Pain Research and Nuffield Department of Anaesthetics, University of Oxford, John Radcliffe Hospital, Oxford, UK.
Eur J Anaesthesiol. 2011 Jun;28(6):427-32. doi: 10.1097/EJA.0b013e328343c569.
Post-operative analgesic consumption is often used as a surrogate measure for pain; analyses of mean data assume a Gaussian distribution and use parametric statistics to assess statistical differences, often in small samples. We used a large individual patient dataset to examine the distribution of analgesic consumption, the validity of such analyses and alternative dichotomous outcomes.
Analysis of individual patient data from 913 patients over 48 post-operative hours in five randomised trials. Patients had either epidural injection of placebo or morphine (as sulphate and extended release epidural morphine) and use of patient-controlled analgesia. Post-operative fentanyl consumption was calculated over 0-24, 24-48 and 0-48 h.
The distribution of analgesic consumption for all patients over the periods 0-24, 24-48 and 0-48 h was exponential. Most patients used less than 750 μg fentanyl over 48 h; 34% used over 1000 μg fentanyl (100 mg morphine), 13% over 2000 μg and 5% over 3000 μg. Mean, median and mode were very different; 20% of patients consumed almost 60% of post-operative analgesic, and standard deviations were generally larger than means. A useful dichotomous outcome was less than 750 μg fentanyl consumed over 48 h, a level associated with very good or excellent patient pain rating. Use of very good or excellent patient pain rating differentiated between different doses of epidural morphine.
Because of a highly skewed distribution, post-operative analgesic consumption is an uncertain method of measuring analgesic efficacy of an intervention designed to limit pain during and after surgery.
术后止痛药物的消耗量常被用作疼痛的替代衡量指标；分析均值数据时假设其呈正态分布，并使用参数统计来评估统计差异，且通常在小样本中进行。我们使用大型个体患者数据集来检验止痛药物消耗量的分布、此类分析的有效性以及替代的二分类结果。
对五项随机试验中 913 名患者超过 48 小时的个体患者数据进行分析。患者接受硬膜外注射安慰剂或吗啡（硫酸盐和长效硬膜外吗啡）以及使用患者自控镇痛。计算术后芬太尼消耗量在 0-24、24-48 和 0-48 小时的情况。
所有患者在 0-24、24-48 和 0-48 小时期间的止痛药物消耗量分布均呈指数分布。大多数患者在 48 小时内使用的芬太尼少于 750 μg；34%的患者使用了超过 1000 μg 的芬太尼（100 mg 吗啡），13%的患者使用了超过 2000 μg，5%的患者使用了超过 3000 μg。均值、中位数和众数差异很大；20%的患者消耗了近 60%的术后止痛药物，且标准差通常大于均值。一个有用的二分类结果是 48 小时内消耗的芬太尼少于 750 μg，这个水平与患者的疼痛评分非常好或极好相关。非常好或极好的患者疼痛评分可区分不同剂量硬膜外吗啡的效果。
由于分布高度偏态，术后止痛药物的消耗量是衡量旨在限制手术期间和之后疼痛的干预措施镇痛效果的一种不确定方法。
