[Multicenter clinical study on umbilical cord arterial blood gas parameters for diagnosis of neonatal asphyxia]

Abstract

Objective: To obtain the normal range of statistics of umbilical artery blood gas parameters of the newborns for diagnosis of neonatal asphyxia.

Methods: From March 2008 through September 2009, 17 978 singleton term appropriate for gestational age (AGA) or larger than gestational age (LGA) newborns in six hospitals of five provinces/autonomous regions were consecutively enrolled in this prospective study. The normal ranges of umbilical artery blood gas parameters were obtained from 17 645 newborns with 1 min Apgar score ≥ 8. The correlations between umbilical artery blood pH, BE and prenatal high-risk factors, Apgar scores, and organ damage were analyzed. The diagnostic criteria for asphyxia included the following: (1) Having high-risk factors that might cause asphyxia; (2) 1 min Apgar score ≤ 7 (the respiratory depression must be present); (3) At least one organ showed evidence of hypoxic damage; (4) Other causes of low Apgar score were excluded. The study focused on the distributive characteristics of umbilical artery blood pH (clinically corrected by Eisenberg formula) and BE values of the asphyxiated and non-asphyxiated cases in low Apgar score group, as well as the sensitivity and specificity of different selected pH and BE threshold spots within their distributing ranges.

Results: Among the 17 978 singleton term AGA or LGA newborns, the statistically normal range of umbilical artery blood pH, BE for the 17 645 cases with 1 min Apgar scores ≥ 8 were 7.20 ± 0.20 (x(-) ± 1.96 s) and -7.64 ± 10.02 (x(-) ± 1.96 s), respectively. The pH well correlated positively with BE (r = 0.734, P < 0.01). The umbilical artery blood pH and BE values correlated positively with the Apgar scores. The umbilical artery blood pH and BE values correlated negatively with organ damage (r = 1, the P values = 0.000 for both). Among the 333 low Apgar score cases, the umbilical artery blood pH corrected values and BE values of the asphyxiated group (163 cases) were 7.011 ± 0.09 (x(-) ± s) and -14.98 ± 2.99 (x(-) ± s), being lower than 7.18 ± 0.07 (x(-) ± s) and -8.56 ± 4.68 (x(-) ± s) of the non-asphyxiated group (170 cases) respectively (t = 14.3, 8.79, P values < 0.001). The distributing ranges of the umbilical artery blood pH corrected values and BE values of the asphyxiated group were < 7.00- < 7.20 and < -10- < -18, respectively. Within the above ranges, none of selected spots with both high sensitivity and high specificity was found.

Conclusions: The statistically normal range of the umbilical artery blood pH and BE for the newborns was 7.20 ± 0.20 (x(-) ± 1.96 s) and -7.64 ± 10.02 (x(-) ± 1.96 s) respectively. Owing to individual differences and the measured blood pH should be clinically corrected, the statistical threshold was not fully equal to the clinicopathological threshold. The pathological threshold of pH or BE for neonatal asphyxia is a range rather than a fixed point. The distributing range of the umbilical artery blood pH clinically corrected values and BE values for neonatal asphyxia were < 7.00- < 7.20 and < -8- < -18, respectively. In the presence of the other four indexes for diagnosing neonatal asphyxia, the blood gas index should be used flexibly in the above ranges.