Welcome to this video on newborn cord blood
gases.
Umbilical cord blood gas is the most objective
way to assess a newborn's metabolic condition
at birth.
It is recommended in all high-risk deliveries,
including intrapartum fever (temp >100.4),
cesarean section for fetal compromise, severe
growth restriction, abnormal FHR tracing,
5-minute Apgar score <7, or multifetal gestation.
Analyzing both the arterial and venous specimen
can give insight into the cause of acidosis
and fetal distress.
For optimal interpretation, a section of umbilical
cord should be clamped on each end to isolate
it from the placenta, and samples drawn soon
after birth.
Use a separate 1mL heparinized syringe for
each vessel, and as soon as the blood is drawn,
place the specimen on ice and send it to respiratory
therapy for analysis.
The umbilical artery is the smaller vessel
and should be drawn first, being careful to
insert the needle superficially and not poke
through the artery and into the vein.
The umbilical vein is the larger vessel and
should be drawn after the artery.
It is important to sample both arterial and
venous blood, especially if the infant is
depressed at birth.
Blood from the umbilical artery represents
the state of the fetus at the time of delivery,
because it is blood returning from the fetus.
Umbilical venous blood provides the placental
status.
In the case of cord compression, the placenta
is still functioning normally, so the venous
gas would still be normal.
However, the arterial gas would reflect a
lower pH and increased PCO2 because the fetus
would be retaining CO2 and not receiving enough
oxygen when the cord is compressed.
Many studies have been done on healthy term
infants to determine a normal reference range
for newborn blood gases.
However, the exact values accepted as normal
vary in literature and in various facilities.
One study example of umbilical cord blood
gas values following uncomplicated term vaginal
deliveries are shown on the chart.
The umbilical artery values were: pH, 7.28
+/- 0.05; PCO2 49.2 +/- 8.4mmHg; PO2, 18.0
+/- 6.2mmHg; and bicarbonate, 22.3 +/- 2.5mEq/L.
The umbilical venous values were: pH, 7.35
+/- 0.05; PCO2, 38.2 +/- 5.6mmHg; PO2, 29.2
+/- 5.9mmHg; and bicarbonate, 20.4 +/- 4.1mEq/L.
A 
pH of <7.1 may indicate birth asphyxia/hypoxia
severe enough to cause neurological deficits.
In a sick newborn, acidosis is seen more often
than alkalosis.
Take note that infants with abnormal blood
gas results may be acceptable for that infant,
depending on the gestational age of the infant
or the disease process.
Remember to look not only at the lab results,
but also Apgar scores, and the child's general
condition.
Disturbances of acid-base balance signal the
body to attempt to return the pH back to a
normal level.
For example, if CO2 levels are increased,
the body attempts to correct the problem by
excreting more of it.
The neonate is usually unable to correct an
acid-base imbalance because of its immaturity,
such as immature lungs.
For more detailed explanation of how to interpret
blood gas disturbances, see our video on "Acid
base balance and Blood gas interpretation.'
In neonates, you may often see respiratory
acidosis, due to hypoventilation, ventilation-to-perfusion
mismatching, or cardiac disease.
The neonate may have decreased lung tissue,
apnea, meconium aspiration, or persistent
pulmonary hypertension of the newborn.
Metabolic acidosis may also occur due to increased
acid formation from inborn errors of metabolism
or hyperalimentation.
It is also seen with diarrhea and renal tubular
acidosis from a loss of bases.
Respiratory alkalosis can occur with hyperventilation
or the CNS response to hypoxia or maternal
heroin addiction.
Metabolic alkalosis occurs with a gain of
bases or loss of acids, which can occur with
gastric suctioning.
Umbilical cord blood gas analysis is recommended
in all high-risk deliveries and some institutions
are collecting samples from all deliveries.
The best results are obtained when both umbilical
artery and venous samples are taken soon after
birth from a segment of cord that has been
clamped in two places to isolate it from the
placenta.
An infant with a low cord pH who is vigorous
at birth and has no other compromise is not
necessarily at an increased risk for adverse
outcomes.
However, an infant with a pH <7.1 at birth,
who is also not vigorous, is at a high risk
for adverse outcome.
In combination with other clinical information,
the umbilical blood gas results provide important
information about the past, present, and possibly
the future condition of the infant.
Thank you for watching this video tutorial
on newborn cord blood gases.
Be sure to check out our other videos!
