Evaluation of morphine sparing effects of gabapentin for relief of postoperative pain in patients undergoing lumbar laminectomy: A double blind study

Gabapentin reduces postoperative pain involving central sensitization and spinal neuroplasticity. It blocks NMDA and other voltage dependent Ca2+ channels, reduces glutamatergic transmission, and improves gabaergic transmission.1 We hypothesized that gabapentin decreased postoperative morphine use following lumbar laminectomy. With ethics committee approval, 40 patients, 16-60 yr old, of either sex, ASA PS 1 or 2, with prolapsed intervertebral disc or lumbar stenosis undergoing lumbar laminectomy with general anesthesia, gave written informed consent and received randomly, in double-blind fashion, either placebo or 800mg gabapentin orally the night before surgery and again 45 min prior to surgery. Patients received 0.1mg/kg morphine at induction, 2 mg increments during surgery to maintain blood pressure and heart rate within 20% of baseline, and PCA morphine after surgery, with 1 mg/h basal rate, 1.5mg doses at lockout time 8 min, and a maximum of 20mg every 4h. A blinded observer scored postoperative pain via a visual analog scale, as well as hemodynamic parameters and side effects, at 2, 4, 6, 10 and 24h after surgery. Student's t-test compared continuous Normally distributed variables, and Chi-square contingency tables compared frequency data, with P<0.05 significant. Gabapentin group patients received 7.0±1.6mg morphine intra-operatively vs. 7.8±1.9mg placebo group patients (P=NS). After surgery, gabapentin patients used 33± 2.6mg morphine over 24h compared to 37± 2.8 for placebo patients (p<0.05). VAS score 24h after surgery was 21±9.0 mm for gabapentin and 28±18 mm for placebo patients (P=NS). Hemodynamics did not differ. Dirk et al. observed decreased morphine consumption after 1200 mg gabapentin to patients undergoing mastectomy.2 Turan et al. showed gabapentin reduced morphine use after spine surgery and tramadol use after hysterectomy.3 Our results agree and extend the gabapentin benefit to patients undergoing lumbar laminectomy. References: 1.Rutkowski MD et al, Spine, 2002; 2.Dirk J et al, Anesthesiology, 2002; 3.Turan A et al, Anesthesiology, 2004.