Preoperative lumbar epidural morphine improves postoperative analgesia and ventilatory function after transsternal thymectomy in patients with myasthenia gravis

Objective: To test the hypothesis that preoperative lumbar epidural morphine improves postoperative pain control and ventilatory function after transsternal thymectomy in patients with myasthenia gravis. Design: The study design was randomized, placebo-controlled, and double-blind. Setting: After surgery, all patients were admitted to the Neuroscience Critical Care Unit for evaluation and treatment. Patients: All patients with myasthenia gravis who presented to the hospital for thymectomy were asked to participate in the study. Twenty patients were randomized to either the placebo or epidural morphine groups. Interventions: Patients received either epidural morphine (7 mg in 14 mL of sterile saline) or saline (14 mL) before induction of anesthesia. Supplemental iv opioids were administered intraoperatively, with need determined by the anesthesiologist. Main Outcome Measures: The main outcome measures were indicators of postoperative pain (e.g., Visual Analog Pain Score, requirement for supplemental opioid administration, respiratory rate) and ventilatory function (e.g., forced vital capacity, negative inspiratory pressure). Results: Immediately after surgery, the Visual Analog Pain Score in the placebo group was twice as high as the score in the epidural morphine group (placebo 7.0 ± 1.3; epidural morphine 3.5 ± 1.2, p ≤ .05). During the first eight postoperative hours, the placebo group required more opioids (0.22 ± 0.03 vs. 0.12 ± 0.04 mg/kg morphine equivalents, p ≤ .06) than the epidural morphine group. Later, both groups received similar amounts of opioids. Patients receiving epidural morphine had better initial recovery of forced vital capacity (at 8 hrs: 55 ± 6% [epidural morphine] vs. 34 ± 5% [placebo] of preoperative value, p ≤ .05). Respiratory rate was lower for the first 12 postoperative hours in the epidural morphine group, without a difference in PaCO₂. There was no difference between groups for the duration of postoperative intubation or ventilation. Conclusions: Preoperative lumbar epidural morphine facilitates postoperative analgesia and improves initial postoperative ventilatory performance.