Measuring the analgesic effect of adding pre-operative single-shot rectus sheath blocks to postoperative rectus sheath continuous blocks for major urological surgery

Editor, Continuous rectus sheath block offers an alternative to epidural analgesia for postoperative analgesia after midline abdominal surgery.1–4 Catheters can be placed under ultrasound guidance3 or under direct vision during closure of the surgical incision.2 A disadvantage of surgically placed rectus sheath catheters is that they are inserted at the end of surgery. Therefore, unlike epidural catheters inserted pre-operatively, the patient does not benefit intra-operatively and the block may not be fully established in the early recovery phase of care. We hypothesised that the addition of ultrasound-guided pre-operative bilateral single-shot rectus sheath blocks to surgically inserted postoperative continuous rectus sheath blocks would improve postoperative analgesia in the first 24 h after surgery. To this end, we designed a prospective, randomised, double-blind, placebo-controlled trial where the primary outcome was opioid consumption in the first 24 h postoperatively. Secondary outcomes included intra-operative opioid requirement, and Numerical Rating Scale (NRS)-11 pain scores in the postanaesthesia care unit (PACU) and at 24 and 48 h postoperatively. This study was approved by the Health Research Ethics Board of the University of Alberta (protocol number 00078459, date of registration 7 February 2018, ClinicalTrials.gov identifier: NCT03458598). Adult patients undergoing cystectomy or cystoprostatectomy who consented to rectus sheath block were eligible for inclusion. Participants were allocated randomly to either the treatment or control group. Prior to induction of anaesthesia, the treatment group underwent ultrasound-guided single-shot bilateral rectus sheath blocks with a mixture of 10 ml of 1% ropivacaine and 10 ml of 0.25% bupivacaine, whereas the control group received an ultrasound-guided bilateral subcutaneous injection of 1 ml of 0.9% saline. In both groups, bilateral rectus sheath catheters were inserted surgically before closure of the incision. The patient, intra-operative anaesthesiologist and surgeon were blinded to study treatment assignment. All patients were premedicated with paracetamol 1 g and gabapentin 200 mg orally. The following intra-operative guidelines were adhered to when possible: fentanyl 1 to 2 μg kg−1 at induction, and ketamine 20 mg and dexamethasone 6 mg after induction. Fentanyl bolus doses of 25 to 50 μg were administered during the procedure for control of haemodynamic parameters to a recommended maximum of fentanyl 250 μg including the induction dose. No long-acting opioids were administered until the end of the procedure, when bolus doses of hydromorphone 0.2 to 0.5 mg were titrated to a target respiratory rate of 8 to 12 bpm. All patients had bilateral rectus sheath catheters inserted prior to closure of the incision. A standard 18-gauge nerve block catheter (Contiplex Tuohy Set; B Braun, Melsungen, Germany) was inserted percutaneously between the rectus abdominis muscle and the posterior rectus sheath bilaterally. Catheters in both the control and treatment groups were used to inject 20 ml of 0.25% bupivacaine per side after insertion. Postoperatively, an infusion of ropivacaine 0.2% was administered through each rectus sheath catheter (1 ml h−1 continuous infusion per side with a 15-ml h−1 bolus per side every 4 h). All patients received patient-controlled analgesia (PCA) with intravenous hydromorphone. Adjunctive analgesia consisted of paracetamol 975 mg four times daily and gabapentin 200 mg twice daily for the first 48 h. Sample size was estimated based on the primary outcome of cumulative 24-h PCA opioid consumption. Using data gathered from a pilot study of 22 patients, we projected that cumulative 24-h intravenous PCA hydromorphone requirements would decrease from a mean of 11.7 to 5.5 mg with a SD of 6. We calculated that 20 patients per group would be required for an experimental design incorporating two equal-sized groups, using an α = 0.05 and β = 0.1. To minimise the effect of data loss, 25 patients per group were recruited. Data were analysed from a total of 43 study participants, 22 in the treatment group and 21 in the control group. There was no significant difference in the primary outcome of cumulative hydromorphone use for 24 h following PACU arrival between the treatment and control groups (mean ± SD 6.4 ± 4.3 vs. 7.04 ± 5.4 mg, P = 0.81) (Table 1). For secondary analgesia outcomes, there was a statistically significant difference for intra-operative fentanyl administration (239 ± 90 vs. 173.8 ± 106.2 μg for control and treatment groups respectively, P = 0.03). There was no significant difference for hydromorphone administration intra-operatively or in PACU. There was a difference between NRS pain scores on arrival at PACU which did not reach statistical significance (3.1 ± 3.0 vs. 1.6 ± 2.9 for the control and treatment groups respectively, P = 0.06). There was no significant difference between groups for NRS pain scores over the first 24 h. There was no significant difference between groups at any time point for the incidences of nausea or vomiting, or antiemetic use, time to first mobilisation after surgery, time to first bowel movement or duration of postoperative hospital stay. Table 1 - Intra-operative, postanaesthesia care unit and cumulative use of fentanyl and hydromorphone for the first 24 h postoperatively Control group Treatment group n=21 n=22 P Intra-operative fentanyl (μg) 239 ± 90 173.8 ± 106.2 0.03 Intra-operative hydromorphone (mg) 0.88 ± 0.7 1.07 ± 0.95 0.56 Hydromorphone use PACU (mg) 0.33 ± 0.58 0.17 ± 0.35 0.30 Postop. hydromorphone use 0 to 24 h (mg) 7.04 ± 5.4 6.4 ± 4.3 0.81 Values are mean ± SD. PACU, postanaesthesia care unit. This is the first study to date to compare the addition of single-shot fascial plane block with a surgically placed continuous block for postoperative analgesia. We found that the addition of a pre-operative single-shot rectus sheath block to a surgically placed catheter did not reduce cumulative opioid consumption in the first 24 h after surgery. A statistically significant reduction in intra-operative fentanyl administration was detected but this is unlikely to be of clinical significance. The reduction in pain score on arrival to PACU in the treatment group, although not reaching statistical significance, is arguably of more relevance clinically. It is possible that the effects of the pre-operative block do not last longer than approximately 6 h after block administration, as suggested by Cho et al.5 in a study evaluating the effects of rectus sheath blockade on early postoperative pain after laparoscopic gynaecological surgery. As the average duration of surgery in our study was 4.25 h, it is possible that the beneficial effects of pre-operative single-shot blockade will not be seen beyond approximately 2 h after surgery. A limitation of this study is the small sample size. It is possible that the large effect size found in our pilot study led to underpowering of the main study. Currently, there is insufficient data available which specifically evaluates the immediate and early postoperative effects of surgically placed rectus sheath catheters.

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