Comparison of Bilateral Thoracic Paravertebral Block to Thoracic Epidural Analgesia for Post Operative Analgesia in Patients Undergoing Abdominal Surgery

A total of 70 patients with ASA physical status 1 to 3, scheduled for elective bowel surgery by laparotomy and deemed suitable to receive either thoracic paravertebral or epidural analgesia will be included in the study. Recruitment will take place in the preoperative clinic. Written informed consent for the participation in the study will be obtained at the visit to the preadmission clinic or in the preparation area at least 2 hours prior to the surgery. They will be randomized to one of two groups prior to the block procedure using a closed envelope system. All patients will be educated regarding the VRS scores on a scale of 0 to 10 where 0 is no pain and 10 is the worst pain ever experienced. All patients will receive perioperative multimodal analgesia using naproxen, gabapentin and acetaminophen.

All blocks will be performed in the block room using standard monitoring, sterile precautions and titrated intravenous sedation with fentanyl and midazolam. During block performance one anesthetist and one assistant will be present. Due to the necessity of handling the equipment these staff will not be blinded. All patients will receive supplemental oxygen.

Group 1: Group 1 will receive a catheter congruent TEA. The catheters will be inserted using ultrasound to assess level as well as the best space to insert the epidural catheter between T7 and T9. The epidural space will be identified using the loss of resistance technique. After a test dose to rule out intravascular and intrathecal placement of the catheter using 3mL of 2% lidocaine with 5mcg/mL of epinephrine, the initial block will be made with 0.25% bupivacaine 5 mL followed by 3 mL aliquots administered every 5 minutes to establish a block between T8 and T12. An infusion will be started at 8 mL/hour with 0.1 % bupivacaine with 10 microgram/mL of dilaudid and continued for 72 hours. Additional nurse administered boluses of 5-10mL of the standard solution will be allowed via the epidural catheter every 6hourly if needed for pain control followed by an increase in the basal infusion rate up to a maximum of 14mL/hr. Patients will be allowed to self-administer additional boluses of 3mL of the standard infusate every 20minutes (PCEA) as per the standard practice at this hospital. Time to initiate the block and the failures will be documented. If the block fails, patients will receive intravenous PCA with dilaudid and the patient will be dropped out of the study for efficacy data.

Group 2 will have bilateral PVB catheters inserted using the ultrasound. Patients will be in prone position and will receive intravenous sedation similar to Group 1. The T8 spine will be identified and marked counting from the lumbar area. A high-frequency linear ultrasound probe will be positioned in the T8/9 intercostal space with the transverse process and pleura in the field as well as the internal intercostal membrane. (about 2.5 cm lateral to the spinous process) Using ultrasound guidance and an in-plane approach, a 17 gauge Tuohy needle connected to 15 mL of 0.5% ropivacaine via an extension tubing will be inserted to puncture the internal intercostal membrane. Injection of local anesthetic will push the pleura away, which will be the end point of needle position (the current standard technique in the the investigators institution). A curved pigtail catheter will be inserted while observing its delivery extrapleurally and further 5mL of local anesthetic will be injected while observing further movement of pleura. A similar procedure will be done on the contralateral side at the same level. The catheter will be secured to the skin and covered with dermabond and tegaderm. Following this, 0.2% ropivacaine will be infused at a rate of 7 mlLhr via each catheter for the next 72 hours post-operatively. They will also receive intravenous patient controlled analgesia with dilaudid at a dose of 0.2mg with a lock out of 6 mins. Additional nurse administered boluses of 5-10mL of ropivacaine 0.2% via the paravetebral catheters will be permitted every 6 hourly to the side of maximal pain. The position of the catheter will be confirmed on the routine post-operative chest x ray following the injection of contrast (Isovue: 2 mL). The sensory block extent will be documented at 15 minutes after the initial injection and prior to moving the patient to the OR. Time to initiate the block and the failure rate will be documented.

US image of paravertebral space before and after LA injection (IIM: internal intercostal membrane; TP: transverse process; LA: local anesthetic)

As soon as the arterial line is inserted in the operating room for monitoring purposes, 10mL of blood will be collected for measuring plasma ropivacaine levels. This measurement will be repeated on arrival in the PACU along with routine postoperative arterial blood gas analysis. Plasma ropivacaine level will be measured on postoperative day 1 at 6AM with the blood drawn along with routine postoperative blood work (venous sample)

Cases with a failure to establish a block 30 minutes after local anesthetic injection will be considered as block failure and the patient will be excluded from the efficacy part of the study. These patients will receive intravenous patient controlled analgesia. Once the effectiveness and level of the block is confirmed the patient will be moved to the operating room for the surgery under standardized general anesthesia using fentanyl 2-3µg/Kg, propofol 2 mg/kg and rocuronium 0.8-1.0 mg/kg for intubation followed by maintenance with desflurane in air-oxygen mixture. Vasopressors (Ephedrine and phenylephrine) will be administered as needed to control hemodynamics and the total dose used will be recorded.

The patients will be assessed for pain during rest and coughing/activity immediately after the surgery, every 15 minutes for first 2 hrs and 6 hourly thereafter until 24 hours after the removal of epidural or block catheters. Patients whose VRS scores are higher than 5/10 in PACU, apart from getting a bolus in the epidural or PVB may also receive IV Hydromorphone 0.2 mg every 5 minutes till pain subsides to a score of 3/10. Nausea will be documented using a categorical scale (none, mild, moderate and severe), pruritus scores will be recorded every 12 hours (categorical scale, none, mild, moderate and severe). Time to onset of bowel sounds, time to first flatus and time to first bowel movement would also be recorded with time 0 being the arrival time in PACU. Post-operative hemodynamic changes, blood pressure and urine output will be documented every 6 hours. Duration of significant hypotension will be computed from the nursing chart, significant hypotension being systolic BP less than 90 mm Hg. Patient satisfaction will be documented on a visual analogue scale where 0 is totally dissatisfied and 100 is totally satisfied. Adverse events such as local anesthetic toxicity, wound infection, dehiscence, urinary retention, cognitive dysfunction and neurological deficits will be prospectively collected. The failure rate of both the techniques and the number of attempts will also be recorded.

This is an open label study to document the effectiveness of bilateral PVB in bowel surgeries. The investigators plan to do a double blind study following the present study if the results are encouraging. The second concern is that 2 different local anesthetics are used for the 2 limbs but at equianalgesic concentrations for the infusion.