Influence of variations in blood haemoglobin concentration on the calculation of blood loss and volumetric irrigating fluid balance during transurethral resection of the prostate.

Blood loss in 38 patients undergoing transurethral resection of the prostate (TURP) was calculated in four different ways by using various reference blood haemoglobin determinations (B-Hb) during the course of preparation and surgery. Blood loss became greater the later the B-Hb was drawn. This increase was because variations in B-Hb acted to underestimate the loss of plasma. The variations also distorted the irrigating fluid balance to give too low values for the absorption of irrigating fluid. It is possible to correct for the errors in blood loss and volumetric fluid balance by the use of haemodilution factors. Haemodilution was greater in patients with complications such as absorption of irrigating fluid or excessive blood loss than in patients without such features if Ringer's acetate was used for i.v. fluid supplementation. With dextran 40, all patients had a similar degree of haemodilution.