Introduction

Despite many advances in our understanding of pain pathophysiology, development of new drugs, and sophisticated drug-delivery systems, a majority of surgical patients continue to receive inadequate therapy for postoperative pain. Historically, the treatment of postoperative pain has been given low priority by both surgeons and anesthesiologists, so that patients have accepted pain as a necessary part of the postoperative experience (Spence, 1980; Mitchell and Smith, 1989; Warfield and Kahn, 1995).

Ineffective pain management has significant implications for patient well-being. Patients in pain suffer more complications, which can lead to longer hospital stays. Although much remains to be done, specialists find that improvements are taking place gradually. Anesthesiology based acute pain services (APS) are playing an increasingly important role in these developments (Ready et al., 1988; Rawal and Berggren, 1994). Evidence is growing that improved analgesia may be associated with less morbidity and mortality and with lower hospitalization costs (Rawal et al., 1984; Yeager et al., 1987; Tuman et al., 1991).

Opioid-Analgesic Drugs

Opioids are the most extensively used analgesics in the management of moderate to severe acute pain and in pain related to malignant disease. Opioids produce their effect by binding to specific opioid receptors located in the brain, spinal cord, and other areas of the body. They have been shown to have specific antinociceptive receptor effects at several sites within the brain, including periaqueductal gray, rostral ventral medulla, and substantia nigra and also within the dorsal horn of the spinal cord.