A simple and accurate method for prescribing plasma exchange.

During plasma exchange, prediction of treatment results requires an estimate of plasma volume (EPV). Using a simplified formula for EPV, EPV = [0.065 X wt(kg)] X [1-Hct], the predicted and actual decline in serum levels of several large molecular weight substances was evaluated during 102 treatments in 18 patients. Predicted as opposed to actual percent of decline in serum levels for IgG was 67 +/- 7% vs. 64 +/- 10% (+/- SD, R = 0.66, n = 40, p = 0.0001); for IgA was 66 +/- 8% vs. 66 +/- 9% (R = 0.59, n = 36, p = 0.0001); and for IgM was 66 +/- 7% vs. 69 +/- 8% (R = 0.63, n = 39, p = 0.0001). For the third component of complement the values were 58 +/- 7% vs. 61 +/- 5% (R = 0.73, n = 17, p = 0.009), and for total cholesterol 66 +/- 3% vs. 70 +/- 4% (R = 0.62, n = 28, p = 0.005). It can be concluded that a simplified method for estimating plasma exchange allows for a reasonably reliable prediction of treatment results.