Abstract 98: New Technique of Gas Adiabatic Expansion for Brain and General Hypothermia in Rabbit
Background: Irreversible brain damage is a major issue in the acute treatment of OHCA. Brain protection by fossa nasalis cooling on the field has been reported. We propose a new technique to produce cooling by adiabatic gas expansion. Preliminary in vitro and animal studies have demonstrated that Carbon Dioxyde was able to produce significant cooling. The purpose of this work was to quantify the amount of cooling produced by this method on a rabbit model.
Method: Study population consisted of 8 New-Zealand rabbits 3.5 kg studied under ketamine anesthesia without ventilation. Three lead ECG were displayed and sampled. Temperatures in °C, were measured by thermocouples every minute: close to the injector exit located inside a 12mm Ø, 2mm thick PVC canula inserted in the mouth up to the oropharynx, in the mouth close to the canula, in the nasopharynx (equivalent to tympanic) and in the rectum. Temperature curves were displayed on line on a computer screen. Data were processed by Statistica v6.0. A p value ≤ 0.05 was considered as significant. After stabilization of temperatures, gas regulated at around 500 psi was delivered during a period of 13 ± 2.7 min and expanded at the exit of the injector.
Results: The initial 90% drop of temperature was obtained near the injector in 3 ± 1.47 minutes. The table below compares the temperatures recorded at the Start of cooling and at the End of this experiment.
A significant low temperature was observed near the injector (-16.9°C), the nasopharynx (37.7°C) and the oropharynx (31.2°C). A tendency not reaching statistical significance was obtained on the core temperature (39.4°C).
No adverse side effect was observed during and after the experiment especially no injury to the throat by direct visual inspection.
Discussion: Core temperature drop was similar to that reported in pigs after nasopharynx PFC evaporation (Yu et al Crit Care Med. 2010). The lowest temperature (-16.9°C) was recorded as expected at the exit of gas, however, oral and nasal temperatures remained within tolerable values. Stronger effect on nasal temperature can be due to better mechanical contact of the canula against the upper oropharynx wall. Non-significant core cooling was probably due to the limit imposed by distance despite normal blood circulation. Nevertheless, a clear tendency was obtained as previously observed with other techniques of fossa nasalis cooling.
Conclusion: This study demonstrates for the first time that carbon dioxyde adiabatic expansion in the mouth is effective for brain and body hypothermia in a rabbit model. This new technique which is simple, not expensive and easy to use by a lay person opens new vistas for the treatment of OHCA which can be started intra-arrest before CPR.
- © 2012 by American Heart Association, Inc.