The safety and efficacy of intrathecal opioid analgesia for acute postoperative pain: seven years' experience with 5969 surgical patients at Indiana University Hospital. - Gwirtz,K.H.; Young,J.V.; Byers,R.S.; Alley,C.; Levin,K.; Walker,S.G.; Stoelting,R.K. (Anesth Analg, 1999)