Reliability of the visual analog scale in children with acute pain in the emergency department

In children, many psychometric properties of the visual analogue scale (VAS) are known, including the minimum clinically significant difference (10 mm on a 100-mm VAS). However, its imprecision or reliability is not well known. Thus, in order to determine the reliability of this scale, a prospective cohort study was performed in patients aged 8-17 years presenting to a pediatric emergency department with acute pain. Pain was graded 4 times using a paper VAS (0-100 mm): T0, T3, T6, and T⩾36 minutes. After T6, patients were asked if their pain had changed since T0 minute. The primary analysis was the repeatability coefficient of the VAS, determined according to the Bland-Altman method for measuring agreement using repeated measures in patients reporting that their pain was the same for T0, T3, and T6. In order to appropriately estimate the within-subject SD, 96 patients were required if we obtained 3 measurements for each patient. A total of 151 patients with a mean age of 12.2 ± 2.5 years were enrolled. Among them, 100 mentioned that their pain was the same for T0, T3, and T6 minutes. The repeatability coefficient of the VAS for these children was 12 mm when the pain did not change. This implies that, for a child, all pain intensity measurements within 12 mm should be considered the same pain intensity on a paper VAS. This measure should also be evaluated on other types of VAS.