Physiological comparison of three spontaneous breathing trials in difficult-to-wean patients
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To compare cardiovascular and respiratory responses to different spontaneous breathing trials (SBT) in difficult-to-wean patients using T-piece and pressure support ventilation (PSV) with or without positive end-expiratory pressure (PEEP).
Prospective physiological study. Fourteen patients who were monitored with a Swan-Ganz catheter and had failed a previous T-piece trial were studied. Three SBTs were performed in random order in all patients: PSV with PEEP (PSV-PEEP), PSV without PEEP (PSV-ZEEP), and T-piece. PSV level was 7 cmH2O, and PEEP was 5 cmH2O. Inspiratory muscle effort was calculated, and hemodynamic parameters were measured using standard methods.
Results [median (and interquartile range)]
Most patients succeeded in the PSV-PEEP (11/14) and PSV-ZEEP (8/14) trials, but all failed the T-piece trial. Patient effort was significantly higher during T-piece than during PSV with or without PEEP [esophageal pressure-time product was 292 (238–512), 128 (58–299), and 148 (100–465) cmH2O·s/min, respectively, p < 0.05]. Left ventricular heart failure was observed in 11 of the 14 patients during the T-piece trial. Pulmonary artery occlusion pressure and respiratory rate were significantly higher during T-piece than with PSV-PEEP [21 (18–24) mmHg versus 17 (14–22) mmHg, p < 0.05 and 27 (21–35) breaths/min versus 19 (16–29) breaths/min, p < 0.05 respectively]. Tidal volume was significantly lower during the T-piece trial.
In this selected population of difficult-to-wean patients, PSV and PSV plus PEEP markedly modified the breathing pattern, inspiratory muscle effort, and cardiovascular response as compared to the T-piece. Caregivers should be aware of these differences in SBT as they may play an important role in weaning decision-making.
KeywordsWeaning from mechanical ventilation Spontaneous breathing trial Pressure support ventilation Heart failure
B.C. was supported by grants from the Instituto de Salud Carlos III (expedient CM04/00096, Ministerio de Sanidad) and the Instituto de Recerca Hospital de la Santa Creu i Sant Pau.
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