Correlation between actual measurement and estimation by hemoglobin dilution method

Background: Hemoglobin dilution occurs after acute blood loss, by shifting extravascular blood components into the intravascular space, providing the theoretical possible to calculate amount of blood loss by comparing this difference. Assessing blood loss during the operative procedure is crucial to provide appropriate treatment, however there are few objective standards by which to make this assessment. In this study, we used the hemoglobin dilution method to predict blood loss following an operative procedure. Methods: During the year 2007, 96 patients who had undergone lumbar spinal fusion surgery were enrolled in this study. On a retrospective basis, we investigated the weight, height, intraoperative blood loss, hemoglobin change, and the amount of transfused erythrocytes by reviewing anesthetic notes from the surgery. On the basis of these data, we calculated estimated blood loss by using Nadler��'s formula. Results: The majority of study participants were female and average age was 60.1 yrs. We observed 2.3 g/dl decrement of postoperative hemoglobin, and estimated blood volume was 3,599 ml. Estimated blood loss was 853.7 ml, and observed blood loss was 1,070 ml, thus creating 217.1 ml difference. Analysis showed a moderate degree of correlation between observed and estimated values and a correlation coefficient of 0.49. We obtained regression equations of y = 0.828x ��� 363.5. Conclusions: Estimated blood loss was underestimated compared to observed values, by 20%, and this discrepancy is was attributed to ethnic differences. To predict a precise estimated blood loss, attempts to make a modified formula targeted to the Korean population are required