Background: Patient-controlled epidural analgesia (PCEA) with background infusion provides better analgesia than the use of a demand dose alone but might be associated with more consumption of PCEA solution and adverse effects. Therefore, we conducted this retrospective study to evaluate the influence of parameters of the drug delivery system on the PCEA requirements of patients receiving thoracic or upper abdominal surgeries. Methods: Patients having operations involving the chest or upper abdomen with postoperative PCEA were included in the analyses. A standardized analgesic solution of bupivacaine (0.0625%) and fentanyl (1 μg/mL) was used for all patients. The cumulative doses of PCEA on the first, second and third postoperative days were recorded. Collected data included patient demographics and their quantity of PCEA. A general linear model was used to compare within-subject time effects and between-subject effects. Interactions with time between subjects were also examined. Results: A total of 228 patients (68 females, 160 males) were included in the study. The PCEA requirements decreased gradually over time (p<0.001). Patients with tower body mass index had a greater difference in their PCEA requirement between the first and second postoperative days (p<0.001). For variables related to PCEA usage, patients using PCEA with the 30-minute lockout interval used less PCEA infusate per day (p=0.04 for main effect, p=0.02 for interaction with time). Moreover, a longer lockout interval was not associated with poorer analgesic effects (p=0.48). Other parameters had no significant influence on daily PCEA requirements. Conclusion: Patients receiving PCEA with a 30-minute lockout and background infusion used the least amount of PCEA infusate and the differences increased over time. Further investigations are recommended to evaluate potential benefits and drawbacks of a longer lockout interval.