Abstract Background The effect of different spontaneous breathing trial (SBT) methods on lung volume and ventilation distribution has not been well clarified in post-cardiac surgery patients. Methods In this prospective observational study, patients underwent 30 min of pressure-support ventilation (PSV)-SBT PS 8 cmH 2 O, zero positive end-expiratory pressure (ZEEP), followed by a 30-min T-piece trial if tolerated. Electrical impedance tomography (EIT) was used to continuously monitor regional lung ventilation and end-expiratory lung volume (EELV) at baseline, PSV-SBT 3 min, PSV-SBT 30 min, T-piece SBT 3 min and T-piece SBT 30 min. EELV loss = VT baseline /tidal impedance variation (TIV) baseline × ΔEELI. EELV loss PSV was defined as volume loss at 30 min of PSV-SBT and EELV loss T-piece was defined as volume loss during T-piece SBT. Results In 60 patients who complied with both SBT steps, 43 succeeded (71.7%) and 17 failed (28.3%) the T-piece SBT. Compared to the success group, the failure group exhibited a higher incidence of pendelluft (52.9% vs. 23.3%, p = 0.045) and significantly greater EELV loss at T-piece SBT 30 min (623459,746 ml vs. 511376,702ml, p = 0.003). However, the success group showed greater EELV loss PSV than the failure group (322247,459 ml vs. 199166, 269 ml, p EELV loss T-piece ) and T-volume loss group ( N = 23, EELV loss T-piece > EELV loss PSV ). In addition, the T-volume loss group had a higher weaning failure rate than the P-volume loss group (52.2% 12/23 vs. 13.5% 5/37, p < 0.001) and was associated with reduced baseline dorsal ventilation (39%37%,43% vs. 44%41%,50%, p = 0.023). ROC analysis suggested that a dorsal ventilation threshold of 40.5% was associated with T -volume loss. Conclusions The successful weaning patients had a higher reduction of EELV loss PSV and a lower reduction of EELV loss T-piece . In the weaning failure patients, the paradox of lower EELV loss PSV that was accompanied by a high RR and low VT might be associated with air trapping. Attention should be paid to using EELV loss PSV to identify weaning failure.
Zhang et al. (Fri,) studied this question.