Predicting success in weaning from mechanical ventilation

Introduction

Failure in weaning from mechanical ventilation (MV) is frequent (25–30%) and associated with high mortality. Indexes predicting success can be helpful clinically. However, their predictive capacity can be low. The goal from this study is to evaluate weaning predictor indexes in patients during weaning from MV.

Methods

We included patients under MV for at least 48 hours, submitted to a spontaneous breathing trial (SBT) for 30 minutes, extubated according to clinical decision and followed for 48 hours. They were evaluated concerning age, sex, clinical characteristics, length of hospital and ICU stays and length of MV. At the first and 30th minutes from the SBT we analyzed: arterial blood gases, hemodynamic and respiratory parameters such as respiratory rate (f), tidal volume (VT), rapid shallow breathing index (f/VT), maximal inspiratory and expiratory pressures. Comparisons were made between two groups of patients: success vs failure, defining failure as return to MV in the first 48 hours.

Results

Four hundred and fifty-eight patients were studied. The overall mortality rate was 14%. Return to MV occurred in 21%. The most important differences comparing success with failure groups were: lower age (56 ± 19 vs 62 ± 17 years, P < 0.01), lower mortality rate (10% vs 31%, P < 0.001), shorter length of ICU stay (15 ± 12 vs 19 ± 13 days, P < 0.01), higher oxygen saturation at the first and 30th minutes (97 ± 3 vs 96 ± 6 and 95 ± 4 vs 94 ± 4, P < 0.05), lower f at the first and 30th minutes (24 ± 6 vs 26 ± 6 bpm and 25 ± 6 vs 28 ± 7 bpm, P < 0.001), lower f/VT at the first minute and principally in the 30th minute (56 ± 32 vs 69 ± 38 and 62 ± 39 vs 84 ± 55, P < 0.001), and lower increase in f/VT (4 ± 28 vs 12 ± 38, P < 0.05) during the test.

Conclusion

In this group of patients a great number failed in the weaning process, showing, as expected, a higher mortality rate. Parameters related to failure were higher age, longer length of ICU stay, lower level of oxygenation, higher f and f/VT and higher increase in f/VT during the test.