Tissue oxygenation in patients with severe sepsis

Abstract

Introduction The aim of this study was to determine the correlation between regional tissue oxygenation (SrO2) measured by near-infrared spectroscopy (NIRS), central venous oxygen saturation (SvO2) and levels of serum lactate (SL) in patients with severe sepsis. Methods An observational pilot study was performed in an ICU of a medium-sized teaching hospital. Adult patients admitted with severe sepsis were included and three NIRS electrodes were attached: on the left side of the forehead (LF), the right side of the forehead (RF) and the right forearm (RA). SL and SvO2 measured in a jugular or subclavian central venous line sample were determined every 4 hours. Descriptive statistics were calculated. Pearson correlation coefficients (PCC) were calculated between SrO2, SvO2 and SL. Normal values for SrO2 were defined as the median + 1 interquartile range in patients with SL <1.7 mmol/l. Differences between groups were calculated by Pearson chi-square tests. P <0.05 was considered statistically significant. Results Twenty-five patients (12 men) were included. Mean age was 68 years, mean APACHE score 31. The most frequent reasons for ICU admission were abdominal sepsis (n = 11) and pneumosepsis (n = 7). Statistically significant correlations were found between SvO2 and SrO2: PCC SrO2 LF, 0.46; PCC SrO2 RF, 0.50; PCC SrO2 RA, 0.21. Low, although statistically significant, correlations were found between SrO2 and SL: PCC SrO2 LF, -0.16; PCC SrO2 RF, -0.15; and PCC SrO2 RA, -0.20. Calculated normal values for SrO2 LF were 60 to 80%, for SrO2 RF were 60 to 76% and for SrO2 RA were 64 to 84%. An out-of-range SrO2 had a high positive predictive value (PPV) for an increased SL. The PPV for out-of-range SrO2 LF was 85% versus 58% for normal SrO2 LF (OR 4.27; 95% CI 2.09 to 8.72), the PPV for out-of-range SrO2 RF was 77% versus 60% for normal SrO2 RF (OR 2.32; 95% CI 1.25 to 4.31) and the PPV for out-of-range SrO2 RA 75% versus 60% for normal SrO2 RA (OR 1.94; 95% CI 0.95 to 4.00). Conclusion This pilot study shows a statistically significant correlation between SvO2 and SrO2 in patients with severe sepsis. An out-of-range SrO2 LF or RF had a high predictive value for increased serum lactate. We therefore conclude that NIRS could have a role in goal-directed therapy of patients with severe sepsis.