Predicting success in weaning from mechanical ventilation in patients with and without cardiac disease

Introduction

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

Methods

We included patients with and without cardiac disease under MV for at least 48 hours, submitted to 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 stay and of MV. At the first and 30th minutes from SBT there were analyzed: arterial blood gases, hemodynamic and respiratory parameters as respiratory rate (f ), tidal volume (VT), rapid shallow breathing index (f/VT), maximal inspiratory and expiratory pressures. Comparisons were done between this group of patients and success × failure, defining failure as a return to MV in the first 48 hours.

Results

Four hundred and thirteen patients were studied, 81 with cardiac disease and 332 without. Overall mortality rate was 14%. Return to MV occurred in 19.7%. The most important differences comparing patients with cardiac disease with the control group were: lower mortality rate (21% × 13.5%, P < 0.006), shorter length of ICU stay (9 ± 3 × 16 ± 13 days). Comparing patients who failed in the weaning process with and without heart disease (20% × 20%, P < 0.55). Comparing f/VT in 30th minute of patients who have had success with those who failed the weaning process (60 ± 38 × 74 ± 47, P < 0.012), a lower increase in f/VT (Δf/VT) (4 ± 27 × 11 ± 33, P < 0.075) during the test.

Conclusions

In this group of patients a great number failed in the weaning process, showing, as expected, a higher mortality rate. Parameters most related to failure in the literature were higher age, longer length of ICU stay, mortality and f/VT. In this study, just the last parameter was sensitive principally in the 30th minute, and higher increase in f/VT (Δf/VT) during the test, demonstrating that patients with cardiac disease not fail more than others during the weaning process, as well as the efficiency of the test to predict success in weaning.

Members of Weaning Study Group R Wickert, LG Borges, ME Alves, ACT Silva, R Condessa, MB Blom, R Zancanaro, F Callefe, KB Pinto, K Hartmann, P Pinheiro, ES Oliveira, C Trevisan.