Circulation: Cooling times & methods for cardiac arrest remain uncertain

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Cooling cardiac arrest patients with IV ice-cold solution en route to the hospital did not improve outcomes at hospital discharge compared with patients whose cooling commenced in the hospital. according to a study published online Aug. 2 in Circulation.

Therapeutic hypothermia in the hospital setting has been shown in two clinical trials to improve neurological outcomes, and laboratory studies indicate that earlier cooling produces better outcomes.

To better determine if earlier cooling improves outcomes in people, Stephen A. Bernard, MD, from Monash University in Melbourne, Australia, and colleagues in the RICH (Rapid Infusion of Cold Hartmanns) trial randomized adults to either prehospital cooling (118) with rapid infusion of two liters of ice-cold lactated Ringer's solution or cooling after hospital admission (116).

Only patients with an initial cardiac rhythm of ventricular fibrillation were enrolled and cooling was commenced only after return of spontaneous circulation (ROSC).

Not all patients in the prehospital arm received the full dose of ice-cold fluids because of the short distance to the hospital. Patients in the prehospital arm had a nonsignificant mean decrease in core temperature of 0.8°C.

The primary outcome measure was functional status at hospital discharge, with a favorable outcome defined as discharge either to home or to a rehabilitation facility.

In the paramedic-cooled group, 47.5 percent of patients had a favorable outcome at hospital discharge compared with 52.6 percent of patients in the hospital-cooled group. The difference was not significant.

Of note is that the patients in the ambulance actually warmed up from 34.4°C to 34.7°C after 60 minutes in the ED, while the patients in the control group decreased their core temperature from 35.2°C to 34.7°C.

"Obviously, the patients who received intravenous saline in the ambulance did not receive another intravenous cold saline bolus or some other method for continued cooling in the ED," wrote Lance B. Becker, MD, from the department of emergency medicine at the University of Pennsylvania in Philadelphia.

Noting that it took six to eight hours to lower both groups' temperatures by only 0.4°C to the target of 34°C," Becker said, "[It] is a stark reality check on the difficulty of cooling protocol implementation in the real world, even in the more controlled setting of EDs and hospitals."

Bernard and colleagues concluded that more research needs to be conducted regarding starting cooling during cardiopulmonary resuscitation (CPR).

Interestingly, in another study published Aug. 2 online in Circulation, researchers found that prehospital intra-arrest transnasal cooling is safe and feasible and is associated with a significant improvement in the time intervals required to cool patients.

Maaret Castrén, MD, from the Karolinska Institute in Stockholm, Sweden, and colleagues evaluated all cardiac arrest patients, irrespective of rhythm, before ROSC. Researchers were part of the multicenter PRINCE (Pre-ROSC IntraNasal Cooling Effectiveness) study.

They randomized 96 patients to the treatment group (RhinoChill, BeneChill) and 104 to the control group. Both groups were cooled after hospital arrival.

Eighteen device-related adverse events were reported: one periorbital emphysema, three epistaxis (one serious), one perioral bleed and 13 nasal discolorations.

The treatment group reached their target temperature in a shorter amount of time for both tympanic (102 vs. 282 minutes) and core (155 vs. 284 minutes) temperatures.

Researchers found no significant differences in ROSC between the two groups, in overall survival of those admitted alive, or in neurologically intact survival to discharge, although the study was not adequately powered to detect changes in these outcomes, they wrote.

In a subgroup analysis of patients with ventricular fibrillation, the absolute improvement in survival rate was 15 percent for transnasally-cooled patients.

In a post hoc analysis of the subgroup of patients in whom CPR was initiated by EMS personnel within 10 minutes of collapse, researchers found significantly improved survival, with a 27 percent absolute increase over patients who received hospital cooling alone.

In the same subgroup with early CPR, neurologically intact survival at discharge was also significantly higher in intra-arrest cooled patients, with an absolute increase of 26 percent over control subjects.

"Although the numbers are too small to reach significance, they provide some tantalizing cooling rates and survival trends that suggest that improved outcomes from intra-arrest nasal cooling may be found in a larger clinical trial," Becker wrote.

The RhinoChill system is not yet for sale in the U.S.