Assessment of neonatal pain: uni- and multidimensional evaluation scales

Neonatal pain is a problem that need to be mentioned and studied. Newborns can feel and respond to painful stimuli. Preterm infants are even more hypersensitive to pain, which may lead to long-term structural and functional changes in pain pathways.¹ Previous studies have shown that newborns during their stay in the hospital need to experience pain stimulus-related operations ranging from dozens to hundreds of times.^2,3,4 Moreover, infants’ brains showed the same level of response as adults’ brain in functional magnetic resonance imaging (fMRI).⁵

Uncontrolled repeated pain episodes may have a negative effect on neonates: in the short term, it may cause physiological and behavioral changes, and in the long term, it may affect the normal development of the brain, leading to problems of emotion, behavior, and learning disabilities at later stages.^1,6,7,8,9,10 Therefore, timely assessment and intervention are very important for neonatal pain management. However, unlike children, newborns do not have the ability to actively express pain, so we can only judge the presence and degree of pain by observing the corresponding pain assessment indicators.

Clinically, neonatal pain is generally divided into the following types: acute pain, procedural pain (refers to the pain caused by invasive procedures, which are commonly observed in heel stick, vein puncture, subcutaneous injection, etc.), and prolonged pain (refers to the pain that lasts for a few hours or a few days, caused by pulmonary hyaline membrane disease with assisted ventilation, early stage of necrotizing enterocolitis, arterioductal atresia, etc., which are often neglected in long-term treatment,¹¹ especially for neonatal patients who cannot express their real feelings). Postoperative pain, that is, pain that lasts for a long time after surgery. These types of pain may be co-existing, especially for premature infants, who are more susceptible to various pain factors, leading to frequent pain. Therefore, how to distinguish and intervene pain in time is very important.

The PIPP/PIPP-R scale is suitable for the evaluation of procedural pain and postoperative pain, and its total score is between 0 and 18 points for term infants and between 0 and 21 points for premature infants <28 weeks of gestational age. For all gestational age neonates, ≤6 suggests no or mild pain, a score of ≥7 indicates pain, a total score > 12 indicates middle or severe pain because there are some other factors that may affect the newborn's response to pain, such as more mature babies, with higher gestational age, and are more active in responding to pain after birth, so gestational age at birth is also included for assessment in the scale. During the evaluation, the status of the baby will also affect the score. When the baby is awake and active, it has the strongest response to pain, so the status of the baby is also included in the score as an influencing factor.^17,18 In the evaluation of this scale, the difference in pain response between premature infants and full-term infants is taken into account, so the range of scores is not consistent, and there are differences in the degree of pain assessment, including no or slight pain, mild pain, moderate pain, and severe pain, which is more clinically practical.

The N-PASS scale is used to assess acute and prolonged pain and sedation. It has 5 assessment dimensions and 2 assessment components: pain/agitation and sedation. The pain/agitation score was between 0 and 10, and the sedation score was between −10 and 0. When scoring, the scale also included the gestational age of the newborn, and the younger the gestational age, the higher the score. As newborns with small gestational age have less obvious response to pain, this factor is used to adjust the score. Some neonates will use sedatives, such as newborns with mechanical ventilation as the appropriate level of sedation can promote oxygen supply and reduce complications of ventilation. The evaluation of sedation is helpful for us to know whether there is excessive sedation in neonates. A score of −5 to −2 is mild sedation, and a score of −10 to −5 is deep sedation. This score can help us determine whether the newborn has a problem with excessive sedation and, if so, may indicate the need for adjustment of treatment. For special situations, such as infants with ventilatory support, deep sedation may be permitted. There may be a negative score for analgesic/sedative use, but a negative score without these medicines may be due to the preterm infant's response to prolonged pain, or the effects of neural inhibition, sepsis, or other medical conditions. For the assessment of pain/agitation, a score of >3 indicates obvious pain and requires intervention, and the intervention goal is ≤3, but it should be noted that if a procedure is known to cause pain, intervention measures can be taken in advance to prevent or relieve pain.¹⁹ The scale takes into account pain/agitation and sedation, and the degree of sedation is classified as mild and deep sedation. If the score is >3, there may be obvious pain. If the score is negative, it may be sedation or prolonged pain. Therefore, it needs to be identified according to the actual situation in clinical application.

The NFCS is a unidimensional scale used to assess procedural pain, that is, specific changes in facial expression, such as brow bulge, eye squeeze, and open lips, are judged to be stress responses to painful stimuli. However, there are some limitations in the evaluation of this scale because the facial coding system requires a long period of professional training, so it is not convenient for clinical use. It was also mentioned in the study that there was a difference in pain response between neonates in different states, that is, whether they were asleep or awake, but this was not included in the scale. The total score of the NFCS was 0–9 for term infants and 0–10 for preterm infants, and >3 indicated pain.²⁰ This scale involves a single dimension, and it is subjective in the judgment of facial expression changes and requires a long time of training, so it is not convenient to use.

