Study finds thresholds for low oxygen leading to acute kidney injury in cardiac surgery
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Key takeaways:
- Thresholds for low oxygen delivery leading to acute kidney injury during cardiac surgery were lower than previously reported.
- The data can be used to help prevent AKI during cardiac surgery.
Researchers identified thresholds for low oxygen delivery leading to acute kidney injury during cardiac surgery that were lower than previously reported.
“Our team has a longstanding interest in evaluating determinants of postoperative acute kidney injury using clinically informed datasets,” Donald S. Likosky, PhD, head of the Section of Health Services Research and Quality at the University of Michigan Health Department of Cardiac Surgery, told Healio. “At the same time, other investigative teams have leveraged the emerging use of electronic perfusion records. These studies have identified the potential role of oxygen delivery during cardiopulmonary bypass, including establishing thresholds of low oxygen delivery that might be associated with acute kidney injury. Our team questioned whether the biostatistical approaches used by other investigative teams were modeling oxygen delivery in a mechanistically intuitive fashion. With that mind, we wanted to evaluate whether the thresholds previously identified by other investigative teams were robust when using a more biologically plausible biostatistical approach.”
Nadir indexed oxygen delivery
To identify relevant thresholds, Likosky and colleagues used a metric called nadir indexed oxygen delivery (nadir DO2i), but calculated it using risk-adjusted Constrained Broken-Stick models, in contrast to the Sudden-Jump model used in most previous studies on this topic.
“DO2i has been used in the literature and makes intuitive sense with the kidney's need for oxygen and lower oxygen delivery contributing to kidney injury,” Likosky told Healio. “However, our goal wasn’t as much to evaluate how good a metric DO2i is. Rather, it was to assess the threshold of oxygen delivery during cardiopulmonary bypass that increases a patient’s risk of postoperative acute kidney injury during cardiac surgery.”
The cohort included 3,933 patients (mean age, 64 years; 34% women) who underwent full cardiopulmonary bypass surgery between May 2016 and December 2021, of whom 29.4% had any postoperative acute kidney injury (AKI) and 7% had stage 2 or 3 AKI.
Median nadir DO2i was lower in those with AKI compared with those without it (197.9 mL/min/m2 vs. 217.2 mL/min/m2; P < .001) and in those with stage 2 or 3 AKI compared with those with stage 1 or no AKI (186.9 mL/min/m2 vs. 213.8 mL/min/m2; P < .001), according to the researchers.
In risk-adjusted analyses, the estimated threshold for nadir DO2i was 231.2 mL/min/m2 for any AKI and 103.3 mL/min/m2 for stage 2 or 3 AKI, the researchers wrote.
One previous study using the Sudden-Jump model had reported a nadir DO2i threshold of 272 mL/min/m2 for any AKI, and others had reported similar figures, they wrote.
Improving patient management
“When using biologically plausible analytical approaches, our findings suggest that thresholds for nadir oxygen delivery during cardiopulmonary bypass that expose a patient to increased risk of acute kidney injury are lower than previously reported,” Chi Chi Do-Nguyen, DO, integrated thoracic surgery resident at University of Michigan Health, told Healio.
The findings need to be replicated in other large multicenter series, Do-Nguyen told Healio.
“The use of DO2i could be part of a broad, multipronged approach to reducing kidney injury during cardiac surgery,” she said. “Institutions should create and support multidisciplinary workgroups (involving members of the perioperative team and quality improvement personnel) to review their own experiences and identify evidence-based protocols to guide their decisions about how best to manage their patients during cardiopulmonary bypass and throughout a patient’s hospital stay.”
For more information:
Donald S. Likosky, PhD, and Chi Chi Do-Nguyen, DO, can be reached at likosky@med.umich.edu.
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