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Figure 1.
CONSORT Diagram for Study Sample
CONSORT Diagram for Study Sample

CBDE indicates common bile duct exploration; ERCP, endoscopic retrograde cholangiopancreatography; LC, laparoscopic cholecystectomy.

Figure 2.
National Trends in Common Bile Duct Exploration for Choledocholithiasis From 1998 to 2013
National Trends in Common Bile Duct Exploration for Choledocholithiasis From 1998 to 2013

Annual national estimates of the number of hospitalizations for choledocholithiasis were calculated from 1998 to 2013 using NIS discharge weights and SAS survey sampling and analysis procedures. All trends were assessed using logistic regression and were significant at P < .001. CBDE indicates common bile duct exploration.

Table 1.  
Nationwide Trends in the Management of Choledocholithiasis
Nationwide Trends in the Management of Choledocholithiasis
Table 2.  
Demographic Information for Length of Stay Analysis Cohort
Demographic Information for Length of Stay Analysis Cohort
Table 3.  
Comparison of Unadjusted and Adjusted Median Hospital Length of Stay Between Patients Treated With LCBDE+LC and ERCP+LC
Comparison of Unadjusted and Adjusted Median Hospital Length of Stay Between Patients Treated With LCBDE+LC and ERCP+LC
1.
Livingston  EH, Rege  RV.  Technical complications are rising as common duct exploration is becoming rare.  J Am Coll Surg. 2005;201(3):426-433.PubMedGoogle ScholarCrossref
2.
Fusaroli  P, Lisotti  A, Syguda  A,  et al.  Reliability of endoscopic ultrasound in predicting the number and size of common bile duct stones before endoscopic retrograde cholangiopancreatography.  Dig Liver Dis. 2016;48(3):277-282.PubMedGoogle ScholarCrossref
3.
 NIH state-of-the-science statement on endoscopic retrograde cholangiopancreatography (ERCP) for diagnosis and therapy.  NIH Consens State Sci Statements. 2002;19(1):1-26.PubMedGoogle Scholar
4.
Prasson  P, Bai  X, Zhang  Q, Liang  T.  One-stage laproendoscopic procedure versus two-stage procedure in the management for gallstone disease and biliary duct calculi: a systemic review and meta-analysis [published online December 30, 2015].  Surg Endosc. doi:10.1007/s00464-015-4657-0.PubMedGoogle Scholar
5.
Rogers  SJ, Cello  JP, Horn  JK,  et al.  Prospective randomized trial of LC+LCBDE vs ERCP/S+LC for common bile duct stone disease.  Arch Surg. 2010;145(1):28-33.PubMedGoogle ScholarCrossref
6.
Healthcare Cost and Utilization Project (HCUP). Overview of the National (Nationwide) Inpatient Sample (NIS). http://www.hcup-us.ahrq.gov/nisoverview.jsp. Accessed January 20, 2016.
7.
Elixhauser  A, Steiner  C, Harris  DR, Coffey  RM.  Comorbidity measures for use with administrative data.  Med Care. 1998;36(1):8-27.PubMedGoogle ScholarCrossref
8.
Poulose  BK, Arbogast  PG, Holzman  MD.  National analysis of in-hospital resource utilization in choledocholithiasis management using propensity scores.  Surg Endosc. 2006;20(2):186-190.PubMedGoogle ScholarCrossref
9.
Bansal  VK, Misra  MC, Rajan  K,  et al.  Single-stage laparoscopic common bile duct exploration and cholecystectomy versus two-stage endoscopic stone extraction followed by laparoscopic cholecystectomy for patients with concomitant gallbladder stones and common bile duct stones: a randomized controlled trial.  Surg Endosc. 2014;28(3):875-885.PubMedGoogle ScholarCrossref
10.
Nguyen  NT, Masoomi  H, Magno  CP, Nguyen  XM, Laugenour  K, Lane  J.  Trends in use of bariatric surgery, 2003-2008.  J Am Coll Surg. 2011;213(2):261-266.PubMedGoogle ScholarCrossref
11.
Helling  TS, Khandelwal  A.  The challenges of resident training in complex hepatic, pancreatic, and biliary procedures.  J Gastrointest Surg. 2008;12(1):153-158.PubMedGoogle ScholarCrossref
Original Investigation
Pacific Coast Surgical Association
December 2016

Nationwide Assessment of Trends in Choledocholithiasis Management in the United States From 1998 to 2013

Author Affiliations
  • 1Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois
  • 2Surgical Outcomes and Quality Improvement Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois
  • 3Center for Healthcare Studies, Northwestern University Feinberg School of Medicine, Chicago, Illinois
  • 4Division of Research and Optimal Patient Care, American College of Surgeons, Chicago, Illinois
  • 5Department of Surgery, University of California, Los Angeles
  • 6Department of Surgery, VA Greater Los Angeles Healthcare System, Los Angeles, California
  • 7Department of Surgery, Sunnybrook Health Sciences Centre, the University of Toronto, Toronto, Ontario, Canada
 

Copyright 2016 American Medical Association. All Rights Reserved.

