Predicting success in weaning from mechanical ventilation: preliminary results from a multicentric study

Introduction

Failure in weaning from mechanical ventilation (MV) occurs in up to 25–30% of patients, being associated with high mortality. Indexes predicting success can be very helpful clinically. However, their predictive capacity is sometimes low and there are controversies concerning which ones have to be used.

Objective

To evaluate weaning predictor indexes in a group of patients during weaning from MV.

Methods

Patients under MV for at least 48 hours, submitted to a spontaneous breathing trial (SBT) during 30 min, extubated according to the clinical assistant physician's decision and followed for 48 hours, were included. They were evaluated concerning age, sex, APACHE score, Glasgow score, causes of ICU admission and mechanical ventilation, length of hospital and ICU stay, time of mechanical ventilation, drugs used and clinical characteristics. At the first and 30th minutes from SBT were analyzed: arterial blood gases, hemodynamic parameters as arterial blood pressure and cardiac rate, respiratory parameters as respiratory rate (RR), tidal volume, rapid shallow breathing index (f/VT), maximal inspiratory (PImax) and expiratory (PEmax) pressures. Comparisons were made between two groups of patients: success versus failure, defining failure as return to mechanical ventilation in the first 48 hours.

Results

Two hundred and one patients were studied. Overall mortality rate was 16%. Return to mechanical ventilation occurred in 32%. The most important differences comparing success with failure groups were: lower mortality rate (12% versus 27%, P < 0.01), shorter length of hospital and ICU stay (27 ± 21 versus 35 ± 21 days, P < 0.001 and 13 ± 12 versus 19 ± 14 days, P < 0.001); less incidence of dyspnea (37% versus 58%, P < 0.001), higher PaO₂ at 30 min (100 ± 30 versus 88 ± 25 mmHg, P < 0.001), lower RR at the first and 30th minutes (24 ± 6 versus 28 ± 7 bpm, P < 0.001, and 24 ± 6 versus 30 ± 8 bpm, P < 0.001), lower f/VT at first and 30th minutes (58 ± 31 versus 78 ± 45, P < 0.01 and 56 ± 38 versus 98 ± 74, P < 0.001), and higher PImax at 30 min (42 ± 15 versus 36 ± 14 cmH2O, P < 0.05).

Conclusions

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 longer length of hospital and ICU stay, higher incidence of dyspnea, higher respiratory rate and f/VT index both at the beginning and at the end of the trial, and lower level of oxygenation and lower PImax at the end of the trial.