All patients admitted to CCU via CCOT (n = 230 patients in 2009) will have StO2 monitored and VOT assessment sequentially throughout the course of their critical illness. Biomarkers to assess severity of illness, inflammatory processes and microcirculatory reactivity will be obtained, and in a subset of patients (n = 30), correlations between these parameters and other indices of microvascular perfusion using sublingual orthogonal polarization spectral (OPS) imaging videomicroscopy will be sought. As it is estimated that 20-30% of CCOT admissions are for sepsis (n = 40-60), the inclusion of other critically ill non-septic patients will enable discrimination of various parameters of VOT to be contrasted between groups to determine relative diagnostic and prognostic significance.