MORTON HOSPITAL AND MEDICAL CENTER
DEPARTMENT OF OBSTETRICS AND GYNECOLOGY
88 WASHINGTON ST.
TAUNTON, MA 02780

CLINICAL GUIDELINE

These guidelines should not be construed as dictating an exclusive course of treatment or procedure

Accepted: December 20, 1996 Chairperson Department Ob/Gyn
Developed by: Myer S. Bornstein, M.D. and Louise Nunnley, R.N.

CORD BLOOD GASES TO DETERMINE UMBILICAL ARTERY ACID-BASE ANALYSIS

(adapted from ACOG Bulletins, Committee Opinions and other areas) Reason: To Provide an objective method of assessing a newborns condition

Discussion: APGAR scores alone can-not be used to define or classify asphyxia. The more appropriate tool is the assessment of fetal and newborn acid-base balance. A review of fetal and neonatal acid- base regulation and its response to acute or chronic hypoxic stress is needed for properly interpreting fetal capillary or umbilical cord blood pH and other measurements.

It has been demonstrated that a more realistic pH threshold for significant or pathological fetal acidemia (ie, that ph associated with adverse neonatal sequelae, including death) is 7.00. Umbilical artery blood pH of less than 7.00 with a metabolic pattern appears to be an important component of a definition of birth asphyxia or hypoxia to a degree of severity that might be associated with subsequent neurological dysfunction. Even when this low pH threshold is used to define significant acidemia, most newborns in this category will be neurologically normal, with no apparent morbidity.

Because only newborns who are severely depressed (ie, those with persistent APGAR scores of 0-3 for 5 minutes or longer and an umbilical artery blood pH of less than 7.00) are at risk of manifesting hypoxic ischemic encephalopathy and subsequent neurologic dysfunction, it seems logical the umbilical cord blood acid-base determination, offers little in the evaluation of a vigorous term newborn with normal APGAR scores.

Umbilical cord blood pH and acid-base balance is most useful in association with the delivery of an infant with a low APGAR score. There is little doubt that the most significance role of umbilical cord blood acid-base analysis is in the evaluation of the very premature infant with a low APGAR scores. APGAR scores of those otherwise uncomplicated preterm infant are typically lower than those of term infants. Many such infants could be classified incorrectly as asphyxiated based solely on the APGAR score. Moreover, premature infants are at higher risk for intracranial hemorrhage and subsequent neurological dysfunction, such as cerebral palsy. Without umbilical cord blood gas analysis, these neurological complications could be incorrectly attributed to intrapartum or birth asphyxia, especially if the latter is solely based on APGAR scores. Normal umbilical cord blood values in the premature infant virtually eliminate the diagnosis of significant intrapartum hypoxia or birth asphyxia.

Umbilical cord blood pH and acid-base analysis to assess newborn acid-base balance can be useful also in pregnancies complicated by meconium staining of the amniotic fluid. Tracheal visualization, intubation, or suctioning could lead to low APGAR score that might be incorrectly attributed to newborn asphyxia. In situations such as post term birth or delivery complications(eg, breech birth or twins) identification and documentation of a normal pH value excludes birth asphyxia as a cause of subsequently detected neonatal abnormality.

PROTOCOL

1. Doubly clamp a segment of the umbilical cord immediately after birth in ALL deliveries. (In order to obtain enough blood for testing you can draw an umbilical artery sample into a heparinized syringe and have it iced).
   • A clamped segment of cord is stable for pH and blood gas assessment or at least 60 minutes.
2. If a serious abnormality that arose in the delivery process or a problem with the neonateÕs condition or both persist at or beyond the first five minutes, obtain an umbilical cord blood specimen for pH and acid-base determinations in a syringe flushed with heparin and have it analyzed.
3. If a specimen cannot be obtained from the umbilical artery, obtain a specimen from the artery on the chorionic surface of the placenta.
4. if the 5-minute APGAR score is satisfactory and the new born appears stable and vigorous, the segment of umbilical cord can be discarded.

Interpretation

Normal Maternal Values: Pregnancy

pH 7.35­7.45

p02 80­100 mm Hg.

Base Excess 4 mEq/Liter

pC02 34 mm Hg.

Bicarbonate 21 mEq/Liter

Cord Gas Values

The umbilical cord blood is studied for the status of the fetal acid base. Cord gases are obtained to detect the presence or absence of acidosis and to decide whether the cause of the acidosis is respiratory or metabolic. Establishing the source and type of acidosis make it easier to a.) plan resuscitation b.) treat complications.

After Birth­Normal Fetal cord blood pH and gas values:

	VEIN	ARTERY
pH	7.25­7.35	7.28
p02	28­32 mmHg.	16­20 mmHg.
pC02	40­50 mmHg.	40­50 mmHg.
Base Excess	0­5 mEq/Liter	0­10 mEq/Liter

 

Abnormal Fetal cord blood pH and gas values

	Respiratory Acidosis	Metabolic Acidosis
	(Variable Decelerations)	(Late Decelerations)
pH	< 7.25	< 7.25
P02	Variable	< 20 mmHg
pC02	> 50 mmHg	45­55 mmHg.
Base Deficit	< 10 mEq/liter	> 10mEq/liter
	Respiratory Acidosis	Metabolic Acidosis
	Low pH	Low pH
	High pC02	Normal to high pC02
	Normal Base Excess	High base excess