The Effect on Airway Pressure when Electrical Power to the Servo Ventilator is Interrupted

Abstract

Loss of electrical power to the Servo ventilator allows unrestricted gas flow through the patient circuit. We studied the effect on airway pressure when this event occurs. Method: Three 900C and two 900B ventilators were fitted with both large-bore circuits and small-bore circuits and were used to ventilate a test lung. At ventilator working pressures of 30, 40, 50, 60, and 70 cm H2O, flowrates and 'airway' pressures were measured after the power switch was turned off, both with no PEEP and with a PEEP device set at 5 cm H2O. Results: Gas flowrate varied from 31 ± 2 to 73 ± 3 L/min. Airway pressure varied from 9 ± 0.9 to 29 ± 3 cm H2O. The preset working pressure, as well as the patient-circuit size, significantly affected both variables. The greater resistance of the small-bore circuit produced higher pressures and lower flowrates. Conclusion: Interruption of electrical power to the Servo ventilator results in continuous gas flow through the patient circuit and exposes the patient to significantly elevated airway pressure.