Therapeutic hypothermia

Today we discussed a complicated case of multifocal sepsis in a patient with hypoxic ischemic injury following cardiac arrest. This provides an opportunity to discuss neurologic recovery following cardiac arrest, the role for cooling as part of post-resuscitation care and examining for coma/brain death.

Cardiopulmonary resuscitation has been around since the 1950's, but its practices weren't widely promoted until the 1970's when the promotion of CPR began in the public sector as well. Since then, it has involved from chest compressions and breathing support, to add defibrillation and consideration of advanced life support techniques. In 2012, a Cochrane review looked at several studies from the previous decades at the benefit of post cardiac arrest therapeutic hypothermia, finding it to be beneficial in terms if patient in hospital neurologic recovery and overall survival. This advantages were seen without any adverse effects. This supported the current guideline recommendations, which include therapeutic hypothermia after cardiac arrest.

Although this is not as relevant for residents rotating through internal medicine, many will at some point complete ICU, CCU, cardiology and emergency medicine rotations, where this practice is important. The basics of therapeutic hypothermia should be known, and include the following:

1. Indications
2. Implementation
3. Rewarming
4. Contraindications

Patients with cardiac arrest that do not have a purposeful movement and are not following commands after return of spontaneous circulation should be considered for therapeutic cooling. There are few contraindications. The things to recognize are the risks of coagulopathy in the bleeding patient and electrolytes shifts (particularly potassium) that can occur with cooling and rewarming. Cooling can be accomplished by many methods, including external cooling blankets, ice packs, cold IV fluids (4 degrees) or internal catheter devices. Which to choose depends on the expertise of the centre and comfort of the physician. Cold IV fluids can rapidly degrees core temperature and run the risk of pushing the patient into pulmonary edema, which should be considered if this method is chosen. Targets for therapeutic cooling are somewhat controversial. A target of 33 degrees is likely reasonable in the first 24 hours, with gradual rewarming until 48 hours is reached. Whether or not cooling should be performed for over 48 hours is unclear. A recent paper in the NEJM, found no difference in outcomes when targeting a core temperature 33 vs 36 degrees. See below for a link to the original article.

After the patient is normothermic, an assessment of neurologic status is needed to try and predict neurologic recovery. Predicting neurologic prognosis after cardiac arrest has the most literature, as compared to neurologic injury from other causes. Several systematic reviews have been performed, and found that the useful predictors include:

Absent pupillary response/absent corneal response at 72h
Absent extensor motor response at 72h

One of the original articles is linke below from Neurology.

Predicting neurologic outcome after cardiac arrest
NEJM cooling after cardiac arrest