The influence of gestational age in the psychometric testing of the Bernese Pain Scale for Neonates.

Background: Assessing pain in neonates is challenging because full-term and preterm neonates of different gestational ages (GAs) have widely varied reactions to pain. We validated the Bernese Pain Scale for Neonates (BPSN) by testing its use among a large sample of neonates that represented all GAs.
Methods: In this prospective multisite validation study, we assessed 154 neonates between 24 2/7 and 41 4/7 weeks GA, based on the results of 1-5 capillary heel sticks in their first 14 days of life. From each heel stick, we produced three video sequences: baseline; heel stick; and, recovery. Five blinded nurses rated neonates' pain responses according to the BPSN. The underlying factor structure of the BPSN, interrater reliability, concurrent validity with the Premature Infant Pain Profile-Revised (PIPP-R), construct validity, sensitivity and specificity, and the relationship between behavioural and physiological indicators were explored. We considered GA and gender as individual contextual factors.
Results: The factor analyses resulted in a model where the following behaviours best fit the data: crying; facial expression; and, posture. Pain scores for these behavioural items increased on average more than 1 point during the heel stick phases compared to the baseline and recovery phases (p < 0.001). Among physiological items, heart rate was more sensitive to pain than oxygen saturation. Heart rate averaged 0.646 points higher during the heel stick than the recovery phases (p < 0.001). GA increased along with pain scores: for every additional week of gestation, the average increase of behavioural pain score was 0.063 points (SE = 0.01, t = 5.49); average heart rate increased 0.042 points (SE = 0.01, t = 6.15). Sensitivity and specificity analyses indicated that the cut-off should increase with GA. Modified BPSN showed good concurrent validity with the PIPP-R (r = 0.600-0.758, p < 0.001). Correlations between the modified behavioural subscale and the item heart rate were low (r = 0.102-0.379).
Conclusions: The modified BPSN that includes facial expression, crying, posture, and heart rate is a reliable and valid tool for assessing acute pain in full-term and preterm neonates, but our results suggest that adding different cut-off points for different GA-groups will improve the BPSN's clinical usefulness.
Trial Registration: The study was retrospectively registered in the database of Clinical Trial gov. Study ID-number: NCT 02749461 . Registration date: 12 April 2016.