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13

Umbilical arteriovenous PO2 and PCO2 differences and neonatal

Morbidity in term infants with severe acidosis

Yitzhak (isaac) belai, MD,b, d T. Murphy goodwin, MD,a manuel durand, MD,b jeffrey S.

Greenspoon, MD,c richard H. Paul, MD,a and frans J. Walther, MD, phdd

Los angeles, california

OBJECTIVE: in term infants umbilical cord gas analysis is a poor predictor of immediate newborn complica-

Tions associated with intrapartum asphyxia, unless the umbilical arterial ph is less than 7.00. We investigated

Whether umbilical arteriovenous blood gas differences may better predict asphyxia-related complications.

STUDY DESIGN: the study population consisted of 82 term, nonanomalous, singleton, live-born infants with

what is anoxic brain injury

Severe umbilical acidosis (ph 25 torr was a highly sensitive and specific parameter in identifying asphyxiated infants with seizures,

Hypoxic-ischemic encephalopathy, cardiopulmonary and renal dysfunction, and abnormal development in the

Neonatal period. Arteriovenous PO2 differences were less sensitive in the detection of neonatal morbidity

Than arteriovenous PCO2 differences.

CONCLUSION: umbilical cord blood arteriovenous PCO2 differences provide a new tool to predict neonatal

Morbidity and permanent neurologic injury in term infants with perinatal asphyxia. (am J obstet gynecol

1998;178:13-9.)

Key words: asphyxia, newborn infants, hypoxic-ischemic encephalopathy, cardiopulmonary dys-

Function, renal dysfunction, developmental outcome, umbilical cord blood gas analysis

what is anoxic brain injury

The ability to distinguish the infant at high risk for hy-

Poxic-ischemic encephalopathy and related sequelae

Would further the development of preventive measures,

Assist the clinicians caring for the infant, and provide

More accurate counseling about outcome to family mem-

Bers. A parameter with a strong relationship to hypoxic-

Ischemic encephalopathy could be evaluated epidemio-

Logically to seek new understanding for the potential

Cause(s) of these events.

Umbilical cord blood gas values for normal term and

Preterm fetuses and neonates have been reported; the

Lower limit of the umbilical artery ph in term infants is

About 7.10 to 7.20.1-5 human umbilical venous cord

Blood gas values are similar to the maternal intervillous

what is anoxic brain injury

Oxygen and acid-base status because oxygen and carbon

Dioxide can equilibrate between these two compart-

Ments,6, 7 whereas umbilical arterial cord blood repre-

Sents the fetal status. When the fetus is unable to mobi-

Lize carbon dioxide from its tissues and to excrete it

Across the placenta (which functions as the lung for the

Fetus), the partial pressure of carbon dioxide increases,

Leading to respiratory acidosis. When delivery of oxygen

To fetal tissues becomes inadequate, anaerobiosis ensues,

Lactic acid is produced, and metabolic acidosis develops

As well.

Term infants born with an umbilical artery ph of 7.00

Or greater are unlikely to have long-term morbidity un-

Less a coexisting illness such as sepsis, pulmonary injury,

what is anoxic brain injury

Trauma, or an antenatal injury is present.8-13 therefore

To study the relationship between umbilical cord acid-

Base status and neonatal outcome, one must study term

Infant cohorts with severe acidosis. We previously de-

Scribed the neonatal outcome (asphyxial complications)

In a cohort of 126 term infants born with severe acidosis

(umbilical artery ph

•

Arteriovenous ph, PCO2, and PO2 differences have

Shown promise in adult critical care medicine as a mea-

Sure of the adequacy of circulation.15-17 umbilical arteri-

Ovenous ph, PCO2, and PO2 differences may therefore

Have a potential to predict the occurrence of hypoxic-is-

Chemic encephalopathy in critically ill newborn infants.

We evaluated the use of umbilical arteriovenous differ-

what is anoxic brain injury

Ences in the partial pressure of ph, carbon dioxide, and

Oxygen by analyzing the data from our recent series of

126 term infants born with severe acidosis.14 clinically

Important neonatal morbidity occurred in 47% of these

Infants, providing an opportunity to study associations

Between biochemical parameters and neonatal outcome.

Infants who were clinically suspect at discharge were fol-

Lowed up at 6 and 12 months. We report a significant and

Clinically important relationship between a large umbili-

Cal cord arteriovenous difference in the partial pressure

Of carbon dioxide and an increased risk for adverse

Neonatal outcome including hypoxic-ischemic en-

Cephalopathy.

Material and methods

The study population included 76,548 infants deliv-

what is anoxic brain injury

Ered over a 54-month period from january 1986 through

June 1990 at los angeles county and university of

Southern california medical center in los angeles.

