Renal Near-Infrared Spectroscopy for Assessment of Renal Oxygenation in Adults Undergoing Cardiac Surgery: A Method Validation Study

Objective: To investigate the correlation between invasively measured renal venous oxygen saturation (SrvO(2)) and tissue oxygenation (rSO(2)) measured with near-infrared spectroscopy (NIRS) in adult patients undergoing cardiac surgery. Design: Prospective observational study. Setting: Single cardiac surgery center at a university hospital. Participants: Thirteen adult patients with skin- to- kidney distance <= 4 cm undergoing open cardiac surgery with cardiopulmonary bypass (CPB). Interventions: All patients received renal vein catheters for invasive measurement of SrvO(2), and NIRS electrodes for assessment of renal rSO(2) were placed over the kidney using ultrasound guidance. Measurements were made before CPB, during CPB at 3 different flow rates (2.4, 2.7, and 3.0 L/min/m(2)), and after CPB. Measurements and Main Results: Repeated- measures correlation analyses and Bland-Altman plots were used to study the correlation and agreement between rSO(2) and SrvO(2). For all measurement points, renal rSO(2) correlated with SrvO(2) (r(rm) = 0.61, p < 0.001), and the mean difference (bias) between rSO(2) and SrvO(2) was -2.71 +/- 7.22 (p = 0.002), with an error of 17.6%. When measurements during CPB and before and after CPB were studied separately, rSO(2) and SrvO(2) were correlated (r(rm) = 0.51, p < 0.007 and r(rm) = 0.73, p < 0.001, respectively). During CPB, renal rSO(2) predicted SrvO(2) with a bias of -3.41 +/- 7.76 (p = 0.009) and an error of 18.8%. Before and after CPB, the mean difference was -1.93 +/- 6.60 (p = 0.092), with an error of 16.2%. Conclusions: Renal rSO(2) is correlated to and predicts SrvO(2) with a small bias and acceptable agreement. Further studies are needed before renal NIRS can be used as a surrogate marker of renal oxygenation in clinical practice. (C) 2020 Elsevier Inc. All rights reserved.