JAMA Surg. 2016;151(12):1125-1130. doi:10.1001/jamasurg.2016.2059
Key Points

Question  Has the use of common bile duct exploration (CBDE) for choledocholithiasis been increasing or decreasing over time?

Findings  In this cohort study, the percentage of patients with choledocholithiasis undergoing CBDE decreased from 39.8% in 1998 to 8.5% in 2013. This trend held true for both open CBDE (30.6% vs 5.5%) and laparoscopic CBDE (9.2% vs 3.0%). From 2011 to 2013, the percentage of patients with choledocholithiasis undergoing laparoscopic CBDE with laparoscopic cholecystectomy ranged from 1.5% to 1.8%, while those undergoing endoscopic retrograde cholangiopancreatography with laparoscopic cholecystectomy ranged from 84.3% to 85.7%.

Meaning  The surgical management of choledocholithiasis is becoming increasingly rare, despite advances in laparoscopy that make laparoscopic CBDE with laparoscopic cholecystectomy a viable treatment option.

Abstract

Importance  There are currently 2 widely accepted treatment strategies for patients presenting to the hospital with choledocholithiasis. However, the rate of use for each strategy in the United States has not been evaluated, and their trends over time have not been described. Furthermore, an optimal management strategy for choledocholithiasis has yet to be defined.

Objective  To evaluate secular trends in the management of choledocholithiasis in the United States and to compare hospital length of stay between patients with choledocholithiasis treated with endoscopic retrograde cholangiopancreatography with laparoscopic cholecystectomy (ERCP+LC) vs laparoscopic common bile duct exploration with laparoscopic cholecystectomy (LCBDE+LC).

Design, Setting, and Participants  In this cohort study, we studied patients with a primary diagnosis of choledocholithiasis that were included in the National Inpatient Sample between 1998 and 2013 from a representative sample of acute care hospitals in the United States. Patients with cholangitis or pancreatitis were excluded.

Main Outcomes and Measures  Unadjusted and risk-adjusted median hospital length of stay.

Results  Of the 37 207 patients included in our analysis, 36 048 (96.9%) were treated with ERCP+LC and 1159 (3.1%) were treated with LCBDE+LC. The mean (SD) age of patients treated with ERCP+LC was 50.7 (21.1) years and was 51.9 (20.9) years for those treated with LCBDE+LC; 25 788 (69.3%) were female. Analysis of the National Inpatient Sample data indicates that there are an average of 26 158 patients with choledocholithiasis admitted in the United States each year. The overall use of CBDE for patients with choledocholithiasis decreased from 39.8% of admissions in 1998 to 8.5% in 2013 (P < .001). A decrease was also seen for open CBDE (30.6% vs 5.5%; P < .001) and laparoscopic CBDE (9.2% vs 3.0%; P < .001) independently. Rates of management with LCBDE+LC decreased from 5.3% to 1.5% (P < .001), while rates of ERCP+LC increased from 52.8% to 85.7% (P < .001). The unadjusted median hospital length of stay was shorter for patients treated with LCBDE+LC than for those treated with ERCP+LC (3.0 vs 4.0 days; P < .001). After risk-adjustment, the median length of stay remained 0.5 days shorter for patients treated with LCBDE+LC than with ERCP+LC (3.5 vs 4.0 days; P < .001).

Conclusions and Relevance  This study highlights the marked decline in the use of both open and laparoscopic CBDE in the United States as well as the benefit to the length of stay LCBDE+LC has over ERCP+LC. Despite a persistent need for CBDE and the potential benefits of LCBDE+LC over ERCP+LC for managing choledocholithiasis, if current trends continue, CBDE may be at risk of disappearing from the surgical armamentarium.

Introduction

There are currently 2 widely accepted treatment strategies for patients presenting to the hospital with choledocholithiasis: (1) endoscopic retrograde cholangiopancreatography (ERCP) with cholecystectomy and (2) common bile duct exploration (CBDE) with cholecystectomy.

