Abstract 1: A Novel Method for Rapid Therapeutic Hypothermia Induction Using Transnasal High-Flow Air
Abstract: Early induction of hypothermia improves survival in out of hospital cardiac arrest. We investigated the ability of high flow transnasal ambient dry air to induce hypothermia in porcine subjects.
Methods: Eighteen adult pigs (wt. ∼80 pounds) were intubated and mechanically ventilated. Core body temperature (Tc) was measured in the right atrium and brain temperature (Tb) was monitored by thermocouples in the frontal, parietal and occipital lobes. Dry air was delivered via nasal cannula. The effect of airflow rate, temperature and humidity of the air on the brain and body temperature was investigated. Temperature gradients in the brain were measured using MR thermography.
Results: Transnasal air caused a flow dependent decrease in Tb and Tc in all animals. Over a 30 min exposure to transnasal dry air at flow rates of 80 LPM, Tb decreased from 36.1 ± 0.3 C to 31.5 ± 0.7 C and Tc decreased from 37.1 ± 0.4 C to 32.5 ± 1.7 C (p<0.001 for both) (Figure 1a). Rate of temperature decline was significantly higher at 80 LPM compared with 40 LPM (0.3 ± 0.1 C/min vs. 0.1 ± 0.2 C/min respectively, p <0.01). Outflow air from the mouth was significantly more saturated (76 ± 16 % vs 3 ± 2 %, p<0.001) and warmer (21.6 ± 0.9 C vs 27.8 ± 1.1 C, p<0.01) compared to inflow air. Humidifying the transnasal air to 100% saturation significantly mitigated the cooling effect. MR thermography demonstrated uniform global brain cooling without gradient from nasopharynx suggestive of cooling via circulation instead of conductive cooling (figure 1b). No adverse hemodynamic or ventilatory effects were observed in the animals.
Conclusions: We have demonstrated a novel cooling method that simply uses transnasal dry ambient air to cause evaporative cooling of the brain and the body with no significant adverse effects in pigs. Clinical studies using this method of rapid induction of hypothermia in human subjects post cardiac arrest and traumatic brain injury will be actively pursued.
- © 2012 by American Heart Association, Inc.