Abstract-Hemofiltration (HF) is a group of blood purification therapies used to treat patients with kidney injury. HF works using a process called ultrafiltration (UF) that removes excess liquid accumulated in the patient's body caused by lack of excretion. UF progress is monitored by the HF machine, but the state-of-the-art method is cumbersome and could be more accurate. In this work, a system composed by two optical sensors is proposed for real-time non-invasive estimation of ultrafiltration rate. This new system is simple, rugged, low-cost and operates on sound theoretical foundations. The sensor system has been tested with two different experimental protocols and showed good correlation between its output and the reference value of the ultrafiltration rate (R 2 =0.97), as well as improved accuracy compared to the available commercial machine (≃12ml/h). This system also has the potential to simplify the architecture required by critical care blood purification machines to perform UF control.Index Terms -Biomedical Measurement, Blood, Blood Purification, Hemofiltration, Hemoglobin, Measurement, Optical Sensor, Ultrafiltration
I. INTRODUCTIONRenal replacement therapies (RRTs) have been developed to treat individuals affected by kidney failure, known as nephropathic patients. RRTs have the following targets:• Removal of excess fluid accumulated by the patient due to lack of kidney excretion.• Re-balancing concentration of specific substances in blood, for example electrolytes such as sodium.• Removal of the toxic by-products of metabolism, such as urea.Several types of therapies and machines have been developed. The main distinction of therapies is between those developed † First two authors A. Visotti and E. Ravagli contributed equally to this work. A. Visotti, C. Perazzini, D. Drudi, and C. Ghidini are with the company IBD Srl (https://www.ibdsrl.com/), Forlì, Italy.E. Ravagli and S. Severi* are with the Department of Electrical, Electronic and Information Engineering "Guglielmo Marconi", University of Bologna, Cesena, Italy (e-mail: stefano.severi@unibo.it).to treat patients with acute kidney injury (AKI), who are expected to partially or fully regain kidney functionality, and those for patients with chronic kidney disease (CKD), who require periodic treatment for the rest of their lives or until kidney transplant. Therapies such as hemodialysis [1]-[3] and peritoneal dialysis [4] are the standard for CKD patients; while for AKI, slow, prolonged, one-time treatments are chosen to perform blood purification until kidney function is regained [5]- [7]. The effect of RRTs on the patient has been studied both clinically and with mathematical tools such as kinetic models, developed to describe the transfer of water and solutes across body compartments during .This work represents a technological improvement for AKI therapies where fluid removal is the main target -therapies also known as hemofiltration (HF). Fluid removal is performed by means of a physical principle called ultrafiltration (UF) [11]-[13]. Example...
