What concentration of sufenatnil should be combined with ropivacaine 0.2 % wt/vol for postoperative patient-controlled epidural analgesia ? - Brodner,G.; Mertes,N.; Van-Aken,H.; Mollhoff,T.; Zahl,M.; Wirtz,Z.; Marcus,M.A.; Buerkle,H. (Anesth Analg, 2000)