Age differences in postoperative pain are scale dependent: a comparison of measures of pain intensity and quality in younger and older surgical patients

As the population ages, research into the assessment of postoperative pain in older patients is urgently needed. The reliability and validity of most pain scales for the assessment of acute postoperative pain in the elderly remain to be demonstrated. The present study reports the analysis of age-related patterns on three pain scales (McGill Pain Questionnaire, MPQ; Present Pain Intensity, PPI; and Visual Analog Scale, VAS) completed by younger (n=95, mean age=56.4+/-5.8 years) and older (n=105; mean age=66.8+/-2.7 years) men following radical prostatectomy. All patients received intravenous morphine via patient-controlled analgesia (PCA) throughout the study. On the first 2 postoperative days (POD), patients completed the pain scales and PCA opioid intake was recorded. An interaction was found between amount of opioid self-administered and POD. In both groups, less opioid was administered on POD 2 than POD 1, but the decrease over time was greater in younger than older men. On both PODs, older men self-administered less opioid than younger men. Age differences in pain were dependent on the pain scale used. Older men had significantly lower scores than younger men on the MPQ and PPI but there were no differences on the VAS. Several age differences in the psychometric properties of the scales were evident. On both PODs, the correlation between VAS and MPQ scores was significantly lower in the older than younger group. POD effect sizes did not differ between the scales or age groups suggesting that all three scales have comparable sensitivity within an age group. However, the different results between the scales for the effect of age suggests that the VAS is not sufficiently sensitive to detect age differences. Therefore, age differences in postoperative pain are better captured by verbal descriptions of pain qualities than non-verbal measures of intensity.