AIR CONTAMINATION IN UMBILICAL-CORD BLOOD-GAS SAMPLING

OBJECTIVE: Our purpose was to determine the effect of air contaminatio n and the length of time before assay on umbilical cord blood gases at delivery. STUDY DESIGN: Umbilical venous cord blood gases (0.5 ml) we re drawn from 21 patients at delivery in 1 and 3 ml heparinized syring es with varying amounts of air contamination (none, 0.5 ml air admitte d and removed from the syringe, and 0.5 ml of air retained). In an add itional 15 patients the 0.5 ml sample was contaminated with 0.1, 0.2, 0.3, 0.4, and 0.5 ml of air. RESULTS: Air contamination had no effect on pH, PCO2, or bicarbonate but did increase the PO2 when the residual air was >37.5% in a 3 ml syringe. No changes occurred in a 1 ml syrin ge. Time from drawing the blood to assay did not significantly alter t he results. CONCLUSION: Umbilical cord blood gases are best drawn in 1 ml heparinized syringes. Only if the residual air contamination excee ds 37.5% will PO2 increase. The level of air contamination will not al ter the evaluation of fetal-neonatal acidosis.