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Studies examine location, temperature of therapeutic hypothermia for cardiac arrest
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DALLAS — Among patients undergoing cardiac arrest who received therapeutic hypothermia, there was no difference in outcomes based on prehospital cooling vs. in-hospital cooling, nor based on temperature management of 33°C vs. 36°C, according to data presented at AHA 2013.
Prehospital cooling did not improve outcomes
Francis Kim
Francis Kim, MD, and colleagues investigated whether prehospital cooling improved outcomes after resuscitation from cardiac arrest in patients with and without ventricular fibrillation (VF). The primary outcomes were survival to hospital discharge and neurological status at discharge.
Adults in King County, Washington, who had prehospital cardiac arrest and were resuscitated by paramedics (n=1,359; 583 with VF) between December 15, 2007, and December 12, 2012, were randomly assigned to receive standard care with or without prehospital cooling. Prehospital cooling to 34°C was performed by infusing up to 2 L of 4°C normal saline following return of spontaneous circulation.
Kim, of the University of Washington, Seattle, and colleagues found that survival to hospital discharge was similar between the two groups. In patients with VF, the intervention group had a survival rate of 62.7% (95% CI, 57-68) compared with a rate of 64.3% (95% CI, 58.6-69.5) for the control group (P=.69). In patients without VF, the survival rate for the intervention group was 19.2% (95% CI, 15.6-23.4) compared with 16.3% (95% CI, 12.9-20.4) for the control group (P=.3).
The rate of full neurological recovery or mild impairment at discharge was also similar between the groups. In patients with VF, 57.5% (95% CI, 51.8-63.1) of the intervention group had good neurological status compared with 61.9% (95% CI, 56.2-67.2) of the control group (P=.69). In patients without VF, the rates of improved neurological status were 14.4% (95% CI, 11.3-18.2) for the intervention group and 13.4% (95% CI, 10.4-17.2) for the control group (P=.3).
The intervention group experienced rearrest in the field more often than the control group (intervention group, 26%; 95% CI, 22-29; control group, 21%; 95% CI, 18-24; P=.008).
“Prehospital cooling does not add benefit to hospital-initiated cooling,” Kim said at a press conference. “Cold fluid has associated risks, and our study findings do not support routine initiation of hypothermia using cold fluid in the prehospital setting.”
Different temperatures produced similar outcomes
Niklas Nielsen*
In the Targeted Temperature Management (TTM) study, Niklas Nielsen, MD, PhD, and colleagues compared outcomes of patients cooled at 33°C and 36°C following out-of-hospital cardiac arrest. International guidelines recommend therapeutic hypothermia to 32°C to 34°C for 12 hours to 24 hours, but the optimal target temperature has not been determined, Nielsen said at a press conference.
Nielsen, of Helsingborg Hospital, Helsingborg, Sweden, and colleagues randomly assigned 950 unconscious adults after out-of-hospital cardiac arrest to receive targeted temperature management at either 33°C or 36°C. “Both levels avoid fever, which is a common feature in cardiac arrest patients,” Nielsen told Cardiology Today.
The primary outcome was all-cause mortality through the end of the trial, which occurred 180 days after the enrollment of the last patient. Secondary outcomes included poor neurologic function or death at 180 days. Poor neurologic function was assessed by the Cerebral Performance Category scale and the modified Rankin scale.
By the end of the trial, 50% of the patients in the 33°C group died vs. 48% of the patients in the 36°C group (HR with 33°C=1.06; 95% CI, 0.89-1.28).
At 180 days, 54% of the patients in the 33°C group died or had poor neurologic function as per the Cerebral Performance Category scale compared with 52% of the patients in the 36°C group (RR=1.02; 95% CI, 0.88-1.16). The rate for death or poor neurologic function using the modified Rankin scale was 52% in both groups (RR=1.01; 95% CI, 0.89-1.14). Adjustment for known prognostic factors did not change the results.
“Earlier trials, which were the basis for the current guidelines, did not treat fever in the control group, so we did not know if the reported effect was a result of hypothermia to 33°C, or just avoiding the fever that is very common in post-cardiac arrest patients,” Nielsen said. “After the TTM trial, we can conclude that the lower temperature might not be needed, and that survival and neurological recovery is as good when the patients are treated at a temperature that is closer to the normal body temperature. We believe that current guidelines must take these findings into consideration when they are updated.”
For more information:
Kim F. LBCT. 01. Acute cardiovascular and cerebrovascular care. Presented at: the American Heart Association Scientific Sessions; Nov. 16-20, 2013; Dallas.
Kim F. JAMA. 2013;doi:10.1001/jama.2013.282173.
Nielsen N. LBCT. 01. Acute cardiovascular and cerebrovascular care. Presented at: the American Heart Association Scientific Sessions; Nov. 16-20, 2013; Dallas.
Nielsen N. N Engl J Med. 2013;doi:10.1056/NEJMoa1310519.
Disclosure: Kim and Nielsen report no relevant financial disclosures.
*Photo by Gustav Wiking