Targeted Temperature Management Post-Cardiac Arrest
The correct answer is B: 32°C to 36°C for 24 hours. The American Heart Association strongly recommends selecting and maintaining a constant temperature between 32°C and 36°C during targeted temperature management (TTM) for at least 24 hours after achieving target temperature in comatose post-cardiac arrest patients 1.
Temperature Range: 32°C to 36°C
The 2015 AHA Guidelines represent a significant update from the previous 2010 recommendations, which had narrowly focused on 32°C to 34°C 1. This broader range is based on:
- Landmark trial evidence: A well-conducted randomized controlled trial found that neurologic outcomes and survival at 6 months after out-of-hospital cardiac arrest were not superior when temperature was controlled at 36°C versus 33°C 1.
- Class I, Level B-R recommendation: This is the strongest level of recommendation for VF/pulseless VT out-of-hospital cardiac arrest 1.
- Applies to all rhythms: The recommendation extends to non-shockable rhythms and in-hospital cardiac arrest (Class I, LOE C-EO) 1.
Duration: At Least 24 Hours
TTM should be maintained for at least 24 hours after achieving target temperature (Class IIa, LOE C-EO) 1, 2:
- The largest trials maintained temperatures for 24 hours or 28 hours followed by gradual rewarming at approximately 0.25°C/hour 1.
- Temperature sensitivity of the brain after cardiac arrest may continue as long as coma is present, making the upper limit of duration unknown 1, 2.
- Even if the selected target temperature is not achieved during this time frame, clinicians should still try to control temperature for at least 24 hours 1.
Patient Selection
All comatose adult patients (defined as lack of meaningful response to verbal commands) with return of spontaneous circulation after cardiac arrest should receive TTM 1:
- There are essentially no patients for whom temperature control somewhere in the range between 32°C and 36°C is contraindicated 1.
- This applies regardless of initial rhythm (shockable vs. non-shockable) or location of arrest (out-of-hospital vs. in-hospital) 1.
Temperature Selection Within the Range
Specific patient features may favor one temperature over another 1:
- Higher temperatures (36°C) might be preferred in patients at risk for bleeding complications 1.
- Lower temperatures (32-34°C) might be preferred when patients have seizures or cerebral edema 1.
- Patients presenting at the lower end of the TTM range might be maintained at that lower temperature rather than actively warming them 1.
Critical Pitfalls to Avoid
Do not actively or rapidly warm patients to reach a higher target temperature—this is not consistent with current recommendations 1. The landmark trial did not use active warming for the 36°C group 1.
Do not allow temperatures to exceed 36°C during the TTM period, as this would be more akin to the control groups in earlier trials and not consistent with current recommendations 1.
Avoid prehospital cooling with rapid infusion of large volumes of cold intravenous saline—this is not recommended due to absence of benefit and presence of complications 1, 3.
Post-TTM Management
After the initial 24-hour period, fever prevention should continue until 72 hours after return of spontaneous circulation, maintaining temperature <37.5°C 2. Rewarming should be gradual at approximately 0.25-0.5°C per hour to avoid rebound hyperthermia and secondary brain injury 2.
Why Other Options Are Incorrect
- Option A (30°C to 34°C for 12 hours): Temperature too low (30°C is below recommended range) and duration too short 1.
- Option C (30°F to 34°F for 24 hours): Uses Fahrenheit instead of Celsius; these temperatures would be fatal (approximately -1°C to 1°C) 1.
- Option D (40°C to 44°C for 12 hours): These temperatures represent severe hyperthermia and would cause harm, not benefit 1.