Comparison of a novel direct measure of rapid pain intensity change to traditional serial 100 mm VAS measurement of pain intensity

OBJECTIVES: Key diagnostic decisions often turn on measurement of change in pain intensity after diagnostic anesthetic blocks. This study aimed to introduce a new direct measure pain intensity change and compare it with percent change as calculated from the traditional preprocedure and postprocedure pain visual analog scales.

METHODS: Shoulder pain patients enrolled in a diagnostic accuracy study comparing clinical variables with image-guided local anesthetic injections were assessed with both the traditional preprocedure and postprocedure visual analog scales and the new direct method. Percent change in pain intensity was calculated with both instruments and were compared using statistical methods. The percentage pain reduction used to classify patients as responders was 80%.

RESULTS: Patients received anesthetic injections to targeted shoulder structures (N=146, 331 procedures). For data above the 80% pain reduction criterion, Lin Concordance statistic ranged from 0.22 to 0.55. Bland and Altman analyses revealed positive bias and the amount of reported pain reduction was higher with the traditional method. For data above the 80% pain reduction criterion, the bias was higher and ranged from 4.8% to 12.6%.

CONCLUSIONS: The 2 methods are not interchangeable. The new method measures the pain intensity change dimension directly, whereas the traditional method estimates change indirectly by calculation. Face validity is better served by adopting the new method for decisions regarding whether a patient is a "responder" or "nonresponder" to diagnostic blocks. The traditional method should be retained for estimation of pain intensity preprocedure and the duration of pain relief postprocedure.