Background Appendicitis is a common condition which represents a significant resource burden for the Scottish National Health Service (NHS). It is unknown whether there are significant differences in Scottish appendicectomy (appendectomy) outcomes which may be explained by hospital volume. In many studies, hospital procedural volume has been shown to be predictive of surgical outcomes. Aims The aim of this study is to compare appendicectomy outcomes in Scotland as they vary by hospital procedural volume. Methods This research study is a retrospective observational enquiry which will utilise administrative data from the Information Services Division (ISD) of NHS National Services Scotland. Patient episodes will be identified by a procedure codes for appendicectomy. A 10 year period will be studied, from January 2001 to December 2010. Primary outcome measures will be risk-adjusted 30 day/inpatient mortality, 30 day readmission rate, 30 day re-operation rate, length of stay and negative appendicectomy rate.
The aim of this study is to explore the possibility of a hospital volume-outcome relationship in Scottish appendicectomy outcomes. This is a retrospective study of all appendicectomies performed in Scotland during the period from 1st January 2001 - 31st December 2010. It will use routinely collected administrative data from the Information Services Division (ISD) of NHS National Services Scotland. The registry which will supply the data for this study is the Scottish Morbidity Record 01 (SMR01), the full title of which is the "General / Acute Inpatient and Day Case dataset" (see http://www.adls.ac.uk/nhs-scotland/general-acute-inpatient-day-case-smr01/?detail). SMR01 is collated and administered by ISD, and data submission is mandatory for all Scottish NHS providers of in-patient or day-case care. Approximately 1.4 million records are added each year. Diagnoses are coded according to International Classification of Diseases (ICD)-10 standards and procedures are coded according to the United Kingdom's Office of Population Census Statistics (OPCS) standards, the most recent of which is version 4.5. The data quality in SMR01 is high and is assured by regular internal audits. In the 2010 audit of accuracy, Main Condition was recorded with an accuracy of 88% and Main Procedure was recorded with an accuracy of 94%. Where data inconsistencies are identified in the extract supplied for this study, further clarification will be obtained where possible with ISD's data retrieval support team. Data completeness is very high in SMR01. However, where significant volumes of data are missing or unusable, the need for data imputation will be explored. The study period was decided on pragmatically by a desire to provide an assessment of current practice, fully within the era of widely practised laparoscopic surgery. A power calculation also suggested that this would provide an adequate sample size to demonstrate differences. Our power calculation- specific to length of stay- was based on Faiz O, Clark J, Brown T, Bottle A, Antoniou A, Farrands P, et al. Traditional and Laparoscopic Appendectomy in Adults. Ann Surg. 2008 Nov;248(5):800-6. In their cohort of 259,735 appendicectomies performed from 1996-2006, the geometric mean length of stay was 3.52, with SD 1.8. We decided that a difference of 0.5 days would be 'clinically significant'. We specified alpha 0.05 and Power 0.9, and an allocation ratio of 2 (allowing comparison of one tertile to two others). A two-sided t-test of difference between two independent means was performed in G\*Power 3.1.7. This demonstrated that a total N of 616 was required to demonstrate this difference. According to ISD figures, there were 3,712 appendicectomy procedures performed in 2010/11, so we will be able to detect a clinically significant difference in length of stay. Hospitals will be placed into tertiles of high, medium and low volume, according to the number of procedures performed over the study period. In the absence of a literature standard appendicectomy outcome measure, the following will be assessed as primary outcome measures: 30 day/in-patient mortality, 30 day re-admission rate, 30 day re-operation rate, post-operative length of stay and negative appendicectomy rates between these 3 groups. Potentially significant confounding variables such as age, gender, and co-morbidity will be studied for their predictive value in a univariate model and included in a multivariate model if they remain significant.
Study Type
OBSERVATIONAL
Enrollment
40,000
All Scottish NHS Hospitals
Multiple Locations, United Kingdom
Post-operative length of stay
(Whole) days from date of laparotomy to date of discharge. Because this is a retrospective study using a complete national data set, with the last admission 2.5 years distant from the time of data collection, we will use actual time period rather than censoring length of stay at a set point.
Time frame: From date of appendicectomy to date of discharge (whole days) - see below
Re-operation
The occurrence of an abdominal procedure either subsequent to appendicectomy and within the index admission, or ≤30 days of discharge.
Time frame: Within the index admission or within 30 days of discharge
Re-admission
Re-admission to any hospital specialty ≤30 days have elapsed since date of discharge.
Time frame: Within 30 days of index discharge
Mortality
Death as an in-patient or ≤30 days of procedure. Deaths will be recognised from SMR01 which is linked to the Registrar General's database of deaths.
Time frame: Either within 30 days of procedure, or during continuous in-patient stay
Negative Appendicectomy Rate
The rate of appendicectomies performed in which the appendix is found to be normal. This will be detected by the use of ICD-10 codes.
Time frame: At time of index procedure
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