Date: July 3rd, 2014
Guest Swedish Skeptics: Katrin Hruska @Akutdok
Case Scenario: A 72 year old man has witnessed arrest at the Goderich beach. By-standard CPR is started and he shocked out of ventricular fibrillation by emergency medical services but does not regain consciousness. We know from SGEM#54 that cooling in the field does not improve survival. His temperature on arrival to the emergency department is 36°C.
Background: Therapeutic hypothermia post cardiac arrest has received a great deal of attention over the last decade. 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 neuro-protection 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.”
The SGEM was skeptical after it covered the issue in Episode#21: Ice, Ice Baby. We looked at the paper by Bernard SA et al. called 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. The question was whether pre-hospital therapeutic hypothermia improve patient outcomes after successful resuscitation? The study had 234 patients and used large volumes of ice-cold lactated Ringer’s. The primary outcome was about 50% of patients survived to functional hospital discharge and there was not benefit to cooling.
The SGEM covered the larger pre-hopsital cooling paper by Kim F et al. in JAMA earlier this year. The bottom line was: Scoop and run after cardiac arrest with no cooling required in the field.
Question: Does cooling to a target temperature of 33°C improve survival to hospital discharge and neurological outcome in unconscious survivors of out-of-hospital cardiac arrest of presumed cardiac cause?
Reference: Nielsen N et al. Targeted Temperature Management at 33°C versus 36°C after Cardiac Arrest. NEJM 2013
- Population: 939 patients from 36 intensive care units (ICUs) in Europe and Australia with OHCA with more than 20 consecutive minutes of spontaneous circulation after resuscitation.
- Intervention: Cooling to 36 degrees celsius for 36 hours, <37.5 for 72 hs post-arrest
- Control: Active cooling to 33 degrees celsius
- Primary: Mortality at the end of the trial.
- Secondary: Mortality, Cerebral Performance Category (CPC) 3-5 or Modified Ranking (mRS) 4-6 at 180 days
Authors’ Conclusions: In conclusion, our trial does not provide evidence that targeting a body temperature of 33°C confers any benefit for unconscious patients admitted to the hospital after out-of-hospital cardiac arrest, as compared with targeting a body temperature of 36°C.
Quality Check List:
- The study population included or focused on those in the emergency department. Unsure
- The patients were adequately randomized. Yes
- The randomization process was concealed. Yes
- The patients were analyzed in the groups to which they were randomized. Yes
- The study patients were recruited consecutively (i.e. no selection bias). Yes
- The patients in both groups were similar with respect to prognostic factors. Yes
- All participants (patients, clinicians, outcome assessors) were unaware of group allocation. No
- All groups were treated equally except for the intervention. Yes
- Follow-up was complete (i.e. at least 80% for both groups). Yes
- All patient-important outcomes were considered. Unsure
- The treatment effect was large enough and precise enough to be clinically significant. No
Results: No difference in mortality. No difference in Cerebral Performance Category (CPC), modified Rankin Score (mRS) or mortality at 180 days.
This is a well conducted multisite randomized controlled trial on targeted temperature management after out-of-hospital cardiac arrest. They excluded very few patients from the trial. The main reasons for exclusion:
- Interval from return of spontaneous circulation to screening of >4 hours
- Unwitnessed arrest with asystole as the initial rhythm
- Suspected or know acute intracranial hemorrhage or stroke
- Body temperature of <30°C
A strength of the study was the multiple sites where the trial was conducted and the various sizes of hospitals.
Another strong feature of this study was that temperature was managed in different ways depending on the site’s preferences. The different methods of cooling did not seem to influence the results. This makes the result applicable to different practice settings depending on local protocols.
There was a risk of bias because of the inherent difficulty of blinding the treating physician to the intervention, but this is unlikely to affect mortality.
Comment on Authors’ Conclusions: Agree with authors’ conclusions.
SGEM Bottom Line: This study did not demonstrate a benefit of a targeted temperature 33C vs. 36C for survival of out-of-hospital cardiac arrest.
Case Resolution: The 72 year old man with the out-of-hospital cardiac arrest who arrived at 36°C. He was actively cooled to maintain this temperature but was not cooled further to 33°C. You plan to check in on him in the intensive care unit on your next shift.
Clinical Application: I will start cooling patients to 36°C and admit them to the intensive care unit for further management based on our own local protocols.
What Do I Tell the Patient: I will tell the patient’s wife that her husband had a cardiac arrest. We were able to bring him back but he is still unconscious. We are going to cool him to improve his chances of survival and a good neurological outcome.
KEENER KONTEST: Last weeks winner was Dr. Neil Dattani from Toronto. He knew cocaine was the first local anesthetic isolated from a plant source?
If you want to play the Keener Kontest this week then listen to the podcast for the question. Email me your answer at TheSGEM@gmail.com with “keener” in the subject line. The first person to correctly answer the question will receive a cool skeptical prize.
- Life in the Fast Lane (December 2013)
- Life in the Fast Lane (March 2014)
- Intensive Care Network
- St. Emlyn’s
Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.