The process of HD involves a dialyzer which contains semipermeable membrane with microscopic holes that allow only some substances to cross. Dialysate, also called dialysis fluid, is a solution of pure water, electrolytes and salts, such as bicarbonate and sodium, passes through one side of the membrane while blood from patients circulate through the other side of the membrane. Due to the difference in concentration, wastes will move through the semipermeable membrane to create an equal amount on both sides. Since there are different compositions of dialysate, electrolytes and other solutes can be manipulated to desired lab values. Dialysis can cause a decrease in osmolality due to removal of urea and other small solutes. HD also removes creatinine, potassium, phosphate, calcium, and magnesium, increase or decrease sodium, and change pH level by removing or infusing bicarbonate.