Applicability, Validity, and Reliability of the Japanese Version of the Behavioral Pain Scale for Critically Ill Mechanically Ventilated Pediatric Patients: A Prospective Cross-Sectional Observational Study

Background: Pain assessment in critically ill, mechanically ventilated pediatric patients is highly complex owing to communication barriers and the frequent use of sedation. A standardized, rapid, and objective tool such as the Behavioral Pain Scale (BPS) is urgently needed in Japanese pediatric intensive care units (PICUs), particularly in mixed adult–pediatric settings, to ensure consistent, multidisciplinary assessment. This study aimed to evaluate the clinical applicability, validity, and reliability of the Japanese version of the BPS in critically ill mechanically ventilated pediatric patients. Methods: This single-center, prospective cross-sectional observational study was conducted between October 2021 and March 2023. The final analysis included 70 observations from 37 pediatric patients who needed mechanical ventilation (MV). Concurrent and convergent validity were assessed using Spearman’s rank correlation coefficients (ρ) between the BPS; the Face, Legs, Activity, Cry, Consolability (FLACC) scale; and the COMFORT-Behavior (COMFORT-B) scale. Interrater reliability was evaluated using intraclass correlation coefficients (ICCs) and weighted kappa values among the three independent observers. The sample size (52 observations) was calculated based on the kappa coefficient estimation. The impact of sedation depth (assessed using the Richmond Agitation–Sedation Scale RASS) and the observers’ prior clinical experience with the evaluations were also analyzed. Results: Concurrent and convergent validity were high, showing strong correlations with the FLACC (ρ = 0.49–0.91) and COMFORT-B (ρ = 0.69–0.87) scales. The total BPS score showed moderate interrater reliability (ICC = 0.66, 95% CI = 0.55–0.76; weighted κ = 0.63–0.71). However, deep sedation (defined as a median RASS score ≤ −4 across observers), present in 68.6% of the observations, caused a pronounced floor effect that suppressed behavioral responses, even during painful procedures. Consequently, the reliability of fine motor subscales like “upper limb movement” (κ = 0.08) was slight and for “facial expression” (κ = 0.38), it was fair. Furthermore, the correlation strength with the FLACC scale varied significantly with observer experience, with the strongest correlation (ρ = 0.91) achieved by the observer with extensive adult ICU experience. Conclusions: As an initial validation, the Japanese version of the BPS has demonstrated acceptable validity and moderate reliability in mechanically ventilated pediatric patients. However, its clinical application requires careful interpretation because of the pronounced floor effect under deep sedation. Furthermore, accurate assessment depends heavily on specific training and familiarity with the adult-derived scale. With adequate training, the BPS has the potential to serve as an alternative tool and a valuable common multidisciplinary language in mixed intensive care settings. Future research should investigate whether implementing this tool improves multidisciplinary communication and clinical outcomes.