Noninvasive assessment by radiotelemetry of antacid effect during labor

A noninvasive radiotelemetry technique was used to study the antacid effect of 15 ml of 0.3 M sodium citrate in 26 women in established labor. The subjects swallowed a pH radio pill, whose signal was detected transabdominally by a radio receiver. The median and range of values for the time to return to the preantacid basal pH for all of the women in labor was 84.0 (11.8-195.8) min. However, there was a significant difference (P less than 0.05) in the duration of action of sodium citrate between the women who had received no analgesia and those given intramuscular meperidine. The median and range of values for the time to return to the preantacid basal pH in patients who had received meperidine during labor was 166.0 (147.7-195.8) min, whilst in those who had received no analgesia the values were 56.7 (11.8-143.0) min. There were no significant differences between patients given no analgesia and those given extradural analgesia. Pretreatment with intravaginal prostaglandins (PGE2) did not influence antacid effect.