Programmed Intermittent Epidural Bolus for Postoperative Analgesia After Laparotomy: Determining the Optimum Dose Using a Biaised Coin Up-and-down Sequential Allocation Protocol

Objective : To identify the optimal volume dosage of epidural bupivacaine administered with a PIEB protocol using a biased coin up-down sequential allocation method. This optimal dose will be determined separately for men and women to account for possible sex-based differences in postoperative analgesia.Only patients undergoing surgery requiring a large laparotomy incision will be included.

Hypothesis : the optimal dose of the PIEB that will provide effective analgesia in 90% of patients on the first postoperative day using an epidural solution of 0,05% bupivacaine + fentanyl 2 µg/mL + adrenaline 2 µg/mL will range between 5 and 10 mL in both groups.

Population : Patients undergoing elective open abdominal surgery via a midline incision extending above and below the umbilicus (>25 cm) with planned TEA.

Screening and recruitment : Eligible patients undergoing gastro-intestinal, gynecological and vascular procedures will be screened by looking at the operating room schedule 2-3 days prior to surgery. The patient files will be checked for inclusion and exclusion criteria, and eligible patients will be contacted preoperatively by phone to further verify eligibility and to inform them of the research project. Written informed consent will be obtained by the research nurse on the morning of surgery. Patients of female sex will be allocated to the female group and patients of male sex will be allocated to the male group. Patients will be instructed preoperatively about the pain scale (11-points pain scale of 0-10, where 0: no pain at all and 10: worst imaginable pain) and about how to use the PCEA pump.

Anesthesia management : Upon arriving in the operating room and after installing a peripheral intravenous access and standard ASA monitoring, patient will be pe-medicated with midazolam 0,5-1 mg IV and/or sufentanil 5-10 mcg IV or fentanyl 50-100 mcg IV. Thoracic epidural catheter will be installed in the sitting position using a loss of resistance technique in the low thoracic spine (preferably T11-T12, or T10-T11 alternatively). To ensure consistency in lumbar level of puncture, spinal ultrasound will be used in all cases. The last and second to last thoracic ribs will be identified and followed medially until the laminas and the T11-T12 and T10-T11 interspaces, respectively, which will then be marked using a skin marker. After skin disinfection and local anesthesia, the epidural space will be identified using a loss of resistance to saline technique and the catheter will be inserted 3-5 cm into the epidural space. Correct placement will be verified with negative aspiration of the catheter and a negative test dose using 3 ml of lidocaine 2% + epinephrine 1:200 000.