PATIENT VENTILATOR INTERACTION DURING SYNCHRONIZED INTERMITTENT MANDATORY VENTILATION

Synchronized intermittent mandatory ventilation (SIMV) intermixes assi sted and spontaneous breaths. Its ability as a weaning technique has b een questioned on the basis that patients show little adaptation to ve ntilator assistance. We studied inspiratory effort and patient-ventila tor interaction at different levels (SIMV, 100, 50, and 0%) of flow-tr iggered SIMV versus pressure-triggered SIMV in patients during the wea ning period. The two triggering systems were evaluated during constant flow and constant pressure mandatory SIMV breaths. Inspiratory effort was estimated as the esophageal pressure time product (PTP) per breat h (PTP/b) and per minute (PTP/min). The PTP/b and PTP/min of both mand atory and spontaneous breaths were significantly lower during flow tri ggering than during pressure triggering SIMV, irrespective of the vent ilatory mode. During pressure-triggered SIMV PTP/b and PTP/min were id entical for mandatory and spontaneous breaths, whereas during flow-tri ggered SIMV PTP/b and PTP/min were significantly lower for mandatory t han for spontaneous breaths. This difference was greatest when flow tr iggering and constant pressure ventilation were associated. These data show that flow triggering reduces inspiratory effort during both mand atory and spontaneous SIMV breaths and obtains a better patient-ventil ator interaction.