Unstable inspiratory pressure may reduce the benefits of intermittent mandatory ventilation and impose a greater work of breathing than some patients can tolerate. The authors evaluated a continuous flow intermittent mandatory ventilation with continuous positive airway pressure apparatus provided with a 10-L high compliance reservoir bag, separated from the ventilator circuit by a one-way valve. A pulmonary simulator was tested to generate a wide range of inspiratory peak flow rates. Pressures and flow rates were examined in different sections of the system, using PEEP levels up to 15 mm Hg and different fresh gas flow rates. The circuit offers many advantages, particularly considering the low inspiratory pressure drop and the low fresh gas flow rates needed for optimal function.