Thenar muscle StO2 was measured non-invasively by NIRS (15mm Probe, InSpectra™, Hutchinson Technology Inc., USA). The values were continuously monitored and stored into a computer using InSpectra ™ software. The StO2 was monitored before, during and after upper arm ischemia-reperfusion test (UIRT) which was standardized as follows: a rapid cuff inflation above elbow towards 260 mmHg to stop flow and to induce a decrease in StO2 for 90 seconds, cuff deflation with continuous measurement of StO2 increase, overshooting and stabilization. Measurements were performed immediately after PAFC insertion (in first 24 to 72 hours after admission), the second measurement was performed 12-24 hours after the first measurement, the third measurement was performed (only if patient was still alive and still had PAFC inserted) in 48 hours after the first measurement. In spontaneously breathing patients and healthy volunteers measurements were performed after 15 minutes of bed rest, avoiding any muscular contractions.