Measuring Pain in Outpatient Surgical Patients: Variation Resulting from Instrument Choice DAVID GOODYEAR, B.S., VIC VELANOVICH, M.D. From the Department of Surgery, Henry Ford Hospital, Detroit, Michigan 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 in- strument, 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 pa- tients as measured by both the VAS and BP-SF-36 (P 5 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. M EASURING PAIN HAS become an increasingly im- portant part of medical practice. In fact, pain has been called the ‘‘fifth vital sign.’’ 1 Several organiza- tions, including the Department of Veterans Affairs, 1 Joint Commission for the Accreditation of Healthcare Organizations, 2 and the American Society of Anes- thesiologists, 3 have made public recommendations of pain assessment to improve pain control as well as a quality indicator. Because of the great interest in measuring pain in general, and in a variety of diseases that manifest in pain in particular, several pain in- struments have been developed. The MAPI Research Institute 4 and Patient-Reported Outcome and Quality of Life Instruments Database 5 have listed 18 different pain measurement instruments. In addition to the pain- specific measurement instruments, many of the generic quality-of-life instruments have a pain domain. Two instruments are used routinely in the senior author’s practice: the numeric visual analog scale (VAS) 6 and the SF-36, 7 which has a bodily pain (BP) domain. During routine clinical practice, there was an impression that the VAS and the BP scores did not necessarily correlate, which seems incongruent given that they both purportedly measure pain. Therefore, this led to the hypothesis that the instrument used in pain measurement will affect the variation in pain assessment as a result of differences in the concep- tual constructs of the instruments. The purpose of this study was to assess the correlation of these in- struments and to determine if particular pain patterns are better assessment by one or the other instrument. Methods and Materials This study was approved by the Henry Ford Health System Institutional Review Board. Instruments There are many versions of the VAS. The style of the VAS used in the Henry Ford Health System is a Likert- type numeric pain rating scale from 0 to 10, in which 0 is no pain at all and 10 is the worst possible pain. The VAS has been assessed in multiple settings in surgical care and is the most common measurement of pain in surgical patients. Of importance, the conceptual con- struct of the VAS measures pain at the time it is ad- ministered with a floor of ‘‘no pain’’ and a ceiling of ‘‘worstpossible pain.’’ Presented in part at the 2010 International Society of Quality of Life Research, London, U.K., October 27–30, 2010. Address correspondence and reprint requests to Vic Velanovich, M.D., Division of General Surgery, University of South Florida, One Tampa General Circle, Tampa General Hospital, F145, Tampa, FL 33606. E-mail: vvelanov@health.usf.edu. Dr. Velanovich’s present affiliation is the Division of General Surgery, University of South Florida, Tampa, Florida. 1292