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
• Cooling to 32-34ºC was found in initial studies, current studies suggest 36ºC to have same benefits
• Therapeutic hypothermia does not appear to provide a survival or improved neurological benefit in the pediatric population
• Therapeutic hypothermia should be initiated immediately after ROSC, and patient may be cooled concurrently with cardiac catheterization
• Cooling should occur prior to CT scan if there is need for intracranial pathology workup
• AHA recommends 12-24 hrs of cooling
• NNT of ~6

Indications

• V-fib arrest
• Other pulseless dysrhythmias (relative)

Contraindications/Exclusions

• >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
  • Drug overdose
  • Status epilepticus
• Sepsis as etiology for arrest
• DNR/DNI status, terminal illness
• Uncontrollable bleeding or known bleeding diathesis with active bleeding
• Significant trauma (especially intra-abdominal)
• Pregnancy
• Therapeutic hypothermia may be safe for postpartum cardiac arrest

Cooling

• Cool to 32-34ºC as soon as possible (within 4 hours)
  • Strict maintenance of temperature at 36ºC may have similar benefits
• Initiate rewarming 24 hrs after target temperature was reached
• Cooling methods
  • Maintain at 32-34ºC with 2 cooling blankets to sandwich the pt, with sheets covering the blankets to protect skin
  • Alternatively, use heat exchange device (Icy Cath) or 4°C IVF at 30 cc/kg over 30 min
  • Cooling pads on the thighs and abdomen (Arctic Sun)
  • Supplement with ice packs to groin, chest, axillae, neck until 34ºC reached
• Prevention of shivering and paralysis

Maintainance

Sedation

• Fentanyl Injection 50 mcg IV every hour as needed for pain
• Fentanyl IV infusion NSS
• Propofol IV infusion
• Lorazepam IV infusion
• Lorazepam Injection 1mg IV every 2 hours as needed for agitation

Shivering

• 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
• Consider meperidine q2hrs:
  • 50mg for normal renal function
  • 25mg if CrCl < 30ml/min
• Pancuronium IV infusion
  • Initiate before initiating cooling. Dosing recommendations: 0.1mg/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
• Cisatricurium for renal/hepatic impairment
  • 0.2mg/kg IV bolus
  • Followed by infusion at 1 mcg/kg/min, max of 3 mcg/kg/min

Rewarming

• If severe dysrhythmia/BP instability/bleeding develops, rewarm pt
• Discontinue K infusions (extracellular K increases)
• Keep paralytic and sedative until rewarmed
• Slow rewarm at 0.5°C to target of 36°C

General Management

Other Concerns

• Head of bed at 30 degrees
• Goal MAP 80 - 100 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%
  • IV NTG starting at 10 mcg/min if hypertensive
• Check skin q2-6 hrs for cold injury
• Maintain tight BG control, 110-150mg/dL
• Replete K, Mg, Phos, Ca (hypothermia induced diuresis is expected)
• Common unconcerning ECG findings during cooling - Osborne wave, HR < 40 bpm
• Consider continuous EEG within 6 hrs, no later than 12 hrs after onset of cooling
• Stress dose steroids for adrenal insufficiency

Labs

• ABG q6 hrs for duration of hypothermia
• CBC, Coags, BMP, Mg, Phos q6 hrs for duration of hypothermia
  • Expect decreased K, Ca, Mg, Phos during, and rebound at rewarming
  • Hyperglycemia as metabolism slows at low temperature and body develops insulin resistance
• Troponins, CK-MB q6 hrs x2 days
• Lipase, LFTs (if abnormal, no need to intervene unless persistent after rewarming)
• Other - Cortisol, UA, Pan-cultures, tox screen

ABG Interpretation

• Rewarm ABG to 37 ℃ for analysis
• If not rewarmed, the following are seen for every 1°C below 37°C:
  • PO2 overestimated by 5 mmHg
  • PCO2 overestimated by 2 mmHg
  • pH underestimated by 0.012

Monitoring

• ECG q8 rule out ACS
• Arterial line
• Foley with temperature probe
• CVP, ScvO2

Imaging

• Consider head CT
• Consider CTPE study

Disposition

• ICU admission

External Links

• Focus On: Therapeutic Hypothermia
• EMRAP:Therapeutic Hypothermiawith Amal Mattu, MD FAAEM

See Also

{{HypothermiaCardiac Arrest Links}}

References

Authors

Ross Donaldson