ABSTRACT
SIMV (synchronized intermittent mandatory ventilation) is a volume assisted mode which a patient inspiratory demand results in a clinician-controlled tidal volume and flow rate. However, PSV (pressure support ventilation) has the ability to augment spontaneous breaths with a variable amount of inspiratory positive pressure with a clinician-selected level of inspiratory airway pressure. To compare the effects of SIMV and PSV on respiratory function, experiments were performed on 12 stable patients during the weaning process and tidal volume, airway pressure, arterial blood gas tensions, blood pressure, and heart rates were measured during SIMV, and after 2 mins after removal of mechanical ventilation support. The same measurement as SIMV (except mandatory respiratory rates) were performed during PSV. The PSV level was reduced in the 5 cm2O step every 10-15 mins. The results of respiratory parameters and hemodynamic data showed that tidal volume, blood pressure, heart rates, and arterial blood gas tensions were similar, but there were significantly lower ventilatory rates, lower peak airway pressure and lower mean airway pressure during PSVmax than SlMV, and PSV resulted in improved patient comfort. It was concluded that PSV could be used to unload the patients ventilatory muscles and provide an appropriate level of mechanical ventilation support similar to SIMV weaning approaches.