Mortality of emergency general surgical patients and associations with hospital structures and processes.

BACKGROUND: Variations in patient outcomes between providers have been described for emergency admissions, including general surgery. The aim of this study was to investigate whether differences in modifiable hospital structures and processes were associated with variance in mortality, amongst patients admitted for emergency colorectal laparotomy, peptic ulcer surgery, appendicectomy, hernia repair and pancreatitis. METHODS: Adult emergency admissions in the English NHS were extracted from the Hospital Episode Statistics between April 2005 and March 2010. The association between mortality and structure and process measures including medical and nursing staffing levels, critical care and operating theatre availability, radiology utilization, teaching hospital status and weekend admissions were investigated. RESULTS: There were 294 602 emergency admissions to 156 NHS Trusts (hospital systems) with a 30-day mortality of 4.2%. Trust-level mortality rates for this cohort ranged from 1.6 to 8.0%. The lowest mortality rates were observed in Trusts with higher levels of medical and nursing staffing, and a greater number of operating theatres and critical care beds relative to provider size. Higher mortality rates were seen in patients admitted to hospital at weekends [OR 1.11 (95% CI 1.06-1.17) P<0.0001], in Trusts with fewer general surgical doctors [1.07 (1.01-1.13) P=0.019] and with lower nursing staff ratios [1.07 (1.01-1.13) P=0.024]. CONCLUSIONS: Significant differences between Trusts were identified in staffing and other infrastructure resources for patients admitted with an emergency general surgical diagnosis. Associations between these factors and mortality rates suggest that potentially modifiable factors exist that relate to patient outcomes, and warrant further investigation.

Association of hospital structures with mortality from ruptured abdominal aortic aneurysm.

BACKGROUND: There is significant variation in the mortality rates of patients with a ruptured abdominal aortic aneurysm (rAAA) admitted to hospital in England. This study sought to investigate whether modifiable differences in hospital structures and processes were associated with differences in patient outcome. METHODS: Patients diagnosed with rAAA between 2005 and 2010 were extracted from the Hospital Episode Statistics database. After risk adjustment, hospitals were grouped into low-mortality outlier, expected mortality and high-mortality outlier categories. Hospital Trust-level structure and process variables were compared between categories, and tested for an association with risk-adjusted 90-day mortality and non-corrective treatment (palliation) rate using binary logistic regression models. RESULTS: There were 9877 patients admitted to 153 English NHS Trusts with an rAAA during the study. The overall combined (operative and non-operative) mortality rate was 67·5 per cent (palliation rate 41·6 per cent). Seven hospital Trusts (4·6 per cent) were high-mortality and 15 (9·8 per cent) were low-mortality outliers. Low-mortality outliers used significantly greater mean resources per bed (doctors: 0·922 versus 0·513, P < 0·001; consultant doctors: 0·316 versus 0·168, P < 0·001; nurses: 2·341 versus 1·770, P < 0·001; critical care beds: 0·045 versus 0·019, P < 0·001; operating theatres: 0·027 versus 0·019, P = 0·002) and performed more fluoroscopies (mean 12·6 versus 9·2 per bed; P = 0·046) than high-mortality outlier hospital Trusts. On multivariable analysis, greater numbers of consultants, nurses and fluoroscopies, teaching status, weekday admission and rAAA volume were independent predictors of lower mortality and, excluding rAAA volume, a lower rate of palliation. CONCLUSION: The variability in rAAA outcome in English National Health Service hospital Trusts is associated with modifiable hospital resources. Such information should be used to inform any proposed quality improvement programme surrounding rAAA.

Failure-to-rescue and interprovider comparisons after elective abdominal aortic aneurysm repair.

