The Science Journal of the American Association for Respiratory Care

1999 OPEN FORUM Abstracts

OPTIMIZING MEAN AIRWAY PRESSURE AT THE INITIATION OF HIGH FREQUENCY OSCILLATORY VENTILATION

Colleen Webster, RRT; Donna Tripp, RRT; Mike Gentile, RRT; Ira M. Cheifetz, MD. Divisions of Pediatric Respiratory Care and Critical Care Medicine, Duke University Medical Center, Durham, NC.

Introduction. The initial mean airway pressure (PAW) setting on high frequency oscillatory ventilation (HFOV) is often subjectively chosen by the clinician. The HFOV PAW is frequently set only slightly higher than on conventional mechanical ventilation (CMV). An initial HFOV PAW that is set too low may result in a prolonged time to achieve effective lung expansion and oxygenation. Thus, we hypothesize that the ideal initial PAW on HFOV should be higher than generally used.

Methods. A retrospective chart review of 41 infants and pediatric pts. ventilated with HFOV (Sensormedics 3100A) for acute lung injury was performed. Pts. ranged from 1 d to 16 yrs of age, and weights ranged from 2 to 93 kg. Measurements included PAW on CMV prior to HFOV, initial PAW setting on HFOV, and effective PAW (PAW corresponding to the best oxygenation within the 1st 12 hours). Additionally, the duration of time between the initial HFOV settings and its peak oxygenation effect (time initial) as well as the time between an increase to the effective PAW and its peak oxygenation effect (time effective) were recorded. Pts. were separated into two groups. Group A (n=14) contains pts. whose effective PAW represented an increase from the initial PAW on HFOV. Group B (n=27) contains pts. whose initial HFOV PAW and effective PAW were equal.

Results.

CMV PAW Initial HFOV PAW Effective HFOV PAW Time Initial (Hours) Time Effective (Hours)
Group A 18.1 ± 3.7 22.0 ± 3.1 25.8 ± 3.4 4.7 ± 3.3 7.3 ± 3.9
Group B 20.6 ± 4.3 26.3 ± 5.5 26.3 ± 5.5 1.0 ± 0.0 4.4 ± 4.2
P Value 0.07 0.01 0.77 <0.0001 0.04

Conclusion. The most effective average HFOV PAW was an increase of 6 cm H2O above CMV (Group B). Pts. whose initial HFOV PAW was <6 from CMV PAW required a second increase in their PAW to optimize oxygenation. This secondary increase led to a prolonged time to achieve optimal oxygenation (Group A). Our data suggest that the initial HFOV PAW in many pts. is set relatively low. However, care must be taken not to excessively increase PAW due to concerns of lung overdistention and secondary pulmonary injury.

OF-99-109

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