Literature Review: Transnasal Cooling in Cardiac Arrest

   Castrén M, Nordberg P, Svensson L, et al. Intra-arrest transnasal evaporative cooling: A randomized, prehospital, multicenter study (PRINCE: Pre-ROSC IntraNasal Cooling Effectiveness). Circ 122(7): 729–36, Aug 17, 2010.

ABSTRACT

   Transnasal evaporative cooling has sufficient heat transfer capacity for effective intra-arrest cooling and improves survival in swine. The aim of this study was to determine the safety, feasibility and cooling efficacy of prehospital transnasal cooling in humans and to explore its effects on neurologically intact survival to hospital discharge.

   Methods and Results--Witnessed cardiac arrest patients with a treatment interval less than or equal to 20 minutes were randomized to intra-arrest cooling with a RhinoChill device (treatment group, n=96) versus standard care (control group, n=104). The final analysis included 93 versus 101 patients, respectively. Both groups were cooled after hospital arrival. The patients had similar demographics, initial rhythms, rates of bystander cardiopulmonary resuscitation and intervals to cardiopulmonary resuscitation and arrival of advanced life support personnel. Eighteen device-related adverse events (1 periorbital emphysema, 3 epistaxis, 1 perioral bleed and 13 nasal discolorations) were reported. Time to target temperature of 34°C was shorter in the treatment group for both tympanic (102 vs. 282 mins., p=0.03) and core (155 vs. 284 mins., p=0.13) temperature. There were no significant differences in rates of return of spontaneous circulation between the groups (38% in treated subjects versus 43% in control subjects, p=0.48), in overall survival of those admitted alive (44% versus 31%, respectively, p=0.26), or in neurologically intact survival to discharge (Pittsburgh Cerebral Performance Categories scale 1 to 2, 34% vs. 21%, p=0.21), although the study was not adequately powered to detect changes in these outcomes.

   Conclusions--Prehospital intra-arrest transnasal cooling is safe and feasible and is associated with a significant improvement in the time intervals required to cool patients.

COMMENT

   The medical evidence suggests that therapeutic hypothermia in the treatment of cardiac arrest patients improves survival. What is still unknown is which patients will benefit and when and how to cool them. The two original trials from 2002 started cooling in the hospital. Laboratory studies have suggested that earlier cooling may further improve outcomes, and intra-arrest cooling may provide even greater benefit.

   This is one of two hypothermia articles in the August edition of Circulation. The other, "Induction of Therapeutic Hypothermia by Paramedics After Resuscitation From Out-of-Hospital Ventricular Fibrillation Cardiac Arrest: A Randomized Controlled Trial" (by Stephen A. Bernard, MD, et al), found that patients infused with chilled saline by prehospital personnel had body temperatures 0.8°C (1.4°F) lower upon emergency department arrival. However, their temperatures were the same as control patients' within an hour, and outcomes were the same: 47% of the prehospital-initiated cooling and 53% of the hospital-initiated cooling patients survived to discharge to home or a rehabilitation facility. The authors noted that one challenge was that the relatively short transport times in their metropolitan area limited the amount of fluid administered: Fewer than half of patients received the full 2,000 ml.

   This study examines the effect of a novel transnasal cooling device. A liquid coolant/oxygen mixture is sprayed into the nasal cavity, and the liquid is rapidly evaporated with high-flow oxygen, causing cooling of the nasal passages and brain. Patients on whom this was used arrived at the ED 1.3°C (2.3°F) cooler than control patients, and their target temperature of 34°C was reached two hours sooner. Patient outcomes trended better: For those patients found in ventricular fibrillation, 63% survived, versus 48% in the control group. However, because of the small size of the study, no definitive conclusions can be made.

   Intranasal cooling has several potential advantages. It is relatively noninvasive and simple to administer. Whereas iced saline has been shown in animal studies to reduce coronary perfusion pressure, NP cooling does not, so it can be used sooner--during resuscitation. It may also be particularly protective of the brain and improve neurological outcome, a particular concern in post-arrest patients.

   Although intriguing, these studies are not the final answer on whether prehospital hypothermia is helpful or, if so, which method is superior. The jury is still out. And, even if we find it is beneficial, hypothermia will remain only one step in the sequence of cardiac arrest care. It will still be critically important to maintain and improve upon the basic foundation of this care: rapid response, continuous high-quality CPR and prompt defibrillation.

   Angelo Salvucci, Jr., MD, FACEP, is medical director for the Santa Barbara County and Ventura County (CA) EMS agencies.