Measuring pain intensity in categories through a novel electronic device during experimental cold-induced pain

Pain assessment is challenging given its subjective nature, and existing assessment tools have limitations, especially for patients having problems with verbal communication. A prior study evaluated the Grasp, a handheld device for assessing pain intensity through squeezing, showing a moderate association with the numeric rating scale (NRS). This study examined an improved version of the Grasp with instant visual feedback through color-coded categories and compared it to NRS.

Healthy adults underwent two consecutive cold pressor tests (CPTs), reporting pain intensity via NRS or Grasp with colour-coded feedback. Two additional CPTs assessed the association of repeated measurements with both instruments. The Grasp was calibrated to individual strength before CPTs.

Forty-six subjects completed all tests. Pain intensity association between Grasp and NRS was moderate with a mean Kendall's τ-b coefficient (τ-b) of 0.45, 95% confidence interval (CI) 0.35-0.56. Repeated Grasp measurements showed a moderate association (τ-b = 0.37, 95% CI 0.27-0.48), while repeated NRS measurements had a stronger association (τ-b = 0.71, 95% CI 0.64-0.78). After adjusting Grasp to individual squeeze strength (resulting in a 0.0-1.0 scale), a simple equation relating NRS value and mean Grasp value was identified: Grasp = 0.091 × NRS. Grouping reports into mild, moderate, and severe pain resulted in agreement proportions across two CPTs of 69% for Grasp and 79% for NRS.

The moderately high agreement proportions for pain intensity categories suggest that the Grasp method with colour-coded feedback may be useful for categorical pain intensity assessment, especially in settings where conventional tools (i.e., NRS) are inconvenient or not feasible.