I believe there is an error in the method used by the Paris group in the calculation of estimated red cell deficit (ERCD). They state that ERCD=estimated red cell volume (ERCV)xpacked cell volume (PCV) in Meyer and colleagues' paper,1 and ERCD=ERCVxdifference in haematocrit in Dahmani and colleagues' paper.2 But, ERCD should be calculated as estimated blood volume (EBV; not red cell volume)xdifference in haematocrit. This method has been used in a number of other studies that have taken ERCD=EBVxdifference in haematocrit.4
Birmingham, UK
Therefore, we agree with Dr Carver that there is a difference between the method of Kearney3 and our method.1 2 With our formula we have taken into account the volume of blood transfused during and after surgery: ERCMtransfused=EBVx0.75, where 0.75 represents the mean haematocrit in packed red cells. From our point of view, this method allows more precise estimation of ERCD. With this mode of calculation we found some negative values indicating overcompensation of blood loss (Table 1). We think that estimating blood loss without taking into account the red cell volume transfused is not appropriate in this kind of haemorrhagic surgery. Dr Carver suggests using another method of calculation of ERCD, with ERCD=EBVxdifference in haematocrit, in accordance with other studies.4 However, using this formula (ERCD=EBVxdifference in haematocrit) does not significantly modify the results or their interpretation. To illustrate this point we have performed the statistical analysis again with both the new,4 and the old formulae,1 2 for ERCD, using the data from the study by Dahmani and colleagues (Table 1).2 As can be seen from this table, there is no significant difference between the results obtained with the two methods of calculation of ERCD. In conclusion, therefore, we think that both methods of calculation of blood loss are useable, but that our method allows more precise estimation of total blood loss.
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Paris, France
References
1 Meyer P, Renier D, Arnaud E, et al. Blood loss during repair of craniosynostosis. Br J Anaesth 1993; 71: 8547[Abstract]
2 Dahmani S, Orliaguet GA, Meyer PG, Blanot S, Renier D, Carli PA. Perioperative blood salvage during surgical correction of craniosynostosis in infants. Br J Anaesth 2000; 85: 5505
3 Kearney RA, Rosales JK, Howes WJ. Craniosynostosis: an assessment of blood loss and transfusion practices. Can J Anaesth 1989; 36: 4737[Abstract]
4 Walters JH, Lee JS, Klein E, O'Hara J, Zippe C, Potter PS. Preoperative autologous donation versus cell salvage in the avoidance of allogeneic transfusion in patients undergoing radical retropubic prostatectomy. Anesth Analg 2004; 98: 53742