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^[1]
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^[2]
Therapeutic hypothermia does not appear to provide a survival or improved neurological benefit in the pediatric population^[3]
NNT of ~6

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

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)
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

Rewarm ABG to 37 ℃ for analysis
If not rewarmed, the following are seen for every 1°C below 37°C^[4]:
- PO2 overestimated by 5 mmHg
- PCO2 overestimated by 2 mmHg
- pH underestimated by 0.012

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 HTN
Check skin q2-6 hrs for cold injury
Maintain tight BG control, 110-150 mg/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

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 - pancuronium at 0.1 mg/kg load, follow with 1 mcg/kg/min infusion (cisatracurium if renal or hepatic impairment)

↑ Nolan, et al. Theraupeutic Hypothermia After Cardiac Arrest. Circulation. 2003; 108: 118-121.
↑ Nielsen N, et al. Targeted Temperature Management at 33°C versus 36°C after Cardiac Arrest. N Engl J Med. 2013; 369:2197-2206. DOI: 10.1056/NEJMoa1310519
↑ Mosler FW, et al. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Eng J Med. 2015; 372:1898-1908.
↑ Kaji, Amy; Ostermayer, Daniel (2015-04-01). The Kaji Review: Emergency Medicine Clinical Question Book (Kindle Locations 717-722). WikEM Press. Kindle Edition.

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