The Science Journal of the American Association for Respiratory Care

2011 OPEN FORUM Abstracts

EFFECTS OF BIAS FLOW ON CARBON DIOXIDE ELIMINATION DURING PEDIATRIC HIGH FREQUENCY OSCILLATORY VENTILATION.

Walter L. Williford1, Anthony Diez1, David Adams2, Phillip B. Smith2, Ira M. Cheifetz2, David Turner2; 1Respiratory Care, Duke University Hospital, Durham, NC; 2Pediatric Critical Care, Duke University Hospital, Durham, NC

Background: Bias flow is the continuous flow of gas provided during high frequency oscillatory ventilation (HFOV). Bias flow is set during HFOV based on patient size and mean airway pressure, 20 liters per minute is the recommended starting point. Increased bias flow may improve patient comfort with regard to spontaneous respirations during HFOV, but CO2 retention is a potential concern. There are limited data demonstrating that bias flow does not impact CO2 clearance during HFOV in animals, but there are no studies in humans. We hypothesized that increased bias flow in pediatric patients receiving HFOV via the 3100A Oscillator would not impact CO2 elimination. Method: Following IRB approval and informed consent from each patient's family, eight pediatric patients receiving HFOV were treated with varying levels of bias flow. Each patient was treated with 12, 24, and 36 liters per minute (lpm) of bias flow in a randomized fashion. At each bias flow setting, data were collected after one hour at a fixed power. Additional data were collected at each bias flow after one hour with a fixed amplitude. The remainder of the HFOV settings remained constant throughout the six hour study. An arterial blood gas sample was obtained hourly and hemodynamics were monitored throughout the study. Results: Data were collected on 8 patients. Mean PaCO2 was 57 torr (5, 95%ile; 37, 89). Controlling for both power and amplitude, there were no significant changes in PaCO2 as bias flow varied between 12, 24, and 36 lpm (p=0.22). There were also no changes in PaO2 or mean airway pressure at each bias flow setting (Table 1). No clinically significant changes in cardiac output, heart rate, or patient stability were noted during the study. Conclusion: Changes in bias flow during HFOV do not affect CO2 elimination. Clinical investigation continues in children with ALI/ARDS being managed with HFOV to assess the impact of bias flow on gas exchange and patient comfort.
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Mean values at set bias flows of 12, 24, and 36 liters per minute.