Comparison of present pain intensity assessments on horizontally and vertically oriented visual analogue scales

Contrary results have been reported from studies comparing horizontal and vertical orientations of the visual analogue scale (VAS) in non-dental pain states. The vertical orientation of the VAS has been used in our department for several years while the horizontal orientation is the most commonly used in other acute pain models. The present study investigated whether a horizontally oriented VAS is as sensitive as a vertically oriented VAS in the assessment of present pain after oral surgery. Seventy-four patients recorded their pain intensity hourly and half-hourly 15 times during 11 hours after surgery on a horizontal and on a vertical 100 mm VAS. Slightly lower mean and median values were observed at 2/3 of the observation time points for the vertical VAS compared to the horizontal VAS. The results from the two scales were compared with analysis of variance for repeated measures. No significant differences between the horizontal and the vertical VAS-values were found (p = 0.099). Distributions (Kolmogorov-Smirnov test) and dispersions of data were also similar with the two orientations of the VAS. This study shows that a vertically oriented VAS is equally sensitive as a horizontally oriented VAS in assessing present pain intensity after oral surgery.