Hidden acidosis: an explanation of acid–base and lactate changes occurring in umbilical cord blood after delayed sampling
Correspondence: Dr P Mokarami, Department of Neurology, Skåne University Hospital, S–20502 Malmö, Sweden. Email firstname.lastname@example.org
To explore the ‘hidden acidosis’ phenomenon, in which there is a washout of acid metabolites from peripheral tissues in both vaginal and abdominal deliveries, by investigating temporal umbilical cord blood acid–base and lactate changes after delayed blood sampling.
Prospective comparative study.
Umbilical cord blood from 124 newborns.
Arterial and venous cord blood was sampled immediately after birth (T0), and at 45 seconds (T45), from unclamped cords with intact pulsations taken from 66 neonates born vaginally and 58 neonates born via planned caesarean section at 36–42 weeks of gestation. Non-parametric tests were used for statistical comparisons, with P < 0.05 considered significant.
Main outcome measures
Temporal changes (T0–T45) in umbilical cord blood pH, the partial pressure of CO2 () and O2 (), and in the concentrations of lactate, haematocrit (Hct), and haemoglobin (Hb).
Delayed umbilical cord sampling affected the acid–base balance and haematological parameters after both vaginal and caesarean deliveries, although the effect was more marked in the group delivered vaginally. The hidden acidosis phenomenon explains this change towards acidaemia and lactaemia. Arterial haemoconcentration was not the explanation of the acid–base drift.