Central venous saturation as a weaning success predictor

Introduction

The frequently used parameters to predict weaning failure (WF) from mechanical ventilation (MV) weaning parameters have low predictive capacity. Although being the most common cause of WF, early detection of respiratory muscle fatigue is difficult. Central venous saturation (ScvO₂) is a marker of oxygen consumption and could be applied for detection of WF.

Objective

To evaluate the predictive capacity of ScvO₂ in detecting WF or success.

Design

A prospective observational clinical multicentric study in three ICUs of Porto Alegre.

Methods

Between August 2003 and December 2004, all patients with more than 48 hours of MV, in the weaning process, were submitted, after informed consent, to a spontaneous breathing trial (SBT) of 30 min and followed during the next 48 hours. All patients in the trial had arterial and venous gas analysis, and hemodynamic (cardiac rate, systolic and diastolic pressure) and ventilatory parameters (respiratory rate, tidal volume, f/VT index and maximal inspiratory pressure) during the MV time and in the 30th minute of SBT. The outcomes were reintubation and mortality rates.

Results

Sixty-three MV patients were included, 55.5% male, mean age 55.8 ± 18.6 years, APACHE II score 18.2 ± 6.3. Septic shock was the most frequent diagnosis with 50.8% of cases; mortality ICU rate in the period 22.2%; weaning failure with reintubation rate 31.7% and mortality higher in WF patients (75% vs 14%, P < 0.001). ScvO₂ at the 30th minute of SBT was lower in WF patients (58.2 ± 7.1 vs 66.3 ± 5.4, P = 0.003). Hemodynamic and mechanic ventilatory parameters were not able to predict WF or mortality. The PaO₂, SaO₂ and ScvO₂ values dropped comparing the MV time and the 30th minute of SBT (110.1 ± 39.8 vs 95.8 ± 28.8, P < 0.01; 97 ± 2.4 vs 95.3 ± 3.7, P < 0.001; and 68.3 ± 7.3 vs 64.6 ± 8.6, P < 0.001, respectively). WF patients had the most accentuated fall in these parameters (102.1 ± 38.5 vs 85.8 ± 20.1, P = 0.008; 96.9 ± 2.7 vs 94.2 ± 3.9, P = 0.001; and 68.2 ± 7.4 vs 59.5 ± 7.3, P < 0.001, respectively).

Conclusion

The reduction of ScvO₂ values during SBT is correlated with the outcome reintubation. This is probably due to an increase in oxygen muscle consumption and not only correlated to changes in oxygen muscle offer.