Heparinized Blood Gas Syringe

To obtain fetal blood for acid-base analysis from the in vivo placenta and cord:

1. Double clamp a 10 to 20 cm segment of umbilical cord as soon as possible after delivery because
   1. Delay in clamping may affect pH and gas values due to gaseous diffusion and continuing metabolism.
2. Draw blood from the umbilical vein into a heparinized blood gas syringe,
3. Remove the needle and transport the capped syringe to the laboratory immediately.

Do not spin, and do not open prior to analysis.

Blood gas syringe

Ambient

Transport specimen to the lab immediately after collection

• Clotted specimen
• Improper labels (unlabeled or mislabeled)
• Leaking container resulting in compromised specimen
• Quantity not sufficient (QNS)

Ion Selective Electrodes

The pH, PCO₂, PO₂ are measured, whereas bicarbonate concentration, percentage oxygen saturation, and base excess (or deficit) are calculated. The most useful values for interpretation of fetal-newborn condition and prognosis are the pH and base excess (or deficit).

Sampling umbilical artery blood is preferable to sampling umbilical vein blood as the arterial pH and base deficit provide the most accurate information on fetal acid-base status and correlate best with newborn morbidity. This is because umbilical arterial blood primarily reflects fetal metabolism while venous blood primarily reflects placental functions.

Some clinicians prefer to obtain two samples, one from the artery and the other from the vein. If both vessels are sampled, the median arteriovenous pH difference is 0.09 (range 0.02 to 0.49).

One advantage to sampling both vein and artery is that the ability to compare both sets of values makes it clearer which set of values reflects the vein versus the artery. If only one sample from one vessel is collected, it is not necessarily readily apparent from the values whether the sample reflects the artery or the vein.