title: Hidden acidosis: an explanation of acid-base and lactate changes occurring in umbilical cord blood after delayed sampling.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Prospective comparative study.
  
  
  METHODS
  University hospital.
  
  
  METHODS
  Umbilical cord blood from 124 newborns.
  
  
  METHODS
  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.
  
  
  METHODS
  Temporal changes (T₀-T₄₅) in umbilical cord blood pH, the partial pressure of CO₂ (PCO₂) and O₂ (PO₂), and in the concentrations of lactate, haematocrit (Hct), and haemoglobin (Hb).
  
  
  RESULTS
  In both groups all arterial parameters, except for PCO₂ in the group delivered by caesarean section, changed significantly (pH decreased and the other variables increased). There were corresponding changes in venous acid-base parameters. When temporal arterial changes were compared between the two groups, the decrease in pH and increase in PCO₂ were more pronounced in the group delivered vaginally. Neonates born vaginally had significantly lower pH and higher lactate, Hct, and Hb concentrations at T₀ and T₄₅ in both the artery and the vein. At T₄₅, arterial PCO₂ and PO₂ levels in the group delivered vaginally were also significantly higher.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institution of Clinical Sciences, Department of Obstetrics and Gynaecology, Skåne University Hospital, Lund University, Malmö, Sweden. parisa.mokarami@med.lu.se
authors.forename: P
authors.initials: P
authors.lastname: Mokarami
authors.forename: N
authors.initials: N
authors.lastname: Wiberg
authors.forename: P
authors.initials: P
authors.lastname: Olofsson
mesh_terms: D000136:Acid-Base Equilibrium; D000138:Acidosis / Q000378:metabolism*; D001784:Blood Gas Analysis; D001800:Blood Specimen Collection; D005260:Female; D005312:Fetal Blood / Q000378:metabolism*; D006801:Humans; D007231:Infant, Newborn; D019344:Lactic Acid / Q000097:blood* / Q000378:metabolism; D011247:Pregnancy; D011446:Prospective Studies; D014470:Umbilical Cord / Q000378:metabolism*
chemical_list: D019344:Lactic Acid