In recent years there has been a drive to reduce the use of intra-operative opioids in morbidly obese populations [1]. The use of Remifentanil infusions intra-operatively, whilst providing good operating conditions and rapid early recovery, has been increasingly questioned, particularly with regard to the issue of rebound hyperalgesia [2].

We have a variety of anaesthetists and techniques used within our bariatric service, and because each surgeon operates with every anaesthetist, linkage bias due to surgical technique in a study should be minimal. We therefore felt in a position to test the hypothesis, that intra-operative remifentanil use would be associated with greater post-operative opioid requirements.

The advent of electronic prescribing systems two years ago has allowed accurate analysis of all post-op opioid administration. A long-standing anaesthetic database of bariatric surgical patients operated on at our institution was matched to a downloaded report of over 6,000 prescriptions from the hospital electronic prescribing system, looking at only uncomplicated primary laparoscopic gastric bypass procedures (hospital stay <72 hours) performed since April 2017. 
We identified and compared the intra-operative and post-operative doses of Remifentanil, Fentanyl, and Morphine. Statistical analysis was performed with GraphPad Prism, using Mann-Whitney t-test for non-parametric data.
Preliminary results are available for 127 patients (94 females, 74% ), the median age of the cohort was 44 and the median BMI 49.

The most striking finding was the increase in post-op opioid use amongst patients who received remifentanil as part of the intra-operative technique. The median total doses of Morphine were 45mg vs 28 mg (fig. 1 below), P value of 0.022. Amongst those who received remifentanil, total fentanyl use was less (reflecting intra-operative administration) but comparing recovery unit (post-operative) fentanyl administration there was an increased requirement, with a median of 50mcg vs 0mcg (fig 3), P value 0.037.

Whilst a retrospective study is inevitably at risk of unrecognized bias, the use of intra-operative Remifentanil was associated with significantly elevated post-operative opioid administration, presumably reflecting increased post-operative pain. Whilst this is preliminary data, it would strongly support the concept of acute opioid induced tolerance using the typical remifentanil regimens used within UK Bariatric practice.

03 / Remifentanil and Post-operative Opioid Administration in Patients undergoing Bariatric Surgery