1636 MEAN AIRWAY PRESSURE-SIGNIFICANCE DURING ASSISTED VEN-TILATION

Abstract

Mean airway pressure (MAP) directly relates to oxygenation in neonates with respiratory distress syndrome (RDS). Variations in the Positive End Expiratory Pressure(PEEP)with concomitant changes of the Duration of Positive Pressure (DPP) while MAP, Peak Inspiratory Pressure, flow, FiO2 and rate remained constant, were investigated in 9 neonates with RDS during the 1st and 2nd day of life. After stabilization on baseline ventilator settings, PEEP was increased by an average of 60% and the DPP was decreased (about 0.3 sec)in order to maintain baseline MAP. Following a return to baseline,a second experimental condition consisted of decreasing PEEP by 60%, increasing DPP accordingly to maintain constant MAP. Arterial BP, heart rate, paO2, paCO2, pH and arterial/Alveolar pO2 ratios (a/APO2) were measured before, during, between and after the experimental conditions. Analysis of the data revealed no significant changes in BP, paO2, a/APO2, heart rate during baseline or experimental conditions. PaCO2 decreased significantly when PEEP was decreased and DPP increased, both on Day 1(37.2 ± 6.6 vs 41.4 ± 6.4 Torr; p<.025)and Day 2(42.1 ± 7.4 vs 46.8 ± 5.6 Torr; p<.05). The changes in pH were inversely related to paCO2 changes. Air leaks occurred in 2 neonates who had MAP greater than 12cmH2O which was statistically higher than MAP in neonates without air leaks(12.9 vs 8.8cmH20;p<.025).This study confirms the importance of MAP in determining oxygenation in neonates with RDS. However, ventilation was significantly affected by variation in PEEP and DPP despite a constant MAP.