Validation of a fluid sampling system and analysis of microplastic release in continuous renal replacement therapy

Acute kidney injury (AKI) is frequently observed in critically ill patients in intensive care unit (ICU). Extracorporeal blood purification therapies, mainly continuous renal replacement therapy (CRRT), are often used in these patients to support the renal function. These treatments work by removing solutes and waste substances through haemodiafiltration membrane. The amount of purification during CRRT identifies the concept of "dose", that is the amount of clearance desired for a given solute. The ability of solutes to pass through the membrane and be eliminated within the waste fluids is dynamically and unpredictably reduced by “membrane fouling”, i.e. clogging of pores of haemodiafiltration membrane due to several causes. The resulting unintentional "undertreatment" can have a detrimental effect on patient outcome, so that careful and frequent monitoring of the “current effective delivered dose” is recommended. To make this happen, a system is developed to sample fluids from the extracorporeal circuit to quantify the actual biological dose administered during continuous dialysis treatment. The system provides for automatic sampling of the biological material, collected in a controlled manner, with a suitable speed and volume, from the sampling sites present in the pre-filter, post-filter and effluent lines. To assess the adequacy of the sampling system, the calculation of the percentage error of mass balance for a particular solute is used. A specific cause of “membrane fouling”, which may have a direct effect on extracorporeal transmembrane clearance of water and waste solutes, is clogging of the pores of the haemodiafiltration membrane due to the release of particles into the extracorporeal circuit. Dialysate and replacement bags are strictly required to perform CRRT. These electrolyte solutions, stored within plastic bags often heat-sealed, are infused into the extracorporeal circuit releasing often microplastic particles pre- and/or post- filter when used in routine practice. Moreover, peristaltic pumps are used to move fluids into the circuit. This compression may release particles into the extracorporeal circuit in a process called spallation. Spallation-induced particles are proportional to the pump speed and correlate with increased production of interleukin (IL-1) by macrophages, local and systemic endothelial activation and finally with patient’s organ damage. Indeed, the microplastic particle loaded both due to replacement/dialysate solutions and spallation may reach the patient inducing the particles-related complications. The aim of the study is to verify the presence of particles in the CRRT solutions, their release into the extracorporeal circuit and to evaluate the qualitative and quantitative effectiveness of in-line filtration for particles retention.