The Healthcare Cost and Utilization Project (HCUP)-NIS database comprises > 3000 hospitals representing more than 7 million annual hospital discharges in the US

The Nationwide Inpatient Sample (NIS) database is the largest US inpatient care database, encompassing hospitals from a total of 46 states, which serve 97% of the U.S. population. The

Healthcare Cost and Utilization Project (HCUP)-NIS database comprises > 3000 hospitals representing more than 7 million annual hospital discharges in the US. The NIS is a database of hospital inpatient stays derived from billing data submitted by hospitals to statewide data organizations across the US.

Inpatient data includes clinical and resource use information typically available from discharge

abstracts. Each discharge is coded with a principal diagnosis for that specific hospitalization in addition to the potential for 14 secondary diagnoses and 15 associated procedures. For this study, HCUP-NIS data from January 1, 2004 through December 31, 2014 was collected.¹

1. Healthcare Cost and Utilization Project (HCUP). Agency for Healthcare Research and Quality (AHRQ): Advancing Excellence in Health Care. https://www.ahrq.gov/research/data/hcup/index.html. Accessed July 6, 2017.

ICD 9 diagnosis codes Diagnosis

304.3*, 305.2* Cannabis use

305.1, V15.82 Tobacco use

303, 303.0, 303.00, 303.01, 303.02, 303.03, 305.0, 305.00, 305.01, 305.02, 305.03, V11.3

Alcohol use

ICD 9 procedure codes Procedure

Diagnostic ERCP codes

51.1 Endoscopic retrograde cholangiopancreatography [ERCP]

51.11 Endoscopic retrograde cholangiography [ERC]

51.14 Other closed [endoscopic] biopsy of biliary duct or sphincter of Oddi

52.13 Endoscopic retrograde pancreatography [ERP]

52.14 Closed [endoscopic] biopsy of pancreatic duct

Therapeutic ERCP codes

51.84 Endoscopic dilation of ampulla and biliary duct

51.85 Endoscopic sphincterotomy and papillotomy

51.86 Endoscopic insertion of nasobiliary drainage tube

51.87 Endoscopic insertion of stent (tube) into bile duct

51.88 Endoscopic removal of stone(s) from biliary tract

52.93 Endoscopic insertion of stent (tube) into pancreatic duct

52.94 Endoscopic removal of stone(s) from pancreatic duct

52.97 Endoscopic insertion of nasopancreatic drainage tube

52.98 Endoscopic dilation of pancreatic duct

This study classified the indications for ERCP into purely diagnostic ERCP and therapeutic ERCP as highlighted in the above table with subsequent indications for ERCP further classified as biliary and pancreatic.

Secular trends in mortality rates were assessed using linear Poisson regression models. The models were used to investigate the effect of the period of diagnosis (independent variable) on the in- hospital mortality rate (dependent variable), while controlling for other variables (i.e. adjusting for age, sex, race, income, insurance status, type of admission, and modified Elixhauser comorbidity index).

Risk estimates and 95% confidence intervals (CI’s) were calculated for all independent variables in the final model. Poisson regression with robust (Huber–White) standard errors was also used to determine incident risk ratios (IRR) for predictors of in-hospital mortality. Prior to our analysis, we tested the Poisson models for over-dispersion using a Pearson goodness-of-fit test. Models were not over dispersed; thus, Poisson regression was then used to determine incident risk ratios (IRR) for clinical outcomes in patients with cannabis use compared to those without cannabis use.