Does Midazolam Affect Postoperative Pain?

Systemic midazolam prescribed perioperatively might have impact on pain, with studies suggesting antinociceptive and hyperalgesic effects. Anxiety might be a confounder in this association. In order to investigate the effect of midazolam on postoperative pain, a prospective cohort study will be conducted in four Portuguese ambulatory surgery units. A convenience sample with consecutive design will include patients admitted for open inguinal hernia repair. After anxiety and pain evaluation, a tailored dose of midazolam will be administered as premedication according to the anesthetist's best judgement within each unit's protocol (routine care; this dose may be null). Subsequent anesthesia and analgesia will be standardized. Postoperative pain will be blindly assessed by telephone interviews at 24h, 7 days, and 3 months. Statistical analysis will be performed separately for each gender, centre and type of anesthesia, adjusting for preoperative anxiety and other confounding variables with multivariate analysis.

The investigators intend to clarify the relation between anxiety, preoperative midazolam and postoperative pain.

Inclusion criteria

• adults proposed for open inguinal hernia repair in Portuguese ambulatory surgery units

Exclusion criteria

• psychiatric disorders
• alcoholism
• illiteracy or poor understanding of the Portuguese language
• history of chronic pain under opioids
• recurrent surgery