Performance of different interfaces for noninvasive ventilation in a lung model simulating a COPD patient with hypercapnia

Abstract

Introduction: noninvasive mechanical ventilation (NIV) is widely used to provide ventilatory support in patients with acute respiratory failure and is particularly effective when hypercapnia is present. The interface used has an impact on the outcome of NIV as it interferes with CO2 washout and patient-ventilator interaction. Full face masks are more comfortable than oronasal masks, but have greater internal volume, which can impact patient-ventilator synchrony and reduce CO2 washout. Objectives: To compare the performance of three different interfaces for NIV using a mechanical simulator in terms of patient-ventilator synchrony and CO2 washout.Methods: We will use the lung simulator ASL5000 (Ingmar Medical, Pittsburgh, PA), a computerized mechanical model consisting of a piston moving inside a cylinder. Compliance and resistance of the respiratory system, and the profile of muscular effort (negative pressure created by the respiratory muscles) are adjusted by the user. For this study, we will simulate a patient with COPD with compliance of 80 mL / cm H2O, inspiratory resistance 10cm H2O/l/s expiratory resistance of 20 cm H2O/l/s. An adult mannequin head of fiberglass will be used to simulate the patient-mask interface. Endotracheal tubes placed through the mannequins’ mouth and nostrils direct air coming from the mask to the simulator. A volumetric capnography with flow, pressure and CO2 sensors will be placed in the circuit between the mannequin's head and the simulator (NiCo2 Philips) . To simulate the production of CO2, 100% CO2 will be added to the system via a flow regulator.A mechanical ventilator (BiPAP Vision, Philips) will be connected to the mask attached to the mannequin´s face through a single limb circuit (Philips). Three types of masks will be adjusted to the mannequin´s head using velcro straps, as recommended by the manufacturers. The following interfaces will be tested: a) oral-nasal mask (Performatrak), b) full face mask (TotalFace), c) full face mask (Performax); interfaces will be tightly adjusted to the mannequin´s face to minimize air leaks during NIV. The flow of CO2 into the system will be adjusted to produce an ETCO2 of 70 mmHg while the mechanical model simulates the patient's efforts with the ventilator set to a continuous positive airway pressure (CPAP) of 5 cm H2O (spontaneous ventilation), and will be kept constant throughout the study . The effects of internal volume of the interface on CO2 washout will be evaluated during noninvasive ventilation in pressure support. The ventilator will be set to spontaneous mode, with an inspiratory pressure (IPAP) = 10 cmH2O and expiratory pressure (EPAP) = 5 cmH2O. Variables evaluated will be obtained with the volumetric capnograph and the lung simulator. The ASL5000 provides values for each breath for trigger time (Ttrig), time to return to baseline pressure (Tbase), trigger pressure (Ptrig), cycling delay (Cdelay) and time to reach 90% of the peak pressure (T90 %)