BACKGROUND: The use of postoperative complication rates to derive metrics such as failure-to-rescue (FTR) is of increasing interest in assessing the quality of care. The aim of this study was to quantify FTR rates for elective abdominal aortic aneurysm (AAA) repair in England using administrative data, and to examine its validity against case-note review. METHODS: A retrospective observational study using Hospital Episode Statistics (HES) data was combined with a multicentre audit of data quality. All elective AAA repairs done in England between 2005 and 2010 were identified. Postoperative complications were extracted, FTR rates quantified, and differences in FTR and in-hospital death rates established. A multicentre case-note review was performed to establish the accuracy of coding of complications, and the impact of inaccuracies on FTR rates derived from HES data. RESULTS: A total of 19 638 elective AAA repairs were identified from HES; the overall mortality rate was 4·6 per cent. Patients with complications (19·2 per cent) were more likely to die than those without complications (odds ratio 12·22, 95 per cent c.i. 10·51 to 14·21; P < 0·001) and had longer hospital stays (P < 0·001). FTR rates correlated strongly with death rates, whereas complication rates did not. On case-note review (661 procedures), 41·5 per cent of patients had a complication recorded in the case notes. There was evidence of systematic under-reporting of complications in HES, leading to an overall misclassification rate of 36·3 (95 per cent c.i. 33·7 to 39·2) per cent (P < 0·001), which was less pronounced for surgical complications (12·6 (11·1 to 13·9) per cent; P <0·001). Despite this, the majority of FTR rates derived from HES were not significantly different from those derived from case-note data. CONCLUSION: Postoperative complication and FTR rates after elective AAA repair can be derived from HES data. However, use of the metric for interprovider comparisons should be done cautiously, and only with concurrent case-note validation given the degree of miscoding identified.

Inter-relationship of procedural mortality rates in vascular surgery in England: retrospective analysis of hospital episode statistics from 2005 to 2010.

BACKGROUND: Wide variations in vascular surgical outcomes have been demonstrated in England. The objective of this study was to determine whether risk-adjusted postoperative mortality rates for elective and emergency vascular surgical procedures were inter-related. METHODS AND RESULTS: A retrospective observational study using National Health Service administrative data on adult patients undergoing elective or emergency vascular surgery from 2005 to 2010. The 10 procedures covered the broad spectrum of workload for a vascular surgical service. The primary outcome measure was in-hospital mortality, and secondary outcomes were 30-day and 1-year mortality. Data were risk-adjusted using multilevel modeling. Analyses comprised a 2-level basket designed to evaluate variations in outcome and whether the outcome of each procedure could be predicted by the composite outcome of all other procedures. A total of 116,596 vascular surgical procedures were performed across 166 providers. For 9 of 10 procedures, there were hospitals lying outside 95% control limits for ≥1 mortality outcome. The key finding was that ≥1 risk-adjusted mortality outcome for any 1 of the 9 vascular surgical procedures could be predicted by the aggregated within provider performance of the other vascular surgical procedures combined. CONCLUSIONS: Hospital-level risk-adjusted mortality for both elective and emergency vascular procedures in England varies considerably, and providers were globally high or low performers. The data should be made available to patients, relatives, and the purchasers of services to drive improvements in the provision of vascular surgical services.

Provider volume and long-term outcome after elective abdominal aortic aneurysm repair.

BACKGROUND: Robust risk-adjusted analyses have demonstrated that a reduction in perioperative mortality is associated with the repair of an abdominal aortic aneurysm (AAA) in centres with a high operative caseload (volume). However, the long-term impact of this volume-related effect on mortality remains unknown. METHODS: Demographic and clinical data were extracted from UK Hospital Episodes Statistics for patients undergoing elective repair of an infrarenal AAA from 1 April 2000 to 31 March 2005. The long-term mortality of this cohort was investigated through linkage to the UK Office for National Statistics (ONS) registry. Risk-adjusted survival was analysed using Cox proportional hazards modelling to identify the effect of hospital volume on long-term mortality. RESULTS: A total of 14 396 patients with mean age of 72 years, of whom 85.7 per cent were men, underwent elective repair of an infrarenal AAA in England. They were linked to follow-up using ONS data. Risk-adjusted analysis of all-cause mortality by Cox proportional hazards modelling demonstrated a significant effect of hospital volume across all quintiles up to 2 years (P = 0.013). Remodelling the data after excluding in-hospital mortality still demonstrated the significant effect of hospital volume on late outcome. CONCLUSION: There is a long-term benefit to patients who undergo elective AAA repair in a high-volume hospital.

Multicentre study of the quality of a large administrative data set and implications for comparing death rates.

