A retrospective case-controlled study of the association between request to discontinue second stage labor epidural analgesia and risk of instrumental vaginal delivery

Background: Epidural dose is often reduced in the second stage of labor with the intention of improving maternal expulsive efforts and decreasing the need for instrumental vaginal delivery (IVD). We conjectured that parturients requiring IVD would have had more analgesic interventions and requests to decrease analgesic density in the second stage. Methods: This retrospective, case-controlled study evaluated parturients with combined spinal-epidural analgesia and IVD over a 22-month period. Data recorded and compared between IVD and spontaneous delivery groups included requests to decrease the density of second stage analgesia and treatment of breakthrough pain. A model was developed from patient characteristics and analgesia interventions to predict the likelihood of IVD. Results: Records from 2072 parturients were analyzed. The number of parturients in whom basal epidural infusion rate was decreased during the second stage of labor was greater in the IVD group (146/1021 (14.3%) vs. 51/1051 (4.9%), P < 0.001), as was the number of parturients requiring treatment of breakthrough pain in the first stage of labor. Logistic regression analysis found that treatment for breakthrough pain was the strongest predictor of IVD. Conclusion: These results support an association between a request to reduce epidural dose in the second stage of labor, as well as supplemental analgesia for treatment of breakthrough pain, with IVD. It is unclear whether administration of more local anesthetic to treat breakthrough pain results in more dense motor blockade, and hence increases risk of IVD, or whether the decrease in infusion rate reflects obstetricians' dissatisfaction with the progress of obstructed labor.