FLOW-TRIGGERING REDUCES INSPIRATORY EFFORT DURING WEANING FROM MECHANICAL VENTILATION

Objective: To investigate whether a new flow-triggered (FT) system can reduce the patient's inspiratory effort compared to a traditional pre ssure-triggered (PT) system during weaning from mechanical ventilation . Design: Prospective study. Setting: Intensive care unit of a General Hospital. Patients and participants: 10 mechanically ventilated patie nts, without chronic airway disease, ready to wean. Measurements: Minu te ventilation, breathing pattern, lung mechanics, inspiratory work of breathing (WI) and pressure time product (PTP) of Pp1 were obtained i n two conditions: 1) unsupported spontaneous breathing through the ven tilator circuit (SB); 2) spontaneous breathing with continuous positiv e airway pressure set at 5 cmH(2)O (CPAP). Two triggering systems, nam ely PT and FT, were used in each condition. Results: Though there was no change in breathing pattern, minute ventilation, and lung mechanics , the magnitude of the inspiratory effort decreased significantly with FT compared to PT in both instances. The added resistance (total flow resistance minus pulmonary resistance) decreased by 37% on average wh en FT replaced PT. PTP decreased, on average, 27% and 15% during SE an d CPAP, respectively, with FT compared to PT (p<0.05). A similar signi ficant decrease was observed in WI. Conclusion: The new FT system, i.e . flow-by system, reduces the unintentional ventilatory workload upon the patients' inspiratory muscles compared to traditional PT system du ring weaning from mechanical ventilation.