Noninvasive Urine Oxygen Monitoring and the Risk of Acute Kidney Injury in Cardiac Surgery

Abstract

Background Acute kidney injury (AKI) is a common complication of cardiac surgery. An intraoperative monitor of kidney perfusion is needed to identify patients at risk for AKI. The authors created a noninvasive urinary oximeter that provides continuous measurements of urinary oxygen partial pressure and instantaneous urine flow. They hypothesized that intraoperative urinary oxygen partial pressure measurements are feasible with this prototype device and that low urinary oxygen partial pressure during cardiac surgery is associated with the subsequent development of AKI. Methods This was a prospective observational pilot study. Continuous urinary oxygen partial pressure and instantaneous urine flow were measured in 91 patients undergoing cardiac surgery using a novel device placed between the urinary catheter and collecting bag. Data were collected throughout the surgery and for 24 h postoperatively. Clinicians were blinded to the intraoperative urinary oxygen partial pressure and instantaneous flow data. Patients were then followed postoperatively, and the incidence of AKI was compared to urinary oxygen partial pressure measurements. Results Intraoperative urinary oxygen partial pressure measurements were feasible in 86/91 (95%) of patients. When urinary oxygen partial pressure data were filtered for valid urine flows greater than 0.5 ml · kg–1 · h–1, then 70/86 (81%) and 77/86 (90%) of patients in the cardiopulmonary bypass (CPB) and post-CPB periods, respectively, were included in the analysis. Mean urinary oxygen partial pressure in the post-CPB period was significantly lower in patients who subsequently developed AKI than in those who did not (mean difference, 6 mmHg; 95% CI, 0 to 11; P = 0.038). In a multivariable analysis, mean urinary oxygen partial pressure during the post-CPB period remained an independent risk factor for AKI (relative risk, 0.82; 95% CI, 0.71 to 0.95; P = 0.009 for every 10-mmHg increase in mean urinary oxygen partial pressure). Conclusions Low urinary oxygen partial pressures after CPB may be associated with the subsequent development of AKI after cardiac surgery. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Year in Review 2021: Noteworthy Literature in Cardiothoracic Critical Care

“…Silverton et al performed a feasibility trial with a device providing noninvasive, real-time measurement of urine oxygen partial pressure, a measure previously shown to be predictive of postoperative AKI in cardiac surgical patients. 9 Using a prototype investigational urinary oximeter placed between the collection bag and urinary catheter, they monitored oxygen content and flow rate throughout the intraoperative period and into the ICU, with the device being removed no later than 24 h following separation from cardiopulmonary bypass (CPB). Data analysis was limited to flow rates at or above an arbitrary threshold of 0.5 cc/kg/h, as accuracy at lower flow rates was unknown and it was posited that below this rate would be classified as AKI even without additional supporting data.…”

The Role of Circadian Clock Genes in Critical Illness: The Potential Role of Translational Clock Gene Therapies for Targeting Inflammation, Mitochondrial Function, and Muscle Mass in Intensive Care

“…This leads to local inflammation and also microthrombosis, the occlusion of capillaries by small clots (Chang, 2018)which reduces oxygen supply to tissues; renal tissue hypoxia is associated with AKI and can be measured directly in animals (Iguchi et al, 2019) and noninvasively in human patients. (Silverton et al, 2021) In addition to these observations, metabolic deficits have been seen in AKI, for example, abnormal fission and fusion of mitochondria (Brooks et al, 2009;Yan et al, 2020). In particular, the abnormal fission may be driven by dynamin-related protein 1 (DRP-1) (Perry et al, 2018).…”

Urine Oxygen Monitoring in Cardiac Surgery: Comment

“…Silverton et al 1 nicely described their work with a prototype monitor that measures oxygen partial pressure in the urine at the exit from the urinary catheter. I commend the authors for further emphasizing the association between oxygen partial pressure in the urine and postoperative acute kidney injury (AKI) and stressing the potential benefit of real-time continuous kidney monitoring.…”