The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

EVALUATION OF HYPOPHARYNGEAL PRESSURE GENERATED BY A HIGH FREQUENCY HIGH FLOW NASAL CANNULA DEVICE

Steven B. Powell1, Toni M. Podgorak2, Janie B. Voyles2



Background: High Frequency Ventilation by Endotracheal Tube (ETT) has been used to treat various forms of lung disease in the newborn. Several types of High Frequency devices have been studied, all by ETT. Some proponents of Bubble Nasal Continuous Positive Airway Pressure (Bubble-CPAP) have suggested that the bubbling causes benefit by its high frequency oscillatory movement. One study showed increased CO2 elimination of Bubble-CPAP compared to standard CPAP by ETT, and measured the frequency and amplitude generated by bubbling. Heated, Humidified, High Flow Nasal Cannulas are now widely used and have been shown to generate positive hypopharyngeal pressures consistent with therapeutic range of traditional CPAP devices. We believe a mechanical device in a continuous flow nasal cannula could provide even stronger oscillatory effect than provided by bubbling which may provide greater benefit to the patient.

Methods: We evaluated two devices which mechanically generate an oscillatory movement by the passive flow in a High Flow Nasal Cannula. A standard infant nasal cannula was used with the nose tips inserted into a model of the nares and nasal/pharyngeal airway. A pressure sensor in the pharyngeal model captured continuous pressure readings. Each device was inserted into the nasal cannula circuit and evaluated at flow rates of 4-8 L/min. For each device, waves of the hypopharyngeal pressure were generated and plotted. Frequency, Amplitude, and Mean Airway Pressure (MAP) were calculated for each device at each flow rate.

Results: For both devices, the MAP was directly proportional to the flow rate, with similar values for the two devices generating 1.1 and 1.3 cmH2O at 4 L/min, rising to 6.5 and 6.7 cmH2O at 8 L/min. The frequency initially rose in both devices, and then reached plateaus at 40 and 55 Hz. For device 1, the amplitude remained constant at 0.5-0.6 cmH2O regardless of flow rate, whereas for device 2, the amplitude increased with flow, from 0.3 cmH2O at 4 L/min to 1.2 cmH2O at 8 L/min.

Conclusion: A passive mechanical High Frequency oscillatory device along the circuit of a High Flow Nasal Cannula can produce an oscillatory effect measurable in the hypopharynx. This effect may enhance gas exchange, decrease apnea/bradycardia, and/or prevent intubation and mechanical ventilation in newborns with mild to moderate lung disease. Additional clinical studies would be needed to evaluate the effect of this new ventilation modality on these parameters.