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A Rhonda Anderson, RN, MSN, CCRN, replies:
Mild hypothermia is considered a class IIa recommendation by the American Heart Association for unconscious, adult patients with return of spontaneous circulation (ROSC) after out-of-hospital ventricular fibrillation (VF) cardiac arrest. Other patients experiencing out-of-hospital non-VF arrest or an in-hospital arrest may find similar benefits with this type of postresuscitative support as well (class IIb).1
Patient Selection
For patients to be considered for induced hypothermia, time of collapse to ROSC should be less than 1 hour, with the time to the initiation of hypothermia within the first 6 hours after ROSC. In addition, these patients should be at least 18 years of age; be able to maintain a blood pressure with or without vasopressors after cardiopulmonary resuscitation; and be comatose within 6 hours after cardiac arrest (nonperfusing ventricular tachycardia or VF). Coma is defined as not following commands, no speech, no eye opening, and no purposeful movements to noxious stimuli. Brainstem reflexes and pathological and/or posturing movements are permissible.
Induced hypothermia for pulse-less electrical activity, asystole arrest, or in-hospital arrest has not been studied, but may be applied at discretion of the treating physician. This intervention is not recommended for patients with an isolated respiratory arrest.2–4
Exclusion Criteria
For some patients, induced hypothermia may pose an increased risk. These patients include those with the following:
Goal
The goal of induced hypothermia in patients who have had a cardiac arrest is to reach a core body temperature of 33°C to 34°C in 6 to 8 hours.3–5
Methods
If using a "conventional" approach, obtain 2 cooling blankets and cables (1 machine) to "sandwich" the patient. A sheet should be placed between each blanket and the patient to protect the skin. Pack the patient’s groin, neck, and axilla with ice bags and replace these frequently to aid in reaching the goal temperature as quickly as possible. Monitor the core body temperature continuously via a bladder or Foley catheter probe, rectal probe, or pulmonary artery catheter to aid in achieving the target temperature and to avoid "overshooting." Once the goal is met, remove the ice packs and maintain the temperature with blankets alone.3–5
If using an endovascular approach, prepare the system per the operation manual once the central venous catheter has been inserted (a femoral catheter is preferred because it has 3 balloons and more surface area) and initiate cooling by connecting the heat exchange balloon ports of the catheter to the tubing and begin treatment at the maximum rate. The patient’s core temperature will be continuously monitored throughout the procedure.
In order to facilitate cooling in both the conventional and endovascular methods, cold sodium chloride (4°C) at 30 mL/kg up to 2 L may be infused over 30 minutes via a peripheral or femoral intravenous catheter.6
Monitoring
Vital signs should be documented every 30 minutes during induction, then every hour once the goal temperature has been met. Vital signs should also be documented during the rewarming phase. Complete blood cell count, prothrombin time, partial thromboplastin time, international normalized ratio, chemistries, magnesium, and arterial blood gas values should be monitored every 12 hours during rewarming until the patient is normothermic.
Shivering Management
Shivering is a normal response in an attempt to maintain home-ostasis, but it is uncomfortable and it generates heat, thereby impairing the ability to achieve the goal temperature. Therefore, shivering must be controlled. If using the conventional approach or an external cooling device, neuromuscular blocking agents will be necessary to control the shivering, along with continuous sedation and analgesia. If endovascular methodology is used, continuous sedation and analgesia will be required with neuromuscular blocking agents, either on an as-needed basis or as a continuous infusion depending on the individual patient. If using endovascular cooling, the nurse can use warm blankets on the patient, especially the head, hands, and feet to help with the shivering and can keep the tubing out of contact with the skin.
Rewarming Phase
After the treatment time is completed (18–24 hours), the patient should be rewarmed slowly. The literature recommends that the patient be rewarmed at 0.5°C to 1.0°C an hour. It will take approximately 8 hours to rewarm the patient. Sedation, paralysis, and analgesia must be continued during this phase.
If conventional therapy is used, remove the cooling blankets (and ice bags) and place blankets on the patient. Continue to monitor the body temperature. If the endovascular therapy is used, set the goal temperature and the desired rate at 0.5 degrees per hour and begin warming. Once normothermia is achieved (37°C), the neuromuscular blocking agent can be discontinued and sedation dose can be decreased by 50%, and then titrated down slowly until off.3,4
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References
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