The EDIN scale is a tool designed to assess prolonged pain in premature infants. The EDIN scale requires a long observation time during the evaluation, and the comprehensive judgment and score should be calculated after 8 h of observation. There are 5 dimensions with behavioral indicators, 0–3 points for each, and 0–15 points for the total score, and ≥7 indicated pain. The reason why the scale does not include physiological indicators is that the change of physiological indicators is usually an acute stress response, which is not suitable for the assessment of prolonged pain. This scale has certain limitations. First, the evaluator must be a ward nurse who has frequent contact with the neonate and is familiar with the neonate, and it requires a long observation time. At the same time, the evaluator needs to interact with the neonate, which may lead to nonobjective assessment results, and the evaluator is limited, so it is not convenient to use. Another problem is that newborns with hypoxic brain injury cannot be evaluated because they do not interact well and affect the evaluation results. And prolonged pain is sometimes overlooked clinically, such as abdominal distension caused by enteral nutrition and nasal continuous positive airway pressure caused by nasal injury. If assessment is not routine, or may be ignored, neonates cannot get timely and effective treatment, so it is recommended that for neonates who may be at risk for prolonged pain, at least regular assessments 1–2 times a day is necessary.¹¹ The evaluation of this scale requires a long observation time, and there are limitations on evaluators and evaluation content. Nurses who are familiar with the neonates are required to evaluate and observe them for a long time, which makes it inconvenient to use the scale, and interaction may lead to less objective evaluation results. In addition, this is not applicable to neonates with poor interaction such as cerebral hypoxia.

The CRIES scale is used to assess postoperative pain in neonates, but cannot be used for intubation or paralysis. Crying is one of the behavioral indicators, and infants with small gestational age may need intubation for mechanical ventilation after birth and cannot cry. Therefore, the scale is suitable for infants with a gestational age ≥32 weeks at birth. The scale contains 5 dimensions, 0–2 points for each dimension and 0–10 points for the total score. When pain was identified, the score averaged 4 points, suggesting interventions were needed when a score ≥4 points. The study was aimed at postoperative pain, so the recommended evaluation time was at least once every hour after surgery, depending on the duration of the disease lasting from 24 h to 72 h.²¹ The limitation of this scale is that it cannot be used to evaluate intubated or paralyzed infants due to their inability to cry.

The COMFORTneo scale was used to assess prolonged pain in preterm infants and contained 7 dimensions with an overall score of 6–30. Studies have shown that scores of 14 and above may require appropriate interventions. The gestational age, birth weight, and diseases at risk of nerve damage, such as perinatal asphyxia and intraventricular hemorrhage, should be considered in the specific operation, which may affect the response to pain or the implementation of analgesic measures. Prolonged pain may result from surgery, inflammation, skin burns, birth injuries, or prolonged mechanical ventilation. Interventions, especially medications, also need to be evaluated regularly to avoid excessive sedation. Considering that there may be excessive sedation during sedative use, NICU use of the COMFORTneo scale indicates that dosage reduction may be considered when the score is ≤8, but a low score during quiet sleep at night generally does not require dosage change.²² However, if the deep sleep exceeds 12 h, gradual reduction of medication dose should be considered.²³ It takes 2 h of training to proficiently use the scale for evaluation. Neonates need to be observed 2 min before the evaluation and evaluated regularly after the intervention. The scale takes into account the differences between intubation and spontaneous breathing in neonates, and the risk of excessive sedation when the score is too low, which requires nursing staff to timely identify and cooperate with doctors to intervene. The scale can be skillfully used within 2 h of training, which is relatively convenient.

The COVERS scale is a multidimensional scale used to assess procedural pain in premature and term infants. It contains 6 dimensions, including physiological indicators and behavioral indicators, with a total score of 0–12. When the painful procedure was performed, the mean score for all neonates is about 7, and ≥7 indicates pain for all gestational age. It has a wider range of evaluation objects. For example, it can assess the pain of patients who are intubated because they cannot cry. For these neonates, crying is judged by recognizable crying expressions, which has good clinical practicability. In general, the COVERS scale can be used to evaluate premature infants, very low–birth weight infants, intubated neonates, and neonates in the postoperative recovery period, with a wide range of application.²⁴ The scale can be used to assess pain in intubated infants and is more widely used than the CRIES scale.

