Cooling patients who have been hospitalized after a heart attack has emerged as a promising strategy to protect the brain from damage related to the attack. But a study published in JAMA this week finds that cooling patients earlier, while they are being transported to the hospital, does not appear to help and may hurt.
Brain injury contributes to neurological impairment and death among many patients who have been resuscitated from a heart attack. Cooling patients who have been resuscitated from a heart attack at the hospital has been shown in clinical trials to improve survival and neurological function. But it can take hours to cool patients at the hospital and some have proposed that starting cooling in the ambulance may improve outcomes further.
To test this approach, Francis Kim, MD, an associate professor of medicine at the University of Washington, and his colleagues randomized 1359 patients who were resuscitated by paramedics from cardiac arrest either to receive usual care or to be “precooled” using intravenous (IV) administration of chilled saline by paramedics. Nearly 583 patients who had ventricular fibrillation (VF) were included in the study.
Although the cooled saline did reduce patients’ body temperatures and helped reduce the time it took patients to reach the target temperature in the hospital, the researchers found no improvement in survival or neurologic status in those cooled en route to the hospital compared with those who were not. In addition, the cooled patients had an increased risk for pulmonary edema (fluid in the lungs) and were more likely to have a rearrest and to receive diuretics. They did not find a difference between patients with VF and those without.
Dr Kim discussed the results with news@JAMA.
news@JAMA: Why did you decide to do this study?
Dr Kim: We did the study mainly because cooling is usually initiated in the hospital for ventricular fibrillation patients. But a lot of animal studies suggest that cooling needs to start as soon as possible after cardiac arrest. The paramedic usually starts an IV so cooled saline was a very feasible way for emergency medical teams to cool patients.
news@JAMA: What did the results tell you about this cooling strategy?
Dr Kim: The main findings were that the strategy of rapid cooling in the field did not improve survival or neurologic status, both for non-VF patients and VF patients. Furthermore, we saw some harm from the fluid. People who received fluid had an increase in rearrest, and they had evidence for an increased pulmonary edema, which resolved by the second day.
news@JAMA: How do these results compare with results from other studies about prehospitalization hypothermia for cardiac arrest?
Dr Kim: Ours was the largest randomized trial. There was another a few years ago by Bernard et al in Australia that randomized 234 patients with VF to cold fluid or standard care and didn’t see a significant difference in survival or neurologic outcomes. The results came out during the middle of our trial. Our study, in conjunction with the Bernard study, really doesn’t support cold fluid as a means of cooling patients with cardiac arrest in the field.
news@JAMA: Why do you think you did not find an advantage to prehospitalization hypothermia?
Dr Kim: One reason may be that the cooling technique didn’t cool patients fast enough, but it was the easiest tech to use. Cooling at the time of arrest may be even more beneficial. Perhaps the fluid caused early harm, which masked any benefit from the hypothermia. The last possibility is that prehospitalization cooling won’t improve survival or neurologic outcomes.
news@JAMA: How do you explain the harms you saw?
Dr Kim: Fluid volume load during cardiac arrest may decrease coronary artery perfusion and impair heart function. Other cooling technologies that cool the body externally may avoid this problem.
news@JAMA: What do you think is the main take-away message?
Dr Kim: This strategy of cooling with cold fluid doesn’t improve survival and should be abandoned. Further research is needed on whether cooling [during the cardiac arrest] or using other cooling technologies may be beneficial.