Costa-Martins, J. M.; Dias, C. C.; Pereira, M.; Tavares, J. Effects of Local Anesthetic on the Time Between Analgesic Boluses and the Duration of Labor in Patient-Controlled Epidural Analgesia: Prospective Study of Two Ultra-Low Dose Regimens of Ropivacaine and Sufentanil. Acta Med Port 2015, 28, 70-76.