Evaluating blood loss in children's orthopaedic surgery: a simplified method of photometric analysis of eluted swabs.

Assessment of intraoperative blood loss by the traditional method of weighing swabs (4 x 4-in. gauze) is propounded to estimate approximately 75% of total loss, although many believe this still underestimates actual loss. The various components of this technique were studied by using the method of colorimetric analysis of eluted swabs, but utilising a modern spectrophotometer. We modified and simplified the technique, resulting in > 95% accuracy in all instances, and by so doing, created a potential technique for use in children's orthopaedic surgery. Weighing swabs was found to estimate only approximately 50% of total loss, and this was supported in the pilot clinical study by a postoperative decrease in haemoglobin of 8-17%, despite transfusion, when transfusion was based on the traditional "75%" rule. Because it is impractical to elute theatre apparel and instruments to increase the accuracy of the elution method in the perioperative time scale necessary, a compromise may be to use the new "50%" rule as a better estimate of total blood loss when calculating transfusion requirements.