The evaluation of acute pain in individuals with cognitive impairment: a differential effect of the level of impairment.

The present study investigated whether the level of cognitive impairment (CI) affects acute pain behavior and how it is manifested. Participants were 159 individuals (mean age 42+/-12), 121 with CI (divided into four groups according to the level of CI: mild, moderate, severe, profound) and 38 with normal cognition (controls). The behavior of the participants before and during acute pain (influenza vaccination) was coded by two raters with the Facial Action Coding System (FACS - scores facial reactions to pain) and the Non-Communicating Children's Pain Checklist (NCCPC-R - scores both facial and general body reactions). Individuals with severe-profound CI exhibited elevated FACS and NCCPC-R values at baseline compared with all other groups (p<0.01). Both FACS and NCCPC-R scores of individuals with mild-moderate CI and controls increased significantly during vaccination (p<0.001). In contrast, individuals with severe-profound CI exhibited high rates of "freezing reaction" (stillness) during vaccination, manifested mainly in the face and therefore resulting in elevation of only NCCPC-R scores but not of FACS's. The results suggest that the level of CI affects baseline as well as pain behavior and it is therefore necessary to choose an appropriate behavioral tool to measure pain in these individuals accordingly. For example, tools based on facial reactions alone might provide the false impression that individuals with severe-profound CI are insensitive to pain (due to freezing).