The PAIN scale is used to measure postoperative pain and procedural pain for preterm and full-term newborns, which includes 7 dimensions, including physiological and behavioral indicators, with a score of 0–10 points, where a score of 4 points or higher indicates pain. During evaluation, the nurse was required to observe the neonate for 2 min before evaluation, but whether the observation time was too short needs further discussion. In addition, attention should also be paid to when pain assessment should be carried out. Assessment should be performed before 30–60 min of pain events for the neonates, but in the actual process, the assessment time may be delayed, which will affect the accuracy of the assessment results.²⁵ For this scale, the nurse is required to observe the neonate for 2 min before the evaluation, and the infant is evaluated within 30–60 min after experiencing pain events. However, there may be problems of short observation time and timely evaluation. Therefore, appropriate extension of observation time and standardized evaluation time can be considered, such as evaluation twice a day after surgery or evaluation immediately after pain-causing operation.

The NIPS scale is used to measure pain in premature and full-term neonates. It is a single-dimension scale, excluding physiological indicators, with 6 dimensions and a total score of 0–7. When the total score is ≥4, pain is indicated. It can also be used for neonates on mechanical ventilation. Like the COVERS scale, crying expressions will be scored.²⁶ The evaluation index of this scale is a single dimension and does not include physiological indicators, which may have some limitations. However, like the COVERS scale, it can also be used for infants with mechanical ventilation.

In this article, 9 different neonatal pain assessment scales were summarized. The pain types applicable for the assessment included acute pain, procedural pain, prolonged pain, and postoperative pain. The assessment includes preterm and term neonates. The evaluation indexes include physiological indications and behavioral indications. Many of these scales have the threshold value of pain score, which has practical significance. The PIPP/PIPP-R scale and N-PASS scale included the adjustment items. The PIPP/PIPP-R scale took into account the gestational age and the status of the newborn at the time of evaluation, such as small gestational age and in the sleep state during evaluation of the newborn with higher scores. The N-PASS scale also took gestational age into account. These factors will affect the pain response of neonates, resulting in deviation of evaluation results; therefore, it needs to be appropriately adjusted.

According to the table, some scales contain only behavioral indications For example, the physiological manifestations of prolonged pain may show a tendency of inhibition, such as expressionless face, decreased HR, and weakened respiratory changes, which are not suitable for direct correlation with pain. Therefore, some prolonged pain assessment scales do not include physiological indicators. It is debatable whether multidimensional or unidimensional items are better included in the scale when assessing neonatal pain. One study has shown that in an evaluation of procedural pain caused by vitamin K injection in newborns, 2 unidimensional scales (NFCS and behavioral indicators of infant pain [BIIP] scale,²⁷ which only contained behavioral indicators) and a multidimensional scale (PIPP scale) were used simultaneously to evaluate the pain response to vitamin K injection in newborns, and the results showed that in 80% of the neonates, the pain response could be detected using the NFCS, while only 70% of the neonates’ pain response could be detected using the PIPP scale.²⁸ Therefore, further consideration and evaluation are needed when choosing a suitable scale.

In addition to using scales for neonatal pain assessment, there are many other methods, such as HR variability analysis,²⁹ electroencephalogram (EEG) detection,³⁰ functional magnetic resonance imaging,³¹ near-infrared spectroscopy,³² and other new assessment methods. These methods have the advantage of automation and labor-saving and also limitations. For example, it is difficult to take into account other factors that influence neonatal pain response. In future, itcan be considered to combine with the scale to find abetter way to evaluate neonatal clinical pain. Furthermore, there are many other neonatal pain assessment scales, including Pain Assessment Tool (PAT) scale,³³ Scale for Use in Newborns (SUN),³⁴ and Bernese Pain Scale for Neonates (BPSN).³⁵ They can also be used to measure neonatal pain, and more neonatal pain assessment scales can be better interpreted in future studies.

This article summarized the progress of 9 common neonatal pain assessment scales, and they can be used to evaluate acute pain, postoperative pain, procedural pain, persistent pain, etc. They are applicable for premature or term infants. In clinical use, nurses should understand the applicable scope of the common pain assessment scales, to form a set of suitable pain assessment programs, such as for different pain types, and choose one of the most suitable scales. In the process of assessment, appropriate improvement should be made, such as the timing of assessment, and assessment methods should be adjusted to form a set of neonatal pain assessment systems suitable for their own departments. At present, there have been relevant research in China, such as LAN's Neonatal Pain Assessment Scale for the assessment of acute pain in neonates on mechanical ventilation,³⁶ the development and research of neonatal facial expression pain scale,³⁷ and the localization and reliability and validity evaluation of the N-PASS scale,³⁸ but they are far from enough. Researchers can also adapt and apply more locally applicable pain assessment scales to gradually promote the development of neonatal pain management in China.