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Paediatricians are faced with considerable clinical uncertainty when making decisions about blood transfusion. 1 There is a paucity of data on which to base transfusion decisions. 2 A systematic review of the literature highlighted only three randomised controlled trials of red cell transfusion in children. 3 Key unresolved issues include the haemoglobin (Hb) threshold at which a child should receive a blood transfusion and the target Hb that the clinician should aim to achieve. Lack of evidence leads to variation in transfusion practice. A recent survey of paediatric critical care physicians in Canada, using a number of hypothetical clinical scenarios, found wide variation in the physicians' Hb threshold for transfusion from 7 to 13 g/dl. 4
Once a decision is made to transfuse blood a reliable formula is needed to estimate the volume of blood that must be transfused to achieve a target Hb concentration. Paediatric and haematology textbooks provide a number of formulae, each of which takes account of the child's weight, estimated circulating blood volume, and the Hb concentration or haematocrit of the blood to be transfused. 5- 9 This relation can be summarised as:
Commonly used formulae vary according to the value that is assumed for total blood volume (TBV) and for the Hb/Hct of each unit of packed cells (table 1). Surprisingly, despite being used in everyday practice for many years, these formulae do not appear to have been validated in clinical practice.
Formula (reference) | Assumptions | Derivation |
Volume(ml) = 3 x delta Hb(g/dl) x weight(kg) 7, 8 | Donor unit Hb 23 g/dl | - |
TBV=70 ml/kg | ||
Volume = 4 x delta Hb(g/dl) x weight(kg) 6 | Donor unit Hb 23 g/dl | - |
TBV=90 ml/kg | ||
Volume = 1 x delta Hct(%) x weight(kg) 3 | Donor unit Hct 70% | - |
TBV=70 ml/kg |
We formed a clinical impression that use of the standard formulae in paediatric intensive care results in a lower than expected post-transfusion Hb level, sometimes necessitating a further transfusion within a few days. This study was undertaken to test this hypothesis and, if confirmed, to derive a more reliable formula for clinical use.
METHODS
Phase 1
The case notes of all children admitted to the paediatric intensive care...