Noninvasive measurement of gastric emptying in obstetric patients.

An epigastric impedance technique was used to measure gastric emptying in nonpregnant women, women in the third trimester of pregnancy, and women within 60 min of delivery. The basis of the technique is the increase in epigastric impedance after the ingestion of a nonionic fluid. The subsequent decline in impedance is used as a measure of gastric emptying. The impedance epigastrograph used consisted of a four-electrode array (two source, two detector) that was applied over the epigastrium. The method was sufficiently sensitive to measure the effects of pregnancy, labor, and narcotics on gastric emptying. There was no difference in the rate of gastric emptying between pregnant and nonpregnant females. Labor appeared to cause a significant delay in gastric emptying; the mean +/- SEM time taken for the gastric volume to decrease to 50% (T0.5) was 7.2 +/- 0.6 min during pregnancy and 13.0 +/- 1.9 min in the immediate postpartum period. However, the principal factor associated with the delay in gastric emptying in the group studied within 60 min of delivery was probably the use of meperidine and promethazine, because there was a significant difference (P less than 0.05) between subjects who received meperidine and promethazine during labor and those in another group who had received either no analgesia or extradural analgesia, the T0.5 values for the two groups being 18.2 +/- 4.0 and 10.3 +/- 1.4 min, respectively.