Assessing the Impact of Renal Function on Trajectory of Intravenous Patient-controlled Analgesic Demands Over Time After Open and Laparoscopic Colorectal Surgery Using Latent Curve Analysis

Objectives Intravenous 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 methods Patients 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. Results Data 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). Conclusion Laparoscopic-assisted surgery and renal function affected the baseline trajectory of IVPCA demand over time, but had no significant effect on its shape.