- Witnessed cardiac arrest with ROSC (regardless of initial rhythm)
- ROSC < 30 minutes from EMS arrival
- ROSC < 6 hours from time of hypothermia protocol initiation
- Comatose (does not follow commands)
- MAP > 65 mmHg (with no more than 1 vasopressor)
- Initial temp > 30C
- Pt is DNR, has poor baseline status or terminal disease with poor prognosis
- Acute or severe ICH
- Active bleeding or high risk for bleeding (known bleeding diathesis and/or major surgery in the past 14 days)*
- Traumatic etiology of cardiac arrest
- History of cryoglobulinemia
- Age < 18 years
*Hypothermia slows coagulation.
- Pregnant (consider Gyn consult first)
- Relatively recent major surgery (> 14 days)
- Septic etiology of cardiac arrest*
*Hypothermia depresses the immune system and slightly increases the risk of infection.
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For how long?
Patients should be rapidly cooled to the target temperature (32-34C, or 32-36C, depending on your institution’s protocol), then tightly maintained at that temperature for 12-24 hours, then gradually rewarmed.
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Why the debate about 34C vs 36C?
Back in 2002, two large trials demonstrated improved survival and brain function when post-cardiac arrest patients were cooled to 32-34C. Based on this, the American Heart Association came up with therapeutic hypothermia guidelines in 2005 that targeted 32-24C, which many hospitals around the country adopted in the 2000s. However, in 2013, a large European trial found that a target temperature of 36°C had similar outcomes. This was confirmed by a meta-analysis in 2015. This prompted the AHA to revise its guidelines in 2015 to target temperatures of 32-26C, which only some institutions have adopted so far. Others are still catching up and sticking with the original 32-24C target temperatures. Still others are targeting 32-34C, but have a separate 36C protocol for some patients who may be excluded by the original AHA criteria from 2005 (for instance, see the University of Pennsylvania protocol).
- First, insert a Foley catheter with a temperature probe. If the patient cannot receive a Foley, consider an esophageal or rectal temperature probe instead. A combination of surface and internal cooling is then initiated.
- Surface cooling is achieved with the Arctic Sun device (or other temperature management device) with a set target temperature of 32-36C on Automatic Mode.
- Inter cooling is achieved with a cold Normal Saline infusion, which is stopped once the target temperature is reached OR once 30ml/kg total IV bolus has been given. Cold NS is stored at 4.4C in the med room refrigerator.
MAINTENANCE
- Tightly control the patient’s temperature for 12-24 hours using a combination of the Arctic Sun, cold NS infusion, or a cooling blanket (if the Arctic Sun or other similar device is not available).
- Watch out for hypotension, hypokalemia, and shivering.
- Stop cooling and start rewarming immediately if the patient develops dysrhythmia or severe bleeding.
- Repeat vital signs (including core temperature) every hour.
- Hypothermia tends to cause hyperglycemia, so perform serial fingersticks and maintain the blood glucose at <140.
REWARMING
- Unlike cooling, rewarming should be gradual and take place over 8-24 hours. If the patient is stable, simply reset the Arctic Sun at 37C with a rewarming rate of 0.1C/hr. If the patient develops hemodynamic instability, dysrhythmia, or severe bleeding while being cooled, start rewarming to 37C immediately at a rate of 0.3C/hr.
- Meperidine (50 mg IV q 6 hrs)
- Buspirone (30 mg po q 8 hrs)
- Sedation (midazolam, fentanyl, propofol, lorazepam)
- Neuromuscular blocker (vecuronium 0.1 mg/kg bolus; cisatracurium infusion 0.15 mg/kg bolus followed by 1-10 mcg/kg/min infusion)
Keep in mind that using a neuromuscular blocker can hide seizure activity, so use your best judgement. Rapid on/off sedation medications are preferable to permit serial neuro checks.
Thank you to Dr. Greg Fernandez for inspiring this Pearl. Stay cool.
