Fluid dynamics in chronic kidney patients - exploring bioimpedance innovations.

Abstract

People with kidney failure have a much higher risk to die from a cardiovascular event compared to patients without kidney failure. One of the causes is the fluctuation between too much and too less fluid in the body, and the associated high or low blood pressures. These dynamics in fluid balance were examined in this doctoral dissertation by use of electrical impedance measurements in the body. If our kidneys fail, less waste products and less fluid volume are excreted. Fluid accumulation can cause high blood pressure, which increases the risk of cardiac or cerebral infarction and accelerates kidney failure. Fluid accumulation can also oppress our lungs, which leads to acute respiratory distress. If we could monitor whether a certain amount of fluid overload will cause damage, we could treat it in time and avoid these complications. However, precisely detecting fluid overload is challenging because fluid is distributed throughout the body and therefore only visible when the body is several liters overloaded. When kidney failure has reached an end-stage, patients can be treated by hemodialysis. This means that three times per week, 2 - 4 liters of excess fluid is removed by the dialysis machine in a short time. This fast removal of large amounts of volume can induce low blood pressure, which causes low blood flow and dysfunction of organs like the brain, heart, intestines, kidneys and muscle. In-between two dialysis sessions, fluid accumulates again. These dynamics from too less to too much fluid, and from too low to too high blood pressure, are an additional burden to the heart. If we could monitor when a patient gets to the point of too less fluid during hemodialysis, and risks a low blood pressure, or when too much fluid has been accumulated in-between the dialysis days, then we could act on this and possibly avoid complications. However, patient-friendly diagnostic monitoring tools are lacking. In clinical practice, we estimate fluid balance by physical examination and the follow up of body weight before the start of each dialysis treatment. Additionally, we monthly measure electrical impedance of the whole body before the start of a dialysis treatment, by which we can estimate how much fluid the body contains. Because water is a good conductor, little impedance will be present in case of fluid overload, and impedance will increase when fluid is removed from the body. Commercial devices do not allow impedance measurements during hemodialysis and therefore, they are not suited for longitudinal measurements. Blood pressure is monitored by a standard device with a cuff, as well as before as during dialysis, but this device knows some limitations. In-between two dialysis sessions, fluid balance or blood pressure is not monitored. The goal of this doctoral dissertation was to explore whether bioimpedance measurements by an innovative device can contribute to the monitoring of fluid balance and blood pressure in patients with kidney failure. A wearable device, designed by imec The Netherlands, has been tested on reliability and applicability compared to commercial devices. Several interpretations of bioimpedance have been examined. The results of two scientific studies are described. The first study has been conducted in a hemodialysis population (Bigfoot study). In the second study, patients with kidney failure not on dialysis were included (Horuz study). These studies have shown that measurements of bioimpedance not necessarily should be conducted throughout the whole body. The best place to monitor fluid balance and blood pressure seemed to be the chest. This opened the door for measurements during hemodialysis. Indeed, the wearable device was capable to conduct frequent measurements during dialysis. In addition, volume changes during dialysis could be tracked accurately by bioimpedance measurements of the chest. This also seemed to be a promising technique to monitor changes in blood pressure during dialysis. On top of that, we discovered important findings on how fluid behaves in-between two dialysis sessions by visiting patients at home and measuring their blood pressure and bioimpedance. Finally, we have learned that bioimpedance measurements of the chest in patients with kidney failure not on dialysis can provide more knowledge in the distribution of their fluid balance. In the future, this wearable device should be further developed to a patientfriendly format. Patients will be able to monitor their own fluid balance and blood pressure, as well as during dialysis as at home, and anticipate complications. We believe that an ongoing innovation of wearable bioimpedance, and hemodynamic monitoring in general, will contribute to more autonomy for the patient with kidney failure and reduce their cardiovascular risk.