The psychometric properties of the stoplight pain scale in children with sickle cell disease

Abstract Background: Effective pain management begins with accurate pain assessment for children with sickle cell disease (SCD) experiencing a vaso-occlusive episodes (VOE). While most scales measure pain, these traditional tools do not guide therapeutic intervention directly and rely on a healthcare provider to decide what to do instead of allowing the child to direct it. The Stoplight Pain Scale (SPS) is a novel, child friendly, 3-face scale that integrates pain assessment with guidance for its management. Combining a red-yellow-green color scheme with cartoon faces and directive action phrases, SPS categorizes pain as “green” (I'm ok; I feel fine right now), “yellow” (I'm not sure; Ask me again later), and “red” (I hurt; I need something to feel better). SPS has shown early promise in assessing acute pain in children, but its validity for use in SCD-VOE, particularly for repeated measures over time, has not been previously investigated. Objective: To evaluate the validity of the SPS in children with SCD-VOE presenting to the emergency department. Methods: This prospective observational cohort study was a planned sub-study of a multicenter phase-3 randomized controlled trial evaluating the efficacy of intravenous arginine for SCD-VOE. Endorsed by the Pediatric Emergency Care Applied Research Network (PECARN) and conducted at 10 US sites from 2022-2024, the study enrolled children aged 3 to 21 years. Participants rated their pain using the SPS and verbal Numeric Rating Scale (NRS) at enrollment and daily through hospital discharge. Descriptive statistics and correlations were calculated overall and then stratified by age using cluster bootstrapped 95% confidence intervals to account for repeated measures. Pearson correlation coefficients between the two scales at the first, last, lowest, and highest recorded measures were also computed and assessed. Results: Ninety-eight participants contributed 394 assessments for up to 8 hospital days. The mean (SD) child age was 13.0 (4.6) years; 46% were male, 74% had HB-SS genotype, and 44% reported >3 hospitalizations in the prior year. At enrollment, pain severity using SPS was “green” in 17.2%, “yellow” in 37.9%, and “red” in 44.8%. Median (IQR) NRS pain score was 7 (5, 9). SPS and NRS scores were strongly correlated (r=0.77; 95% CI 0.72, 0.82), supporting convergent validity which demonstrated the degree to which these two tools that are intended to measure pain produced similar results. Correlation was strong for lowest reported values (r =0.73; p<0.001) and moderate for highest reported values (r=0.64; p=0.001). Correlation was better for children aged 6-12 years (r=0.83; 95% CI 0.77, 0.89) compared to 13–17-year-olds (r=0.70; 95% CI 0.59, 0.80) and those greater than 17 years (r=0.65; 95% CI 0.45, 0.78). Discriminant validity was supported by changes in pain scores from the first to the last recorded measure: “green” increased from 19.6% at enrollment to 62.9% at discharge, while “red” decreased from 43.3% to 13.4%. SPS demonstrated responsiveness to change by detecting meaningful changes over time, particularly in response to hospital interventions resulting in decreasing “red” and increasing “green” responses over hospitalization days; for example, “red” decreased from 50% on day 1 to 18% on day 8; and “green” increased from 17% on day 1 to 55% on day 3. Conclusion: The SPS demonstrated good convergent validity, discriminant validity and responsiveness to change in children with SCD-VOE. Overall, there is evidence that this simple, easy-to-implement SPS is a valid assessment tool for children with SCD-VOE. This holds value in the pediatric emergency department setting to rapidly indicate need for analgesia, and its applications extend into reassessments in the inpatient setting. Notably, SPS may be particularly suitable for younger children, a vulnerable group for whom reliable pain assessment is challenging. Further research is warranted to investigate the role of this tool in improving the quality and timeliness of VOE pain management for children with SCD.

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