BACKGROUND: The aim was to compare the completeness and accuracy of the English Hospital Episode Statistics (HES) with a 'gold standard' data set for a sample of hospitals and to determine the effect of data quality on comparisons of hospital death rates. METHODS: A multicentre audit of data quality was undertaken, based on a sample of all elective abdominal aortic aneurysm (AAA) repairs performed in England. All elective AAA repairs in nine collaborating hospital trusts were included over a 2-year interval. Cases were identified from HES, local databases, hospital administration systems and theatre records. The main outcome measures were the numbers of cases and deaths according to HES compared with case-note review. The recording of co-morbidities and the effect of data accuracy on mortality analyses and risk adjustment were quantified. RESULTS: A total of 1102 elective AAA repairs were identified from HES data. Of 962 procedures with case-note review, 827 (86·0 per cent, 95 per cent confidence interval 84·0 to 88·0 per cent) were confirmed as elective AAA repair. The survival status with HES was 99·8 per cent accurate on comparison with the Office for National Statistics death registry. There was no significant difference in mortality assessment between the HES data and the 'gold standard' data set (5·3 versus 5·0 per cent; P = 0·753). Smaller hospitals were more affected by data inaccuracies than larger hospitals. CONCLUSION: This study confirmed that HES data can be used effectively to compare mortality between hospitals. Administrative data will be used increasingly for assessing performance and clinicians should accept responsibility to improve coding.

Diagnostic quality of 50 and 100 µm computed radiography compared with screen-film mammography in operative breast specimens.

OBJECTIVE: To compare reader ratings of the clinical diagnostic quality of 50 and 100 µm computed radiography (CR) systems with screen-film mammography (SFM) in operative specimens. METHODS: Mammograms of 57 fresh operative breast specimens were analysed by 10 readers. Exposures were made with identical position and compression with three mammographic systems (Fuji 100CR, 50CR and SFM). Images were anonymised and readers blinded to the CR system used. A five-point comparative scoring system (-2 to +2) was used to assess seven quality criteria and overall diagnostic value. Statistical analysis was subsequently performed of reader ratings (n = 16,925). RESULTS: For most quality criteria, both CR systems were rated as equivalent to or better than SFM. The CR systems were significantly better at demonstrating skin edge and background tissue (p < 1 × 10(-5)). Microcalcification was best demonstrated on the CR50 system (p < 1 × 10(-5)). The overall diagnostic value of both CR systems was rated as being as good as or better than SFM (p < 1 × 10(-5)). CONCLUSION: In this clinical setting, the overall diagnostic performance of both CR systems was as good as or better than SFM, with the CR50 system performing better than the CR100.

Sizing fenestrated aortic stent-grafts.

INTRODUCTION: Fenestrated aortic stent-grafts are increasingly being used to treat patients with juxtarenal abdominal aortic aneurysms (AAA). Sizing of these stent-grafts is critical to ensure success and requires detailed expert assessment of aortic morphology. At present little is known about how sizing of these stent-grafts varies between observers and the necessary tolerances involved to ensure a successful procedure. METHODS: CT scans of 19 consecutive patients with juxtarenal aortic aneurysms that underwent successful endovascular repair with fenestrated stent-grafts were selected. Sizing of fenestrated aortic stent-grafts was performed independently by four experienced endovascular surgeons and results were compared. Data from the stent-graft manufacturer was available for comparison in 12 cases. RESULTS: All observers agreed on the number of fenestrations; 16 devices had 3 fenestrations and 3 had 4. The overall inter-observer measurement error for all target vessel orientation was ± 12.6° (10.8-14.4 95% CI), and for distance between target vessels ± 5.3 mm (4.4-6.2 95% CI). The median difference in internal stent-graft diameter was 1 stent size. Agreement on fenestration type ranged from (84-95%). Comparison was performed with the manufactured stent-graft in 12 cases. The overall mean difference of target vessel orientation between the manufactured devices and the four observers was -1.3° (SD ± 6.9,-3.8-1.2 95% CI). There was less agreement between observers and device manufacturers on body and limb lengths and distal limb diameters. CONCLUSIONS: There was generally a high level of agreement between experienced endovascular surgeons in sizing the fenestrated stent component. There were differences in component lengths but these could have been accommodated by varying the degree of overlap between components.

Centralization harnessing volume-outcome relationships in vascular surgery and aortic aneurysm care should not focus solely on threshold operative caseload.

