SIMVENT – patient simulator to test mechanical ventilators

Abstract

Background: Patient simulators for ventilators are usually passive devices consisting of rubber balloons, springs and tubes. In all but one simulators reviewed the ventilator under test (VUT) provides energy: simulation is limited to passive resistance/compliance with no sham spontaneous breathing to trigger the mechanical ventilator (MV). Objective: We improved our SIMVENT, a simulator to materialize lung equations with user selected ventilatory mechanics parameters, capable of producing spontaneous breathing to test MV operation. SIMVENT evaluates ventilators as VUTs. We designed an assisted ventilation training software to operate SIMVENT. Method: SIMVENT includes a cylinder with a step-motor powered piston, a cylinder mimicking residual volume, sensors for “alveolar” & “airway” pressures, a step-motor compressed tubing to simulate variable airway resistance, a microcontroller and a computer interface. SIMVENT acts as a patient with programmed values of airway resistance and lung compliance. SIMVENT compares flow and pressure signals with those shown by the VUT. Spontaneous inspiration attempts are created by SIMVENT to test VUT: breathing pressure drops are selected (5 cmH2O e.g.) either at random or phase-locked to the respiratory cycle. A report is generated for each VUT. SIMVENT was designed with "User centered" methodology. Results: Four ventilators were tested. VUT tidal volume differed up to 15%, airway pressure was within 8% and respiratory frequency within 4% of SIMVENT values. Conclusions: SIMVENT proved to be useful to test and compare ventilators as to their ability to detect spontaneous breathing. For the first time ventilators can be fully evaluated prior to clinical use. SIMVENT may also be used to train physicians.