End-Expiratory Lung Volumes During Spontaneous Breathing Trials in Tracheostomized Subjects on Prolonged Mechanical Ventilation

BACKGROUND: The role of end-expiratory lung volume (EELV) during a spontaneous breathing trial (SBT) in patients who were tracheostomized and on prolonged mechanical ventilation is unclear. This study aimed to assess EELV during a 60-min SBT and its correlation with weaning success. METHODS: Enrolled subjects admitted to a weaning unit were measured for EELV and relevant parameters before and after the SBT. RESULTS: Of the 44 enrolled subjects, 29 (66%) were successfully liberated, defined as not needing mechanical ventilation for 5 d. The success group had fewer subjects with chronic kidney disease (41% vs 73%, P = .044), stronger mean +/- SD maximum inspiratory pressure (41.6 +/- 10.4 vs 34.1 +/- 7.1 cm H2O; P = .02) and mean +/- SD maximum expiratory pressure (46.9 +/- 11.7 vs 35.3 +/- 16.9 cm H2O; P = .01) versus the failure group. Toward the end of the SBT, the success group had a significant increase in the mean +/- SD EELV (before vs after: 1,278 +/- 744 vs 1,493 +/- 867 mL; P = .040) and a decrease in the mean +/- SD rapid shallow breathing index (83.8 +/- 39.4 vs 66.3 +/- 29.4; P = .02), whereas there were no significant changes in these 2 parameters in the failure group. The Cox regression analysis showed that, at the beginning of SBT, a greater difference between EELV with a PEEP of 0 cm H2O and with a PEEP of 5 cm H2O was significantly correlated to a higher likelihood of weaning success. Toward the end of the SBT, a greater EELV level at a PEEP of 0 cm H2O was also correlated with weaning success. Also, the greater difference of EELV at a PEEP of 0 cm H2O between the beginning and the end of the SBT was also correlated with a shorter duration to weaning success. CONCLUSIONS: The change in EELV during a 60-min SBT may be of prognostic value for liberation from prolonged mechanical ventilation in patients who had a tracheostomy. Our findings suggest a model to understand the underlying mechanism of failure of liberation from mechanical ventilation in these patients.