• Pei-Wen Chao, Shih-Pin Lin, Mei-Yung Tsou, I-Ting Kuo, and Kuang-Yi Chang.
• *Department of Anesthesiology, Taipei Veterans General Hospital and School of Medicine, National Yang-Ming University ‡Institute of Biomedical Engineering, National Yang-Ming University †Department of Anesthesiology, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan, Republic of China.
• Clin J Pain. 2016 Aug 1; 32 (8): 695-701.

ObjectivesIntravenous patient-controlled analgesia (IVPCA) is often used to relieve pain after colorectal surgery. This study aimed to model the trajectory of analgesic demand over time after colorectal cancer surgery and explore potentially relevant influential factors using latent curve analysis, focusing on laparoscopic-assisted surgery and renal function.Materials And MethodsPatients receiving colorectal surgery with postoperative IVPCA were randomly divided into 2 equal parts to enable model construction and cross validation. Archived data were retrieved from the IVPCA pump. Latent curve modeling with 2 latent variables that reflected the baseline and slope of IVPCA demand trajectory over time was used and the effects of potentially influential factors on the 2 latent variables were evaluated. Goodness-of-fit indices were used to assess the model fit to both the model construction and validation data sets.ResultsData were collected from 834 patients, of whom 112 had laparoscopic-assisted surgery. Latent curve analysis revealed that body weight increased the baseline analgesic demand over time, whereas increasing age, female sex, poor renal function, and laparoscopic-assisted surgery decrease it. By contrast, only age and weight exerted significant effects on the slope parameter to modify the trajectory of IVPCA demand. Patients with higher age or less weight tended to have a smoother decreasing trajectory of analgesic demands over time. There was good cross validation, as the parameter estimates derived from the model construction data set fitted well to the validation data set (root mean square error of approximation: 0.05).ConclusionLaparoscopic-assisted surgery and renal function affected the baseline trajectory of IVPCA demand over time, but had no significant effect on its shape.

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