Therapeutic Hypothermia Post-Cardiac Arrest

Primary Recommendation

Comatose adult patients (not responding meaningfully to verbal commands) with return of spontaneous circulation after out-of-hospital ventricular fibrillation cardiac arrest should be cooled to 32-34°C for 12-24 hours. 1

Patient Selection Criteria

Definite Indications

Out-of-hospital cardiac arrest with VF/pulseless VT as initial rhythm 1
Persistent coma after ROSC (Glasgow Coma Scale ≤8, not responding to verbal commands) 1, 2
Intubated and mechanically ventilated 1

Probable Benefit (Weaker Evidence)

Non-shockable rhythms (asystole, PEA) after out-of-hospital arrest 1, 2
In-hospital cardiac arrest of cardiac etiology 1
- Note: A large retrospective study of 8,316 in-hospital arrest patients showed no survival benefit (OR 0.90,95% CI 0.65-1.23), though only 40% achieved target temperatures 3

Contraindications

Severe cardiogenic shock or life-threatening arrhythmias 1
Pregnancy 1
Primary coagulopathy 1
Non-cardiac causes of arrest (head injury, drug overdose, cerebrovascular accident) 1

Target Temperature and Duration

Temperature Parameters

Target: 32-34°C 1, 2
Duration: 12-24 hours 1, 2
Critical warning: Do not allow temperature to fall below 32°C as complications (arrhythmias, infection, coagulopathy) increase significantly 4

Timing of Initiation

Initiate as soon as possible after ROSC 1, 4
Still effective if delayed 4-6 hours 1, 4
Registry data showed median initiation at 90 minutes (IQR 60-165 minutes) was not independently associated with outcome, though earlier is theoretically better 1

Cooling Methods

Rapid Induction Phase

Cold IV fluid bolus is the fastest initial method:

30 mL/kg of 4°C normal saline or Ringer's lactate over 30 minutes 1, 2, 4
Can reduce core temperature by up to 1.5°C 1
Never use rapid IV push due to profound bradycardia risk 4
Can be initiated in prehospital setting 1

Maintenance Phase (Additional Methods Required)

Surface cooling:

Ice packs to groin, axillae, and neck 1, 4
Servo-controlled cooling blankets (water or air circulation) 1, 4
Cooling helmets (less common) 1, 4

Intravascular cooling:

Endovascular heat exchange catheters provide most precise temperature control 1, 4
Too invasive for prehospital/ED use 4
Not used in pediatrics due to thrombosis risk 4

Temperature Monitoring

Continuous core temperature monitoring is mandatory 4:

Bladder temperature probe (reliable, preferred) 4
Esophageal temperature probe (accurate) 4
Rectal temperature probe (reliable) 4
Pulmonary artery catheter if already in place 4
Avoid intermittent tympanic measurements (unreliable) 4

Rewarming Protocol

Passive rewarming only 1, 4
Avoid rapid active rewarming as rebound hyperthermia is common and worsens outcomes 1, 4
Normothermia should be restored slowly 1

Evidence of Benefit

Neurological Outcomes

55% favorable neurological outcome at 6 months with hypothermia vs. 39% with normothermia in the European trial 1
Number Needed to Treat = 6 for one additional patient with intact neurological recovery 2, 5, 6
Relative risk 1.41 (95% CI 1.12-1.76) for favorable neurological outcome across 11 studies with 3,914 participants 7

Mortality Benefit

Relative risk 0.74 (NNT=7) for mortality reduction at 6 months 2
Cochrane review confirms mortality benefit with low certainty evidence 7

Concurrent Interventions

Percutaneous Coronary Intervention

Therapeutic hypothermia is feasible and safe during PCI 1, 2

Do not delay PCI due to hypothermia 2
Five studies confirmed safety of combined hypothermia and PCI 1

Thrombolytic Therapy

Not a contraindication to therapeutic hypothermia 1
Patients receiving thrombolytics were included in landmark trials 1

Adverse Effects and Management

Common Complications

Increased with hypothermia:

Pneumonia (NNH=12) 1, 7
Bleeding (NNH=14) 1
Sepsis (NNH=16) 1
Severe arrhythmias (RR 1.40,95% CI 1.19-1.64) 7
Hypokalaemia (RR 1.38,95% CI 1.03-1.84) 7

Metabolic Derangements

Hypokalemia, hypophosphatemia, hypomagnesemia, hypocalcemia develop during cooling and may precipitate arrhythmias 4
Close electrolyte monitoring required, especially during induction 4
Hyperglycemia due to decreased insulin sensitivity 2, 4

Cardiovascular Effects

Lower cardiac index and higher systemic vascular resistance 1
Bradycardia and hypotension observed 4

Shivering Prevention

Shivering must be prevented as it increases oxygen consumption and causes warming 8, 4:

Sedation plus neuromuscular blockade is the standard approach 4
This was the protocol used in definitive trials 4

Critical Pitfalls to Avoid

Do not cool below 32°C - complications increase exponentially 4
Do not use rapid IV push of cold saline - causes profound bradycardia 4
Do not allow rapid rewarming - rebound hyperthermia worsens outcomes 1, 4
Do not use intermittent temperature monitoring - continuous monitoring mandatory 4
Do not forget to prevent shivering - negates cooling benefit 8, 4
Do not withhold from hemodynamically compromised patients - hypothermia is safe even in shock 5

Guideline Endorsements

Both the American Heart Association and International Liaison Committee on Resuscitation (ILCOR) recommend therapeutic hypothermia for unconscious adult patients with spontaneous circulation after out-of-hospital VF cardiac arrest 1, 8, 5

What is the evidence for induced hypothermia (therapeutic cooling) post cardiac arrest?

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