Cost-effectiveness Analyses for the Prevention of Acute Kidney Injury in Patients Undergoing Cardiac Surgery in the UK

1.1 BACKGROUND Cardiac surgery associated acute kidney injury (CSA-AKI) is reported in 25-40% of patients. This variability is due to a spectrum of definitions used to classify AKI. AKI definition and staging are based on the Risk, Injury, Failure, Loss, End-stage kidney disease (RIFLE) criteria and the Acute Kidney Injury Network (AKIN) criteria, which have been further refined in the Kidney Disease: Improving Global Outcomes (KDIGO) AKI work group guidelines. It is now customary to use the KDIGO definition or its modified version - the AKIN consensus criteria. The development of AKI in the post-op cardiac surgery setting is associated with significant morbidity, mortality, prolonged intensive care (ICU) & in-hospital stays, increased treatment costs and poorer long-term survival and quality of life. Till now, no satisfactory strategy has been successful in preventing CSA-AKI despite the pre-operative knowledge of those patients who are at risk of developing it.

RenalGuard Therapy® (Cardiorenal Systems, Boston, USA) is an automated fluid management system which measures the volume of urine output and enables the physician to set a personalized, instantaneous fluid replacement rate based on the measured urine output. The RenalGuard Therapy® is comprised of a console, a single-use sterile IV infusion set, urine collection set and a cart. The console is a microcontroller device that has a means for measuring urine output and automatically controls the hydration infusion pump based on the measured urine output and clinician settings. The system is designed for infusion of hydration solutions only. The patient is connected to the console by the IV Infusion set connected to the patient's peripheral IV cannula and the urine collection set connected to the patient's indwelling Foley urinary catheter. The console continuously monitors urine production by measuring the weight of urine in the collection set, converts the urine weight to volume and then, automatically infuses the pre-set volume of hydration fluid to compensate for this output. The system is placed on a cart that is designed to hold the console, infusion set, and urine collection set. Safety mechanisms and patient's protection have been designed and incorporated into the RenalGuard Therapy® to support appropriate balance and rates of IV infusion without fluid overloading or dehydrating the patient.

The use of the RenalGuard® Therapy was initially investigated at reducing AKI in patients at risk of contrast-induced nephropathy (CIN) when undergoing either percutaneous coronary intervention (PCI) or transcatheter aortic valve implantation (TAVI). These studies showed that in patients with chronic kidney disease, the RenalGuard® Therapy reduced the incidence of AKI by 60 to 75% as compared to controls.

The use of the RenalGuard® Therapy in patients undergoing cardiac surgery has only been reported recently. The recent RCT data showed that in patients at risk of developing AKI during cardiac surgery, the RenalGuard® Therapy reduced CSA-AKI rate from 20.9% to 10%.

1.2 RATIONALE FOR CURRENT STUDY AKI is known to be associated with significant costs in healthcare delivery in patients undergoing cardiac surgery. It is estimated that AKI in that group of patients could increase costs by $19,212. In a more recent study published in 2018, the estimated additional cost for AKI post cardiac surgery was reported at $38,358 with a 10-fold increase in mortality (13.9% vs 1.3%) as well as a doubling in the in-hospital stay (mean 18.2 vs 8.6 days) when compared to non-AKI patients. ICU stay has also been reported to be prolonged in patients, post CABG, who developed AKI (mean 5.5 vs 2.2 days).