Measuring pain in outpatient surgical patients: variation resulting from instrument choice

Our hypothesis is that the type of instrument will affect variation in pain assessment. A sample of 269 patients administered the visual analog pain scale (VAS) and the generic quality-of-life instrument, and the SF-36 were evaluated for gender, age, the VAS score and the bodily pain domain of the SF-36 (BP-SF-36) score, primary surgical diagnosis, preoperative or postoperative status, and type of operation. Patients were grouped into preoperative (Preop) and postoperative (postop) status and those with chronic pain (CP) conditions and acute/no pain (AP) conditions. Linear regression analysis showed statistically significant (all P value ≤ 0.0006) correlations between the VAS and BP-SF-36 scores all patients, preoperative patients, postoperative patients, acute pain patients, and chronic pain patients. However, the strength of these correlations were moderate (r values between 0.51 and 0.61). Preoperative had more pain compared with postoperative patients as measured by both the VAS and BP-SF-36 (P = 0.05). Similarly, chronic pain patients had more pain compared with acute pain patients as measured by both scales (P < 0.0001). Although there are statistically significant associations between the BP-SF-36 and VAS, the correlations are moderate. Different instruments may measure different aspects of pain and the precision with which pain is measured in surgical patients.