Analgesic requirements for patients undergoing lower extremity orthopedic surgery--the effect of combined spinal and epidural magnesium.

BACKGROUND: Polypharmacological approach is the most common practice to treat perioperative pain, as no single agent has yet been identified to specifically inhibit nociception without associated side effects. Opioids such as Fentanyl is commonly added to local anesthetics to produce spinal and epidural anesthesia. However, significant adverse effects, such as pruritus, respiratory depression, hemodynamic instability and occasionally severe nausea and vomiting, may limit their use. Our present study was designed to assess the effectiveness of using combined intrathecal and epidural magnesium (Mg) in reducing intra-and postoperative analgesic requirements and improving the quality of analgesia. METHOD: Eighty patients ASA I, II, III who scheduled for lower extremity orthopedic surgery were included in the study. Patients were randomly allocated to one of two groups, 40 patients each. The Control Group: patients received intrathecal 10 mg of Bupivacaine 0.5% (2 ml), plus 25 microg of Fentanyl (0.5 ml), plus 0.9% NaCl solution (1 ml) and an epidural infusion of 0.9% NaCl at a rate of 5 ml/hr. The Magnesium Group: patients received intrathecal 10 mg of Bupivacaine 0.5% (2 ml), plus 25 microg of Fentanyl (0.5 ml), plus 50 mg of 5% Mg (1 ml) and an epidural infusion of 2% Mg at a rate of 100 mg/hr (5 ml/hr). RESULTS: Intrathecal Mg prolonged fentanyl analgesia as indicated by increased duration of anesthesia in the Mg group, and thus improving the quality of spinal anesthesia. The effectiveness of the postoperative analgesia was confirmed by markedly lower perioperative analgesic requirements (38.3 % less than the Control group), the patient's low VAS score, the longer time for the patients first requirements of post-operative analgesia in the Mg group. CONCLUSION: For lower extremity orthopedic procedure, supplementation of spinal anesthesia with combined intrathecally injected and epidurally infused Mg, considerably reduced the perioperative analgesic requirements without any side effects.