RESUMO
In recent human and animal studies, intrathecal administration of various doses of neostigmine produces analgesia without neurotoxicity. Intrathecal neosrtigmine has been used as an adjunct to intrathecal local anaesthetic or opioid to prolong regional analgesia and improve haemodynamic stability, with variable results. The present study was designed to compare the effects of the addition of IT neostigmine or IT morphine on the characteristics of spinal anesthesia with bupivacaine and to assess their postoperative analgesic efficacy and safety in patients undergoing total knee replacement surgery under spinal anesthesia. Sixty patients scheduled for elective total knee replacement under spinal anesthesia were randomly divided into three equal groups which received IT 0.5% hyperbaric bupivacaine 15 mg with either normal saline 0.5 mL, neostigmine 50 micro g. or morphine 300 micro g. The maximal level of sensory block, duration of analgesia, time to use of rescue analgesics, the overall 24-hr and four-hour interval visual analogue scale [VAS] pain score, and the incidence of adverse effects were recorded for 24 hr after administration. There was no significant difference in maximal level of sensory block among the three groups. The morphine group had a later onset of postsurgical pain and longer time to first rescue analgesics than the neostigmine group [P <0.05]. Overall 24-hr VAS pain scores were significantly higher in the saline group vs the morphine and neostigmine groups [P <0.05]. Motor block lasted significantly longer in the neostigmine group than in the morphine and saline groups [P <0.05]. The incidence of adverse effects was similar in the neostigmine and morphine groups except for pruritus [70%] occurring more frequently in the morphine group than in the neostigmine and saline groups [0%; P <0.05]. Overall satisfaction rates were better in the neostigmine group than in the morphine and saline groups [P <0.05]. IT neostigmine 50 pg produced postoperative analgesia lasting about seven hours with fewer side effects and better satisfaction ratings than IT morphine 300 micro g