Pocket ObGyn – Fetal Cord Blood Gas Analysis

Pocket ObGyn – Fetal Cord Blood Gas Analysis
See Abbreviations

Provides an assessment of neonat metabolic status
May be useful to determine whether an asphyxic event (acidemia + metabolic acidosis + hypoxia) accompanied neonat depression
If nml, rules out asphyxia at time of deliv as a cause of neonat complications
Collect 1–2 mL of bld from both umbilical vein & artery in heparinized Can collect from clamped cord for up to 60 min w/ valid result. If samples are not immediately sent to laboratory, store on ice for up to 60 min.

Indications (Obstet Gynecol 2006;108:1319)

May be obtained w/: Cesarean deliv for suspected fetal compromise, low 5-min Apgar score, abn FHR tracing, mat thyroid dz, intrapartum fever, multifetal gest, other indications

Obst of bld flow through umbilical cord leads to retention of fetal CO₂ (ie,respiratory acidosis) ® prolonged respiratory acidosis leads to mixed respiratory/ metabolic acidosis & then metabolic acidosis alone

Normal values
Term	Preterm
pH: 7.15–7.38	pH: 7.14–7.40
pCO₂: 49.2–50.3	pCO₂: 49.2–51.6
− HCO₃ : 22–23.1	− HCO₃ : 22.4–23.9
BE: -2.7– -3.6	BE: -2.5– -3.3
From Riley RJ, Johnson JW. Collecting and analyzing cord blood gases. Clin Obstet Gynecol. 1993;36(1):13–23.

If pH is lower than nml limits, ACIDEMIA exists

If pCO₂ is higher than nml limits, RESPIRATORY ACIDOSIS exists

If BE is more negative than nml limits, METABOLIC ACIDOSIS exists

Potentially clinically significant acidemia requires pH <7 & metabolic acidosis w/ BE <-12 (Obstet Gynecol 2003;102:628). 10% of neonates w/ BE -12– -16, & 40% w/ BE <-16 will have mod or sev complications (CNS, respiratory, renal, CV).
Respiratory acidosis alone at the time of birth is not considered suff to cause CP
Criteria to define acute intrapartum hypoxic event suff to cause CP: Arterial cord pH <7 w/ BE -12 or worse

Early onset of mod or sev encephalopathy CP of spastic, quadriplegic, or dyskinetic type Exclusion of other identifiable etiologies