USING MEMORY FOR PAIN IN ANALGESIC RESEARCH

OBJECTIVE: To determine the validity of pain intensity recall at 24 and 48 hours as a substitute for hourly pain assessments in repeated-dose analgesic studies. SETTING: Orthopedic unit of an acute care teaching hospital. PARTICIPANTS: Eighty-four patients undergoing arthroscopic reconstruction of the anterior cruciate ligament, using the patellar tendon, who were participating in a randomized, double-blind, parallel-group analgesic study. INTERVENTIONS: Patients rated their pain intensity every hour (while awake) for 48 hours and their recall of worst, least, and usual pain intensity at 24 and 48 hours using a visual analog scale (VAS). MAIN OUTCOME MEASURES: This study examined the relationship between recall of worst, least, and usual pain intensity at 24 and 48 hours and the experienced maximum, minimum, and mean pain intensity VAS scores obtained from hourly assessments over the 0-24- and 0-48-hour periods, respectively. The significance of differences between recalled and experienced pain intensity variables was assessed. RESULTS: Worst, least, and usual pain recall at 24 and 48 hours were highly correlated with experienced maximum, minimum, and mean pain from hourly reports, respectively, over the 0-24- and 0-48-hour periods (Pearson correlation coefficients, r=0.80-0.89, p<0.0001). Among the three pain recall variables, usual pain showed the highest correlation with hourly measurements. There were no significant differences between recalled pain and the corresponding measures of pain from the hourly VAS scores, except in the case of 48-hour recall of worst pain (Student's t-test, p=0.001). CONCLUSIONS: The close agreement between actual pain experience and recall of pain provides support for the use of pain recall in assessing analgesic efficacy in clinical trials.