There has been great interest in the setting of threshold operative volumes for safety to guide centralisation of vascular surgical services by healthcare commissioners. This editorial examines the evidence for designing services around a numeric safety threshold in the relationship between volume and outcome in vascular surgery. Thresholds should be aimed at the best outcomes and equity of care. Equity means access to the most up-to-date technology and all the relevant support services for elective and emergency cases. The relationship of volume and outcome with quality is complex, and demands a shift in focus to infrastructural and procedural improvements that drive high-quality services rather than the concentration of planning exclusively around an operative volume threshold.

Screened individuals' preferences in the delivery of abdominal aortic aneurysm repair.

BACKGROUND: This study aimed to determine preferences for service attributes in a population screened for abdominal aortic aneurysm. METHODS: A questionnaire was designed to encompass various aspects of service provision. Questions were calibrated against the time an individual was willing to travel to access specific attributes. Subjects attending an aneurysm screening programme were asked to complete a questionnaire before their screening ultrasound scan. Statistical analysis was through pairwise analysis of the median travel times with the signed rank test. The Wilcoxon rank sum, analysed by the Kruskal-Wallis test, was used to compare preference ratings. RESULTS: A total of 262 individuals were asked to complete the questionnaire; the response rate was 98.5 per cent. Approximately 92 per cent of individuals stated a willingness to travel for at least 1 h beyond their nearest hospital in order to access services with a 5 per cent lower perioperative mortality rate, a 2 per cent lower amputation or stroke rate, a high annual caseload of aneurysm repairs, and routine availability of endovascular repair. CONCLUSION: Patients attending aneurysm screening were willing to travel beyond their nearest hospital to access a service with better outcomes, higher surgical volumes and endovascular surgery.

Propensity scored analysis of outcomes after ruptured abdominal aortic aneurysm.

BACKGROUND: This study examined the population outcome of ruptured abdominal aortic aneurysm (rAAA) in England, the role of endovascular repair (EVAR), and the relationship between outcome and hospital workload. METHODS: Data were retrieved from Hospital Episode Statistics between 1 April 2003 and 31 March 2008. Propensity scoring was used to compare the outcomes of stratified patients undergoing EVAR and open repair. The relationship between workload and outcome was determined. RESULTS: Some 3725 urgent and 4414 rAAA repairs were included. Mortality rates were 21.3 per cent for urgent repair and 46.3 per cent for rAAA repair. EVAR was employed for 16.3 and 7.6 per cent of urgent and rAAA repairs respectively. EVAR was associated with significantly reduced mortality for urgent repair (odds ratio (OR) 0.531, 95 per cent confidence interval 0.415 to 0.680; P < 0.001) and rAAA repair (OR 0.527, 0.416 to 0.668; P < 0.001). A propensity scored analysis confirmed the benefit of EVAR for rAAA repair (P < 0.001). Repair of rAAA at hospitals with a higher elective aneurysm workload was associated with lower mortality rates irrespective of the mode of treatment (P < 0.001). Higher-volume hospitals were more likely to operate on rAAA (P = 0.033). CONCLUSION: EVAR offered a survival advantage over open repair for non-elective aneurysm procedures. Services for the treatment of rAAA should incorporate access to EVAR and would benefit from being based in units with a high elective caseload.

The National Bowel Cancer Audit: the risks and benefits of moving to open reporting of clinical outcomes.

BACKGROUND: The government's proposals to openly report clinical outcomes poses challenges to the National Bowel Cancer Audit now funded by the UK department of health. AIM: To identify the benefits and risks of open reporting and to propose ways the risks might be minimized. METHODS: A review of the literature on clinical audit and the consequences of open reporting. RESULTS: There are significant potential benefits of a national audit of bowel cancer including protecting patients from sub-standard care, providing clinicians with externally validated evidence of their performance, outcome data for clinical governance and evidence that increases in government expenditure are achieving improvements in survival from bowel cancer. These benefits will only be achieved if the audit captures most of the cases of bowel cancer in the UK, the data collected is complete and accurate, the results are risk adjusted and these are presented to the public in a way that is fair, clear and understandable. Involvement of clinicians who have confidence in the results of the audit and who actively compare their own results against a national standard is essential. It is suggested that a staged move to open reporting should minimise the risk of falsely identifying an outlying unit. CONCLUSION: The fundamental aim of the National Bowel Cancer Audit is the pursuit of excellence by identification and adoption of best practice. This could achieve a continuous improvement in the care of all patients with bowel cancer in the UK. The ACPGBI suggests a safer way of transition to open reporting to avoid at least some of its pitfalls.

