Procedural pain in newborn infants: The influence of intensity and development

Objective. Previous reports have shown that pain is managed inadequately in newborn infants. Ironically, clinicians believe that infants can experienc e pain much like adults, that infants are exposed daily to painful procedur es, and that pain protection should be provided. In adults, a close relatio nship has been shown in how adults behave in response to pain, how painful they sense the stimulus to be, and physical measurements of the intensity o f the stimulus. Whether similar parallels exist in newborn infants has not been examined. If these parallels do not exist in infants, it may help expl ain why clinicians fail to manage procedural pain in infants more effective ly. The objective of this study was to determine whether the magnitude of i nfants' responses to nursing/medical procedures: 1) differs as a function o f the invasiveness or intensity of the procedure; 2) differs as a function of intrauterine (gestational age at birth) and/or extrauterine (conceptiona l age) development; and 3) parallels the subjective pain ratings of clinici ans for those procedures. Methods. A broad developmental and clinical range of newborn infants was st udied shortly before (baseline and preparatory periods), throughout, and sh ortly after (recovery period) required nursing/medical procedures during ho spitalization. Heart rate, oxygen saturation, mean arterial pressure, and b ehavioral state (percentage of time spent in sleep or in agitation) were me asured, and the magnitude of change in each in response to procedures was c alculated. Procedures were categorized as mildly, moderately, and highly in vasive to examine differences in response magnitude as a function of proced ural invasiveness. Responses were compared as a function of prematurity and postnatal age. Clinicians' procedural pain ratings were compared with the magnitude of infants' responses. Results. Of the original 152 infants, 135 were studied at least two times ( range 2-27). Significant changes occurred in physiologic and behavioral mea sures in response to procedures indicative of pain responses. The magnitude of response generally increased with increased procedural invasiveness alt hough there was considerable overlap of magnitude with invasiveness. Both p remature and full-term infants differentiated procedural invasiveness. Very premature infants (<28 weeks' gestational age) exhibited increased increme nts in response magnitude with increasing postnatal age. Clinician's rating s of procedural painfulness were correlated with and predicted the magnitud e of heart rate response to individual procedures. Conclusions. Similar to what has been shown in adults, newborn and developi ng infants show increased magnitude physiologic and behavioral responses to increasingly invasive procedures, demonstrating that even very prematurely born infants respond to pain and differentiate stimulus intensity. However , the considerable overlap of magnitude with invasiveness suggests that the re is not a physiologic or behavioral threshold that clearly marks the pres ence of pain. Inconsistencies in physiologic and behavioral responses make reliance on a pain index difficult. The best approach may be one of univers al precaution to provide pain management systematically to reduce the acute and long-term impact of early procedural pain.