52 in 52 – #37: POLAR trial – Hypothermia for Severe TBI

Welcome back to the “52 in 52” series. This collection of posts features recently published must-know articles. This week we cover the POLAR RCT on hypothermia for neuroprotection in those with severe TBI.

Author: Christiaan van Nispen, MD (Resident, Emergency Medicine Physician, San Antonio, TX); Brannon Inman, MD (Chief Resident, Emergency Medicine Physician, San Antonio, TX) // Reviewed by: Alex Koyfman, MD (@EMHighAK); Brit Long, MD (@long_brit)

Effect of Early Sustained Prophylactic Hypothermia on Neurologic Outcomes Among Patients with Severe Traumatic Brain Injury


AKA: The “POLAR” Trial


Clinical question:

In patients with severe traumatic brain injury, does early prophylactic hypothermia improve long-term neurologic outcomes?


Design: Multi-centered, single-blinded, randomized controlled trial




  • Inclusion Criteria:
    • Patients aged 18-60 years
    • GCS < 9
    • Actual or imminent endotracheal intubation
  • Out of Hospital Exclusion Criteria:
    • SBP < 90 mm Hg
    • Heart rate > 120 per minute
    • Pregnancy
    • Possible or suspected uncontrolled bleeding
    • GCS = 3 with unreactive pupils
    • Ability to intubate the patient without the use of medications
    • Cardiac arrest
    • Illicit drugs or alcohol ingestion suspected
    • Known use of anticoagulation
    • Penetrating injuries to the neck or torso
  • In Hospital Exclusion Criteria:
    • All above out of hospital criteria, if not already identified by emergency medical services
    • Failure by EMS to transport the patient to a participating hospital
    • Patient was determined to likely need a surgery or embolization procedure for hemostasis
    • Cooling deemed to be not in patient’s best medical interest, according to the judgement of the attending physician
  • Enrollment/Randomization:
    • Randomization was performed in the field by 5 emergency medical services units
    • Randomization was performed in hospital at 14 emergency departments
    • Randomization sites were spread across 6 countries
    • Total of 511 patients recruited with 466 completing primary outcome evaluation
      • Of these, 231 were enrolled out of hospital
    • Enrollment was conducted from 2010-2017, with final follow-up completed in 2018
    • There was a similarity in characteristics between the two groups


  • Prophylactic cooling to between 33C and 35C was performed through patient exposure, up to 2000 mL intravenous normal saline at 4⁰C, and surface cooling wraps
  • Hypothermia was maintained for at least 72 hours
  • Rewarming at 72 hours if intracranial pressures (ICPs) were less than 20 mm Hg; patients remained cooled for up to 7 days if intracranial pressure was elevated



  • Enforced normothermia, with target temperature of 37⁰C ±5⁰C
    • Use of surface cooling wraps for pyrexia and/or refractory intracranial hypertension



  • Primary outcome: favorable neurological outcomes defined by Glasgow Outcome Scale-Extended (GOS-E) Score, 5-8 at 6 months
    • Occurred in 117 patients (48.8%) in the hypothermia group
    • Occurred in 111 patients (49.1%) in the normothermia group
  • No significant differences in most secondary outcomes, including:
    • Mortality at 6 months after injury
    • Time to death
    • Time to reach target temperature
    • Days of mechanical ventilation
    • Intensive care unit length of stay
    • Hospital length of stay
    • Mean GOS-E score at 6 months
    • Unfavorable GOS-E score for survivors
  • Some secondary outcomes with significant, worse outcomes in hypothermia group:
    • Pneumonia (as measured in per protocol analysis): 70.5% vs. 57.1%
    • Bradycardia: 18.8% vs. 4.2%
    • Average ventilator days (8.3 vs. 6.9)

Take Aways:

  • The data do not suggest that targeted hypothermia improves neurological function, reduces death, or reduces hospital length of stay as compared to normothermia.
  • Several secondary outcomes suggest a signal toward harm with hypothermia, including incidence of pneumonia, bradycardia, and more days ventilated.
  • Multiple centers, strong follow-up, and rapid induction of hypothermia are strengths of the trial.
  • That 19% of patients were withdrawn from the study decreases generalizability.


My take:

  • This trial is consistent with other recent data which demonstrate lack of support for prophylactic hypothermia as a standard of care in traumatic brain injury.


Source Article:

Cooper DJ, Nichol AD, Bailey M, et al. Effect of Early Sustained Prophylactic Hypothermia on Neurologic Outcomes Among Patients with Severe Traumatic Brain Injury: The POLAR Randomized Clinical Trial. JAMA. 2018; 320(21):2211-2220. DOI: 10.1001/jama.2018.17075



Glasgow Outcome Scale – Extended

  • 1: Dead
  • 2: Vegetative state (only reflex responses and periods of eye opening)
  • 3: Low severe disability (requires full assistance with acts of daily living)
  • 4: Upper severe disability (requires partial assistance with acts of daily living)
  • 5: Low moderate disability (Some disability which presents resumption of work or school, but independent)
  • 6: Upper moderate disability (Some disability, but can at least partly resume work or other activities)
  • 7: Low good recovery (Minor deficits that affect daily life)
  • 8: Upper good recovery (Any deficits still present are not disabling)

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