Evaluation of visible diffuse reflectance spectroscopy in liver tissue: validation of tissue saturations using extracorporeal circulation

Abstract

Significance: Real-time information about oxygen delivery to the hepatic graft is important to direct care and diagnose vascular compromise in the immediate post-transplant period.Aim: The current study was designed to determine the utility of visible diffuse reflectance spectroscopy (vis-DRS) for measuring liver tissue saturation in vivo.Approach: A custom-built vis-DRS probe was calibrated using phantoms with hemoglobin (Hb) and polystyrene microspheres. Ex vivo (extracorporeal circulation) and in vivo protocols were used in a swine model (n ¼ 15) with validation via blood gas analysis.Results: In vivo absorption and scattering measured by vis-DRS with and without biliverdin correction correlated closely between analyses. Lin's concordance correlation coefficients are 0.991 for μ a and 0.959 for μ s 0 . Hb measured by blood test and vis-DRS with (R 2 ¼ 0.81) and without (R 2 ¼ 0.85) biliverdin correction were compared. Vis-DRS data obtained from the ex vivo protocol plotted against the PO 2 derived from blood gas analysis showed a good fit for a Hill coefficient of 1.67 and P 50 ¼ 34 mmHg (R 2 ¼ 0.81). A conversion formula was developed to account for the systematic deviation, which resulted in a goodness-of-fit R 2 ¼ 0.76 with the expected oxygen dissociation curve. Conclusions:We show that vis-DRS allows for real-time measurement of liver tissue saturation, an indicator for liver perfusion and oxygen delivery.

Hepatic artery flow, inspired oxygen, and hemoglobin determine liver tissue saturation measured with visible diffuse reflectance spectroscopy (vis‐DRS) in an in vivo swine model

“…We have recently validated the ability of vis‐DRS technology to measure liver tissue saturation and reached a goodness‐of‐fit ( R 2 ) of .76, compared to hepatic venous blood gas analysis 4 . The current data highlight the short delay between changes in oxygen delivery and tissue saturation (Figure 4).…”

“…Initial testing showed no change in saturations over the 2–3 data sets; the results thus show the pooled values for all data sets per flow rate. In our previous study, the coefficient of variation for similar data sets was 0.1–1% 4 . Flow was then increased in 25% increments to baseline.…”

“…The setup consisted of a self‐calibrating fiber optic probe and a portable vis‐DRS system equipped with a laptop computer for data acquisition as described before 5 . In brief, our spectroscopy system included a white‐LED as the light source and two visible spectrometers (Avantes BV, The Netherlands) for spectrum detection 4 . The fiber optic probe was composed of nine 200/220‐µm multimode optical fibers with six for DRS illumination, the seventh one for DRS detection, and the remaining two for self‐calibration illumination and detection, respectively.…”

“…5 In brief, our spectroscopy system included a white-LED as the light source and two visible spectrometers (Avantes BV, The Netherlands) for spectrum detection. 4 The fiber optic probe was composed of nine 200/220µm multimode optical fibers with six for DRS illumination, the seventh one for DRS detection, and the remaining two for self-calibration illumination and detection, respectively. At the distal end, the six DRS illumination fibers are arranged as a ring around the DRS detection fiber.…”

“…In our previous study, the coefficient of variation for similar data sets was 0.1-1%. 4 Flow was then increased in 25% increments to baseline. Protocols were performed at FiO 2 values 0.3 and 1.0.…”