[Measurement of postoperative pain: analysis of the sensitivity of various self-evaluation instruments]

This study compared the sensitivity of two one-dimensional scales (a visual analog scale [VAS] and a verbal scale of pain intensity [VSPI]) and one multidimensional scale (McGill Pain Questionnaire-Spanish Version [MPQ-SV]) for detecting changes in pain after a variety of surgical procedures with postoperative analgesia provided by one of two methods.

Forty-two patients who underwent abdominal surgery, hysterectomy, cesarean, inguinal herniorrhaphy, subcostal or medial laparoscopic cholecystectomy were studied. Postoperative analgesia consisted of 1 mg/Kg of intravenous pethidine every 4 h in group one (n = 20) and intramuscular diclofenac every 12 h in group two. Assessment was at 24 h and/or at 48 and 72 h using the VAS, the VSPI and the MPQ-SV.

All the scales were useful for assessing postoperative pain, giving estimates that were sensitive to variations in pain on days after the operation. The MPQ-SV was able to detect different pain-producing capacities for the surgical procedures more effectively than were the one-dimensional scales. The MPQ-SV was also able to discriminate the qualitative and quantitative differences among the mechanisms of action of opioid and nonsteroidal anti-inflammatory drugs, whereas the one-dimensional scales were unable to distinguish therapeutic approach.

All the scales were sensitive to changes in postoperative pain, but the MPQ-SV gave more precise information of differences between analgesic treatments and among operations.