Midazolam may affect postoperative pain, with studies suggesting conflicting effects. Anxiety may be a confounder. We aim to clarify the relation between anxiety, midazolam and pain.

We prospectively collected perioperative data of inguinal hernia repair patients in 4 Portuguese ambulatory units, with blind telephone interview at 24h, 7 days and 3 months after surgery. Association between pain intensity and midazolam was assessed, including subgroup analysis; alpha=0.05. 

Thirty men and two women were recruited in four ambulatory surgery units May-August 2018; 22% were smokers and 97% ASA< 3. Patients administered midazolam (any dose) were more anxious than patients not administered midazolam (p=0,001).
Spinal block provided better pain control than general anaesthesia, in all time frames (p=0,043 at 24h); spinal block patients were also administered higher midazolam doses (p<0,001). Chronic benzodiazepine users referred less 24h-pain (p=0,035) but more features of neuropathic pain at three months (p=0,019); however, they were also older (p=0,051). 24h-pain was related to 7-day (p=0,002) and 3-month pain (p=0,006).
After controlling for confounders, there was no association between midazolam dose and pain (p=0,197); however, the pilot study sample was not powered to find such association. Our main study (300 patients) might reach statistical power to uncover a possible association of perioperative midazolam and postoperative pain.

THE IMPACT OF MIDAZOLAM ON POSTOPERATIVE PAIN - A MULTICENTRIC PROSPECTIVE PILOT STUDY