Skin oxygenation and relative hemoglobin concentration measured by hyperspectral imaging based method as prognostic indicators in septic shock

Introduction: Skin mottling is extreme manifestation of microcirculatory changes in septic shock. Skin discolouration is thought to be due to heterogenous changes in oxygen saturation and volume of microcirculatory blood which results in alterations in the amount of reflected light in various parts of the spectrum. These alterations can be captured using hyperspectral imaging. We aim to describe mottled knee skin relative total hemoglobin concentration and microcirculatory saturation values in survivors and non survivors of septic shock and assess their prognostic information. Methods: Hyperspectral imaging was performed in 62 intensive care patients with septic shock enrolled within 24 hours of admission in single centre observational study to obtain relative oxy/deoxyhemoglobin concentration maps and numerical values from mottled area around the knee. Images were processed to identify areas with purple blue discolouration. Nonlinear fitting of optical density spectra was used to calculate relative oxy/deoxy haemoglobin concentration and obtain total hemoglobin concentration (a.u.) and microcirculatory oxygen saturation values (%). In addition, demographic (age, sex, primary site of infection), hemodynamic (mean arterial pressure, dose of vasopressor agents) and disease severity (SAPS II, SOFA score) data were collected. Results: It was possible to obtain analysable images in 55 patients, 26 survivors and 29 non survivors. There was no statistical difference in terms of age (60 (53-73) vs 70 (62.5-82)yrs), gender (42.3 vs 55.2% male), severity of disease (SAPS II 44.5 (32.0-50.0) vs 44.0 (36.0-57.5)) and dose of noradrenaline (0.02 (0-0.09) vs 0.08 (0-0.12 mcg/kg/min) between those who survived the episode of septic shock and those who died. In non survivors relative total hemoglobin concentration in mottled areas was significantly higher (267.6 ± 249.7 a.u. vs 72.3 ± 36.7 a.u.; P < 0.001) and skin microcirculatory oxygen saturation values were significantly lower (29.7 ± 36.1% vs 76.3 ± 30.7%;P < 0.001). Skin microcirculatory oxygen saturation of more than 22% provided 72% specificity and 69% sensitivity for predicting survival. Increase of relative skin total haemoglobin concentration (RR 1.11 (1.05-1.20)) and decrease of skin oxygen saturation by 5 units (RR 1.19 (1.09-1.30)) was associated with increase in hospital mortality. Conclusions: We used a non contact hyperspectral imaging system to quantify total haemoglobin and oxygen saturation in dermal microcirculation of septic shock patients. Increase in total dermal hemoglobin and decrease in oxygen saturation was strongly predictive of 28 day mortality.