Historically, ERCP provided a less invasive option for managing choledocholithiasis than CBDE, which required an open abdominal operation. This has resulted in ERCP largely replacing CBDE in the treatment of choledocholithiasis since its introduction in the late 1970s.1 Endoscopic retrograde cholangiopancreatography remains a safe and effective way to remove stones from the CBD, although its success relies on the size and location of the CBD stone(s), the foregut anatomy of the patient, and the experience of the endoscopist performing the procedure.2 Additionally, ERCP often cannot be accomplished at the same time as cholecystectomy and instead must follow a sequential, 2-stage treatment algorithm.

Advances in laparoscopy have made laparoscopic CBDE (LCBDE) an alternative to ERCP that is far less invasive than open CBDE, making it a viable, minimally invasive alternative. Laparoscopic CBDE has been shown to be safe and effective in treating choledocholithiasis and can be performed concurrently with cholecystectomy using a 1-stage management approach.3-5 Despite the importance and potential benefits of CBDE in the treatment of choledocholithiasis, to our knowledge, the rate at which it is being used in the United States has not been described. Additionally, a nationwide length of stay analysis comparing the 2 treatment options has not been performed.

To evaluate the status of CBDE in the United States, we sought to evaluate secular trends in the management of choledocholithiasis and identify differences in hospital length of stay between LCBDE in combination with laparoscopic cholecystectomy (LCBDE+LC) and ERCP in combination with laparoscopic cholecystectomy (ERCP+LC).

Methods

We performed a retrospective cohort study of patients with choledocholithiasis who were discharged from acute care hospitals in the United States from 1998 to 2013. Data were derived from the National (formerly “Nationwide”) Inpatient Sample (NIS), a component of the Agency for Healthcare Research and Quality’s Healthcare Cost and Utilization Project. To our knowledge, the NIS is the largest all-payer inpatient database, comprised of a 20% stratified sample of inpatient acute care hospital discharges in the United States.6 The sampling and weighting methods used by the NIS allow for annual national estimates to be calculated regarding a variety of components of inpatient health care across all diagnoses.

Quiz Ref IDPatients were included in this study if they were 18 years or older, had a primary diagnosis of choledocholithiasis, and had documentation of CBDE with cholecystectomy, ERCP with cholecystectomy, or CBDE and ERCP with cholecystectomy within the same hospitalization (Figure 1). Choledocholithiasis was defined as having any of 14 International Classification of Diseases, Ninth Revision (ICD-9) diagnosis codes entered as the primary diagnosis in the discharge record (eAppendix 1 in the Supplement). Procedures were defined using their respective ICD-9 procedure codes in the discharge record (eAppendix 2 in the Supplement). The included procedural combinations were limited to CBDE with cholecystectomy, ERCP with cholecystectomy, and CBDE and ERCP with cholecystectomy, as these are the 3 major treatment options for choledocholithiasis. Of note, the timing of procedures with respect to each other could not be determined from the data available in the NIS. The Northwestern University Feinberg School of Medicine Institutional Review Board approved this study and granted a waiver of informed consent because of the deidentified nature of administrative data.

Discharge records with a diagnosis of cholangitis or acute pancreatitis were excluded (Figure 1). These diagnoses were identified by their ICD-9 diagnosis codes (eAppendix 1 in the Supplement). Patients with cholangitis or acute pancreatitis were excluded because they represent a subset of patients with choledocholithiasis that may be managed differently than others, given the presence of either of these complicating diagnoses. Additionally, these diagnoses may result in variable lengths of stay compared with patients admitted for uncomplicated choledocholithiasis and could have introduced bias into the length of stay analysis.

To evaluate secular trends in the use of CBDE, annual national estimates of the number of hospitalizations for choledocholithiasis were calculated from 1998 to 2013 using NIS discharge weights and SAS survey sampling and analysis procedures. Using these estimates, the proportion of all admitted patients with choledocholithiasis undergoing CBDE over the study period was identified, as were the proportions specific to both open and laparoscopic CBDE. Trends over time were assessed using logistic regression by examining the odds ratios and P values between 3 year groupings (1998 to 2002, 2003 to 2008, and 2009 to 2013). Specifically, annual rates of LCBDE+LC, ERCP+LC, and LCBDE+ERCP+LC over the study period were assessed.

