WIP 81 - Umbilical Cord and Infant Blood Gases and their Relationship to Severity of Brain Injury in Hypoxic Ischemic Encephalopathy

Publication Number: WIP 81.7574

Brenda Rieger, CHOC Children's Hospital of Orange County / University of California, Irvine, Newport Beach, CA, United States; Justin Shen, CHOC Children's Hospital of Orange County, Orange, CA, United States; Sameeia Iqbal, CHOC Children's Hospital of Orange County, Anaheim, CA, United States; Tricia Morphew, CHOC Children's Hospital of Orange County, Bothell, WA, United States; Terrie E. Inder, Children’s Hospital of Orange County, Orange, CA, United States

Background: The umbilical arterial cord gas is used to assess acidemia reflective of hypoxic-ischemic insults to the fetus. It is also used in the selection of infants for therapeutic hypothermia (TH). A recent study suggested that postnatal infant gas measures were better predictors of the severity of neonatal encephalopathy (NE) but found no relationship to the extent of brain injury on magnetic resonance imaging (MRI).

Objective: The purpose of this study is to analyze the relationship between umbilical cord blood gas, infant blood gas, severity of NE, and degree of brain injury on MRI.

Design/Methods: This IRB approved, retrospective, single-site cohort study includes infants born at ≥35 weeks treated for hypoxic-ischemic encephalopathy (HIE). Data was collected on umbilical venous, arterial, and postnatal blood gases, and MRI results. MRIs were independently graded by two readers using the Weeke scoring system. Our cohort included 126 infants with a goal of including 250 infants in the cohort over the next few months.
Logistic regression analyses were conducted using a generalized linear mixed-effects model to determine the odds associated with each mmol/L change in gas pH, base deficit (BD), and bicarbonate (HCO₃) levels on the likelihood of moderate-to-severe MRI Weeke and HIE scores. Blood gas pH was rescaled to examine the increased odds of outcomes per 0.1 mmol/L increase.
Preliminary analysis shows that postnatal blood gas measurements were most strongly associated with the odds of a moderate-to-severe MRI Weeke score. Each 0.1 mmol/L increase in postnatal pH was linked to a 42% reduction in odds (OR=0.58, 95% CI: 0.36, 0.95, p=.029). Each 1.0 mmol/L increase in postnatal HCO₃ reduced the odds by 20% (OR=0.80, 95% CI: 0.67, 0.96, p=.015). Each 1.0 mmol/L increase in postnatal BD resulted in 1.29 increased odds of a moderate-to-severe Weeke score (OR=1.29, 95% CI: 1.11, 1.50, p=.001).
Similar weaker associations were observed with umbilical venous and arterial blood gas measurements. We plan to further expand the cohort to complete our analyses with greater power.