Therapeutic Hypothermia Protocol (THP) in Cardiac Arrest Patients
THP stands for Therapeutic Hypothermia Protocol, and for comatose cardiac arrest patients, you should implement targeted temperature management at 32-34°C for 12-24 hours, initiated as rapidly as possible after return of spontaneous circulation (ROSC). 1, 2
Definition and Core Protocol
Targeted Temperature Management (TTM) is the current term encompassing therapeutic hypothermia, reflecting that various temperature targets are now acceptable 3:
- Target temperature range: 32-36°C (with 32-34°C having strongest evidence for VF/pulseless VT) 3, 1
- Duration: Maintain constant temperature for 12-24 hours 3, 1
- Rewarming: Gradual at approximately 0.25°C/hour, avoiding rapid active rewarming 3, 2
Patient Selection Criteria
Strong Indications (Class I Recommendation)
Comatose patients (not responding meaningfully to verbal commands, GCS ≤8) with ROSC after: 3, 1, 2
- Out-of-hospital VF/pulseless VT cardiac arrest (strongest evidence) 3, 1
- Out-of-hospital non-shockable rhythms (asystole, PEA) - reasonable to consider 3, 1
- In-hospital cardiac arrest of cardiac etiology - reasonable to consider 3, 1
- STEMI patients requiring PCI - do NOT delay angiography or PCI for cooling 3, 1, 2
Absolute Contraindications
Do NOT initiate THP in patients with: 3, 1
- Severe cardiogenic shock (SBP <90 mmHg despite vasopressors) 1
- Life-threatening arrhythmias 1
- Primary coagulopathy 3, 1
- Pregnancy (per older guidelines, though case reports exist) 3, 1
- Cardiac arrest from clearly non-cardiac etiology (head injury, drug overdose, CVA) 1
Implementation Protocol
Timing
Initiate cooling as rapidly as possible after ROSC - the sooner, the better for neurologic outcomes 3, 1:
- Optimal: Begin immediately upon ROSC 1
- Acceptable delay: Up to 4-6 hours post-ROSC still shows benefit 3, 1
- Target achievement: Reach target temperature within 4 hours of ROSC when possible 1
Cooling Methods
Initial rapid cooling (choose one or combine): 3, 2
- Cold IV fluid bolus: 30 mL/kg of 4°C normal saline or lactated Ringer's over 30 minutes (reduces core temperature by ~1.5°C) 3, 2
- Ice packs: Apply to groin, axillae, and neck 3, 2
Maintenance cooling (additional strategies required after IV bolus): 3, 2
- Ice-water soaked towels over torso 3, 2
- Cooling blankets (water or air circulation) 3, 2
- Intravascular heat exchange devices (most precise control) 3, 2
- Cooling helmets 3
Essential Monitoring and Management
Temperature monitoring: 3
- Continuous core temperature via bladder probe or pulmonary artery catheter 3
- Avoid tympanic measurements (unreliable) 3
Prevent shivering (increases oxygen consumption and causes rewarming): 3, 2
- Monitor for arrhythmias if temperature drops below 32°C 3
- Manage hyperglycemia (target <180 mg/dL) 3
- Correct hypokalemia 2
- Prevent hyperthermia during and after rewarming 3, 2
Evidence-Based Outcomes
For VF/pulseless VT out-of-hospital cardiac arrest, therapeutic hypothermia at 32-34°C demonstrates: 3, 2
- Improved neurologic outcomes: NNT = 6 for favorable neurologic outcome at 6 months 2
- Reduced mortality: NNT = 7 at 6 months 2
Recent evidence shows that 33°C versus 36°C produces similar outcomes, but both involve active temperature control (not passive normothermia) 3. The 2024 guidelines confirm insufficient evidence to recommend one specific temperature over another within the 32-36°C range 3.
Critical Prognostic Factor
Time from collapse to ROSC is the strongest predictor of survival, independent of initial rhythm or presence of shock 4:
This helps identify patients most likely to benefit from THP, though it should not exclude patients from treatment if they meet inclusion criteria 4.
Special Considerations for STEMI Patients
Do NOT delay PCI for therapeutic hypothermia - cooling during PCI is feasible, safe, and may improve outcomes 3, 1, 2. Initiate cooling as soon as possible without postponing urgent catheterization 3, 1.