Zeitschrift für Geburtshilfe und Neonatologie
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Z Geburtshilfe Neonatol · Jun 2011
The clinical significance of base excess (BEB) and base excess in the extracellular fluid compartment (BEEcf) with and without correction to real oxygen saturation of haemoglobin.
Besides actual pH, base excess [ctH (+)(B) (mmol/l)] is of major importance since it is meant to reflect lactate acidosis due to foetal hypoxia; In vivo BE (B) is not independent from pCO (2). Independence is achieved by using the extended extracellular fluid (Ecf) for dilution of haemoglobin (cHb (B)) thus reducing cHb (B) to cHb (B)/3 (in the foetus to cHb (B)/4). Correction of ctH (+)(B) from the normally low foetal oxygen saturation by reoxygenation of Hb increases ctH (+)(B), resulting in 4 different variables: ctH (+)(B,act) (=BE (B)), ctH (+)(Ecf,act) (standard BE), ctH (+)(B,ox.) and ctH (+)(Ecf,ox). 3 questions arise: (i) which variable is most appropriate for perinatal acid-base studies? (ii) are there clinical advantages for using BE when compared with actual pH (UA), and (iii) what are the thresholds of the BE parameters? ⋯ Actual pH (cH (+)) offers the closest correlation with 2 essential clinical parameters: FHF and Apgar scores; the advantages of ctH (+)(B) and ctH (+)(Ecf), are not self-evident; if determination of the metabolic component becomes necessary standard BE, (ctH (+)(Ecf)) should be used with correction to 100% oxygen saturation (ctH (+)(Ecf,ox.)) of haemoglobin (HbF), because this quantity (after pH (UA)) correlates best with clinical indices. However if the 'correction' is omitted the difference seems clinically irrelevant.