The latest article in our Clinical Therapeutics series, “Targeted Temperature Management for Comatose Survivors of Cardiac Arrest,” comes from Dr. Michael Holzer at the Medical University of Vienna.
Targeted temperature management, also known as therapeutic hypothermia, is a therapeutic intervention that is intended to limit neurologic injury after a patient’s resuscitation from cardiac arrest. Hypothermia causes a reduction in brain metabolism, including a reduction in oxygen utilization and ATP consumption.
• What are the indications for therapeutic hypothermia?
Therapeutic hypothermia should be considered for adult patients successfully resuscitated from a witnessed out-of-hospital cardiac arrest of presumed cardiac cause, though patients after in-hospital cardiac arrest may also benefit. This measure should also be considered in patients who are comatose, and in patients with an initial rhythm of ventricular fibrillation or nonperfusing ventricular tachycardia (or other initial rhythms such as asystole or pulseless electrical activity).
• How is therapeutic hypothermia achieved?
Several different cooling methods are available for use in therapeutic hypothermia. In the pivotal clinical trials, cooling was achieved by the application of numerous ice packs around the head, neck, torso, and limbs or with the use of a cold-air mattress covering the entire body. Other methods of surface cooling include the use of water-circulating cooling blankets or pads, refrigerated cooling pads, and thermal beds. Core cooling can be achieved with the use of intravascular cooling catheters (made of metal or containing balloons filled with cold saline) or by means of intravenous infusion of cold fluids. The objective is to reach a target temperature of 32 to 34 degrees C and to maintain that temperature for 24 hours, if feasible.
Morning Report Questions
Q: What additional patient management is necessary before hypothermia is induced?
A: Before hypothermia is induced, sedation, analgesia, and paralysis should be initiated to prevent shivering (which can lead to increased oxygen consumption, excessively laborious breathing, increased heart rate, and a general stress-like response, in addition to impeding the cooling process) and to minimize the patient’s discomfort.
Q: What metabolic disturbances are induced by therapeutic hypothermia?
A: Hypothermia can induce metabolic disturbances, including hypokalemia, hypomagnesemia, hypophosphatemia, and hyperglycemia. Therefore, regular measurement of electrolyte and glucose levels is necessary to guide the appropriate amount of electrolyte substitution and insulin therapy. Leukopenia and thrombocytopenia may occur but typically do not require intervention.
Table 1. Indications and Contraindications for Targeted Temperature Management in Comatose Patients after Cardiac Arrest.