EFFECT OF GABAPENTIN ON POSTOPERATIVE ANALGESIA AFTER SPINE SURGERY

Background: Postoperative analgesia is not only a human right but also very important to avoid harmful effect of pain. Multimodal pain management can result in additive or synergistic analgesic effects with less drug side effects. Gabapentin is an anticonvulsant used to treat neuropathic pain and has been used as adjuvant with other analgesics for postoperative analgesia. The aim of this study was to assess the effect of gabapentin 600 mg oral capsule before surgery on acute postoperative pain in patients undergoing spinal surgery. Patients and methods: Eighty patients of both sexes, age between 20 60 years; ASA I-II, who were submitted to elective spine surgeries were included in the present study. Patients enrolled in the study were divided randomly into two equal groups:  Group P: Patients received placebo capsules 2 hours before surgery.  Group G: Patients received 600 mg gabapentin capsules 2 hours before surgery. The primary outcome measures were pain assessment by the visual analogue pain scale (VAS) during the first 24 hours postoperatively (VAS; 0 no pain and 10 worst pain imaginable), the time of the first request for postoperative analgesic, and total postoperative pethidine consumption. Secondary outcome measures were: • Perioperative mean arterial blood pressure, heart rate, peripheral oxygen saturation, and respiratory rate. • Postoperative sedation level using the following scoring system: 1 = awake and alert; 2 = awake but drowsy, responding to verbal stimulation; 3 = drowsy but arousable, responding to physical stimulation, and 4 = unarousable, do not respond to physical stimulus. • Side effects; nausea and vomiting, dizziness, headache and respiratory depression. Results: The data was collected and analyzed including demographic data, duration of surgery, postoperative pethidine consumption, VAS, and postoperative nausea and vomiting. Data were expressed as mean values ± standard deviation, percentages (%), and numbers (n) by using Windostat Version 9.2. Total postoperative pethidine consumption was 256.50 mg ± 44.18 vs 120.50 mg ± 15.34 for group P and group G respectively and this difference between both groups was statistically highly significant (p-value < 0.001). The average time of the first postoperative analgesic requirement for group P and G, it was 47.53 min. ± 30.71 vs 208.65 min. ± 39.37 respectively and this difference between both groups was highly significant (p-value < 0.001). Conclusion: Intake of gabapentin 600 mg oral capsule decreased pain scores in the early postoperative period and decreased postoperative pethidine consumption while decreasing postoperative nausea and vomiting in patients undergoing spine surgeries. Mohamed Abd-Allah et al AAMJ ,VOL 13 , NO 4 , OCTOBER 2015 SUPPL-2 316 | P a g e INTRODUCTION Postoperative analgesia is not only a human right but also very important to avoid harmful effect of pain. Multimodal pain management can result in additive or synergistic analgesic effects with less drug side effects. Gabapentin is an anticonvulsant used to treat chronic neuropathic pain and it is commonly used for herpetic neuralgia and diabetic neuropathy. Gabapentin reduces the activity of calcium channels in GABAergic neurons (Jianren and Lucy, 2000). This in turn activates the noradrenergic spinal pathway and reduces the expression of the spinal cord excitatory amino acids glutamate and aspartate. Recently, gabapentin has been used for acute pain as a part of a multimodal pain management strategy. The aim of the present work was to study the effect of gabapentin on postoperative analgesia after spine surgery (Rosner et al. 1996). PATIENTS AND METHODS The study was carried out in Al-Azhar university hospitals after approval of Medical Ethics Committee; eighty patients of both sexes, age between 20 60 years; ASA I-II, who were submitted to elective spine surgeries were included in the present study. The study has been done during the period from February 2012 to July 2015. All patients had significant lumbar disc prolapse evidenced by clinical presentations and magnetic resonance imaging (MRI) of lumbosacral spine. Patients were divided randomly into two equal groups with forty patients each. Group P: Patients received placebo capsules 2 hours before surgery. Group G: Patients received 600 mg gabapentin capsules 2 hours before surgery. Exclusion criteria included cardiovascular dysfunction, renal or hepatic diseases, uncontrolled diabetes mellitus, pregnancy, antidysrhythmic drugs or calcium channel blockers intake, psychiatric disease, epilepsy, corticosteroid intake, or chronic treatment with opioids and sensitivity to the administered drugs. Also, patients presented with more than two levels of disc prolapse or had spinal instability were excluded. On the morning of surgery, group G patients received gabapentin 600 mg oral capsule 2 hours preoperatively, while group P patients received oral placebo capsules. In the operating room, intravenous cannula was inserted and standard monitors were applied to the patient including ECG, noninvasive arterial blood pressure measurement, SpO2, and capnography. Anesthesia has been inducted with i.v. fentanyl 1 μg/kg, propofol 2 mg/k, and atracurium 0.5 mg/kg, then intubation was done. Anesthesia was maintained with isoflurane 1.5-2% and top up doses of atracurium (0.15 mg/kg) to maintain muscle relaxation. All patients operated by the same approach that was posterior lumbar laminectomy and discectomy. The level of disc was identified both before skin incision and prelaminectomy using C-arm image. During surgery, the muscles were separated subperiosteally using sharp knife with minimal use of cauterization. Partial laminectomy was done up to the upper border of midline part of ligamentum flavum. After good meticulous dissection from the dura and foraminotomy of nerve root exit foramen, ligamentum flavum was removed. The disc was opened by sharp knife and then discectomy was done using disc rongeur of different direction. After satisfactory disc removal and nerve root release, good AL-AZHAR ASSIUT MEDICAL JOURNAL AAMJ ,VOL 13 , NO 4 , OCTOBER 2015 SUPPL-2 317 | P a g e hemostasis was achieved followed by closure of fascia, subcutaneous and skin in layers. After recovery, postoperative analgesia was provided by pethidine 20 mg, which was given intravenously when the visual analogue pain scale (VAS) score ≥ 4. The primary outcome measures were, pain assessment by VAS during the first 24 hours postoperatively (VAS; 0 no pain and 10 worst pain imaginable), the time of the first request for postoperative analgesic, and total postoperative pethidine consumption. Secondary outcome measures were: • Perioperative mean arterial blood pressure (MAP), heart rate (HR), peripheral oxygen saturation (SpO2), and respiratory rate. • Postoperative sedation level using the following scoring system: "1 = awake and alert; 2 = awake but drowsy, responding to verbal stimulation; 3 = drowsy but arousable, responding to physical stimulation, and 4 = unarousable, do not respond to physical stimulus". • Side effects; nausea and vomiting, dizziness, headache and respiratory depression. Statistical analysis of data Data were expressed as mean values ± standard deviation, percentages (%), and numbers (n). Windostat Version 9.2 was used for performing the statistical analysis of this study. Two statistical tests were primarily used to analyze the data and p-value < 0.05 was considered statistically significant. These tests are ttests (it was used to analyze differences between 2 groups) and analysis of variance (ANOVA) to analyze differences in parameters as HR, SBP, DBP, VAS score and sedation scores over a period of time. RESULTS As regards demographic data and duration of surgery, there were no significant differences between gabapentin group and placebo group (Table 1). Concerning mean arterial blood pressure, HR, SpO2, and respiratory rate, the differences between both groups of the study were statistically nonsignificant. Table (1): Comparison between group G and group P according to demographic data and duration of