Acute cholecystitis is the most common acute complication of gallstone disease. Although there are diverging opinions about optimal timing for surgery, the general recommendation is that surgery is performed as soon as possible after admission when the diagnosis is established. The study will compare acute cholecystectomies for acute cholecystitis performed during weekends with procedures where patient have been waiting during weekend and surgery performed during a subsequent weekday.

Hypothesis: Performing acute cholecystectomies for acute cholecystitis during weekends are associated with higher risk for complications.

Acute cholecystitis is the most common acute complication of gallstone disease. About 15-20% of all cholecystectomies is performed because of acute cholecystitis. Laparoscopic cholecystectomy is one of the most common acute surgical procedure, and several studies have tried to identify the optimal time between debut of symptoms and surgery.

Although there are diverging opinions about optimal timing for surgery, the general recommendation is that surgery is performed as soon as possible after admission when the diagnosis is established. According to the latest Tokyo Guidelines, early laparoscopic cholecystectomy is the recommended treatment for all severity grades of acute cholecystitis, and delayed surgery is only recommended for selected high-risk patients. An English study based on data from a national register have shown that surgery within three days after admission is recommended for patients with acute cholecystitis. A randomised controlled trail (RCT) with the same formulation of question would need a large number of patients to reach sufficient power, which makes it impossible to perform a study of that kind during a reasonable time. An alternative to RCT studies is studies based on national register data which provides a large number of patients to achieve sufficient statistical power.

In daily clinical practice, there are often other acute surgical procedures with higher priority, leading to down prioritizing of acute cholecystectomies causing the surgery to be delayed. This is common despite that early cholecystectomy generally is accepted as golden standard for acute cholecystitis. Although there are sufficient evidence that risk for complication, days admitted at hospital and risk for conversion to open surgery are increased for every day that surgery is postponed, the phenomenon of delay is usual. To avoid delay of surgery, many clinics perform cholecystectomies during weekends and out-of-hours. Results from studies that compare complication rate between cholecystectomies performed during out-of-hours and office-hours are contradictive. This difference seems to be even larger for cholecystectomies that are performed during weekends, when there are often surgeons during internship and surgeons not specialized in upper GI-surgery on call. To this day, there are no published studies that investigates acute cholecystectomies following acute cholecystitis performed during weekend compared to operations that are delayed until the next following weekday.

The study will be a population-based cohort studie. Data will be extracted from the Swedish gallstone surgery and Retrograde Cholangiopancreatography register (GallRiks). The register is established and have collected data about patients undergoing cholecystectomies and ERCPs since 2005. More than 90% of all cholecystectomies and endoscopic retrograde cholangiopancreaticographies (ERCPs) performed in Sweden are registered. About 20 000 procedures (12 000 cholecystectomies and 8000 ERCPs) are annually registered, and data about indication for surgery, surgical technique, duration of surgery and complications.

Inclusion Criteria:

• Patients with the diagnosis of ongoing acute cholecystitis.
• Undergoing surgery on a weekend or national holiday.
• Staying in hospital during weekend and undergoing surgery on any subsequent weekday.

Exclusion Criteria:

• Paediatric patients (<18 years)
• Patients who underwent surgery more than 7 days after admission
• Patients admitted and operated on during weekdays during the same week
• Patients with missing data regarding age, sex, American Society of Anesthesiologists Classification system (ASA grade), surgical approach, operating time, or complications.

Patients undergoing cholecystectomy with ongoing acute cholecystitis that are registered in GallRiks (the Swedish Gallstone Surgery and ERCP register)