Maternal catecholamines decrease during labor after lumbar epidural anesthesia.

To determine whether epidural anesthesia during labor affects maternal circulating catecholamines, blood samples were obtained from 15 patients at the peak of and immediately after two consecutive painful contractions. A lumbar epidural local anesthetic without epinephrine was then administered. After the onset of analgesia, four blood samples were again drawn. All samples were analyzed by a radioenzymatic assay for epinephrine and norepinephrine concentrations. Before anesthesia, the mean (+/-SEM) plasma epinephrine level was 280 +/- 49 pg/ml, and the mean norepinephrine level was 866 +/- 122 pg/ml. After anesthesia, epinephrine levels decreased 56% (p less than 0.01). Although norepinephrine levels decreased approximately 19%, this reduction was not statistically significant. At the height of a contraction, catecholamine levels did not differ significantly from those occurring between contractions. Lumbar epidural anesthesia during labor reduces maternal epinephrine levels, probably by eliminating the psychological and physical stress associated with painful uterine contractions or by denervating the adrenal medulla. Whatever the mechanism, reducing pain and activity of the sympathetic nervous system should increase uterine blood flow.