In this study, we focus on the characteristics of neonatal pain response, through a comprehensive data collection and meticulous screening process, involving a literature review, panel meetings, and a Delphi study, we aim to develop a neonatal pain response variable set, which serves as a crucial theoretical foundation for future research in the field of neonatal pain.

In its revised definition of pain in 2020, the International Association for the Study of Pain (IASP) emphasized the significance of respecting a person’s report of pain as a valid experience, the inability to communicate does not negate the possibility that a human or a non-human animal experiences pain [21]. Due to limited verbal communication, the primary mode of assessing neonatal pain responses is through observation. Nevertheless, the absence of a “gold standard” results in not all assessment indicators from existing scales being suitable for clinical practice, and the influence of situational factors, such as demographic contextual factors, on neonatal pain responses is frequently disregarded.

From a neurological standpoint, no individual behavioral or physiological component is adequate in alerting to the presence of pain responses that occur on a cortical level [22]. Our constructed variable set aligns with recommendations from the previous studies and guidelines [23, 24], emphasizing the importance of a multidimensional assessment approach that considers both behavioral and physiological responses. It aims to overcome the limitations of single-dimensional assessments, which often fail to adapt to the complexity of clinical environments and capture the sometimes-subtle pain behaviors exhibited by neonates. Furthermore, our variable set also incorporates contextual variables to address individual differences in neonatal pain, providing a comprehensive assessment framework composed of three key dimensions: behavioral, physiological, and contextual.

To enhance discrimination, we selected descriptors with improved discriminatory capabilities. Upon analyzing and comparing each variable’s descriptors, we considered the appropriateness of their scope and the clarity of their grade divisions. In the behavioral variables, the assessment of facial expressions expanded to include five dimensions: “Facial muscles fully relaxed, relaxed open mouth”, “Normal facial tension”, “Intermittent eye squeeze and brow furrow”, “Continuous eye squeeze and brow furrow”, and “Facial muscles contorted and grimacing”. These descriptions offer greater clarity and understanding compared to existing assessment scales, with well-defined boundaries closely aligning with neonatal pain-related facial expressions. For descriptors related to “crying” and “breathing pattern”, we used the contents of the NIPS scale, incorporating dimensions like “no cry”, “whimper”, and “vigorous crying” for crying assessment, and “relaxed” and “change in breathing” for breathing patterns. While some scales previously mentioned assessing “extremity movement” via finger and toe movements, we recognized the impracticality of these observations due to medical interventions or protective measures. Therefore, we opted to assess the frequency of arm and/or leg movements, categorizing them as “no movement”, “up to three arm and/or leg movements”, and “more than three arm and/or leg movements”, which enhances assessment applicability, efficiency, and accuracy.

Concerning physiological variables, we defined “SpO2” in terms of its deviation from baseline values, categorizing it as a decrease in Oxygen Saturation: “0 ~ 2”, “3 ~ 5”, “6 ~ 8”, or “ > 8”, or indicating an “increased oxygen requirement”. This definition deviates from the BPSN scale’s “decrease ≤ 1.9%”, “decrease 2 ~ 2.9%”, “decrease 3 ~ 4.9%”, and “decrease ≥ 5%”. Experts noted that a broader fluctuation range better reflects actual SpO2 changes in clinical newborns. Furthermore, our clinical observations revealed that SpO2 levels do not necessarily decrease during painful episodes, thus our descriptors extend beyond mere increases or decreases. For assessing “heart rate”, we employed a straightforward definition based on specific numerical changes compared to baseline values, categorizing them as “0 ~ 5 times”, “6 ~ 20 times”, or “ > 20 times”. It offers greater intuitiveness and practicality compared to percentage-based calculations used in some assessment tools.

The limitations of this study encompass the included literature’s language restriction to 2 languages, did not explicitly consider the potential influence of regional factors on neonatal pain response, and the articles primarily focused on hospitalized newborns, potentially overlooking research on healthy newborns, which could affect the comprehensiveness of included literature and the factors related to neonatal pain extracted in this study. Our next objective is to construct a neonatal pain response model, that serves as a valuable tool for healthcare practitioners. This model aims to empower healthcare professionals in assessing the significance of each pain-related variable.