Near-infrared spectroscopy (NIRS) is a non-invasive and user-friendly technique that enables real-time monitoring of tissue oxygen content. It is most commonly used in clinical practice to assess cerebral tissue oxygenation, particularly in cardiac surgery, where significant hemodynamic fluctuations are frequently encountered. NIRS measures cerebral tissue oxygen saturation from the frontal region and reflects the balance between local cerebral oxygen supply and demand. Light applied to the forehead is emitted within the near-infrared spectrum and detected by sensors positioned at specific distances from the light source. Using a modified version of the Beer-Lambert law, NIRS provides a measurement of oxygenated hemoglobin concentration relative to total hemoglobin concentration. Algorithms are subsequently applied to the raw data to generate a quantitative estimate of tissue oxygen saturation.
Numerous studies have demonstrated a correlation between cerebral desaturation and postoperative neurological complications. Consequently, specific management algorithms have been developed for the use of NIRS in cardiac surgery. In the presence of cerebral desaturation, recommended interventions include correction of cannula positioning, elevation of mean arterial pressure, increasing the inspired oxygen concentration, normalization of PaCO₂ levels, correction of hemoglobin concentration, augmentation of cardiac output, and reduction of cerebral metabolic rate.
Renal oxygen supply is primarily provided via the renal artery, while venous drainage occurs through the renal veins into the inferior vena cava. Adequate renal perfusion during liver transplantation is essential to minimize postoperative renal complications. For vascular anastomosis of the liver graft, clamping of the inferior vena cava is required, a process that results in significant hemodynamic alterations and impaired renal venous drainage. These changes may substantially affect renal oxygenation and perfusion. Although renal blood flow adequacy can be indirectly assessed by monitoring urine output after reperfusion, this method does not allow for objective evaluation of renal tissue oxygenation. We hypothesize that intraoperative monitoring of renal tissue oxygenation using NIRS may provide valuable real-time information and contribute to the early identification of postoperative acute kidney injury.
