Validation of the Individualized Numeric Rating Scale (INRS): a pain assessment tool for nonverbal children with intellectual disability

Clinical observations suggest that nonverbal children with severe intellectual disability exhibit pain in a wide variety yet uniquely individual ways. Here, we investigate the feasibility and describe the initial psychometrics properties of the Individualized Numeric Rating Scale (INRS), a personalized pain assessment tool for nonverbal children with intellectual disability based on the parent's knowledge of the child. Parents of 50 nonverbal children with severe intellectual disability scheduled for surgery were able to complete the task of describing then rank ordering their child's usual and pain indicators. The parent, bedside nurse and research assistant (RA) triad then simultaneously yet independently scored the patient's post-operative pain using the INRS for a maximum of two sets of pre/post paired observations. A total of 170 triad assessments were completed before (n=85) and after (n=85) an intervention to manage the child's pain. INRS inter-rater agreement between the parents and research nurse was high (ICC 0.82-0.87) across all ratings. Parent and bedside nurse agreement (ICC 0.65-0.74) and bedside nurse and research nurse agreement (ICC 0.74-0.80) also suggest good reliability. A moderate to strong correlation (0.63-0.73) between INRS ratings and NCCPC-PV total scores provides evidence of convergent validity. These results provide preliminary data that the INRS is a valid and reliable tool for assessing pain in nonverbal children with severe intellectual disability in an acute care setting.