Cord blood sampling for lactate must not be delayed

Blood gas analysis of umbilical cord blood provides the means for establishing the acid-base status of babies at the time of birth. If there is to be any delay in sampling, the portion of cord from which the sample is to be taken should be double-clamped and thereby isolated from the placenta. 

Previous studies have demonstrated that so long as blood is sampled from a length of cord clamped at the time of birth, measurement of pH, pCO₂ and pO₂ is reliable for up to an hour after birth. 

According to the results of a recently published study this is not the case if lactate is to be measured. Paired samples of blood from clamped and unclamped cord blood vessels were taken for lactate measurement at 0, 20, 40 and 60 minutes after birth of 38 full-term healthy infants. Both arterial and venous blood lactate were significantly higher at 20 minutes after birth than at the time of birth. 

The increase continued with time. The rate of increase in blood lactate was, as expected, greater in unclamped vessels than clamped vessels, but even in clamped vessels the increase was of sufficient magnitude (on average 0.7 mmol/L at 20 minutes and 2.2 mmol/L at 60 minutes) for the authors to conclude that "cord blood samples taken after 20 minutes delay are unreliable for lactate measurement, even if the vessel has been doubly clamped". 

If cord blood is to be used to measure lactate, blood must be sampled at the time of birth or certainly within 20 minutes of birth.