2Ven den,Nieuwenhuyzen MC,Burm AG,et al.Epidural vs intravenous infusion of alfentanil in the management of postoperative pain following laparatomies.Acta Anaesthesiol Scand,1996,40:1112-1118.
3Krystal JH,Karper LP,Seibyl JP,et al.Subanethetic effects of the nonvcompetitive NMDA antagonist,ketamine,in human.Psychotomimetic,perceptual,congnitive and neuroendocrine responses.Arch Gen Psychiatry,1994,51:199-214.