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Brian M. Lappas

April 26, 2013

Umbilical Cord Blood Gas Analysis

Umbilical cord blood gas is the most objective way of assessing a newborns metabolic condition at birth.

Specifically, arterial cord pH and base deficit can determine perinatal hypoxia/asphyxia (potential causes

of hypoxic-ischemic encephalopathy or cerebral palsy) and give insight into causes of intrapartum fetal

distress.

When are cord blood gases indicated? including but not limited to:

 – High risk pregnancies -C-section for fetal compromise

-Abnormal fetal heart rate patterns -Low (≤3) Apgar score 

-Intrapartum fever >100.4 C -Multifetal gestation

Why do neonates get hypoxic/asphyxia?

3 main etiologies:-Maternal oxygen compromised

-Maternal perfusion of placenta reduced

Preeclampsia, chronic hypertension, hypotension/hypovolemia, cyanotic heart disease

-Delivery of oxygenated blood from placenta to fetus is impaired

Placental abruption, cord prolapse, repetitive cord occlusion

How should it be collected and stored?

-10 to 20cm section of cord double clamped and put on ice

- Assessed accurately up to 60min, pH fall 0.05 at 30min, 0.087 at 60min, and 0.112 at 90min.

-Sample via cord artery, although “paired” venous sample recommended (artery < 0.09 venous)

What do the blood gases tell us?

Mean umbilical artery blood pH and gas in pre-term & term infants are similar

Pre-Term Term

 pH 7.21 -7.29 7.27 -7.28

 pCO2 (mmHg) 49.2 -51.6 49.2 -50.3

HCO3 (mEq/L) 22.4-23.9 22.0-23.1

Base deficit (mEq/L) 2.5 - 3.3 2.7 - 3.6

Results of hypoxia/asphyxia on infants?

Pathological academia; increased association with ≤7.24 with mortality, hypoxic ischemic

encephalopathy, intraventricular hemorrhage, or cerebral palsy.

Severity of Deficit Amount of base deficit Motor/Cognitive deficits 4-8 yo

Mild 4-8 mmol/L None

Moderate 8-12 mmol/L

Severe ≥12 mmol/L 10% had moderate/severe

≥16 mmol/L  40% had moderate/severe

-Only 4% of neonatal encephalopathic patients had hypoxia in absence of antepartum risk factors

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Criteria to define aute intrapartum hypoxic event as sufficient to cause cerebral palsy:

- Evidence of metabolic acidosis (pH <7.0 and base deficit greater/equal 12 mmol/L)

- Early onset of moderate/severe neonatal encephalopathy in infants >34 week gestation

- Cerebral palsy of spastic quadriplegic or dyskinetic type

- Exclusion of other identifiable etiologies

Why does UNC do universal sampling?

Because there is a treatment to help reduce the risk of death or major disability in hypoxic-ischemic

encephalopathy by 20-30%.

-Hypothermia: whole body cooling or head selective cooling is the neuroprotective therapy for

neonatal encephalopathy.

Resources:- ACOG Committee Opinion No. 348, November 2006: Umbilical cord blood gas and acid-base analysis. Obstet Gynecol . 2006 Nov;108(5):1319-22.

-Low JA, Lindsay BG, Derrick EJ. Threshold of metabolic acidosis associated with newborn complications. Am J Obstet Gynecol 1997; 177: 1391-4

-Malin GL, Morris RK, Khan KS. Strength of association between umbilical cord pH and perinatal and long term outcomes: systematic review and meta-analysis.

 BMJ . 2010 May 13;340:c1471

-UNC Umbilical Cord Blood Gases: Fetal acid base assessment at time of delivery. www.mombaby.org 2013

-Yeomans ER, Ramin SM. Umbilical cord blood acid-base analysis. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2013.