Physiopathological Determinants of Patient-Ventilator Interaction and Dyssynchrony During Weaning

Abstract

During weaning from mechanical ventilation, the patient assumes a greater proportion of the work of breathing as ventilatory assistance is gradually withdrawn. The gradual withdrawal of ventilator assistance can be accomplished by the application of pressure-support ventilation (PSV) (Brochard et al. 1994; Esteban et al. 1995), synchronous intermittent mandatory ventilation (SIMV) (Brochard et al. 1994; Esteban et al. 1995), proportional assist ventilation (PAV) (Georgopoulos 1998), bi-level continuous positive airway pressure ventilation (Bi-level CPAP) or airway pressure release ventilation, mandatory minute ventilation (Davis et al. 1989), adaptive lung ventilation (Linton et al. 1994), or continuous positive airway pressure (CPAP) with or without automatic tube compensation (Stocker et al. 1997). Sometimes short intervals of T-piece trials (Esteban et al. 1995) are interspersed between high levels of ventilatory assistance or prolonged T-piece trials are applied (Esteban et al. 1997). Among the available methods of weaning, only PSV, SIMV, and T-piece have been studied prospectively (Brochard et al.1994, Esteban et al.1995; Esteban et al.1997). With PSV or SIMV the patient receives partial ventilatory support, whereas with T-piece the patient assumes full spontaneous breathing effort. In one prospective study (Esteban et al. 1994), the prevalence of weaning with either PSV, SIMV, or a combination of both PSV and SIMV with or without T-piece in succession was 75%. Thus, the majority of weaning was accomplished with the application of partial ventilatory support.