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.

Non-invasive assessment of the microcirculation in critically ill patients.

Sepsis is associated with abnormalities of muscle tissue oxygenation and of microvascular function. We investigated whether the technique of near-infrared spectroscopy can evaluate such abnormalities in critically ill patients and compared near-infrared spectroscopy-derived indices of critically ill patients with those of healthy volunteers. We studied 41 patients (mean age 58 +/- 22 years) and 15 healthy volunteers (mean age 49 +/- 13 years). Patients were classified into one of three groups: systemic inflammatory response syndrome (SIRS) (n = 21), severe sepsis (n = 8) and septic shock (n = 12). Near-infrared spectroscopy was used to continuously measure thenar muscle oxygen saturation before, during and after a three-minute occlusion of the brachial artery via pneumatic cuff. Oxygen saturation was significantly lower in patients with SIRS, severe sepsis or septic shock than in healthy volunteers. Oxygen consumption rate during stagnant ischaemia was significantly lower in patients with SIRS (23.9 +/- 7.7%/minute, P < 0.001), severe sepsis (16.9 +/- 3.4%/minute, P < 0.001) or septic shock (14.8 +/- 6%/minute, P < 0.001) than in healthy volunteers (35.5 +/- 10.6%/minute). Furthermore, oxygen consumption rate was significantly lower in patients with septic shock than patients with SIRS. Reperfusion rate was significantly lower in patients with SIRS (336 +/- 141%/minute, P < 0.001), severe sepsis (257 +/- 150%/minute, P < 0.001) or septic shock (146 +/- 101%/minute, P < 0.001) than in healthy volunteers (713 +/- 223%/minute) and significantly lower in the septic shock than in the SIRS group. Near-infrared spectroscopy can detect tissue oxygenation deficits and impaired microvascular reactivity in critically ill patients, as well as discriminate among groups with different disease severity.

Predisposing factors for critical illness polyneuromyopathy in a multidisciplinary intensive care unit.

OBJECTIVE: To investigate risk factors of critical illness polyneuromyopathy (CIPM) in a general multidisciplinary intensive care unit (ICU). PATIENTS AND METHODS: Prospective observational study in a 28-bed university multidisciplinary ICU. Four hundred and seventy-four (323 M/151 F, age 55 +/- 19) consecutive patients were prospectively evaluated. All patients were assigned admission Acute Physiology and Chronic Health Evaluation (APACHE II; 15 +/- 7) and Sequential Organ Failure Assessment (SOFA; 6 +/- 3) scores and were subsequently evaluated for newly developed neuromuscular weakness. Other potential causes of new-onset weakness after ICU admission were excluded before CIPM was diagnosed. RESULTS: Forty-four (23.8%) of 185 patients developed generalized weakness that met the criteria for CIPM. Patients with CIPM had higher APACHE II (18.9 +/- 6.6 vs 15.6 +/- 6.4, P = 0.004) and SOFA scores (8.4 +/- 2.9 vs 7.1 +/- 2.9, P = 0.013). According to multivariate logistic regression analysis, the following risk factors were independently associated with the development of CIPM: severity of illness at the time of ICU admission, administration of aminoglycoside antibiotics and high blood glucose levels. Analysis according to severity of illness stratification revealed the emergence of Gram (-) bacteremia as the most important independent predisposing factor for CIPM development in less severely ill patients. CONCLUSIONS: CIPM has a high incidence in the ICU setting. Our study revealed the association of aminoglycosides, hyperglycemia and illness severity with CIPM development, as well as the association between Gram (-) bacteremia and development of CIPM in less severely ill patient population.