Therapeutic hypothermia
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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 may help 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 in initial studies, current studies suggest 36ºC equally beneficial[2]
- Treatment should be initiated immediately after ROSC
- 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
- Pediatrics[3][4]
- Two large RTCs for TH, one in out-of-hospital and another in in-hospital arrests
- Therapeutic hypothermia does not appear to provide a survival or improved neurological benefit[5]
- In both studies, no difference in survival, function at 12 months post-arrest, blood product use, infection rates
Indications
- Vfib 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[6]
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
- Use benzodiazepines
- Paralytics only if needed, and ensure patient fully sedated
Maintenance
Sedation
- Fentanyl bolus 50 mcg IV every hour as needed for pain
- Fentanyl IV infusion NSS
- Propofol IV infusion
- Lorazepam IV infusion
- Lorazepam bolus 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[7][8]:
- 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
- Cisatracurium for renal/hepatic impairment
- 0.2mg/kg IV bolus
- Followed by infusion at 1 mcg/kg/min, max of 3 mcg/kg/min
- Columbia University anti-shivering protocol
Rewarming
- If severe dysrhythmia/BP instability/bleeding develops, rewarm
- 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 nitroglycerin starting at 10 mcg/min if hypertensive
- Check skin q2-6 hrs for cold injury
- Maintain normoglycemia
- Do not treat hyperglycemia aggressively, as enzymatic functions are decreased at low temperatures, and rebound hypoglycaemia possible with rewarming
- 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
- ?Seizure prophylaxis
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 37C for analysis (controversial)
- A warmed ABG from a hypothermic patient will show a higher PaO2, higher PaCO2, and a lower pH than that actually present in the patient’s blood in vivo
- PaO2 is decreased by 5 mmHg for each degree below 37C
- PaCO2 is decreased by 2 mmHg for each degree below 37C
- Change in pH = 0.015 pH units per degree C change in temperature
- If measured pH is 7.360 at 37C, then the pH at 34C is calculated as follows:
- pH = [7.360 + (37-34)(0.015)] = 7.405
- If measured pH is 7.360 at 37C, then the pH at 34C is calculated as follows:
Monitoring
- ECG q8 rule out ACS
- Arterial line
- Foley with temperature probe
- CVP, ScvO2
Imaging
- Consider head CT
- Consider CTPE study
Other Considerations
- GI prophylaxis
- Modify prophylactic heparin or LMWH dosing as there is hypothermic coagulopathy[9]
- No clear best way for monitoring of anticoagulation until further studies
- Consider modified dosing:
- Heparin 40 units IV bolus
- Followed by 7 u/kg/hr during TH with scheduled repeated coags, plus or minus heparin levels
Disposition
- ICU admission
External Links
- Focus On: Therapeutic Hypothermia
- EMRAP:Therapeutic Hypothermiawith Amal Mattu, MD FAAEM
See Also
Hypothermia Cardiac Arrest Links
References
- ↑ Nolan, et al. Therapeutic HypothermiaAfter 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
- ↑ Moler FW et al. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med 2017; 376:318-329January 26, 2017.
- ↑ Moler FW et al. Therapeutic Hypothermia after Out-of-Hospital Cardiac Arrest in Children. N Engl J Med 2015; 372:1898-1908May 14, 2015.
- ↑ Mosler FW, et al. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Eng J Med. 2015; 372:1898-1908.
- ↑ Song et al. Safely completed therapeutic hypothermia in postpartum cardiac arrest survivors. Am Jour Emer Med. June 2015. Volume 33, Issue 6, Pages 861.e5–861.e6.
- ↑ Choi HA, Ko SB, Presciutti M, et al. Prevention of Shivering During Therapeutic Temperature Modulation: The Columbia Anti-Shivering Protocol. Neurocrit Care. 2011; 14(3):389-394.
- ↑ Fox Chase Cancer Center. Therapeutic HypothermiaProtocol. University of Pennsylvania. https://www.med.upenn.edu/resuscitation/docs/protocols/FoxChaseCancerCenterTherapeuticHypothermiaOrderSetafterCardiacArrest-latestrevision8-4-11.doc
- ↑ Wahby KA et al. Heparin dosing in critically ill patients undergoing therapeutic hypothermia following cardiac arrest. Resuscitation. 2014 Apr;85(4):533-7.