Changes in thenar muscle tissue oxygen saturation assessed by near-infrared spectroscopy during weaning from mechanical ventilation.

BACKGROUND: Tissue oxygen saturation (StO₂) measured by near-infrared spectroscopy (NIRS) has been used to provide information on local tissue oxygenation in different clinical settings. This study aims to determine the effect of weaning from mechanical ventilation on thenar muscle StO₂. METHODS: In consecutive critically ill mechanically ventilated patients, StO₂ at the thenar eminence, along with a vascular occlusion test (VOT), were measured by NIRS, on mechanical ventilation and during a 2-hour T-piece spontaneous breathing trial (SBT). Hemodynamic, gas exchange and respiratory variables were recorded. RESULTS: Forty-four patients were included in this study, 25 tolerated the SBT and 19 failed. On mechanical ventilation, no differences in any measured variable were observed between patients who succeeded or failed. Two minutes after SBT start, StO₂ was decreased in patients who failed whereas it did not change in patients who succeeded (P<0.001). For all data, 2 minutes after the start of SBT, StO₂ significantly correlated with SaO₂ (r=0.32, P=0.037) and with the respiratory frequency/tidal volume (f/VT) index (r=-0.34, P=0.023). VOT-derived StO₂ downslope and StO2 upslope did not change significantly along the SBT test. The maximum StO₂ value, its ratio to minimum StO2, and the post-VOT StO₂ value decreased significantly in patients who failed whereas no change was found in those who succeeded the SBT (P=0.003, P=0.025 and P<0.001 respectively). StO₂ and f/VT at the second minute of SBT yielded a receiver operator characteristics curve area value of 0.77 and 0.80, P=0.002, respectively, in detecting the SBT outcome. CONCLUSION: SBT failure was associated with a significant impairment of thenar muscle StO₂. A decrease of StO₂ at 2 minutes after disconnection from the ventilator was associated with SBT failure. Further validation is warranted.