LAUSR

Editor Thank you to Xue et al. for their review of our paper1, highlighting common concerns regarding perioperative administration of intravenous contrast media. Our study was one of the largest prospective, multicentre studies on acute kidney injury (AKI) in this population1. We agree there are several additional data points that may have been of interest within the current analysis. However, the granularity of data collected was limited due to a pragmatic approach to study design within a student/traineeled group; typically having to be limited to 10–15 pre-, intraand postoperative unique data points. Given radiology guidelines generally advise to use the minimum effective dose of contrast media for imaging and no evidence that commonly used contrast media (isoor low osmolarity) were significantly associated with AKI2, it was felt that there was insufficient justification to prioritize collection. We agree with the recent shift within radiology to distinguish between AKI that is contrast-associated (CA-AKI) and contrast-induced (CI-AKI)3. Reduced renal perfusion (whether in the context of haemodynamic instability or hypovolaemia) is a well-established risk factor for postoperative AKI, but has not been demonstrated conclusively to be a specific risk factor for CI-AKI within well controlled studies4. As postoperative AKI frequently involves pre-renal factors, the common practice of periprocedural hydration in this patient population is likely appropriate. We acknowledge within our paper this may have ameliorated the true risk of postoperative AKI in our study, even if the evidence for prevention of CI-AKI itself is mixed3,5. In the absence of evidence from RCTs on administration of contrast for CT, we rely on high-quality and well controlled observational studies to provide answers. With the common practice of periprocedural hydration, there is currently limited evidence of risk from CI-AKI in the general surgical population.