• A patient’s plasma volume may be estimated at 40 mL/kg, determined from a nomogram based on the patient’s sex, height, weight, and Hct, or estimated according to the weight and Hct by the following formula:
  • Circulating blood volume = patient weight (kg) × 70 mL/kg
  • Circulating plasma volume = circulating blood volume × (1 − Hct [expressed as a decimal])
• After exchange of 1 or 1.5 plasma volume exchange, approximately 62% or 88%, respectively, of the original plasma has been removed. The efficiency of plasma exchange decreases with further exchange.
• IgM, which is largely confined to the intravascular space, is removed most efficiently.
• IgG is removed less efficiently by plasma exchange because only one-third of the body’s IgG is located in the intravascular space, although IgG levels can be reduced by repeated TPE.
• Patients receiving plasma exchange for immunologic diseases generally have 1.0 to 1.5 plasma volumes exchanged at each procedure; this is often repeated, for a total of five exchanges over a period of 7 to 10 days. Such plasma exchange schedules have been determined empirically based on calculations that a 1-log (90%) reduction of IgG is achieved after five TPE.