End-expiratory lung volumes during spontaneous breathing trials in tracheostomized subjects on prolonged mechanical ventilation

Abstract

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.