Term (gestational age ³37 completed menstrual weeks)

Delivery occurred in 69,340 cases. Arterial and venous

Umbilical cord blood gases were obtained when fetal dis-

Tress required operative delivery or neonatal depression

Occurred. Umbilical cord blood samples were obtained

From 8100 (10.06%) infants. An umbilical artery ph

Value

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Age, the stanford-binet test. The examiner was not

Blinded to the diagnosis.

Data were stored in a spreadsheet and the relation be-

Tween variables measured or derived from umbilical cord

Blood and clinical outcome variables was analyzed by lin-

what is anoxic brain injury

Ear regression and analysis of variance using the BMDP

New system 1.0 statistical package (BMDP statistical

Software inc., los angeles, calif.). A p value 14 days in neonatal intensive care unit 15 18

Seizures 21 26

Hypoxic-ischemic encephalopathy 27 33

Cardiac dysfunction 25 30

Ventilator support 41 50

Days on ventilator

7 days 12 15

Oliguria 24 hours 16 20

Elevated creatine phosphokinase 19 23

Other morbidity

Meconium aspiration 18 22

Other 9 11

Abnormal developmental examination

At discharge 25 30

Table IV. Association between umbilical paco2 and

Neonatal morbidity

PaCO2 paco2

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Thy (p = 0.0087) but did not correlate with any of the

Other clinical outcome measures. The incidence of

Seizures, cardiac and renal dysfunction, and abnormal

what is anoxic brain injury

Development at discharge increased significantly with in-

Creasing difference in umbilical arteriovenous PO2 (fig.

3). Using a cutoff value of â20 torr, the sensitivity of the

Difference in umbilical arteriovenous PO2 for the predic-

Tion of the clinical outcome measures varied between

56% and 71% and the specificity varied between 64%

And 70% (table VI).

Neonatal morbidity decreased significantly with in-

Creasing apgar scores at 1 and 5 minutes, and apgar

Scores of 0 to 2 at 1 minute and 0 to 4 at 5 minutes were

Associated with a high incidence of seizures, hypoxic-is-

Chemic encephalopathy, cardiopulmonary and renal

Dysfunction, and abnormal development. A 1-minute

Apgar score of 0 to 2 had a sensitivity of 69% to 77% and

what is anoxic brain injury

A specificity of 62% to 72%. A 5-minute apgar score of 0

To 4 had a lower sensitivity (40% to 59%) than a 1-

Minute apgar score of 0 to 2, but a higher specificity

(90% to 96%).

Decreasing umbilical arterial ph was associated with a

Higher incidence of neonatal morbidity (fig. 4).

Sensitivity of an umbilical arterial ph

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Umbilical arteriovenous PCO2 and, to a lesser extent, PO2

Differences. These parameters, derived from umbilical

Cord blood gas analysis, have been reported in normal

Term infants10 but have not been used routinely in clini-

Cal neonatal practice and have not previously been inves-

Tigated for their association with long-term adverse out-

Comes. We studied a large population, unlike previous re-

what is anoxic brain injury

Ports, with a 35% incidence of hypoxic-ischemic en-

Cephalopathy, allowing for in-depth analysis of the

Association of various parameters with clinical outcome.

A difference in umbilical arteriovenous PCO2 value ³25

Torr was found to be a useful parameter to identify as-

Phyxiated infants at increased risk for neonatal morbid-

Ity. Because this parameter can be easily calculated from

Routine umbilical blood gas values, the difference in um-

Volume 178, number 1, part 1 belai et al. 17

Am J obstet gynecol

Fig. 3. Incidence of adverse clinical outcome among 82 term

Newborn infants with an umbilical arterial ph

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Bilical arteriovenous PCO2 should be considered in con-

Junction with the standard blood gas acid-base parame-

what is anoxic brain injury

Ters in asphyxiated infants. The difference in umbilical

Arteriovenous PO2 is a less sensitive indicator of neonatal

Morbidity and therefore less useful as a predictor of ad-

Verse outcome. This difference between the difference in

Umbilical arteriovenous PCO2 and PO2 may be related to

The observation that carbon dioxide diffuses better and

Equilibrates 20 times faster than oxygen across the

Human placenta.

Although a large difference in umbilical arteriovenous

PCO2 indicates very low fetal-placental blood flow, this

Model does not fit all the data. As the lower end of fig. 2

Shows, three cases had a bad outcome when the paco2

Was 65 torr, but the difference in umbilical arteriove-

Nous PCO2 was

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Volume 178, number 1, part 1 belai et al. 19

Am J obstet gynecol

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