Cord blood gas analysis - a review

Umbilical cord blood gas analysis has for many years been recommended for assessment of newborn babies after high-risk delivery associated with possible hypoxic stress and consequent risk of permanent brain damage. More recently there has been an increasing trend towards its routine use after all deliveries. 

With umbilical cord blood gas analysis becoming increasingly common, a timely wide-ranging review of the topic was recently published. Issues discussed include: obtaining the umbilical cord blood sample; normal (reference range) of measured parameters; and interpretation of results. The authors emphasize and justify the importance of sampling both arterial and venous cord blood. 

In discussion of fetal acidosis, a consequence of hypoxia, the authors state that there is rarely any serious outcome for babies whose cord blood pH is greater than 7.0. Even for those with pH less than 7.0, pH alone is a poor predictor of outcome. 

However, the combination of pH <7.0 and other adverse clinical features (e.g. reduced 5-min Apgar score) is highly predictive of seizures and permanent neurological deficit. 

As evidence that worsening acidosis is associated with increasing risk of adverse outcome, a study is cited which found that hypoxic-ischemic encephalopathy occurred in 12 % of infants whose cord blood pH was 6.9-7.0, but 80 % of those whose cord blood pH was <6.7. Conversely, normal blood gas results of paired (arterial and venous) cord blood samples provide robust contributory evidence that delivery was not complicated by a hypoxic-ischemic event. 

With 73 references, this paper provides a useful overview of current knowledge relating to an increasingly requested blood gas analyzer test.