The Science Journal of the American Association for Respiratory Care

2007 OPEN FORUM Abstracts

ROOM AIR ENTRAINMENT DUE TO LOSS OF CIRCUIT FLOW DURING NON-INVASIVE VENTILATION

J. S. Emberger1, J. Brown1


Background: During non-invasive ventilation, loss of flow to the patient due to device or circuit failure could cause patient harm. Current commercial full face masks are generally equipped with an entrainment mechanism in the event of a circuit or device failure. We wanted to determine if the entrainment mechanisms adequately perform their intended function during loss of flow to the patient.

Method: We used a manikin (Airman, Laerdal Medical) connected to a standard double test lung setup with lifting bar to simulate a spontaneously breathing patient with a non-invasive mask. We collected volume and pressure waveforms (CO2SMO Plus, Respironics) at the tracheal level of the manikin. We tested 5 non-invasive full face masks including: Comfort Full 2 (Respironics), Hospital Full Face Mask (ResMed), FlexiFit431 (Fisher & Paykel), Total Face Mask (Respironics) and Downs CPAP Mask (Vital Signs Inc). All masks listed have an entrainment port except the Downs CPAP Mask. The change in tidal volume and the change in airway pressure were collected for each mask with the patient breathing through the functioning circuit and then the occluded circuit. The patient was set to breathe 20 breaths per minute with a tidal volume of approximately 600 mL.

Results: See Table 1 for the change in pressure and change in volume when the non-invasive circuit was occluded and the patient was forced to entrain air since the circuit was not patent.

Conclusion: All four mask's entrainment mechanisms performed similarly, causing less than 3 cmH2O negative pressure at the tracheal level and minimal tidal volume loss. The Downs CPAP Mask, not equipped with an entrainment mechanism, caused a negative inflection of greater than 33 cmH2O and a loss of nearly half of the tidal volume. During full face non-invasive ventilation a mask with an entrainment mechanism should be used to protect the patient if there is a loss of flow.

  ComfortFull2 Hospital Full Face Mask FlexiFit431 Total Face Mask Downs CPAP Mask
Pressure Change after Circuit Occluded -0.6 cmH2O -0.5 cmH2O -1.1 cmH2O -2.5 cmH2O -33.5 cmH2O
Volume Change after Circuit Occluded -6 mL -9 mL -20 mL -10 mL -252 mL