Dynamic analysis of variations in postoperative pain trajectories over time in patients receiving epidural analgesia using latent curve models

Although epidural analgesia (EA) provides reliable pain relief after major operations, few studies have explored how postoperative pain trajectories change over time in patients receiving EA and the associated factors. This study aimed to model the dynamic features of pain trajectories after surgery and investigate factors associated with their variations using latent curve analysis.

This retrospective study was conducted at a single medical center in Taiwan, and data were obtained from patients receiving perioperative EA by electronic chart review. Mean numeric rating pain scores were recorded daily in the first five postoperative days. Patient demographics, surgical sites, and infusion pump settings were also collected. Latent curve models using two latent variables, intercept and slope, were developed to explain the variations in postoperative pain scores over time. The influences of potential predictors of postoperative pain trajectories were further evaluated for the final model determination.

Of the 1294 collected patients, the daily pain scores averaged 2.0 to 2.9 for different surgical sites. Among the nine significant factors influencing pain trajectories, chest and lower extremity surgery tended to induce less and more baseline pain, respectively, than those with abdomen surgery (both p < 0.001). In addition, male patients and those with a shorter anesthesia time had less baseline pain (p < 0.001 and p = 0.016, respectively). The older and lighter patients and those with chest surgery or American Society of Anesthesiologists class ≥ 3 tended to have milder decreasing trends in pain trajectories. A higher infusion rate was associated with an elevated baseline level and smoother decreasing trend in pain trajectory. The final model fit our data acceptably (root mean square error of approximation = 0.05, comparative fit index = 0.97).

Latent curve analysis provided insights into the dynamic nature of variations in postoperative pain trajectories. Further studies investigating more factors associated with pain trajectories are warranted to elucidate the mechanisms behind the transitions of pain scores over time after surgery.