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A7223 - Improvement of Surfactant Activity by Hypothermia in Asphyxiated Neonates with or Without Meconium Aspiration Syndrome
Author Block: C. Autilio1, M. Echaide2, D. De Luca3, J. Perez-Gil2; 1Biochemistry and Molecular Biology, Faculty of Biology - UCM, Madrid, Spain, 2Biochemistry and Molecular Biology, Faculty of Biology - UCM, MADRID, Spain, 3A. Béclère” Medical Center, Paris, France.
Rationale. Whole-body hypothermia (WBH) is used to improve neurological outcomes in perinatal asphyxia. Cooling is applied at a servo-controlled temperature of 33.5°C, starting earlyafter birth and continuing for the following 72 hours. Recent studies have suggested a beneficial effect of WBH in some types of acute respiratory failure. In a previous study, we showed improved interfacial adsorption of surfactant after 48h of hypothermia using a test that assesses surfactant accumulation into the air/liquid interface. We also demonstrated an improvement in surfactant activity of a cooled baby whose amniotic fluid was meconium stained. On this basis, we have conducted a biophysical study by captive bubble surfactometry (CBS) of surfactant from asphyxiated neonates with or without meconium aspiration syndrome (MAS) to better define the effect of WBH on surfactant function and to investigate on short term physiological adaptations that may be relevant in surfactant behaviour.Methods. Non-bronchoscopic bronchoalveolar lavage (BAL) has been collected from 10 asphyxiated neonates (2 with MAS, 8 without lung disease) at different time-points (pre-WBH, 24h, 48h, 72h of WBH and post-WBH). Surfactant was precipitated and tested by CBS in triplicate, at 37°C and 33.5°C, through initial adsorption and dynamic compression-expansion cycling. Choline and cholesterol were assayed using enzymatic methods. Results. Minimum surface tension under dynamic cycling was significantly lower at 33.5°C than at 37°C: the difference was evident after at least 48h of WBH and remained significant 6h after rewarming (48h: p=0.031; 72h: p=0.015; rewarming: p=0.002). Total cholesterol showed a trend to decrease during WBH. Similar results were obtained in MAS patients who experienced the best oxygenation and gas exchange when surface tension and cholesterol were maximally reduced.Conclusions. Surfactant biophysical properties improve after 48h of WBH in asphyxiated neonates and the improvement is maintained shortly after rewarming. Total cholesterol content in surfactant showed a trend to decrease during WBH, suggesting that the improvement may be partially explained by a time-dependent structural reorganization and/or a compositional adaptation of surfactant under hypothermia. Similar changes, especially in cholesterol concentration, have been already described during adaptive variations of surfactant in hibernating animals.