Re-interventions, readmissions and discharge destination: modern metrics for the assessment of the quality of care.

AIM: To determine whether administrative data can be used to determine metrics to inform the quality agenda. To determine the relationship between these metrics and the method of abdominal aortic aneurysm (AAA) repair undertaken. METHODS: The Hospital Episode Statistics (HES) data were taken for a 5-year period (01.04.2003-31.03.2008). Cases of elective AAA repair were identified. Outcomes were determined in terms of mortality, discharge destination, re-intervention rates and emergency readmission rates. The results were interpreted in light of whether AAA repair was open or endovascular and whether patients were octogenarians or younger patients. RESULTS: There were 18,060 elective AAA repairs with a mean in-hospital mortality rate of 5.9%. Of these 14,141 were open repairs with a mean mortality of 6.5% and 3919 EVAR (22%) with a mean mortality of 3.8%. EVAR patients were less likely to be discharged to ongoing care (p < 0.001) but were associated with a higher rate of re-intervention (p = 0.001) than open repairs. No differences were seen in one-year readmission rates. Octogenarians were more likely to undergo EVAR (p = 0.001), to be readmitted within 30-days (p = 0.009), to require further interventions on their index admission (p < 0.001) and less likely to be discharged home (p < 0.001) than younger patients. CONCLUSION: Administrative data can be used to identify metrics other than mortality and length of stay. These metrics might be used to inform service provision. In particular for AAA repair, differences in these outcomes were identified between open repair and EVAR and between octogenarians and younger patients.

Model for the reconfiguration of specialized vascular services.

BACKGROUND: This article built on previous work to develop an algorithm for elective abdominal aortic aneurysm (AAA) repair and carotid endarterectomy (CEA), with the aim of improving patient survival by regionalization of services. Vascular procedures were used as an example of specialized surgical services. METHODS: A model was generated based on a national data set that incorporated the statistical demonstration of procedural safety, hospital annual surgical case volume, and travel distance and time. Elective AAA repair was used to construct a hub-and-spoke model that was tested against CEA. The impact of the model was quantified in terms of mortality rates, and travel distance and time. RESULTS: Only 48 vascular hubs were required to provide adequate coverage in England, with the majority of patients travelling for less than 1 h to access inpatient vascular surgery. The model predicted a reduction in the number of deaths from elective surgery for AAA (P < 0.001) and CEA (P = 0.016). CONCLUSION: Adoption of this strategic model may lead to improved outcome after AAA and CEA. It could be used as a model for the regionalization of specialized surgery. The model does not take into account the complexity of providing a comprehensive vascular service in every locality.

Demonstrating safety through in-hospital mortality analysis following elective abdominal aortic aneurysm repair in England.

BACKGROUND: The aims were to assess the evidence that individual hospitals had mortality rates in excess of the national average after abdominal aortic aneurysm (AAA) repair and to develop an effective method for monitoring mortality using local data. METHODS: Hospital Episode Statistics identified patients undergoing elective infrarenal AAA repair. A technique was developed that compared individual hospital mortality rates with the mortality rate in the remainder of England. The strength of evidence that the death rate was less than elsewhere, and less than twice elsewhere, was quantified using a test of statistical significance. A moving average chart technique was devised using local data for mortality monitoring and comparison to the national average. RESULTS: For 30 hospitals, the mortality rate was significantly greater than elsewhere, and in three hospitals it was demonstrably greater than twice that in the remainder of England. The moving average chart appeared to provide a useful technique for local mortality monitoring. CONCLUSION: Different mortality rates exist for AAA repair within England. Mortality can be monitored locally and compared with the national average.

The relationship between hospital case volume and outcome from carotid endartectomy in England from 2000 to 2005.

