Dialysis is a medical treatment that filters waste products and excess fluid from the blood when kidneys can no longer perform effectively. It helps regulate blood pressure and maintain a balance of important minerals like potassium, sodium, and calcium. While it supports patients with kidney failure, dialysis is not a cure.
The Need for Maximum Fluid Removal
Fluid overload, or hypervolemia, occurs when kidneys fail to remove enough water, leading to its accumulation. This can cause swelling in the face, ankles, and feet, and discomfort from cramping or headaches. Excess fluid also elevates blood pressure, straining the heart and potentially leading to heart failure. Fluid buildup in the lungs can cause shortness of breath, making maximum fluid removal necessary to prevent severe complications. Such interventions are often required in severe fluid overload, pulmonary edema, congestive heart failure, or acute kidney injury where fluid accumulation is rapid.
How Fluid is Removed During Dialysis
Fluid removal during dialysis primarily relies on ultrafiltration. In hemodialysis, blood passes through a dialyzer, a filter with a semipermeable membrane. A pressure difference, the transmembrane pressure (TMP), is created across this membrane, causing water and small dissolved substances to move from the blood into the dialysate fluid. Modern dialysis machines precisely control the volume of fluid removed by adjusting the ultrafiltration rate (UFR) based on the patient’s fluid gain since their last treatment.
The dialyzer’s membrane properties, specifically its ultrafiltration coefficient (KUF), and the pressure gradient across it influence the amount of fluid removed; a higher KUF indicates a leakier membrane, allowing for more fluid removal at a given TMP. Peritoneal dialysis removes fluid using the patient’s peritoneal membrane, with dextrose in the dialysate solution creating an osmotic gradient that draws water from the blood into the solution.
Risks and Considerations in High Fluid Removal
Removing large volumes of fluid rapidly can lead to several complications. A common side effect is intradialytic hypotension, a sudden drop in blood pressure, causing symptoms like shortness of breath, muscle cramps, nausea, vomiting, or dizziness. This rapid fluid removal can also increase the risk of blood clots, potentially leading to stroke or heart damage.
Patients may also experience muscle cramps. Another less common complication is dialysis disequilibrium syndrome (DDS), causing neurological symptoms such as headache, dizziness, and changes in mental status. This syndrome occurs due to rapid shifts in fluid and solute concentrations between the blood and brain. Rapid ultrafiltration has been linked to “organ stunning,” where organs like the heart or brain may experience temporary dysfunction from acute fluid shifts. Healthcare professionals carefully monitor patients’ blood pressure and symptoms throughout the procedure to mitigate these risks.
Achieving Ideal Fluid Balance
The objective of fluid removal in dialysis is to achieve the patient’s “dry weight.” This is the lowest weight a patient can safely reach after dialysis without experiencing symptoms of dehydration or fluid overload. This target weight represents the optimal fluid volume in the body, where there is no excess fluid placing strain on organs like the heart and lungs.
Determining dry weight involves careful clinical assessment, considering factors such as blood pressure, the presence of swelling, and the patient’s tolerance to fluid removal. It is not a static number and requires regular reassessment by the medical team, typically every three to six weeks, as a patient’s body mass can change due to nutritional status or illness. Achieving this balance helps prevent complications from both too much and too little fluid, contributing to better long-term cardiovascular health and overall well-being for dialysis patients.