Effect of decreased synchronized intermittent mandatory ventilation (SIMV) support in acute respiratory distress syndrome (ARDS)

Effects of decreasing synchronized intermittent mandatory ventilation (SIMV) support on the work of breathing per liter of ventilation in patients with acute respiratory distress syndrome. Inspiratory work per unit volume (work per liter Wp/L) done by the patient is shown during assisted cycles (blue bars) and spontaneous cycles (red bars). As machine support was withdrawn, the patients performed an increasing amount of inspiratory work per liter of ventilation. The increased work was significantly greater at all levels of machine support less than or equal to 60 percent (p≤0.01). Spontaneous breaths required 25 percent more work per liter of ventilation than assisted breaths at these levels of machine support. The pressure-time index exceeded a fatiguing level of work at all levels of machine support less than 80 percent. It was suggested that, when using the SIMV mode, the back-up rate should result in at least 80 percent of the minute ventilation coming from the machine in order to prevent fatigue.