2 Clinical need and practice
2.1 The purpose of this assessment is to evaluate the clinical and cost effectiveness of using multiple frequency bioimpedance devices to monitor the hydration status of a person with chronic kidney disease who is having either haemodialysis or peritoneal dialysis treatment.
2.2 Dialysis is used to replace renal function in people with severe chronic kidney disease, including removing excess fluid from the blood. It is important that a correct volume of fluid is removed; removing too little will result in the person becoming overhydrated and may lead to oedema, increased blood pressure and an increased risk of cardiovascular events. Alternatively, if too much fluid is removed during dialysis the person will become underhydrated, which can result in the loss of residual renal function and an increased incidence of symptoms such as cramps, nausea and dizziness.
2.3 In current practice, the fluid status of a person on dialysis is usually determined by clinical assessment, taking into account clinical features and symptoms that suggest overhydration or underhydration. People who are over or underhydrated are often asymptomatic, so clinical assessment may not identify this. Multiple frequency bioimpedance devices give an objective assessment of a person's fluid status which, when used with clinical assessment, may help make decisions about the amount of fluid to remove in dialysis. Using the devices may help reduce the incidence of overhydration or underhydration and their associated clinical consequences.
2.4 Chronic kidney disease can be categorised into 5 stages of severity, in accordance with NICE's clinical guideline on chronic kidney disease. If chronic kidney disease progresses to the most severe stage (stage 5), kidney failure occurs and renal replacement therapy (transplantation or dialysis) is needed for survival.
2.5 Dialysis replicates many of the functions of a healthy kidney, for example, filtering waste products and excess water from the blood, and is available in 2 types: haemodialysis and peritoneal dialysis. When used as longer-term renal replacement therapy, dialysis can be delivered in an outpatient setting or at home (see NICE's technology appraisal guidance on home compared with hospital haemodialysis for patients with end-stage renal failure).
2.6 The management of chronic kidney disease and renal replacement therapy is described in NICE's guidelines on chronic kidney disease, peritoneal dialysis, anaemia management in chronic kidney disease and hyperphosphatemia management in chronic kidney disease.
2.7 One of the main aims of dialysis is to remove fluid which builds up because of reduced renal function. Determining the volume of fluid to be removed by dialysis involves identifying a target weight for a person. This is often defined as how much a person should weigh at the end of a haemodialysis session or, for people who have peritoneal dialysis, how much they should weigh in the morning. Comparing a person's current and target weight helps to decide the amount of fluid to be removed during dialysis.
2.8 Assessing fluid status to set, or adjust, a person's target dialysis weight is usually based on clinical judgement and identifying symptoms of over or underhydration. Clinical parameters assessed include blood pressure, the presence of oedema, weight and any intradialytic or interdialytic symptoms that could suggest overhydration or underhydration (such as cramps, fatigue or nausea). Identification of a person's first target weight often involves gradually reducing a person's post-dialysis weight over successive dialysis sessions until it is as low as can be tolerated.