 [95% CI, 1.1-3.62]; P = .02).²

In addition to severity of hypothermia, other important prognostic factors exist for occurrence of hypothermic cardiac arrest. In a retrospective study of 182 patients with severe accidental hypothermia, compared with patients who did not experience hypothermic cardiac arrest, those who developed hypothermic cardiac arrest presented with a lower median heart rate (40/min vs 50.5/min; P < .001), lower median systolic blood pressure (70 mm Hg vs 90 mm Hg; P = .03), higher incidence of ventricular arrhythmia (32% vs 10%; P = .001), and lower median temperature-corrected arterial oxygen partial pressure (53 mm Hg vs 87 mm Hg; P = .002).³ However, even with profound biochemical disturbances and severely compromised vital signs, a favorable outcome is possible in patients with hypothermia.^4,5

ECLS for Hypothermic Cardiac Arrest

For patients experiencing hypothermic cardiac arrest, extracorporeal life support, primarily venoarterial extracorporeal membrane oxygenation (VA-ECMO), is an important rewarming and life-sustaining modality that involves a multidisciplinary team typically including a cardiothoracic surgeon, anesthesiologist, perfusionist, and specialist nurse. VA-ECMO uses arteriovenous cannulation to establish an extracorporeal circuit. A pump generates blood flow to provide circulatory support, a membrane oxygenator facilitates gas exchange, and an integrated heater-cooler unit regulates the temperature of the circulating blood. In addition to rewarming to normothermia, VA-ECMO can help restore tissue perfusion and reverse metabolic disturbances, primarily hyperlactatemia and severe acidosis. Except for patients with unequivocal signs of death (eg, frozen chest wall), uncontrolled bleeding, or terminal illness, there are no absolute contraindications to initiating extracorporeal cardiopulmonary resuscitation for hypothermic cardiac arrest. In a retrospective multicenter study of 65 patients with hypothermic cardiac arrest who received ECLS and were older than 70 years, had unwitnessed cardiac arrest, or experienced asystole, 37% (24/65) survived to hospital discharge and 83% of them had a favorable neurological outcome, defined as a Cerebral Performance Category score of 1 or 2.⁴

An analysis of individual patient data from cohorts identified in a systematic literature review reported that among 221 patients with unwitnessed hypothermic cardiac arrest, 60 (27.1%) survived and 83.3% of survivors achieved favorable neurological outcomes (Cerebral Performance Category 1-2).⁶ Among neurologically intact survivors, the median duration of cardiopulmonary resuscitation was 105 minutes. In this study, 48.3% (28/58) had asystole, and 78.6% of them achieved favorable neurological outcomes.⁶ End-tidal carbon dioxide (ETCO₂) in patients with hypothermia is often substantially lower than 35 to 45 mm Hg due to the increased solubility of CO₂ in cold blood and reduced metabolic CO₂ production. Although ETCO₂ is a key indicator of adequate perfusion during normothermic cardiopulmonary resuscitation, in patients with hypothermic cardiac arrest, even an ETCO₂ value less than 10 mm Hg does not predict a poor outcome.⁴

Prognostic Tools

The decision to initiate ECLS should consider the likelihood of a favorable outcome. To aid this prognostication, 3 scoring systems have been developed to predict survival after hypothermic cardiac arrest in patients treated with ECLS (eTable in the Supplement), although they should not substitute for clinical judgment. The ICE score emerged from a meta-analysis of 658 cases of hypothermia, derived from 84 articles (44 retrospective cohort studies and 40 case reports), and 42.4% of included patients had asphyxia from events such as water submersion or snow burial without a breathable air pocket.⁷ The HOPE score (Hypothermia Outcome Prediction After ECLS), which is externally validated and currently the most commonly used prognostic tool for hypothermic cardiac arrest, was developed using patient data from a systematic literature review and individual hospital cases and included both non–asphyxia-related cases (eg, exposure to cold) and asphyxia. The most recent HELP score (Hemoglobin, Exposure, Lactate, Potassium) was generated from a cohort of 141 patients with nonasphyxial hypothermic cardiac arrest from a Polish hypothermia registry.⁸

Application of ECLS in Hypothermic Cardiac Arrest vs Hemodynamic Instability

ECLS in patients with hypothermic cardiac arrest is associated with higher rates of survival and favorable neurologic outcome compared with patients with cardiac arrest from acute coronary syndrome, arrhythmia, cardiomyopathy, and myocarditis. In a retrospective multicenter registry study of ECLS, compared with cardiac causes of cardiac arrest, patients with hypothermic cardiac arrest had significantly higher survival rates to discharge (45.1% vs 25.6%; adjusted odds ratio, 5.19 [95% CI, 3.15-8.56]; P < .001) and increased rates of favorable neurologic outcome (27.5% vs 13.0%; adjusted odds ratio, 5.12 [95% CI, 2.98-8.80]; P < .001).⁵

However, the role of ECMO in hemodynamically unstable patients with severe hypothermia not in cardiac arrest is uncertain. A multicenter retrospective observational study that included 135 patients with hypothermia without cardiac arrest reported a higher survival rate in those who underwent extracorporeal rewarming vs less invasive rewarming methods such as forced air warming, warmed intravenous fluids, warming mattress, intravascular warming system, hemodialysis and bladder lavage (79% vs 59%; P = .049).⁹ Conversely, a multicenter prospective observational study in Japan reported that among 185 patients with hypothermia not in cardiac arrest, ECMO was not associated with improved 28-day survival (76.5%) compared with treatment without ECMO (75.9%), and there was no improvement in neurological outcomes. Moreover, ECMO was associated with increased frequency of bleeding (73.2% vs 21.9%; P < .001).¹⁰

Conclusions

For patients with hypothermic cardiac arrest, use of ECLS is associated with a significantly increased survival and more favorable neurological outcome compared with patients with other causes of cardiac arrest.