What are the criteria for starting therapeutic hypothermia (TH) in patients?

Criteria for Starting Therapeutic Hypothermia

Therapeutic hypothermia should be initiated in comatose patients (Glasgow Coma Scale ≤8, no response to verbal commands) after out-of-hospital cardiac arrest due to ventricular fibrillation or pulseless ventricular tachycardia, with target temperature 32-34°C maintained for 12-24 hours. 1, 2

Primary Inclusion Criteria

Adult Patients

• Comatose state after return of spontaneous circulation (ROSC) - patient remains unconscious and does not respond to verbal commands 1, 2
• Out-of-hospital cardiac arrest with initial rhythm of ventricular fibrillation (VF) or pulseless ventricular tachycardia - this represents the strongest evidence base 1
• Witnessed cardiac arrest with estimated interval of 5-15 minutes from collapse to first resuscitation attempt 1
• Interval of ≤60 minutes from collapse to ROSC 1
• Age 18-80 years 3

Neonatal Patients

• Infants ≥36 weeks gestational age 1
• Moderate to severe hypoxic-ischemic encephalopathy defined by strict clinical criteria 1
• Treatment must be initiated within 6 hours of birth 1
• Maintained for 72 hours with slow rewarming over at least 4 hours 1

Extended Indications (Reasonable to Consider)

Therapeutic hypothermia may also benefit patients with:

• Non-shockable rhythms (asystole or pulseless electrical activity) - though evidence is less robust 1, 2
• In-hospital cardiac arrest of cardiac etiology - particularly if patient remains comatose 1
• Post-cardiac arrest patients with STEMI requiring primary PCI - hypothermia should be started as soon as possible and does not delay PCI 1

Absolute Exclusions

Do not initiate therapeutic hypothermia in patients with:

• Severe cardiogenic shock (systolic blood pressure <90 mmHg despite vasopressors) 1, 3
• Life-threatening arrhythmias 1
• Pregnancy (per older guidelines, though case reports show successful use) 1, 4
• Primary coagulopathy 1
• Cardiac arrest of clearly non-cardiac etiology (head injury, drug overdose, cerebrovascular accident) 1

Timing Considerations

Cooling should be initiated as rapidly as possible:

• Optimal timing: as soon as possible after ROSC 1, 5
• Acceptable delay: up to 4-6 hours after ROSC - hypothermia still appears successful even with this delay 1, 5
• Target temperature should be reached within 4 hours of ROSC when possible 1

Special Population Considerations

Post-Cardiac Arrest with STEMI

• Therapeutic hypothermia is a Class I recommendation for comatose patients with STEMI and out-of-hospital cardiac arrest from VF/pulseless VT 1
• Do not delay angiography or PCI - hypothermia is feasible and safe during percutaneous coronary intervention 2

Pediatric Patients

• Late preterm infants (33-35 weeks GA): Evidence is controversial and limited 6
• Consider TH at 35 weeks GA in select cases, but routine use at ≤34 weeks should be limited to research settings 6
• Children after out-of-hospital cardiac arrest: Recent trial showed no significant benefit compared to normothermia, though practice varies 7

Common Pitfalls to Avoid

• Do not exclude patients who received thrombolytic therapy - this does not preclude hypothermia use 1
• Do not wait for transfer to a specialized center - cooling can be initiated pre-hospital with ice packs 3
• Do not apply hypothermia to patients with persistent severe hemodynamic instability requiring high-dose vasopressors 1, 3
• Ensure Glasgow Coma Scale score is ≤8 before initiating - patients with better neurological status may not benefit 1, 2