Changes of pH-values during storage of fetal blood samples

In recent years increased attention has been given to the degree of acidity of fetal blood during the course of labor or immediately after delivery. As it is not always possible to measure the blood pH immediately after sampling, it is important to know whether or not the pH is likely to change if the blood sample is stored for some time. 30 heparinized whole blood samples were collected from the umbilical artery of 30 newborn infants immediately after delivery and were stored at room temperature. pH -measurements were made every 5 minutes up to 80 minutes. In a second group the same number of samples were stored in a refrigator. pH-measurements were performed after 30 minutes and then every hour for up to 7 hours, and finally after 24 hours. The pHact-values did not change at room temperature (about 24 degrees C) for up to 25 minutes; pHqu40-values decreased initially more rapidly but at 50 minutes the decrease was the same as in pHact-values namely 0.02 units. Afterwards the pHact-values decreased at a mena rate of about 0.03 units per hour and pHqu40-values at a mean rate of about 0.017 units per hour. If the storage temperature was lowered by refrigeration (about 6 degrees C) the pHact-values remained between 0 and -0.02 units for 6 hours and pHqu40-values for 3 hours. From these experiments it can be concluded that fetal blood samples must be kept in a refrigerator in order to inhibit autoxidation, if they have to be stored for longer than 50 minutes.