The indicators of acid-base balance and the gas composition of umbilical cord arterial and venous blood in health and fetal hypoxia

The assessment of lactate and pH cord blood levels is of crucial importance for predicting such neonatal complications as transient tachypnea of the newborn, metabolic disorders, hypoxic-ischemic encephalopathy [1–6]as an early predictor of significant consequences and/or a fatal outcome in term neonates after a perinatal asphyxia. BACKGROUND Severe perinatal asphyxia can generate multiple organ dysfunction and neonatal mortality. METHODS In routine clinical practice, after an admission to the Intensive Care Unit, lactate concentration was determined in capillary blood samples during the first one to six hours after birth in 55 term newborns with the post-asphyxial hypoxic-ischemic encephalopathy. The control group consisted of 36 healthy term neonates randomly selected in the maternity ward at the Gynecology and Obstetrics Clinic. RESULTS Significantly higher concentrations of lactate (p 8.7 mmol/L with 80 % sensitivity and 82% specificity indicated the development of the hypoxic-ischemic encephalopathy stage II/III, while the lactate level>9.95 mmol/L was a predictor of death, with 75% sensitivity and 74.4% specificity. CONCLUSION Determination of lactate concentrations in serum of term newborns associated with risk factors -for the perinatal asphyxia is a useful tool in diagnosing metabolic disorders and ischemic damage, particularly severe clinical forms (Tab. 2, Fig. 3, Ref. 34. Fetal venous blood flows through the umbilical cord arteries to the placenta, where it becomes saturated with oxygen and nutrients and where it loses carbon dioxide. Then, through the umbilical cord vein arterial blood returns to the fetus. According to some authors, lactate level in venous and capillary blood samples is higher than in arterial ones [4]. Kruse O. et al. (2011) consider that these differences are not clinically significant [7]. Others indicate that blood sampling source does not affect the result of the analysis [8, 9]with respect to measurements of pH, bicarbonate, base excess and lactate, in critically ill term and premature newborns. METHODS Arterial blood samples (0.5-1 mL).

Despite the high accuracy of laboratory diagnostics, the pre-analytical procedures can vary significantly. Blood sampling source and method are not always clearly described [1, 2, 10], which may lead to difficulties in comparison with the results of different researches.

The aim of this study was to compare the indicators of acid-base balance (pH, lactate, base excess (ВЕ), oxygen partial pressure (pO2) and carbon dioxide partial pressure (pCO2) in the umbilical cord artery and vein blood of newborns after uncomplicated labor and labor complicated with hypoxia.

Materials and Methods

The study was conducted in the First Maternity Department of the National Medical Research Center for Obstetrics, Gynecology and Perinatology named after Academician V.I.Kulakov, Moscow. A prospective observational study was performed using 98 umbilical cord blood samples, which were obtained immediately after delivery. Three clamps were placed on the umbilical cord. The umbilical cord was cut between the first and second clamps. Blood was taken from the umbilical artery (n = 49) and vein (n = 49) between the 2-nd and 3-rd clamps. The gas analyzer ABL800 FLEX (Radiometer Medical ApS, Denmark) was used to assess pH, lactate, ВЕ, pO2 and pCO2 levels within 10 minutes after sampling.

GraphPad Prism (GraphPad Software, USA) statistical software package and R statistical programming language with RStudio 1.0.143 (RStudio, USA) were used for statistical analysis and plotting. We used a paired t-test to compare the related parametric data and Wilcoxon test to compare the related nonparametric data. Value of p < 0.05 was considered as statistically significant. The study was approved by the local institutional review board.

Results

Mean patient age was 31.4 ± 5.3 years, mean body mass index was 24.3 ± 6.3 kg/m2. Twenty-seven (55.1%) patients were primiparous and twenty-two (44.9%) were multiparous. No severe somatic diseases or pregnancy complications were observed. All deliveries were vaginal and term (39.3 ± 1.2 gestation weeks). Newborns weight ranged from 2540 g to 4320 g (3298 ± 380 g) and height ranged from 46 cm to 56 cm (51.4 ± 2.0 cm). Apgar score ranged from 5 to 9 points (95% CI: 6 – 8 points) at 1 minute and from 7 to 9 points (95% CI: 7 – 9 points) at 5 minutes.