To identify differences in hospital length of stay between patients treated with LCBDE+LC and with ERCP+LC, the study sample was limited to records containing 1 of these 2 specific treatment approaches. We further limited this analysis to discharges from 2006 to 2013 to obtain more contemporary length of stay data (Figure 1). National Inpatient Sample discharge weights were not applied for this portion of the analysis, and each record represented a single hospital admission. Wilcoxon and χ2 tests were used to test for differences in demographic factors and unadjusted hospital length of stay, where appropriate. Because of the clustered nature of the data, a hierarchical linear regression model using a negative binomial distribution with hospital random intercepts was used to obtain predicted length of stay for each patient, adjusting for age, sex, primary payer, and Elixhauser comorbidities.7 The predicted length of stay was then used to calculate an adjusted median length of stay for both management approaches.

All analyses were performed using SAS version 9.4 (SAS Institute). Significance was set at P < .05.

Results

Of the 123 089 272 discharge records in the NIS from 1998 to 2013, 254 158 contained a primary diagnosis of choledocholithiasis. After applying the inclusion and exclusion criteria of this study, 87 859 records remained (Figure 1). Quiz Ref IDApplication of NIS discharge weights to the study sample yielded an estimated mean of 26 158 hospitalizations each year due to choledocholithiasis, a number that remained relatively consistent from 1998 to 2013 (Table 1). Quiz Ref IDThe percentage of individuals admitted for choledocholithiasis who received CBDE as part of their treatment steadily declined, from 39.8% in 1998 to 8.5% in 2013 (P < .001) (Figure 2). This decrease was seen independently for both open CBDE (30.6% vs 5.5%; P < .001) and LCBDE (9.2% vs 3.0%; P < .001) (Figure 2). Conversely, the use of ERCP increased over the study period, with 76.8% of patients with choledocholithiasis undergoing ERCP in 1998 and 95.1% undergoing ERCP in 2013 (P < .001).

Trends in the use of specific management strategies for choledocholithiasis also changed over the study period (Table 1). Among all included admissions, the rate of LCBDE+LC decreased from 5.3% to 1.5% (P < .001 for all tests of decreasing trends; eAppendix 3 in the Supplement), Quiz Ref IDwhile the rate of ERCP+LC increased from 52.8% to 85.7% (P < .001 for all tests of increasing trends; eAppendix 3 in the Supplement). The percentage of individuals requiring all 3 procedures (LCBDE+ERCP+LC) decreased from 3.9% to 1.5% (P < .001 for all tests of decreasing trends; eAppendix 3 in the Supplement).

Of the 37 207 discharges identified between 2006 and 2013 with a primary diagnosis of choledocholithiasis, 1159 underwent LCBDE+LC and 36 048 underwent ERCP+LC as their treatment approach (Figure 1). Patients managed with LCBDE+LC were slightly older than those managed with ERCP+LC (mean [SD] age, 51.9 [20.9] years vs 50.7 [21.1] years; P = .048) and had fewer Elixhauser comorbidities (mean [SD] value, 1.41 [1.57] vs 1.54 [1.59]; P < .001) (Table 2). There were no significant differences between the 2 treatment groups with respect to sex or primary payer.

The median unadjusted hospital length of stay was shorter for patients undergoing LCBDE+LC than for those undergoing ERCP+LC (3.0 vs 4.0 days; P < .001). Quiz Ref IDAfter adjusting for age, sex, payer, and Elixhauser comorbidities using a hierarchical regression model, a 0.5-day shorter median length of stay persisted for patients managed with LCBDE+LC compared with those managed with ERCP+LC (3.5 days vs 4.0 days; P < .001) (Table 3).

Discussion

The number of patients admitted to the hospital for choledocholithiasis remained relatively consistent between 1998 and 2013, while the percentage of these admissions undergoing CBDE (both open and laparoscopic) as a component of their management significantly declined. Evaluating nationwide trends in the specific management approaches for choledocholithiasis demonstrated that the rate of LCBDE+LC declined steadily from 1998 to 2013, while the rate of ERCP+LC increased, with ERCP+LC being the predominant treatment strategy. The rate of LCBDE+ERCP+LC also declined over the study period, although the inability to determine the order in which these procedures were performed makes it unclear whether this represents increased efficacy of LCBDE, ERCP, or perhaps both. In addition to identifying the declining rates of CBDE use in the United States, this study also demonstrated that patients with choledocholithiasis managed with LCBDE+LC experienced shorter hospitalizations than those undergoing ERCP+LC.

