DISEASE SEVERITY AND OPTIMUM MEAN AIRWAY PRESSURE LEVEL ON TRANSFER TO HIGH-FREQUENCY OSCILLATION

The aim of this study was to assess whether the severity of the infant 's lung disease determined the most appropriate change in mean airway pressure (MAP) level to use on transfer from conventional ventilation to high frequency oscillation (HFO). In addition, we wished to assess whether the oscillatory frequency employed affected gas exchange. Ten premature infants with respiratory distress syndrome (RDS) were studie d at a mean postnatal age of 1.5 days. During HFO, the infants were st udied at a MAP equivalent of that used during conventional ventilation (baseline MAP), then at 2 and 5 cmH(2)O above baseline at 10 Hz. At t he MAP identified as optimum, that is, the one associated with the bes t oxygenation, the infants were then studied at 10, 15 and 20 Hz. Each oscillatory setting was maintained for 20 minutes after which time ar terial blood gases were measured. Prior to transfer to the oscillator, the peak inspiratory pressure was recorded, the P((A-a)O2) calculated and compliance of the respiratory system (C-rs) measured. In nine inf ants, the optimum baseline MAP was +5 cmH(2)O. Oxygenation at that lev el was better than on conventional ventilation (P < 0.05), but there w as no significant change in CO2 elimination. The optimum MAP was relat ed to the peak pressure during conventional ventilation (P < 0.01) and inversely related to C-rs (P < 0.01). There was no significant relati onship with the P((A-a)O2). At the optimum MAP, the only significant e ffect of frequency was an impairment of oxygenation at 20 Hz. We concl ude that if a volume optimization strategy is pursued among infants wi th stiff lungs due to RDS, the appropriate starting level of MAP can b e identified by stepwise changes in MAP. Impairment of oscillator perf ormance at high frequencies can affect gas exchange. (C) 1994 Wiley-Li ss, Inc.