Improving individual measurement of postoperative pain: the pain trajectory.

UNLABELLED: The purpose of this study was to demonstrate a method for increasing the precision and information yield of postoperative pain assessment. We recorded pain intensity ratings over 6 days after surgery in 502 elective surgery patients and examined individual pain trajectories. A linear fit of an individual patient's scores defines a trajectory with two features: (1) the intercept or initial pain intensity; and (2) the slope, or rate of pain resolution. Three pain trajectory patterns emerged from examination of the pain trajectory slopes. Most patients (63% of the sample) demonstrated a negative slope trajectory characterized by a decline in pain intensity over days after surgery. Other patients (25% of the sample) demonstrated a flat trajectory with no meaningful change over 6 days from pain they reported initially. A third patient group (12% of the sample) had a positive slope trajectory in which pain scores increased over 6 days after surgery. Measures derived from individual pain trajectories yielded much lower standard errors of measurement and therefore had better measurement precision than did conventional pain assessment methods. Pain trajectory measures proved sufficiently precise to characterize pain patterns reliably in individual patients. PERSPECTIVE: Progress in acute pain management requires effective pain assessment. The acute pain trajectory quantifies rate of pain resolution as well as pain intensity. It affords more precise measurement than conventional pain assessment and can identify abnormal postoperative pain resolution.