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A new technique of localized brain hypothermia to produce cooling by adiabatic gas expansion is an emerging strategy for brain protection in out-of-hospital cardiac arrest (OHCA) and stroke. Two approaches can be considered to achieve this goal: fossa nasalis up to the nasopharynx and mouth up to the oropharynx. The purpose of our study is to compare the possible respective benefits, risks and limitations of these two approaches.
22 cadavers obtained from the “School of surgery” of Assistance Publique des H?pitaux de Paris mean age 77 ± 11.4 SD (56-96 years old) were studied after getting the ethic approve. One case was not valid because of major clots in both fossa nasalis. Slightly curved brass tubes (4mm2) were inserted perpendicular to the head axis in the two nostrils up to block. Depth of penetration in cm was measured on both sides of the nasal septum.
Depth of penetration was mean 10.8 ±1.47 SD (7-13) for the right nostril and 10.7 ±1.46 for the left nostril, this difference was not significant (P = 0.7). However, the difference in depth was 0.1 ±1.28 cm. A difference P≥ 0.5 cm was observed in 6 cases (27%). Nasalis fossa is closer to the brain; however, distortion of the nasal septum may reduce penetration in 27% of patients. This may explain that cases of epistaxis have been reported by Castren et al (Circulation 2010) using cooling by evaporation of PerFluoroCarbon (PFC) in a flow of Oxygen. In addition, if the angle of introduction is not perpendicular to the head axis as it should be but follows the direction of the nose a blockage always occurs before entering the target area. This could reduce the effectiveness of cooling and subsequently the success of the brain protection in OHCA and stroke. Mouth approach is easy to access, no block is observed up to the oropharynx, and can be used by a lay person with no training with no risk of injury. In addition, mouth and tongue offer a large surface exchange area which can be important for general cooling (in addition to localized cooling) for the protection of the heart and other noble organs as the liver, kidney and the lungs. However, oropharynx is more distant from the brain than nasal cooling. Therefore, cold produced will take longer time to reach the brain area. This has been studied by a special technique of infrared imaging on severed pig heads and also on alive pigs showing a delay of 4′30′′ longer with mouth injection as compared to nose (Fontaine EHRA Poster presentation 2015). However, this limitation can be counterbalanced by faster administration of cooling before EMS arrival on the field.
Mouth approach is less aggressive than nasal approach for cooling the posterior part of the head and more specifically the brain, for the treatment of OHCA and stroke. It can be performed by non-CPR trained bystanders with minimal training and therefore start before the intervention of fire brigade and emergency medical services.