Umbilical Cord Blood Gas Analysis

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 Mild Moderate Severe

Amount of base deficit Motor/Cognitive deficits 4-8 yo 4-8 mmol/L None 8-12 mmol/L ≥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

Criteria to define aute intrapartum hypoxic event as sufficient to cause cerebral palsy: - Evidence of metabolic acidosis (pH 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.