Carbon dioxide elimination varies with piston positioning when ventilating with high frequency oscillation
Introduction. Carbon dioxide (CO2) elimination for patients being ventilated with the high frequency oscillator is most often manipulated by adjusting the amplitude (AP), frequency, and inspiratory time. The piston is frequently placed in the center and not adjusted. This practice may limit the clinician's ability to optimize CO2 elimination. We hypothesized that varying piston positioning may alter patient PaCO2 elimination. Methods. Twenty- four consecutive patients ventilated with the SensorMedics 3100A (Yorba Linda, CA) high frequency oscillator were studied. Ages ranged from 1 day to 14 years. Weights ranged from 0.77 to 35 kg. All patients were monitored with the use of a transcutaneous (T-com) monitoring device (Model 850; Novametrix Medical Systems; Wallingford, CT). Arterial blood gas analysis was performed to confirm correlation between the PaCO2 and the value displayed on the T-com (TCO2). TCO2 reading and piston position were documented with the piston in the centered position as well as shifted to the right of the center and the left of the center. The three positions were studied in a random order. A twenty-minute stabilization period occurred between each of the position changes and prior to data collection. All the measurements were obtained without changes to other ventilator settings. Results. Of the 24 patients studied, twelve (50%) had improved CO2 elimination with the piston positioned to the left. Nine (37.5%) benefited from having the piston positioned in the center. Three patients (12.5%) showed improved CO2 elimination when the piston was positioned to the right. Piston Position Improved CO2 Elimination Left 12/24 (50%) Center 9/24 (37.5%) Right 3/24 (12.5%) Conclusion. This data does not conclusively indicate which piston position is most beneficial for a given patient. However, the data does conclude that altering the piston position during high frequency oscillatory ventilation may provide another means for improving CO2 elimination.
Tripp, D; Webster, C; Lawson, D; Meliones, JN; Cheifetz, IM
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