Therapeutic hypothermia

Background

• Determination of Neurologic Prognosis is unreliable before at least 72 hours after ROSC. Do not neuroprognosticate until 72 hours post rewarming.
• Greatest benefit in out-of-hospital V-fib, though evidence suggests hypothermia helps in other dysrhythmias
• Two most likely mechanisms of action:
  • Reduces cerebral metabolism by 6-8% per degree C
  • Reduces oxygen free radical production and lipid peroxidation

Exclusion/Contraindications

• >12hrs since ROSC
• Glasgow Motor score >5
• Minimal pre-morbid cognitive status
• Unable to maintain SBP > 90 mmHg, with or without pressors, after CPR
• Other reason for coma
  • intracranial pathology (i.e. intracranial hemorrhage, ischemic stroke)
  • subarachnoid hemorrhage
  • sedation
• Sepsis as etiology for arrest
• DNR/DNI status
• Uncontrollable bleeding or known bleeding diathesis with active bleeding
• Significant trauma (especially intra-abdominal)

Sedation and Paralytics

Should administer one or more of the following:

• Fentanyl Injection 50 mcg IV every hour as needed for pain.
• Fentanyl IV infusion NSS
• Propofol IV infusion
• Lorazepam IV infusion
• Lorazepam Injection 1 mg IV every 2 hours as needed for agitation.
• Pancuronium IV infusion
  • Initiate before initiating cooling. Dosing recommendations: 0.1 mg/kg loading dose followed by a continuous infusion of 0.33-2 mcg/kg/minute.
  • Do not use in patients with renal and/or hepatic insufficiency.

Prevention of shivering is important to avoid warming and needless oxygen consumption

• May require train of four monitor with goal of 1-2/4 twitches with neuromuscular blockade
• Lower doses of NMB work against shivering
• Higher doses of NMB used to paralyze the diaphragm in these scenarios:
  • Need to decrease O2 consumption
  • Decrease plateau pressures
  • Hypoxemia is present

Workup

• Labs

1. 1. ABG q6 hrs for duration of hypothermia
   2. CBC, Coags, BMP, Mg, Phos q6 hrs for duration of hypothermia (expect decreased K, Ca, Mg, Phos during, and rebound at rewarming)
   3. Troponins, CK-MB q6 hrs x2 days
   4. Lipase, LFTs (if abnormal, no need to intervene unless persistent after rewarming)
   5. Other - Cortisol, UA, Pan-cultures, tox screen

Management

• Consider head CT
• Head of bed at 30 degrees
• Goal MAP > 80 mmHg
  • Titrate with norepinephrine (start 2-4 mcg/min) if EF > 50%
  • Titrate with dobutamine (start 2.5-20 mcg/kg/min) if EF < 50%
• If life-threatening dysrhythmia/hemodynamic instability/bleeding develops, rewarm pt
• Check skin q2-6 hrs for cold injury
• Maintain tight BG control, 110-150 mg/dL (hyperglycemia in hypothermia and hypoglycemia in rewarming)
• Replete K, Mg, Phos, Ca (hypothermia induced diuresis is expected)
• Common ECG findings during cooling - Osborne wave, HR < 40 bpm not concerning in absence of hemodynamic instability
• Consider continuous EEG within 6 hrs, no later than 12 hrs after onset of cooling
• Monitor for acute adrenal insuffiency, and consider stress dose steroids

Cooling

• Cool to 32-34º C as soon as possible (within 4 hours)
• Initiate rewarming 24 hrs after target temperature was reached
• Cooling methods
  • 2 cooling blankets to sandwich the pt, with sheets covering the blankets to protect skin
  • Alternatively, use heat exchange device, per manufacturer's recs
  • Ice packs to groin, sides of chest, axillae, sides of neck until 34º C reached, and maintain with cooling blankets or heat exchange device

Disposition

• ICU admission

See Also

• Post Cardiac Arrest
• Hypothermia

Source

• University of Pennsylvania Targeted Temperature Management Protocol
• eMedicine - Adler, Jonathan et Al. Therapeutic Hypothermia.