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The efficacy of morphine analgesia for procedural pain in preterm infants : subjective judgements as a measure McMurtry, Bruce William


The purposes of this study were twofold. The first was to determine the efficacy of morphine analgesia in reducing procedural pain in preterm neonates. Efficacy in this context was considered a question of whether objectively measurable reductions in facial response to painful stimuli possess clinical and social validity. Subjective judgements made by untrained adults were employed to address the question of efficacy in three ways; 1) to determine whether the changes in facial expression achieved with morphine analgesia represented perceptible changes in pain levels, 2) to determine whether the morphine analgesia resulted in a judged reduction in the need for pain control intervention and 3) to determine whether judges believed morphine to provide an adequate level of pain reduction. The second purpose was to examine the effect of judges' empathic concern on their judgements of pain in this population. It was also expected that infant post-conceptional age would affect pain judgements due to a previously demonstrated attenuation of pain responses in post-conceptionally very young newborn infants. The judges were 20 university students, a sample size providing a high level of inter-judge reliability. The patients were 50 preterm infants who had been administered morphine analgesia and were subjected to heel stick for blood testing as a part of their hospital treatment in a Neonatal Intensive Care Nursery. The judgement stimuli consisted of three ten-second video clips of each infant. Each of the three clips showed the infant either at rest (no pain), undergoing heel, stick with no morphine analgesic (untreated pain) or undergoing a heel stick with morphine (treated pain). The procedure was not visible in the video clips. Judges were divided into high and low empathic concern groups based on their scores on an empathic concern scale. They were asked to perform two judgement tasks. In the first, they were blind to the condition portrayed in each clip and clips were presented in random order. Judges rated the sensory intensity and unpleasantness of each clip and whether the infant portrayed required pain control intervention (yes or no). In the second, judges were presented with untreated and treated pain clips consecutively for each infant, and they were asked to rate the pain level of the infant in each clip on a visual analogue scale. They were also asked indicate whether the pain reduction achieved was adequate (yes or no). The results confirmed that the effects of morphine analgesia on preterm infants undergoing painful procedures have social and clinical validity. Judges average ratings of sensory intensity and unpleasantness were significantly reduced when the infants were receiving morphine analgesia. The need for intervention was also significantly reduced with the administration of morphine analgesia. The results were more equivocal with respect to the adequacy of these changes. The general pattern Of results suggested that morphine analgesia reduced the suffering experienced during heel stick to a level comparable to "at rest" ratings. However, judges believed even the infants at rest to be experiencing some pain. In the majority of cases (64%), infants were rated as receiving adequate pain reduction, but this percentage indicates that adequate reduction was not universally achieved, possibly due to a need for dosage adjustments. Contrary to expectations, infant post-conceptional age had no consistent effect on judged pain responses or the rated adequacy of pain reduction. Conforming with expectations, judge empathic concern had a significant effect on pain judgements, but the relationship was more complex than expected with high . empathic concern judges providing higher ratings of sensory intensity and unpleasantness, but lower visual analogue ratings of pain. Overall, judges appeared to be quite sensitive to changes in pain related facial expression. Possible reasons for the lack of infant age related differences and for the complexity of judge empathic concern results, were discussed with attention paid to differences between the two rating tasks. The results of the present study suggest that morphine analgesia can reduce procedural pain in preterm infants in a clinically and socially meaningful way. The non-universality of these findings and the fact that efficacy and clinical significance are ultimately case by case determinations, suggest that the use of morphine analgesia is warranted on a general basis in this population, but individual responses need to be considered. The finding of apparent suffering even in the absence of an acute pain stimulus suggests that more attention needs to be focused on minimizing ongoing low-level suffering. The significant effects of judge empathic concern argues for closer attention to the characteristics of those who must assess pain in preterm infants arid for the need to examine the effects of these characteristics on judgements made by different groups of judges (e.g. professional health care providers) and on other populations (older children and adults).

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