Intraoperative Assessment of Renal Tissue Oxygenation Using NIRS

Overview

The kidney is one of the most vital organs in the human body. Renal perfusion is primarily supplied by the renal artery, while the removal of metabolites and venous drainage are provided by the renal vein. Although anatomical variations may exist, the renal artery typically originates from the abdominal aorta. In patients undergoing liver transplantation, renal function may be affected by multiple factors. Impairment of renal function significantly influences postoperative mortality, morbidity, graft survival, and length of hospital stay. Intraoperative assessment of renal perfusion has traditionally relied on monitoring hourly urine output and serum renal function tests. However, these methods may be insufficient and delayed in evaluating renal function, particularly during clamping of the inferior vena cava for hepatic graft venous anastomosis. Although Doppler ultrasonography can provide information regarding blood flow, it does not offer direct insight into the adequacy of tissue perfusion. Near-infrared spectroscopy (NIRS) is a non-invasive technique that has gained increasing attention in recent years due to its ability to accurately assess tissue oxygenation. Based on the Beer-Lambert law, NIRS enables the measurement of tissue oxygen saturation without the need for invasive procedures. The technique requires no intervention and is not associated with known complications or adverse effects. NIRS is most commonly used in clinical practice to assess cerebral oxygenation via measurements obtained from the frontal region. The aim of the present study is to evaluate renal oxygenation using near-infrared spectroscopy and to determine whether this technique provides clinically useful information during the liver transplantation procedure.

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.