Changes in operative trends and short‐term outcomes of surgery for congenital biliary dilatation in adults using real‐world data: A multilevel analysis based on a nationwide administrative database in Japan

Abstract Aim We aimed to evaluate the operative trends and compare the short‐term outcomes between open and laparoscopic surgery for congenital biliary dilatation (CBD) in adults using real‐world data from Japan. Methods Data from the Japanese Diagnosis Procedure Combination database on 941 patients undergoing surgery for CBD at 357 hospitals from April 1, 2016, to March 31, 2021, were analyzed. The patients were divided into two groups: open surgery (n = 764) and laparoscopic surgery (n = 177). We performed a retrospective analysis via a multilevel analysis of the short‐term surgical outcomes and costs between open and laparoscopic surgery. Results The rate of laparoscopic surgery has been increasing annually and had almost doubled to 25% by 2021. There were no significant differences in the in‐hospital mortality rate or postoperative morbidity between the two groups. The length of anesthesia was significantly longer in the laparoscopic than open surgery group (8.80 vs 6.16 hours, p < .001). The time to removal of the abdominal drain and length of hospital stay were significantly shorter in the laparoscopic than open surgery group (6.12 vs 8.35 days, p = .001 and 13.57 vs 15.79 days, p < .001, respectively). The coefficient for cost was 463 235 yen (95% confidence interval, 289 679‐636 792) higher in laparoscopic than open surgery (p < .001). Conclusion The short‐term results were comparable between laparoscopic and open surgery for CBD. Further investigation is needed to validate our findings and long‐term outcomes.


| INTRODUC TI ON
Congenital biliary dilatation (CBD) has a higher incidence in Asia than in Europe and the United States and is three to four times more common in female than in male individuals. 1 CBD is associated with a risk of malignant transformation of the dilated portion of the biliary tract and gallbladder because of its association with pancreaticobiliary maljunction, which causes pancreatic juice to reflux into the bile duct and cause chronic inflammation. [2][3][4] Surgical management of CBD involves bile duct resection with cholecystectomy followed by biliary reconstruction. 5,6 Although the surgical procedure is relatively difficult among hepato-biliary-pancreatic surgeries because of the need to perform dissection of the intrapancreatic bile duct and hepaticoenteric anastomosis, the advantages of laparoscopic surgery for CBD include its safety, feasibility, and satisfactory shortand long-term outcomes. [7][8][9][10][11] Two meta-analyses of laparoscopic versus open surgery for CBD in children have been reported 12,13 ; however, no meta-analysis or randomized controlled trial of adults has been performed. A health insurance system for all citizens that provides reimbursements in proportion to the total medical treatment fee has been in place since 1961 in Japan. Insurance reimbursements have covered laparoscopic surgery for CBD since April 2016 in Japan. The diagnosis procedure combination/per-diem payment system (DPC/ PDPS) of Japan for acute injuries or illness is a prospective payment system that uses a classification code based on the disease diagnosis and aims to standardize medical care, similar to the diagnosis-related groups/prospective payment system, which was launched as part of the health insurance system in 2003. 14,15 The DPC includes inpatient data from an expansive list of hospitals throughout Japan and is assumed to reflect the real-world circumstances within Japan's medical fields.
In the present study, a multilevel analysis of real-world data from the DPC database was performed to evaluate the operative trends and short-term outcomes of surgery for CBD in adults after insurance reimbursements since April 2016 and compare the outcomes between laparoscopic and open surgery.

| Data source
This retrospective observational study was based on data from the DPC database, a Japanese administrative database and case-mix system used as a tool to standardize medical profiling and payment.
Of the approximately 1700 hospitals participating in the DPC database, 1540 institutions provided data during the study period. These data included disease names, costs, comorbidities on admission and during hospitalization coded according to the International Statistical

Classification of Diseases and Related Health Problems 10th revision
(ICD-10), age, sex, body mass index (BMI), smoking status, length of postoperative hospital stay, medical procedures (including surgery), and discharge status (including in-hospital death). We obtained these data from the DPC Study Group, which has data on 39 915 530 inpatient cases from 1540 hospitals from April 1, 2016, to March 31, 2021. The DPC Study Group, a government-funded academic group, also collects copies of the DPC electronic data independently of the Ministry of Health, Labour, and Welfare for research purposes. 16

| Patients
The study population comprised inpatients who had been diagnosed with CBD (ICD-10 code Q 444) from April 1, 2016 to March 31, 2021.
The inclusion criteria were age ≥18 years, an inpatient status and admission to undergo open or laparoscopic surgery for CBD (K-codes K674 and K674-2, respectively). The exclusion criteria were patients with biliary cancer and missing data. The patients were divided into two groups according to their surgical procedure (laparoscopic or open surgery).

| Endpoints
The following endpoints were selected to serve as surgical out-

| Statistical analysis
Associations between surgical outcomes and age groups were evaluated by multilevel regression models using a two-level structure of individuals nested within the 357 institutions (multilevel analysis).
Two-level random-intercept and fixed-slope models were employed; these procedures consider independent violations among individuals in the same facilities and eliminate the possibility of the ordinary least-squares estimator underestimating the true standard error. [17][18][19] Investigating the contextual effects of laparoscopic and open surgery on surgical outcome requires adjustment for compositional individual factors. We used a multivariable model that included patient-level factors that potentially correlated with outcomes. This model included the following possible confounding factors: sex, BMI, smoking status (current/ever or never), transfusion prior to surgery, duration of anesthesia, and number of surgeries for CBD during the observation period in the hospital to which the patient was admitted.
We conducted multilevel logistic regression for binary outcomes and multilevel linear regression for outcomes that were treated as continuous variables, hospital codes being assigned to each hospital as a random effect. The STATA release 16 software program (StataCorp, College Station, TX, USA) was used for all calculations.

| Basic characteristics of study participants
The basic characteristics of the study participants are shown in Table 1. CBD was approximately three times more common in women than men and was common in young people (48.2 ± 15.2 years of age). There were no tendencies regarding BMI, smoking status, or preoperative comorbidities between the two groups. Laparoscopic surgery tended to be performed more frequently than open surgery in hospitals in which relatively large numbers of surgeries for CBD were performed. Table 2  aroscopic surgery group, despite no significant differences in these outcomes occurring between the two groups. Previous reports support our results regarding these operative outcomes. [21][22][23][24] Because CBD is a benign disease that is common in young female patients, an optimal cosmetic outcome is desirable, and laparoscopic surgery can be considered safe and feasible for CBD in these patients.

| Postoperative outcomes
The present study revealed that the rate of laparoscopic surgery was relatively low at 25% in 2021, although it had been increasing F I G U R E 2 Changes in operative trends. CBD, congenital biliary dilatation