Quantification of neonatal procedural pain severity: a platform for estimating total pain burden in individual infants

There is increasing evidence that long-term outcomes for infants born prematurely are adversely affected by repeated exposure to noxious procedures. These interventions vary widely, for example, in the extent of damage caused and duration. NICU (neonatal intensive care unit) procedures are therefore likely to each contribute differently to the overall pain burden of individual neonates, ultimately having a different impact on their development. In order for researchers to quantify the procedural pain burden experienced by infants on NICU, we aimed to estimate the pain severity of common NICU procedures using published pain scores. We extracted pain scores over the first minute (pain reactivity) from the literature, using 59 randomized controlled trials for 15 different procedures. Hierarchical cluster analysis of average pain scores resulted in five discrete severity groups; mild (n=1), mild to moderate (n=3), moderate (n=7), severe (n=3) and very severe (n=1). The estimate of the severity of individual procedures provided new insight into infant pain reactivity which is not always directly related to the invasiveness and duration of a procedure; thus both heel lance and skin tape removal are moderately painful procedures. This estimate of procedural pain severity, based on pain reactivity scores, provides a novel platform for retrospective quantification of an individual neonate's pain burden due to NICU procedures. The addition of measures that reflect the recovery from each procedure, such as brain activity and behavioural regulation, would further improve estimates of the pain burden of neonatal intensive care.