Abstract: Remifentanil For LRYGB: Is Opioid-Induced Hyperalgesia Important Following Bariatric Surgery?
Elizabeth Perritt, Nicole Robin, Santokh Singh
Countess of Chester, Chester, UK
Email address: elizabethperritt@nhs.net

Introduction
Laparoscopic Roux-en-Y gastric bypass (LRYGB) is an established surgical procedure for the management of morbid obesity. Sedation, immobilisation and hypoventilation can result from administration of opioid analgesics and are of particular concern as they may increase the risk of post operative complications such as venous thrombosis and respiratory tract infection. The use of remifentanil facilitates optimum intubating conditions, haemodynamic stability and reduces both intra operative use of muscle relaxants and long acting opioids. Of concern, however, is the possibility of acute opioid-induced tolerance or hyperalgesia (OIH) that may increase postoperative pain. The evidence is conflicting, and specific data on OIH in bariatric surgery is lacking. We investigated whether intra-operative remifentanil for LRYGB was associated with any differences in post-operative analgesic consumption or patient outcomes. 

Methods 
A retrospective review of LRYGB surgery at the Countess of Chester Hospital between 17/01/13 and 03/11/14 was performed. Data were collected from an existing surgical database, electronic prescribing system (Meditech) and review of anaesthetic charts. Thirty eight consecutive patients anaesthetised by the same consultant anaesthetist were reviewed. Patients who had received remifentanil intra operatively were compared with those who had not received remifentanil. All other aspects of the anaesthetic technique were consistent, in particular intraoperative analgesia. Analgesia included intravenous paracetamol, parecoxib and morphine. Port-sites were infiltrated with levobupivacaine.

Results
In 20 cases, intra-operative remifentanil was used. In 18 cases, remifentanil was not used. There was a trend towards an increased opioid consumption in recovery in the remifentanil group (7.3mg vs 5.0 mg p=0.24). This group also spent significantly longer in the recovery room (83.6 vs 54.7 minutes, p=0.0058). There was no significant difference in the mean overnight morphine consumption, time to mobilisation or length of stay (LOS).

Conclusion
We have examined small, but well matched, groups of patients having LRYGB with and without intraoperative remifentanil, and found a trend to reduced opioid consumption with a significant reduction in recovery time. It has been suggested that high intra-operative doses of remifentanil are associated with a small but significant increase in acute pain after surgery[1]. Systematic review has found conflicting evidence regarding the existence of OIH: outcomes evaluating measures of hyperalgesia frequently concluded that remifentanil OIH exists, while those evaluating opioid consumption did not[2]. The improved recovery time seen in our sample may reflect reduced sedation or improved analgesia in the absence of OIH. It must be acknowledged that conclusions are limited by the small numbers involved, and there is potential for confounding variables within the recovery area. It is nonetheless an important observation which, given the conflicting evidence, ought to prompt larger scale studies into remifentanil and OIH in the Bariatric population.

References
1. Fletcher, D., & Martinez, V. (2014). Opioid-induced hyperalgesia in patients after surgery: a systematic review and a meta-analysis. British journal of anaesthesia, 112(6), 991-1004.
2. Rivosecchi, R. M., Rice, M. J., Smithburger, P. L., Buckley, M. S., Coons, J. C., & Kane-Gill, S. L. (2014). An evidence based systematic review of remifentanil associated opioid-induced hyperalgesia. Expert opinion on drug safety, 13(5), 587-603.

Remifentanil for LRYGB: Is opioid-induced hyperalgesia important following bariatric surgery?