TTM: 33°C vs 36°C After Out-of-Hospital Cardiac Arrest

33 and 36 were equivalent. The story shifted from 'mild hypothermia' to 'avoid fever.'

Population

950 unconscious adults after out-of-hospital cardiac arrest of presumed cardiac cause across 36 ICUs.

Intervention

Targeted temperature management at 33°C × 24 h.

Comparison

TTM at 36°C × 24 h.

Outcome

All-cause mortality at end of trial.

Multicenter RCT. Sedation + paralysis + active cooling/warming via surface or intravascular device. Both arms had identical management except temperature target. Neurologic outcome (CPC + modified Rankin) at 180 days.

• Mortality: 50% (33°C) vs 48% (36°C). HR 1.06, 95% CI 0.89-1.28. NO DIFFERENCE.
• Poor neurologic outcome (CPC 3-5): 54% vs 52%. NO DIFFERENCE.
• Adverse events similar; bleeding + arrhythmias slightly more in 33°C arm but not significant.

TTM upended a decade of practice (which favored 33°C based on Bernard 2002 + HACA 2002). The current AHA 2020 guideline says 'TTM in the range of 32-36°C × ≥24 h.' Most institutions standardized at 36°C because it's easier (less shivering, less hemodynamic instability) with equivalent outcomes. The newer TTM2 trial (NEJM 2021) compared 33°C to normothermia (with fever avoidance) and again found no difference — pushing further toward 'just avoid fever.'

• Predominantly cardiac etiology — non-cardiac arrest may differ.
• Selected population: witnessed arrest, presumed cardiac cause, ROSC achieved.
• Both groups had aggressive fever avoidance — the comparison is between two cooling targets, not vs no temperature management.

1. Has your institution moved from 33°C to 36°C? What was the operational driver?
2. TTM2 (2021) compared 33°C to normothermia and found no difference. Should we abandon active cooling entirely + just block fever?
3. How aggressive should we be at preventing the rebound fever that follows ROSC if we don't actively cool?