Adaptive support ventilation versus conventional ventilation for total ventilatory support in acute respiratory failure

OBJECTIVE: To compare the short-term effects of adaptive support ventilation (ASV), an advanced closed-loop mode, with conventional volume or pressure-control ventilation in patients passively ventilated for acute respiratory failure. DESIGN: Prospective crossover interventional multicenter trial. SETTING: Six European academic intensive care units. PATIENTS: Eighty-eight patients in three groups: patients with no obvious lung disease (n = 22), restrictive lung disease (n = 36) or obstructive lung disease (n = 30). INTERVENTIONS: After measurements on conventional ventilation (CV) as set by the patients' clinicians, each patient was switched to ASV set to obtain the same minute ventilation as during CV (isoMV condition). If this resulted in a change in PaCO(2), the minute ventilation setting of ASV was readjusted to achieve the same PaCO(2) as in CV (isoCO(2) condition). MEASUREMENTS AND RESULTS: Compared with CV, PaCO(2) during ASV in isoMV condition and minute ventilation during ASV in isoCO(2) condition were slightly lower, with lower inspiratory work/minute performed by the ventilator (p < 0.01). Oxygenation and hemodynamics were unchanged. During ASV, respiratory rate was slightly lower and tidal volume (Vt) slightly greater (p < 0.01), especially in obstructed patients. During ASV there were different ventilatory patterns in the three groups, with lower Vt in patients with restrictive disease and prolonged expiratory time in obstructed patients, thus mimicking the clinicians' choices for setting CV. In three chronic obstructive pulmonary disease patients the resulting Vt was unacceptably high. CONCLUSIONS: Comparison between ASV and CV resulted either in similarities or in minor differences. Except for excessive Vt in a few obstructed patients, all differences were in favor of ASV