The current trends in choledocholithiasis management identified by this study are concerning, particularly given the potential benefits of LCBDE+LC over ERCP+LC. In 2002, the National Institutes of Health deemed both LCBDE and ERCP to be safe and reliable treatment modalities for choledocholithiasis.3 More recently, an increasing body of research has identified benefits to using the LCBDE+LC approach, including lower hospital costs while still offering similar safety and effectiveness.4,5,8,9 Additionally, this study and others have demonstrated shorter hospital lengths of stay for patients undergoing LCBDE+LC compared with ERCP+LC, which is likely in part owing to the use of a concurrent, 1-stage approach to clearing the CBD and removing the gallbladder rather than a sequential, 2-stage approach.4,5

The decreasing trend in CBDE use in the management of choledocholithiasis may not be without consequence. In the hands of skilled endoscopists, there continues to be an approximately 5% failure rate of ERCP.5 Additionally, there are an increasing number of individuals with complex foregut anatomy not amenable to ERCP, such as those who have undergone Roux-en-Y gastric bypass.10 For these patients, CBDE may be their only treatment option, yet the progressive decline in the rate of CBDE has resulted in surgeons having less experience with the surgical management of choledocholithiasis and surgical residents completing their training with an average of only 2.4 CBDEs (1.7 open and 0.7 laparoscopic).1,11 Because decreasing rates of CBDE in the United States have been shown to be associated with increasing rates of technical complications during CBDE,1 it is important to recognize the potential clinical implications of these trends.

To our knowledge, this study represents the only evaluation of trends in the management of choledocholithiasis in the United States over the last 15 years. Use of the NIS not only facilitated a thorough evaluation of nationwide management trends for choledocholithiasis, it also provided a large study sample for conducting a national length of stay analysis. One major benefit of using the NIS for these analyses was that it included a representative sample of all acute inpatient hospital admissions in the United States. By including records representative of all admissions nationwide, these analyses provide a broader evaluation of the choledocholithiasis management in the United States than existing studies, many of which are single-center analyses and meta-analyses.

However, this study is not without limitations. The NIS is a large administrative database containing retrospectively collected data from discharge records. Therefore, all analyses are limited to information available from individual hospitalizations. As a result, postdischarge complication and readmission information is not available. Additionally, analyses rely on the quality of the data that are entered and the availability of variables across states and over time. Specifically, records were included or excluded from the analyses based on ICD-9 diagnosis and procedure codes, which rely on the assignment of the appropriate codes. When administrative data lack the necessary specificity, inferences must be made based on the information that is available. Lastly, the NIS contains limited data regarding the timing of diagnoses and procedures, which made it impossible for us to determine procedural order and to specify postprocedural length of stay. As a result, we were unable to determine whether patients undergoing LCBDE+ERCP+LC received both LCBDE and ERCP due to an ineffective LCBDE or due to an ineffective ERCP. Furthermore, this limitation also precluded the determination of whether pancreatitis was due to ERCP, leading to the possibility of underestimating the length of stay in the ERCP+LC group, as patients with post-ERCP pancreatitis are likely to experience longer hospitalizations and the diagnosis of pancreatitis excluded them from the analyses. This likely did not affect the length of stay analyses for patients in the LCBDE+LC cohort.

Although this study identified the declining use of LCBDE+LC in the management of choledocholithiasis and the shorter hospital length of stay associated with this approach, further research is needed before widely advocating for the use of LCBDE+LC over ERCP+LC. The reasons underlying the decreasing use of LCBDE+LC remain unclear. However, the wide availability of ERCP, lack of familiarity and comfort with LCBDE, or perhaps even the perception of ERCP+LC as a superior approach to managing choledocholithiasis may be contributing factors. Until conclusive evidence regarding an optimal treatment strategy exists, efforts should be made to train surgeons to safely, effectively, and efficiently manage choledocholithiasis using LCBDE. If such efforts are not put forth, it may be difficult to reverse the trend toward decreasing use of CBDE, and surgeons may ultimately lose the ability to surgically manage choledocholithiasis.

Conclusions

The results of this study highlight the marked decline in the use of CBDE in the treatment of choledocholithiasis that has occurred in the United States since 1998 as well as the length of stay benefit associated with LCBDE+LC compared with ERCP+LC. These findings warrant future investigation to determine when and why this effect is seen. There continues to be a need for CBDE when CBD clearance is unable to be achieved with ERCP, and if current trends continue, both open and laparoscopic CBDE are at risk of disappearing from the surgical armamentarium.

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Article Information

Corresponding Author: Michael W. Wandling, MD, MS, Department of Surgery, Northwestern University Feinberg School of Medicine, 251 E Huron St, Ste 3-150, Chicago, IL 60611 (m-wandling@northwestern.edu).

