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
  • Cardiac surgery–associated acute kidney injury is associated with significant morbidity and mortality.
  • A major contributor to acute kidney injury is renal hypoxia.
  • Assessing for acute kidney injury using rise in serum creatinine often delays identification to 1 to 3 days after onset of acute kidney injury.
  • There is a need to develop methods for real-time assessment for renal hypoxia, as this should allow for earlier interventions to prevent acute kidney injury.
What This Article Tells Us That Is New
  • This prospective single-center observational pilot study measured urinary oxygen partial pressure and urine flow in 91 patients undergoing cardiac surgery using a novel device placed between the urinary catheter and collecting bag. Urinary oxygen partial pressure was successfully measured in 86 of these patients.
  • Mean urinary oxygen partial pressure in the period after cardiopulmonary bypass was significantly lower in patients who subsequently developed acute kidney injury than in those who did not.
  • Future studies are needed to validate these findings at other centers.