Physiological response to pressure support ventilation delivered before and after extubation in patients not capable of totally spontaneous autonomous breathing

We designed a prospective, physiological study in 12 patients affected by c hronic respiratory disorders. The study was aimed at assessing the diaphrag m energy expenditure (PTPdi), lung resistance (RL) and elastance (Et), arte rial blood gases (ABG), breathing pattern, and dyspnea measured by a visual analog scale during invasive pressure support ventilation (i-PSV) and noni nvasive PSV (n-PSV). The ventilator settings were kept the same. Both i-PSV and n-PSV significantly reduced the PTPdi per minute, compared with that d uring a T-piece trial (204.4 +/- 93.8 cm H2O x s/min [i-PSV]; 197.5 +/- 119 .8 [n-PSV]; 393.8 +/- 129.0 [T-piece]). Expired tidal volume (VTe) was sign ificantly higher (p < 0.05) during n-PSV (615 +/- 166 ml) than during i-PSV (519 +/- 140 ml). The respiratory pump (PTPdi/VTe) was more effective (p < 0.05) with noninvasive ventilation (22.3 <plus/minus> 2.3 cm H2O x s/L for i-PSV versus 17.2 +/- 3.3 for n-PSV). Rt and Et were similar with the two modes of ventilation. Overall dyspnea was significantly (p < 0.05) better d uring n-PSV than i-PSV, whereas ABG were similar. We have shown, in patient s affected by stable chronic respiratory disorders not ready to sustain tot ally spontaneous breathing, that i-PSV and n-PSV are equally effective in r educing the PTPdi and in improving ABG, but that n-PSV seems to be better t olerated.