Clinical Review

How and when umbilical cord gas analysis can justify your obstetric management

Three cases illustrate how umbilical cord gas values can provide insight into a newborn’s status

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Umbilical cord blood (cord) gas values can aid both in understanding the cause of an infant’s acidosis and in providing reassurance that acute acidosis or asphyxia is not responsible for a compromised infant with a low Apgar score. Together with other clinical measurements (including fetal heart rate [FHR] tracings, Apgar scores, newborn nucleated red cell counts, and neonatal imaging), cord gas analysis can be remarkably helpful in determining the cause for a depressed newborn. It can help us determine, for example, if infant compromise was a result of an asphyxial event, and we often can differentiate whether the event was acute, prolonged, or occurred prior to presentation in labor. We further can use cord gas values to assess whether a decision for operative intervention for nonreassuring fetal well-being was appropriate (see “Brain injury at birth: Cord gas values presented as evidence at trial”). In addition, cord gas analysis can complement methods for determining fetal acidosis changes during labor, enabling improved assessment of FHR tracings.1−3

Brain injury at birth: Cord gas values presented as evidence at trail

At 40 weeks' gestation, a woman presented to the hospital because of decreased fetal movement. On arrival, an external fetal heart-rate (FHR) monitor showed nonreassuring tracings, evidenced by absent to minimal variability and subtle decelerations occurring at 10- to 15-minute intervals. The on-call ObGyn requested induction of labor with oxytocin, and a low-dose infusion (1 mU/min) was initiated. An internal FHR monitor was then placed and late decelerations were observed with the first 2 induced contractions. The oxytocin infusion was discontinued and the ObGyn performed an emergency cesarean delivery. The infant's Apgar scores were 1, 2, and 2 at 1, 5, and 10 minutes, respectively. Cord samples were obtained and values from the umbilical artery were as follows: pH, 6.86; Pco2, 55 mm Hg; Po2, 6 mm Hg; and BDECF, 21.1 mmol/L. Values from the umbilical vein were: pH, 6.94; Pco2, 45 mm Hg; Po2, 17 mm Hg; and BDECF, 20.0 mmol/L. The infant was later diagnosed with a hypoxic brain injury resulting in cerebral palsy. At trial years later, the boy had cognitive and physical limitations and required 24-hour care.

The parents claimed that the ObGyn should have performed a cesarean delivery earlier when the external FHR monitor showed nonreassuring tracings.

The hospital and physician claimed that, while tracings were consistently nonreassuring, they were stable. They maintained that the child's brain damage was not due to a delivery delay, as the severe level of acidosis in both the umbilical artery and vein could not be a result of the few heart rate decelerations during the 2-hour period of monitoring prior to delivery. They argued that the clinical picture indicated a pre-hospital hypoxic event associated with decreased fetal movement.

A defense verdict was returned.

Case assessment
Cord gas results, together with other measures (eg, infant nucleated red blood cells, brain imaging) can aid the ObGyn in medicolegal cases. However, they are not always protective of adverse judgment.

I recommend checking umbilical cord blood gas values on all operative vaginal deliveries, cesarean deliveries for fetal concern, abnormal FHR patterns, clinical chorioamnionitis, multifetal gestations, premature deliveries, and all infants with low Apgar scores at 1 or 5 minutes. If you think you may need a cord gas analysis, go ahead and obtain it. Cord gas analysis often will aid in justifying your management or provide insight into the infant’s status.

Controversy remains as to the benefit of universal cord gas analysis. Assuming a variable cost of $15 for 2 (artery and vein) blood gas samples per neonate,4 the annual cost in the United States would be approximately $60 million. This would likely be cost effective as a result of medicolegal and educational benefits as well as potential improvements in perinatal outcome5 and reductions in special care nursery admissions.4

CASE 1: A newborn with unexpected acidosis

A 29-year-old woman (G2P1) at 38 weeks’ gestation was admitted to the hospital following an office visit during which oligohydramnios (amniotic fluid index, 3.5 cm) was found. The patient had a history of a prior cesarean delivery for failure to progress, and she desired a repeat cesarean delivery. Fetal monitoring revealed a heart rate of 140 beats per minute with moderate variability and uterine contractions every 3 to 5 minutes associated with moderate variable decelerations. A decision was made to proceed with the surgery. Blood samples were drawn for laboratory analysis, monitoring was discontinued, and the patient was taken to the operating room. An epidural anesthetic was placed and the cesarean delivery proceeded.

On uterine incision, there was no evidence of abruption or uterine rupture, but thick meconium-stained amniotic fluid was observed. A depressed infant was delivered, the umbilical cord clamped, and the infant handed to the pediatric team. Cord samples were obtained and values from the umbilical artery were as follows: pH, 6.80; Pco2, 120 mm Hg; Po2, 6 mm Hg; and base deficit extracellular fluid (BDECF), 13.8 mmol/L. Values from the umbilical vein were: pH, 7.32; Pco2, 38 mm Hg; Po2, 22 mm Hg; and BDECF, 5.8 mmol/L. The infant’s Apgar scores were 1, 2, and 7 at 1, 5, and 10 minutes, respectively, and the infant demonstrated encephalopathy, requiring brain cooling.

What happened?

Read how to use cord gas values in practice

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