Hypothermia Part 2: Prognostication and Protocols

Here we present part two on our series on hypothermia. For more on the assessment, resuscitation, and management of the hypothermic patient, see part one.

Prognostication of cardiac arrest in hypothermia

Indicators of cardiac arrest before cooling (Brown 2012)

• Major trauma
• Witnessed normothermic arrest
• Avalanche burial <35 min

Patients with primary hypothermia and cardiac stability who have been treated with active external and minimally invasive rewarming have a rate of neurologically intact survival of approximately 100%.  (Brown, 2012, Kornberger 1999)

Saczkowski (2018) did a meta-analysis of patients who underwent ECLS, and identified features predictive of survival:

• Predictive of poor outcome: asphyxia, elevated potassium, rewarming rate, gender (male)
• NOT predictive: age, CPR duration, pH, lactate, initial rhythm, mechanism, initial core temperature
• Asphyxiation
  • In the Saczkowski (2018) data, 279 of 658 (42.4%) patients who underwent ECLS likely had asphyxiation as a cause of their cardiac arrest. Of the patients with completed follow up, 24 of 265 (12.8%) survived with good neurologic outcome.

In the subset of patients with presumed asphyxia, only 12.8% survived with good neurologic outcome

• Potassium
  • Among the most reliable prognostic measures
  • Potassium is released due to traumatic and hypoxic cell death, and is interpreted as a marker of hypoxia prior to cooling
  • Recommended cut-off value is 12 mmol/L (AHA, ERC)
  • Recommended cut-off value in avalanche victims is 8 mmol/L (AHA, ERC, WMS)
  • Highest K successfully resuscitated:
    • 11.8 mmol/L in a 31-month-old child (Dobson 1996)
    • 9.5 mmol per liter in a 13-year-old child (von SegesserLK 1991)
    • 7.9 mmol/L in a 34-year-old (Farstad 2001)
    • 6.4 mmol/L in an adult in an avalanche (Locher 1996)
  • Sazckowski 2018 data showed an roughly dose-dependent response:
    • <5: 35%–85% good neurologic outcome
    • 5-10: 10%–50% good neurologic outcome
    • >10: 0%–20% survival
    • >12: 0% survival

• Temperature
  • Classifying severity is useful
  • Absolute temp is not very predictive in outcomes
  • The lowest reported core body temperatures in patients with full neurologic recovery are slightly less than 13.7°C (57°F) in a case of accidental hypothermia. (Gilbert 2000)
• Resuscitation time
  • is not predictive of survival
  • Longest time in a case report: 31 year old man, rock climbing when he became trapped on a rock face with cold running water. Core temperature was 26.0 °C.  He underwent CPR with a LUCAS device for 3 hours and 42 minutes, then ECMO for 5 hours, for a total of 8 hours and 42 minutes.
  • 65 year old, found on a snow-covered riverbank. No vital signs, in asystole. Core temperature initially 28 °C rectal, lowest 20.8 °C. Underwent CPR (4 h 48 m) and ECLS (3 h 52 m), for a total of 8 h 40 min. (Meyer 2014)
  • Longest persistent VF in a case report: 25 year old, buried by an avalanche. After extrication, had witnessed VF arrest at core temp 17.0°C. Had 3 unsuccessful shocks.  Underwent ECMO rewarming for 6 h, 45 min, with successful 4th shock at 24.8 °C. Full neurologic recovery. (Kosinski 2016)
  • Most number of shocks in a case report: 42 year old, found outdoors, no vital signs. Bystander CPR started. On EMS arrival was in VF. Continued CPR with repeated shocks. In hospital temp 22°C, EtOH 90.  CPR continued, with a total of 38 shocks delivered. Eventually underwent ECLS rewarming after 130 min CPR. Successful shock was at 30°C.  Full neurologic recovery. (Nordberg 2014)
• Chest compressions pattern/quality
  • What we typically rely on is not reliable
  • Prolonged period of no compressions
    • Longest case of no CPR in a case repor: 42 year old, found in crevasse buried under 7m of snow. No vital signs. CPR started 70 minutes later, after arrival to the hospital.  Asystolic on arrival, with core temp 19 °C. Underwent ECLS.  Full recovery. (Althaus 1982)
  • Intermittent compressions
    • Case report of alternating CPR 1min on, 1 min off, with good neurologic recovery. 57 year old, missing in Grenoble in French Alps at 2000m altitude, witnessed cardiac arrest on rescue. Transported on foot to EMS vehicle 1.1 km away.  Underwent 1 min CPR alternating with 1 min walking for 25 min, and a total of 5 h CPR before ECLS rewarming.  Full recovery. (Boue 2014)
  • Trauma
    • Standard trauma TOR criteria still apply
    • BUT polytrauma is NOT an absolute contraindication to ECLS
    • Concern with heparinization required for CPB/ECMO
    • Case report of survival with ECMO despite polytrauma – Male, found down on street by police, unknown circumstances of injury. Noted “extremely untidy”. Core temp 28. Trauma CT findings of pericerebral hematoma, signs of previously right craniotomy, multiple right-sided rib fractures, intraperitoneal fluid, and likely traumatic pancreatitis. Underwent warming and ECMO.  Full neurologic recovery. (Darocha 2015)
  • Drowning
    • If history suggests immersion in cold water (ie. able to breath) prior to submersion, cooling likely occurred prior to hypoxia and neurologic outcomes are better
    • The longest submersion times reported are 83min (7 year old child) and 66min (25 year old). Both underwent ECLS, and both had full recoveries. (Bolter 1988, Romlin 2015)
    • If history suggests submersion first, then asphyxiation is likely to cause of arrest, and prognosis is grim.
  • Avalanche
    • Death from asphyxia is much more common than hypothermia
    • Poor prognostic signs
      • Unwitnessed arrest with asystole predicts very poor survival chances, as hypoxia likely preceded cooling. Chances are better with VF or PEA. (Paal 2016)
      • Airway packed with snow
      • Burial time < 35 minutes, because this is insufficient time for cooling
      • Temperature >32°C and in cardiac arrest on extrication
    • Highest potassium in an avalanche victim was 6.4 mmol/L. (Locher 1996)

Pre-Hospital Considerations

• Most EMS systems do not make use of core temperature measurements or have low-sensing temperature probes.  It is typically not feasible.
• Swiss classification was developed to allow rescuers to have clinical data to aid in identifying severe hypothermia.
  • Must check for pulse for at least 60 seconds
  • If no signs of life, CPR should be started

ECMO bypass protocols?

• Challenging to implement due to limits of EMS capabilities to measure core temperature
• Generally relies on an order from EMS base hospital (“patch call”) for redirect based on a case-by-case scenario
• Those with hemodynamic instability or in cardiac arrest should be transported to a center capable of providing CPB or ECMO.

When is prehospital TOR appropriate?

• If risk to the responder is unacceptable
• Obvious signs of irreversible death: decapitation, truncal transection, decomposition of the whole body, and a chest wall that is not compressible
• If the chest is too stiff to provide compressions

Use of mechanical CPR in hypothermia

• Hypothermia can cause stiffness of the chest wall, making ventilations and chest compressions difficult. Consider the use of mechanical chest compression devices. (ERC)
• Putzer 2013 – prospective RCT using manikins that compared LUCAS device to manual cardiopulmonary resuscitation during helicopter rescue. Showed less hands-off time, but longer time to first defibrillation.  Showed the feasibility of prolonged CPR with the LUCAS.

Sample Hypothermia Protocol