Accepted for Publication: May 19, 2016.

Published Online: August 24, 2016. doi:10.1001/jamasurg.2016.2059

Author Contributions: Drs Wandling and Pavey had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Wandling, Hungness, Stulberg, Bilimoria, Ko, Nathens.

Acquisition, analysis, or interpretation of data: Wandling, Hungness, Pavey, Stulberg, Schwab, Yang, Shapiro, Ko.

Drafting of the manuscript: Wandling, Hungness, Stulberg, Nathens.

Critical revision of the manuscript for important intellectual content: Wandling, Pavey, Stulberg, Schwab, Yang, Shapiro, Bilimoria, Ko.

Statistical analysis: Wandling, Pavey, Stulberg.

Obtained funding: Wandling, Bilimoria.

Administrative, technical, or material support: Wandling, Hungness.

Study supervision: Hungness, Stulberg, Yang, Shapiro, Bilimoria, Ko, Nathens.

Conflict of Interest Disclosures: None reported.

Funding/Support: Research reported in this publication was supported by grant F32GM113513 from the National Institute of General Medical Sciences of the National Institutes of Health and by the Department of Surgery at the Northwestern University Feinberg School of Medicine.

Role of the Funder/Sponsor: The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Previous Presentations: This work was presented at the 87th Annual Pacific Coast Surgical Association Meeting; February 16, 2016; Kohala Coast, Hawaii.

References
1.
Livingston  EH, Rege  RV.  Technical complications are rising as common duct exploration is becoming rare.  J Am Coll Surg. 2005;201(3):426-433.PubMedGoogle ScholarCrossref
2.
Fusaroli  P, Lisotti  A, Syguda  A,  et al.  Reliability of endoscopic ultrasound in predicting the number and size of common bile duct stones before endoscopic retrograde cholangiopancreatography.  Dig Liver Dis. 2016;48(3):277-282.PubMedGoogle ScholarCrossref
3.
 NIH state-of-the-science statement on endoscopic retrograde cholangiopancreatography (ERCP) for diagnosis and therapy.  NIH Consens State Sci Statements. 2002;19(1):1-26.PubMedGoogle Scholar
4.
Prasson  P, Bai  X, Zhang  Q, Liang  T.  One-stage laproendoscopic procedure versus two-stage procedure in the management for gallstone disease and biliary duct calculi: a systemic review and meta-analysis [published online December 30, 2015].  Surg Endosc. doi:10.1007/s00464-015-4657-0.PubMedGoogle Scholar
5.
Rogers  SJ, Cello  JP, Horn  JK,  et al.  Prospective randomized trial of LC+LCBDE vs ERCP/S+LC for common bile duct stone disease.  Arch Surg. 2010;145(1):28-33.PubMedGoogle ScholarCrossref
6.
Healthcare Cost and Utilization Project (HCUP). Overview of the National (Nationwide) Inpatient Sample (NIS). http://www.hcup-us.ahrq.gov/nisoverview.jsp. Accessed January 20, 2016.
7.
Elixhauser  A, Steiner  C, Harris  DR, Coffey  RM.  Comorbidity measures for use with administrative data.  Med Care. 1998;36(1):8-27.PubMedGoogle ScholarCrossref
8.
Poulose  BK, Arbogast  PG, Holzman  MD.  National analysis of in-hospital resource utilization in choledocholithiasis management using propensity scores.  Surg Endosc. 2006;20(2):186-190.PubMedGoogle ScholarCrossref
9.
Bansal  VK, Misra  MC, Rajan  K,  et al.  Single-stage laparoscopic common bile duct exploration and cholecystectomy versus two-stage endoscopic stone extraction followed by laparoscopic cholecystectomy for patients with concomitant gallbladder stones and common bile duct stones: a randomized controlled trial.  Surg Endosc. 2014;28(3):875-885.PubMedGoogle ScholarCrossref
10.
Nguyen  NT, Masoomi  H, Magno  CP, Nguyen  XM, Laugenour  K, Lane  J.  Trends in use of bariatric surgery, 2003-2008.  J Am Coll Surg. 2011;213(2):261-266.PubMedGoogle ScholarCrossref
11.
Helling  TS, Khandelwal  A.  The challenges of resident training in complex hepatic, pancreatic, and biliary procedures.  J Gastrointest Surg. 2008;12(1):153-158.PubMedGoogle ScholarCrossref
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