Resistance to flow through the valves of mouth-to-mask ventilation devices

We conducted this study to determine the inspiratory and expiratory flow resistance of the valves of eight commercially available mouth-to-mask ventilation devices.

We evaluated the valves of Intertech, Laerdal, Life Design Systems (LDS), Res-Q, Respironics, Rondex, Vital Signs, and White. The devices were supplied by the manufacturers and included the valve and any filter or extension tube supplied with the valve. Expiratory resistance was evaluated by directing air through the valve in the direction of flow when the patient exhales. Inspiratory resistance was evaluated by directing air through the valve in the direction of flow when a breath is delivered to the patient. Flow was controlled by a Timeter 0-75 flowmeter and measured using a calibrated Timeter RT-200. Flows of 10, 20, 30, 40, 50, 60, 70, 80, and 90 L/min were used. 'Back' pressure due to the resistance of the valves was measured using a calibrated Timeter RT-200. Resistance was calculated by dividing back pressure by flow. Five measurements were made at each flow setting for each valve.

We observed significant differences in back pressures and resistances between the flows evaluated (p < 0.001 for both inspiratory and expiratory flows), and between the commercially available devices (p < 0.001 for both inspiratory and expiratory flows). At a flow of 50 L/min, the inspiratory back pressures produced by the devices were [mean (SD) in cm H2O] Intertech 5.2 (0.06), Laerdal 4.6 (0.09), LDS 4.7 (0.03), Res-Q 3.1 (0.04), Respironics 3.3 (0.04), Rondex 1.1 (0.02), Vital Signs 4.0 (0.06), and White 4.3 (0.10). At this same flow, the expiratory back pressures were Intertech 4.8 (0.30), Laerdal 9.1 (0.10), LDS 3.3 (0.02), Res-Q 3.7 (0.35), Respironics 0.5 (0.01), Rondex 1.4 (0.01), Vital Signs 3.6 (0.05), and White 13.7 (0.48).

In some cases, the resistance through these devices might be considered excessive; however, most of the devices meet the International Standards Organization (ISO) standard (back pressure < 5 cm H2O at 50 L/min).