Preconditioning Against Renal Damage Under Contrast Examination

Intravenous contrast for diagnostic and therapeutic interventions is a leading cause of hospital-acquired acute renal failure (1). Contrast-induced acute kidney injury (CI-AKI) occurs through a complex mechanism including toxic and hypoxic renal tubular injury, diminished renal parenchymal circulation and renal endothelial dysfunction with the production of oxygen free radicals due to post-ischaemia oxidative stress (2). With increasing numbers of diagnostic and therapeutic interventions, the incidence of CI-AKI will rise over the next few decades. Already, 40% of general surgical in-patients undergo cross-sectional imaging with computed tomography (CT), largely using contrast (3). Optimal clinical care in many specialties such as oncology, emergency medicine and surgery relies upon information derived from contrast-enhanced cross-sectional imaging. In consequence, large numbers of patients are exposed to the risk of CI-AKI. Current CI-AKI preventive measures comprise identification of at-risk patients, minimisation of contrast dose and the use of intravenous volume expansion (4). Simple, cost-effective methods to reduce CI-AKI are required.

Risk factors for CI-AKI include advanced age, diabetes mellitus, pre-existing renal insufficiency and congestive cardiac failure. Dehydration also increases the risk (5). While patients over the age of 65 years currently account for 11% of the Irish population, they account for 30% of surgical admissions (6). In a recent cohort study of 1800 surgical in-patients in a major Irish teaching hospital, acute renal failure was a common major complication, occurring in 2.4% of patients (6). Multivariate analysis of this cohort demonstrated that increasing age and emergency admission were both independent risk factors for complications (6). Emergency surgical patients constitute a high-risk group in whom simple methods to minimise complications are required.

Remote ischaemic preconditioning (RIPC) is a simple technique whereby brief periods of skeletal muscle ischaemia and reperfusion triggers a period of resistance to ischaemia-reperfusion injury in distant tissues e.g. heart or kidney (7). It reduces renal damage following endovascular aneurysm repair, a procedure requiring considerable contrast-volumes (8). A recent meta-analysis demonstrated that RIPC significantly reduced post-procedure creatinine levels following cardiovascular procedures, though there was considerable clinical heterogeneity between the included trials (9). We hypothesise that RIPC induced using brief periods of upper limb ischaemia-reperfusion will reduce AKI in patients undergoing contrast enhanced CT scans.

The hypothesis that RIPC will reduce CI-AKI was first explored by Whittaker and Pryzklenk (10). They utilised available data from a patient cohort undergoing emergency coronary angioplasty. Patients with 1 to 3 balloon inflations in the coronary artery served as the control group whilst those with >3 balloon inflations served as the RIPC group.Both groups displayed an immediate improvement in estimated glomerular filtration rate (eGFR). However, the control group then displayed a statistically significant decrease in eGFR by day 3 post-procedure (77 +14 ml/min/1.73m2 versus 70 +12 ml/min/1.73m2). The RIPC group displayed no such difference by day 3 (81 +21 ml/min/1.73m2 versus 80 +14 ml/min/1.73m2) despite having received a larger contrast volume. This observation implied a potential protective effect for RIPC.

Greater availability of CT technology has led to a dramatic increase in the number of patients undergoing ce-CTAP in recent years. Between 1996 and 2010, the number of patients undergoing CT scans in the United States tripled, increasing by 8% per annum (11). Simultaneously, an increasingly elderly and sick population means that many patients now have multiple co-morbidities, increasing their risk of contrast-induced acute kidney injury. Approximately 6.5% of patients undergoing ce-CT develop acute kidney injury defined as a >25% increase in serum creatinine from baseline (12). Simple methods to reduce CI-AKI are required. We propose that the use of remote ischaemic preconditioning could be a simple, cost-effective measure that could decrease the incidence of CI-AKI in high risk patients undergoing contrast enhanced CT scans.