SGEM#21: Ice, Ice, Baby (Hypothermia post Cardiac Arrest)

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Date: 27 January 2013

Case: Stop, collaborate and listen. TheSGEM is back with a brand new edition. A 72-year-old man has witnessed arrest while watching his grandson’s hockey game. By-standard CPR is started and he shocked out of ventricular fibrillation using the automatic external defibrillator (AED). EMS arrives and finds an patient with vital signs stable but unconscious. Paramedic calls base hospital and asks if they should start cooling on-route.

Background: Two randomized control trials showed that hypothermia post cardiac arrest resuscitation was neuroprotective. One trial (n=273) in NEJM 2002 used cooled air mattress to demonstrate good outcome at 6 months (55% vs. 39%). The smaller Australian study (n=77) also published in NEJM 2002 showed good neurologic outcome at time of hospital discharge (49% vs. 26%).

Dr. David Newman has calculated the NNT=6 for mild therapeutic hypothermia for neuroprotection following cardiopulmonary resuscitation. The Cochrane Collaboration updated their review on hypothermia for neurporotection in adults after CPR in 2012. They concluded:

“Conventional cooling methods to induce mild therapeutic hypothermia seem to improve survival and neurologic outcome after cardiac arrest. Our review supports the current best medical practice as recommended by the International Resuscitation Guidelines.”

Question: Does pre-hospital therapeutic hypothermia improve patient outcomes after successful resuscitation?

Reference: Bernard SA et al. Induction of therapeutic hypothermia by paramedics after resuscitation from out-of-hospital ventricular fibrillation cardiac arrest: a randomized controlled trial, Circulation. 2010;122:737-742

Population: Adults (n=234) with out-of-hospital cardiac arrest with an initial rhythm of ventricular fibrillation
Intervention: Prehospital rapid infusion of 2L of ice-cold lactated Ringer’s
Control: Cooling after hospital admission
Outcome: Functional status at hospital discharge. Patients who were discharged directly home or to a rehab facility were considered to have a favorable outcome. Patients who died or were discharged to a long-term nursing facility, either conscious or unconscious, were considered unfavorable outcome.
Exclusion criteria: Not intubated, previously depended on others for activities of daily living before the cardiac arrest, already hypothermic (< 34 degrees Celsius), or pregnant women.

Results: Patients allocated to paramedic cooling received a median of almost 2L (1900ml). The mean decrease in core temperature was 0.8 degrees C (P=0.01).

47.5% paramedic-cooled patients had a favorable outcome at hospital discharge compared vs. 52.6% in the hospital-cooled group (risk ratio 0.90, 95% confidence interval 0.70 to 1.17, P=0.43).

Authors’ Conclusions: “In adults who have been resuscitated from out-of-hospital cardiac arrest with an initial cardiac rhythm of ventricular fibrillation, paramedic cooling with a rapid infusion of large-volume, ice-cold intravenous fluid decreased core temperature at hospital arrival but was not shown to improve outcome at hospital discharge compared with cooling commenced in the hospital.”

There has been a great deal of interest in cooling patients after out of hospital cardiac arrest in the last decade. Some laboratory studies suggest that sooner is better. Therefore, the hypothesis was generated that perhaps prehospital cooling by paramedics would improve outcome.

This study stopped prematurely. The sample size calculated to dectect a change in favourable outcome from 45% to 60% required a sample size of 372 pateints to achieve 80% power at an Type I (alpha) error of 0.005. A planned interim analysis after 200 patients noted no difference in primary outcome and was extremely unlikely that a difference would be found between the two groups.

Although the results of the present trial do not support the pre-hospital use of hypothermia, caveats to the interpretation include the short EMS transport times (may not apply to rural setting where time-to-hospital can be protracted) and premature study closure. In addition, future investigations should assess treatment started during CPR since prior to return of spontaneous circulation, all subjects had received 1L of non-cooled IVF.

Bottom Line: Scoop and run no cooling required in the field.

Case Conclusion: Patient was not cooled in the field but on arrival. He was admitted and one week later he was the 1 in 6 person to walk out the ICU neurologically intact.

Keener Contest: There was no winner to last week’s Keener Kontest. The question was who should NOT get the flu shot according to the CDC.

Listen to the podcast to hear this weeks Keener Kontest question. Email your answer to TheSGEM@gmail.com. Use “Keener” in the subject line. First one to email me the correct answer will win a cool skeptical prize:)

Last chance to sign up for SkiBEEM 2013 Feb 4-6 at SilverStar BC. This is the Best Evidence in Emergency Medicine (BEEM) conference. It presents the critical reviews of practice changing EM literature from the year. Attending SkiBEEM can cut your knowledge translation window to less than 1 year. Come and participate in a live episode of TheSGEM as a PUBcast at the conference!