Background: We hypothesized that the tissue oxygen saturation (StO₂) of skeletal muscle would be related to the inflammation and muscle weakness in patients with critically ill patients (CIPs). We had to clarify which variables would most affect muscle weakness (either nadir, maximal, and average values of StO₂). The purpose of this study was to compare three measurements of the StO₂ in relation to muscle weakness and inflammation in CIPs.

Methods: This was a prospective, observational cohort study. Subjects were recruited CIPs in the critical care medicine center of our university hospital. We measured the StO₂ of the quadriceps muscle by using near-infrared spectroscopy. Measurements were made every other day post-admission. Nadir, maximum, and average values were calculated for analysis. Inflammation was measured by log Interleukin-6 (IL-6). The medical research council (MRC) score was measured to assess the muscle weakness (?48 was diagnosed as ICU-AW).

Results: 32 patients (mean, 65.9 yrs.) were recruited into this study. 12 patients (38%) were admitted with exogenous diseases, others with internal causative diseases. Nadir StO₂ was 41.9±8.6%, maximal StO₂ was 51.7±6.5%, and average StO₂ was 46.1±6.6%. MRC score was 54.7 ±5.5 points. 5 patients (16%) were diagnosed as ICU-AW. Log IL-6 was 5.5±2.5pg/mL. Nadir StO₂ was significantly correlated with log IL-6 and MRC score (r=-0.38, r=0.59, p<0.05). Average StO₂ and maximal StO₂ did not relate log IL-6 and MRC scores.

Conclusion: These findings suggest that nadir StO₂ correlated muscle weakness and inflammation in CIPs. Decrease in StO₂ is important to predict ICU-AW in CIPs.