Abstract
Four brands of ventilator used for noninvasive positive pressure ventilation in the home were assessed to determine their performance on a patient simulator. We tested the tidal volume (VT) preset Companion 2801 (Puritan Bennett), minute volume preset Monnal D (Taema), and two pressure preset ventilators, the Nippy (Friday Medical) and the Bilevel Positive Airway Pressure (BiPAP) (Respironics). A patient simulator was employed to investigate the relationships between VT, peak airway pressure (PAP) and mean airway pressure (MAP), the responses to an additional leak in the circuit and patient effort of a variable duration, which was modelled using a negative pressure pump. For equivalent VTs, >300 mL, the Monnal D and Nippy generated a PAP up to 100% greater than the Companion 2801 and BiPAP. When an additional leak was introduced to the circuit, the VT of the Companion 2801 and Monnal D fell by >50%, while the Nippy and the BiPAP responded by increasing flow and maintained VT close to the level achieved with no leak. When the ventilators were triggered by a simulated patient effort of 0.25 s duration with a frequency 33% greater than that of the ventilator, the minute volume increased by 41% for the Companion 2801, by 18% for the Monnal D (no change expected), and by 17% for the Nippy (less than expected), and fell by 7% for the BiPAP due to irregular triggering. When patient effort was prolonged to 1.5 s, a similar length to the inspiratory time of the ventilators, there was no further change in the minute volume of the Companion 2801 and Monnal D, while that of the Nippy and of the BiPAP increased by 38 and 71%, respectively, compared to baseline. These results show that distinct brands of ventilator respond to changes in the patient and patient circuit in different ways, which are not always predictable from a simple description of their operating principles. This should be borne in mind when choosing a positive pressure ventilator for noninvasive ventilation.
