اشتباهات شایع در بخش آی سی یو 4
ساعت ۱:٢٠ ‎ب.ظ روز ۱۳۸٩/٤/۱٥   کلمات کلیدی: moderate hypothermia ،cardiac arrest

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Consider Moderate Hypothermia After Cardiac Arrest

Bradford D. Winters MD, PhD

Moderate hypothermia has been demonstrated to improve neurologic outcome and mortality in patients who remain comatose despite return of spontaneous circulation (ROSC) after ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT)–induced cardiac arrest. This type of event leads to global cerebral ischemia with the potential for severe anoxic or hypoxic brain injury and progression to brain death. The patient populations studied in the original trials, which demonstrated this benefit, were those who had out-of-hospital events and as such there has been considerable debate as to whether this treatment would be useful for in-hospital cardiac arrests. In-hospital cardiac arrests are often secondary to long-developing deteriorations and are often the end result of a terminal illness. This is in contrast to out-of-hospital arrests, which are usually secondary to an acute coronary event. While the data are imperfect, there is some suggestion that inpatients with witnessed arrests from VF and VT may also benefit from this treatment.

The time between the witnessed arrest and ROSC is important. ROSC may not occur promptly and there is an outer limit that should obviate initiating hypothermia. The time limit adhered to for the out-of-hospital arrests was 60 minutes from time of collapse. Most in-hospital resuscitations do not continue this long and it is unclear what the outer limit for ROSC should be for initiating of cooling for in-hospital arrests.

The earlier the cooling is initiated after return of spontaneous circulation, the better. One of the out-of-hospital studies initiated cooling in the field. The target temperature should be between 32° and 34° Celsius core temperature (based on a bladder pressure pulmonary artery catheter or other “core” temperature measurement). It is desirable to achieve the target temperature within a 2-hour time frame. How long to maintain the hypothermia is unclear. One of the two studies maintained it for 12 hours and the other for 24 hours and both showed improved outcome. Many would advocate that unless there is a contraindication to maintaining the hypothermia for 24 hours, this would be the preferred time. After this point the patient is actively rewarmed to normothermia (37° C).

During the period of hypothermia, very close attention to a wide variety of parameters needs to be maintained. Electrolytes need to be checked frequently and volume needs to be appropriately resuscitated since hypothermia can induce diuresis and electrolyte abnormalities. Shivering must be controlled, usually with sedatives and/or paralytics, as it increases myocardial oxygen demand dramatically. Cardiac dysrhythmias may occur secondary to the hypothermia as well as a result of the original cardiac insult. Some protocols use prophylactic lidocaine infusion to control this. Coagulopathy may occur, though this is generally not a problem until well below the target temperature range. Nevertheless, the prothrombin time/partial thromboplastin time should be monitored frequently. Severe vasoconstriction occurs as a result of the hypothermia and this may place additional work on the heart in terms of increased afterload. It is prudent to place a pulmonary artery catheter to monitor cardiac performance as well as volume status during the treatment and for a period of time after rewarming.

Once the patient is rewarmed, the primary issue is neurologic assessment including frequent neurologic exams, head computed tomography scan, magnetic resonance imaging, and possibly other tests such as evoked potentials to assist in prognostication for neurologic recovery. Assessment and treatment of underlying causes of the original event also need to be performed in parallel.

 

Suggested Readings

Bernard SA, Gray TW, Buist MD, et al. Treatment of comatose survivors of out-of-hospital cardiac arrests with induced hypothermia. N Engl J Med. 2002;346:557– 563.

The Hypothermia after Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. N Engl J Med. 2002;346:549– 556.