Effects of Pregabalin on Post-cesarean Pain

An independent investigator who will not be involved in the study will instruct the patients preoperatively about the use of patient controlled analgesia and visual analogue scale to assess the severity of postoperative pain (0 mm for no pain and100 mm for worst imaginable pain).

Anaesthetic management will be standardized. Oral ranitidine 150 mg and metoclopramide 10 mg will be given the night before and on the morning of surgery, with 0.3 mol/L sodium citrate 30 mL given 15 min before induction.

Ninety minutes before surgery, subjects will be allocated randomly into three groups by drawing sequentially numbered sealed opaque envelopes containing a software-generated randomization code to the placebo (n = 45), pregabalin 150 mg (n = 45) and the pregabalin 300 mg (n = 45) groups. The placebo and pregabalin capsules look identical and will be prepared by a local pharmacy. An anaesthesiologist not otherwise involved in the study and who will be blinded to treatment regimen will provide perioperative care. An independent investigator will collect perioperative data. All staff in the operating room will be unaware of patient allocation group.

Maternal monitoring will include electrocardiography, non-invasive blood pressure, and pulse oximetry. Left uterine displacement will be maintained.

Spinal anesthesia will be performed in all cases in sitting position at L3-L4 or L4-L5 spaces with hyperbaric bupivacaine 0.5% (12.5 mg) and fentanyl 20 µg. After the umbilical cord is clamped, a 10 IU infusion of oxytocin in 500 mL of lactated Ringer's solution will be infused.

A paediatrician blinded to study group allocation will record Apgar scores at 1 and 5 min, umbilical cord blood gas analysis and NACS at 15 min, 2h, 24 and 48 h after delivery. NACS gives a maximum of 40 with a score >35 denoting vigor.The percentage of infants scoring <35 will be determined.

Postoperative analgesic regime will be standardized in all patients with 12-hourly intramuscular diclofenac 75 mg started immediately at the end of surgery and morphine via patient-controlled analgesia (PCA): 1 mg bolus with an 8 minutes lockout. Postoperative nausea or vomiting will be treated with intravenous metoclopramide 10 mg as required.

Statistical analysis:

Based on a previous study,7 the mean postoperative cumulative morphine consumption at 24 h after caesarean delivery was 38 mg with a standard deviation of 14 mg. An a priori power analysis indicated that 45 subjects were required in each group to detect a 25% reduction in the cumulative morphine consumption at 24 h after caesarean delivery, that was assumed to have a clinically significant effect, with a type-I error of 0.0167 (0.05/3 possible comparisons) and a power of 90%. Additional patients (10%) were included for a final sample size of 150 patients to account for patient dropout during the course of the study.

Inclusion criteria

• spinal anesthesia
• elective cesarean delivery
• breech presentation
• cephalopelvic disproportion
• previous caesarean delivery
• American Society of Anesthesiologists class I and II

Exclusion criteria

• communication barriers
• cardiovascular diseases
• renal diseases
• hepatic diseases
• endocrinal diseases
• neuropsychiatric diseases
• morbid obesity
• diabetes mellitus
• anaemia
• bleeding disorders
• prolonged P-R interval
• hypersensitivity to pregabalin
• receiving pregabalin
• receiving anticonvulsants
• receiving antidepressants
• receiving antipsychotics
• alcohol or drug abuse
• Opiates abuse
• benzodiazepines during the last week
• pregnancy-induced hypertension
• evidence of intrauterine growth restriction
• fetal compromise