Renal tissue desaturation and acute kidney injury in infant cardiac surgery: a prospective propensity score-matched cohort study.
This paper purports to show that renal desaturation as measured by near-infrared spectroscopy (NIRS) is a predictor of renal impairment in infants undergoing ventricular septal defect (VSD) repair.
There is some published work (mostly small case series) that has shown that low somatic NIRS in neonates/infants is predictive of gastrointestinal ischaemia or renal impairment. This paper looks at a larger relatively homogeneous group to discern whether there is an association between renal desaturation and renal impairment.
Study
The authors looked at 242 infants undergoing VSD repair and using propensity score matching compared the incidence of renal impairment in those with intraoperative renal desaturation as measured by NIRS versus those without it.
The study was performed over 20 months in infants 1-12 months old and weighing less than 10kg who did not have co-morbidities. Standard anaesthesia management was used and the OR staff were blinded to the NIRS recordings.
Renal desaturation was defined as a 20% plus drop in SrtO2 for greater than 60 seconds.
Primary outcome was acute kidney injury (AKI), defined using modified KDIGO criteria, arising 1-3 days postoperatively.
Power analysis was based on the first 50 patients.
AKI occurred in 31% of infants overall with 77% diagnosed on day 1.
85% were KDIGO stage 1, 11% stage 2, and 4% stage 3. None required renal replacement therapy (RRT).
Propensity matching used a total of 28 confounders and after matching, 38 infants had renal desaturation and 114 did not. 47% of those in the desaturation group and 27% of those who did not exhibit renal desaturation developed AKI. This was statistically significant (p = 0.022). Grades of AKI were similar in each group.
The authors also looked at cumulative time of renal desaturation and showed that this correlated with degree of creatinine rise postoperatively.
Positive points
This study had large numbers of a relatively homogeneous group collected over a short time and well matched.
The intraoperative management of these patients was similar to other centers.
The NIRS methodology is appropriate and validated.
There was an increased incidence of AKI in patients with renal desaturation that appeared to be dose related.
Issues
Applicability to a wider group of cardiac patients.
What is the cause of renal impairment – not solely renal perfusion issue as significant number of patients without desaturation developed renal impairment.
None required RRT – so is the renal impairment important? Probably yes, as there are an increasing number of long-term follow-up studies showing that although renal function (as measured by creatinine/urea) returns to normal values, there is a significant number of these patients that go on to develop chronic renal impairment.
The time and degree of renal desaturation (60sec and >20% below baseline) seem inadequate to cause renal damage.
What is the cause of the renal desaturation? The propensity matching was extensive so it is unclear what resulted in this difference i.e., what could you alter to prevent this?
Takeaway Messages
- Renal hypoperfusion during cardiopulmonary bypass (CPB) for VSD repair as measured by NIRS, results in increased renal impairment postoperatively.
- Renal hypoperfusion may not be detected using standard monitoring from flow rates or mean arterial pressure (MAP).
- The importance of postoperative renal impairment of this degree is unclear.
- Future studies are needed to determine if this is clinically important and if it is, are there any ways of preventing it.
Reviewed by D. Buckley
