Oct. 15, 2001 DALLAS, Oct. 9 – Reducing the body temperature of someone revived from cardiac arrest is feasible and safe, but cooling time must be faster to make it a practical treatment, according to a report in today’s Circulation: Journal of the American Heart Association.
Those who are revived after cardiac arrest often suffer brain damage because the flow of oxygen to the brain was shut off for too long. "Many surviving patients are left with significant neurological disabilities," says senior author J. C. Grotta, a neurologist at the University of Texas–Houston Medical School. In animal studies, lowering body temperature (hypothermia) has consistently reduced brain injury. The sooner hypothermia begins and the longer it lasts, the less chance for severe neurological damage. Exactly how hypothermia protects the brain is unclear. However, reducing body temperature decreases the brain’s demand for oxygen, reduces the release of nerve-killing chemicals, suppresses inflammation, and stabilizes cell membranes.
Grotta and his colleagues studied nine patients whose cardiac arrests did not occur in the hospital. After acute life support, each patient was sedated and wrapped in two cooling blankets, one around the torso and the other around the pelvis and legs. The goal was to lower body temperature to 33 °C (91.4 °F) within 120 minutes after initiating cooling and maintaining that temperature for 24 hours.
Four of the patients survived, three of them without neurological disabilities. The fourth survivor went home but required 24-hour supervision due to memory problems. Achieving a body temperature of 33 °C proved a slow process taking an average of 301 minutes (1 and ½ hours) in some individuals. Initiating hypothermia in the nine patients took between 40 and 109 minutes, and averaged 78 minutes.
"Much of this time was spent obtaining informed consent," Grotta says. "An average of 46 minutes was required obtaining the patient’s or family’s consent to perform hypothermia treatment." It took an average of 391 minutes (6 ½ hours) from cardiac arrest until the patient’s temperature dropped to 33 °C. The time from hypothermia initiation to 33 °C took 90 to 690 minutes and averaged 301 minutes (5 hours). "Mild to moderate hypothermia appears feasible and safe, especially when the poor prognosis after cardiac arrest is taken into account," Grotta says. "It warrants further study, but shortening the time to hypothermia will be important in further evaluations." The team did not assess the efficacy of the technique.
The National Institutes of Health supported this research.
Co-authors are R. A. Felberg; M.D.; D.W. Krieger; M.D.; R. Chuang, D.E. Persse M.D.; W. S. Burgin; S.L. Hickenbottom, M.D.; L.B. Morgenstern; M.D. and O. Rosales, M.D.
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