A method for overcoming the ceiling effect of bounded pain scales

Objective. The Verbal Numerical Scale (VNS) for rating pain is bounded betw een 0 (= no pain) and 10 (= worst pain imaginable). We hypothesized that th e limitations inherent to this boundary when rating extremely painful stimu li may be identified by integrating the VNS with an unbounded score such as magnitude estimation of relative change. Methods.Volunteers received stimu li of increasing current via cutaneous electrodes until they rated > 5 on t he VNS scale. This stimulus, termed S, was arbitrarily assigned a magnitude estimate of 100%. Then, stimuli of varying currents were delivered; two we re 10 mA and 20 mA higher than S (S+10 and S+20), two were 1/2 of the curre nt for the S stimulus (S-1/2), and one was at the original current (S-repea t). The pain elicited by each stimulus was scored in proportion to the S st imulus. The extrapolated VNS score (VNSext) was determined by multiplying t his magnitude estimate (%) by the VNS score for S. Main Results. Seventy pe rcent of the stimuli with higher intensity than S generated a VNSext score above 10. The mean magnitude estimations for S+10 and S+20 were 186% and 24 2%: they generated mean (median) VNS(e)xt values of 12.4 [12] and 16.2 [14] , respectively (p = 0.019 for the difference between them by Wilcoxon signe d rank test). Conclusions. The combined use of VNS and magnitude estimation confirmed that the ceiling of the bounded pain scale may significantly lim it a patient's ability to describe a new pain stimulus. VNSext may provide a means of overcoming this limitation.