In seven (14.3%) cases arterial cord blood pH was ≤7.15. The pH level was significantly lower in the umbilical cord artery (7.252 ± 0.100) than in the umbilical cord vein (7.297 ± 0.097), p < 0.0001.

On the other hand, the lactate level was the same in both vessels (5.929 ± 2.807 vs. 5.661 ± 2.898 mmol/L, respectively; p = 0.1074) as well as the BE level (7.449 ± 4.713 vs. 7.037 ± 4.214 mmol/L, respectively; p = 0.2596).

As we expected, the pCO2 level was significantly higher in the umbilical cord artery (47.56 ± 12.68 vs. 39.69 ± 9.70 mm Hg, respectively; p < 0.0001) and the pO2 level was significantly higher in the umbilical cord vein (17.56 ± 6.134 vs. 23.36 ± 10.09 mm Hg, respectively; p < 0.0001).

Then depending on the umbilical cord artery pH (pHa) we analyzed the same parameters. We used the pHa = 7.15 parameter as a threshold since it is most commonly used in practice [11–15]we analyzed 226 women with term pregnancies complicated by severe neonatal acidosis (umbilical artery pH less than 7.00. The pHa≤7.15 parameter was classified as acidosis subgroup; the pHa > 7.15 parameter was classified as uncomplicated labour subgroup (control).

The umbilical cord artery pH level was significantly lower in both subgroups (Table 1). As in the general sample, the pCO2 level in acidosis was higher in the umbilical artery, and the pO2 level was higher in the umbilical cord vein. The lactate level was the same in umbilical cord artery and vein in both subgroups.

The BE level was significantly higher in the umbilical cord artery in the acidosis subgroup (15.23 ± 1.98 vs. 14.00 ± 2.14 mmol/L, respectively; p = 0.0144) and was the same in the uncomplicated labor subgroup (6.15 ± 3.66 vs. 5.88 ± 3.24mmol/L, respectively; p = 0.5092).

Discussion

The umbilical cord vein had significantly higher levels of pH and pO2, while the umbilical cord artery had a significantly higher level of pCO2. Lactate and BE levels were the same in both vessels. These differences correspond to the fetal-placental circulation physiology [6, 8]with respect to measurements of pH, bicarbonate, base excess and lactate, in critically ill term and premature newborns. METHODS Arterial blood samples (0.5-1 mL. In addition, a decrease in the pCO2 blood level after passing through the placenta can lead to the decrease in blood acidity in the umbilical cord veins because of the carbonic acid decomposition reaction (H+ + HCO3-  CO2 + H2O) [8]with respect to measurements of pH, bicarbonate, base excess and lactate, in critically ill term and premature newborns. METHODS Arterial blood samples (0.5-1 mL.

The above mentioned differences were present both in the acidosis subgroup (pHa ≤ 7.15) and in the control subgroup (pHa > 7.15). However, in acidosis the BE level was significantly higher in the umbilical cord artery, which indicates the exhaustion of the blood buffer resources [8, 11]with respect to measurements of pH, bicarbonate, base excess and lactate, in critically ill term and premature newborns. METHODS Arterial blood samples (0.5-1 mL.

Conclusion

The umbilical cord vein has higher levels of pH and pO2, and the level of pCO2 is higher in the umbilical artery both in healthy newborns and in newborns with metabolic acidosis. The lactate level does not depend on the umbilical cord blood sampling source (artery or vein). Thus, the source of the cord blood collection is critically important in the pH level assessment, whereas any umbilical cord vessel can be used to assess the lactate level. If pH level is normal, the BE level does not differ in umbilical cord artery and vein. However, in acidosis, the BE level increases in the umbilical cord artery more dramatically than in the vein. The revealed patterns should be taken into account in clinical practice, as well as when comparing the results of different studies.