Target-controlled infusion of alfentanil for postoperative analgesia: a feasibility study and pahrmacodynamic evaluation in the early postoperative period. - Van den Nieuwenhuyzen,M.; Engbers,F.H.; Burm,A.G.; Vletter,A.A.; Van,K.J.; Bovill,J.G. (Br J Anaesth, 1997)