Recent advances in the monitoring and control of haemodynamic variables during haemodialysis: a review.

The human body possesses a unique set of organs that are responsible for providing homeostatic balance to the body's fluids. Of these, the kidneys regulate fluid and electrolyte balance in order to maintain the intracellular and extracellular fluid volumes and ion composition within tight limits. When kidneys fail to function normally, fluid is retained and several ions and solutes accumulate. The consequences may be life threatening. Many kidney failure patients rely on haemodialysis (HD) as a life sustaining therapy to remove the waste products and excess fluid from the circulating blood. HD is based on the principle of diffusion of solutes and ultrafiltration of fluid across a semi-permeable membrane. Fluid removal during HD results in relative hypovolaemia during which the stability of a patient relies on compensatory mechanisms to maintain blood pressure (BP). The major compensatory mechanisms include sympathetic nervous system activation of peripheral vasoconstriction together with modest heart rate acceleration to ensure the haemodynamic stability of the patient. Over the years, many monitoring tools have been developed in the hope of predicting intra-dialytic hypotensive episodes. Similarly many methods have been utilized to prevent dialysis-induced complications: ultrafiltration and dialysate sodium profiling, varying ultrafiltration based on frequent BP measurements, etc. This paper provides a comprehensive review of those monitoring and control tools. It starts with a brief introduction to human kidneys and dialysis for non-specialized readers. The paper then reviews the monitoring tools that have been applied to assess the physiological response of patients during HD. This is followed by control techniques used to prevent dialysis-induced complications.

Identification and control for automated regulation of hemodynamic variables during hemodialysis.

This paper proposes a novel model-based control methodology for a computer-controlled hemodialysis system, designed to maintain the hemodynamic stability of end-stage renal failure patients undergoing fluid removal during hemodialysis. The first objective of this paper is to introduce a linear parameter varying system to model the hemodynamic response of patients during hemodialysis. Ultrafiltration rate (UFR) and dialysate sodium concentration (DSC) are imposed as the inputs, and the model computes the relative blood volume (RBV), percentage change in heart rate ( ∆HR), and systolic blood pressure (SBP) during the course of hemodialysis. The model parameters were estimated based on data collected from 12 patients undergoing 4 profiled hemodialysis sessions. The modeling results demonstrated that the proposed model could be useful for estimating the individual patient's hemodynamic behavior during hemodialysis. Based on the model, the second objective is to implement a computer-controlled hemodialysis system for the regulation of RBV and HR during hemodialysis while maintaining SBP within stable range. The proposed controller is based on a model predictive control approach utilizing pre-defined constraints on the control inputs (UFR and DSC) as well as the output (SBP). The designed control system was experimentally verified on four patients. The results demonstrated that the proposed computer-controlled hemodialysis system regulated the RBV and HR of the patients according to individual reference profiles with an average mean square error of 0.24% and 2.6%, respectively, and thus can be potentially useful for ensuring the stability of patients undergoing hemodialysis by avoiding sudden changes in hemodynamic variables.

Linear parameter varying system based modeling of hemodynamic response to profiled hemodialysis.

This paper proposes a novel linear parameter varying (LPV) system to model the hemodynamic response of end-stage renal failure patients to profiled hemodialysis (PHD). Ultrafiltration rate (UFR) and dialysate sodium concentration (Na) are imposed as the control inputs and the model computes the relative blood volume (RBV), percentage change in heart rate (ΔDHR(%)) and percentage change in systolic blood pressure (ΔDSBP(%)) during the course of hemodialysis. Model parameters are estimated using least squares approach based on data collected from 12 patients where each patient underwent 4 profile hemodialysis sessions. Parameter identification based on four profiled sessions of the same patient revealed an average mean square error of 0.11 for RBV, 0.24 for ΔDHR and 0.43 for ΔDSBP. The results provided a good model to estimate the individual patient's hemodynamic behavior during hemodialysis. The developed model can play a vital role in designing a robust control system to automatically regulate the UFR and Na while maintaining the hemodynamic variables within stable range.

Respiration-induced changes in ear photoplethysmography relates to relative blood volume during hemodialysis.

Renal failure patients provide a good model of fluid overload with the process of hemodialysis leading to central hypovolemia. This study aims to assess if hemodialysis induces identifiable changes in ear photoplethysmographic waveform variability (PPGV). The results are based on data collected from 10 kidney failure patients undergoing regular hemodialysis; classified as either fluid removal or non-fluid removal patients. Six minutes of continuous photoplethysmography (PPG) signals were recorded at pre-dialysis, end of dialysis and at regular intervals of 20 minutes during hemodialysis. Baseline and amplitude variabilities were derived from the PPG waveform. Frequency spectrum analysis was applied to these variability signals and spectral powers were then calculated from low frequency (LF), mid frequency (MF) and high frequency (HF) bands. The results indicate that in fluid removal patients, LF (p = 0.04), MF (p = 0.03) and HF (p = 0.0003) powers of amplitude ear PPGV (expressed in mean-scaled units) showed a significant increase at the end of dialysis compared to pre-dialysis. No significant change was observed in non-fluid removal patients. A moderate correlation was found between relative blood volume (RBV) and HF power (median R = 0.64, p 〈 0.05). This study suggests that ear PPG may be a suitable monitor of the systemic circulation and can provide a non-invasive tool to detect blood volume loss.

Outcome of overseas commercial kidney transplantation: an Australian perspective.

Lack of donors has led to a worldwide increase in commercial kidney transplantation programs where recipients acquire kidneys either from executed prisoners or live non-related donors. Commercial transplantation is prohibited by legislation in Australia. Our centres have had 16 patients who have travelled overseas to receive a commercial kidney transplant; five have subsequently died. As has been found previously, patients who received commercial transplants were more likely to develop infections such as HIV, hepatitis B virus, cytomegalovirus and fungal infections. Previous reports have found that patient and graft survival were comparable to local results, whereas we found that patient and graft survival were worse than transplantation within Australia. Patients considering the option of overseas commercial donation should be advised that heightened risks to life and graft survival exist.