JC: Dexmedetomidine and Post-Op Pain

As further proof (if needed) of how journal clubs don’t have to be snooze-inducing analysis and boring powerpoint presentations, the latest NWRAG journal club continued with its fine tradition of a pub based setting and beer lubricated discussion. The target paper this month was selected as ‘The effects of intra-operative dexmedetomidine on postoperative pain, side-effects and recovery in colorectal surgery’, found in the Anaesthesia journal at the link below (1):

Dexmedetomidine and Post-Op Pain

What's It About?

As the authors note there has been plenty of interest in enhanced recovery programs with major surgical procedures, and multi-modal analgesia and morphine sparing have been extensively talked about and studied. This paper took on the challenge of exploring one of the more novel adjuvants in the form of the alpha-2 receptor agonist dexmedetomidine. They highlight the recent meta-analysis (2) looking at dex, noting its significant heterogeneity as a limiting factor factor in its applicability to general clinical practice. As such, they set out with their own study to try and ascertain the impact that dex has on reducing post-op pain, and therefore presumably morphine consumption.

What've They Done?

After a quick look through the methods section we all came to a pretty similar conclusion; this was a pretty well thought out and conducted study. They have put together a double-blinded, randomised control trial comparing dex against placebo with 100 patients enrolled. Pain in the post-operative period was assessed using a numerical rating scale (NRS), morphine usage was noted and the incidence of side effects was documented. In addition, a power calculation was performed prior to patient recruitment and the administration regime was clearly standardised across the trial; lots of boxes being ticked and approving nods.

What've They Found?

Unfortunately, this is the part of the paper where we started to find the flaws. After looking at all the great work that had gone into the study design, the results, or more specifically the conclusions that the authors have dragged from them, left a definite underwhelming feeling. Their central finding is a reduced area under the curve (AUC) of the pain scores between 1-48 hours in the dexmedetomidine group. This difference does reach statistical significance (p = 0.048) but the difference is a reduction to 113.8 compared with 136.7. I’m sure the question you’re now asking the question; is that good? Unfortunately, that is would appear to where the applicability of the study to clinical practice ends. It appears that use of AUC measurement is a valid research method for comparing pain in different groups, but identifying statistical significance from a set of numbers still has to be translatable to patient care. The more frequently cited benefits of reduced post op pain; reduced opioid consumption and related side effects, were not detectable here, leaving us to muse on what these AUC numbers could mean for our patients.

Is It Any Good?

As you may have guessed from the analysis so far, this question has a bit of a two-part answer. In terms of design and conduct this is a pretty good piece of work, only really limited by the relatively low number of patients and some questions about the application of the numbers used in their power calculation (it's not easily apparent where the numbers arise or how the maths has been applied). And all this increases the faith you can put in the results they find; some reduction in pain scores in the first 48 hours. But what we do with this information now we have it? Unfortunately we’re not entirely sure, and the authors have not particularly explore this important facet in their discussion. 

Final Thoughts

To summarise our thoughts:

• Well designed and conducted study
• Statistically significant reduction in AUC pain scores in dexmedetomidine group
• Unclear clinical significance of this reduction
• No evidence of tangible clinical differences of reduced morphine consumption or side effects.

The authors have made a decent effort at exploring this question, but it is perhaps the vagueness of their initial clinical question that has led to some uncertainty in interpreting these results. They rather broadly set out to look for an improvement in post-op pain, rather than a specific change in a measurable value. As such, finding this numerical difference between the groups doesn’t hold a clear meaning for us, and it isn’t explored further by the authors. There are suggestions here about the potential role for alpha-2 agonists as an adjuvant analgesic, but nothing to massively change current practice.

As always please leave your thoughts on this article and on your current clinical experience with dexmedetomidine as an adjuvant analgesic. I must also say a big thanks to NWRAG and fellow journal clubbers Philippa Shorrock, Matt Jackson, Naomi Cochrane, Kunal Lund and Nick Plummer who contributed most of the above. Thanks for reading.


Tom Heaton

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1. Dexmedetomidine and Post-op Pain. Anaesthesia. Nov 2014

2. Dexmedetomidine Meta-analysis: Pain. 2013

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