OBJECTIVES: To assess the outcome of carotid endarterectomy in England with respect to the hospital case-volume. METHODS: Data were from English Hospital Episode Statistics (2000-2005). Admissions were classified as elective or emergency. Risk-adjusted data were analysed through modelling of death rate, complication rate and length of admission with regard to the year of procedure and annual hospital volume of surgery. Hospitals with elevated death rates were identified and the evidence quantified that they had outlying mortality rates. RESULTS: There were 280,081 diagnoses of extra-cranial atherosclerotic arterial disease in which 18,248 CEA were performed. The mean mortality rates were 1.04% for elective and 3.16% for emergency CEA. A volume-related improvement in mortality (p=0.047) was seen for elective CEA. Length of stay decreased as annual volume increased for elective and emergency CEA (p<0.001). 20% of the operations were performed in 67.1% of the hospitals, each of which performed fewer than 10 CEA per annum. A number of hospitals had elevated death rates. CONCLUSIONS: Volume-related improvements in outcome were demonstrated for elective CEA. Minimum volume-criteria of 35 CEA per annum should be established in England. Hospitals performing low annual volumes of surgery should consider arrangements to network services.

Meta-analysis and systematic review of the relationship between hospital volume and outcome following carotid endarterectomy.

OBJECTIVES: This study investigated the relationship between annual hospital volume and the outcomes in carotid endarterectomy and quantified critical volume threshold for this procedure. DATA SOURCES: PubMed, EMBASE and the Cochrane library were searched for all articles on the volume-outcome relationship in CEA. REVIEW METHODS: Articles were included if they presented data on post-operative mortality and/or stroke rates and annual hospital volume of CEA. The review conformed to the QUOROM statement. The data were meta-analysed and a pooled effect estimate of volume on the stroke and/or mortality rates from CEA quantified, along with the critical volume threshold. RESULTS: Twenty-five articles, encompassing 936 436 CEA, were analysed. Significant relationships between mortality rate and stroke rate and annual volume were seen. Overall, the pooled effect estimate was odds ratio 0.78 [95% confidence interval 0.64-0.92], in favour of surgery at higher volume units, with a critical volume threshold of 79 CEA per annum. CONCLUSIONS: Significantly lower mortality and stroke rates were achieved at hospitals providing a higher annual hospital volume of CEA. Hospitals wishing to provide CEA should adhere to minimum volume criteria.

Meta-analysis and systematic review of the relationship between volume and outcome in abdominal aortic aneurysm surgery.

BACKGROUND: This study investigated the volume-outcome relationship for abdominal aortic aneurysm (AAA) surgery and quantified critical volume thresholds. METHODS: PubMed, EMBASE and the Cochrane library were searched for articles on the operation volume-outcome relationship in elective and ruptured AAA surgery. UK Hospital Episode Statistics data were also considered. Elective and ruptured AAA repairs were dealt with separately. The data were meta-analysed, and the odds ratios (95 per cent confidence interval) for mortality at higher- and lower-volume hospitals were compared. Volume thresholds were identified from each paper. RESULTS: The analysis included 421,299 elective and 45,796 ruptured AAA operations. Significant relationships between mortality and annual volume were noted for both groups. Overall, the weighted odds ratio was 0.66 (0.65 to 0.67) for elective repair at a threshold of 43 AAAs per annum and 0.78 (0.73 to 0.82) for ruptured aneurysm repair at a threshold of 15 AAAs per annum, both in favour of high-volume institutions. CONCLUSION: Higher annual operation volumes are associated with significantly lower mortality in both elective and ruptured AAA repair. This suggests that AAA surgery should be performed only at higher-volume centres.

Epidemiological study of the relationship between volume and outcome after abdominal aortic aneurysm surgery in the UK from 2000 to 2005.

BACKGROUND: The aim was to assess the relationship between hospital volume and outcome after abdominal aortic aneurysm (AAA) surgery in the UK. METHODS: Hospital Episode Statistics (2000-2005) were classified as elective, urgent or ruptured AAA repair. Analysis was by modelling of mortality rate, complication rate and length of hospital stay with regard to the annual operative volume, after risk adjustment. RESULTS: There were 112,545 diagnoses, or repairs, of AAAs, of which 26,822 were infrarenal aneurysms. The mean mortality rate was 7.4, 23.6 and 41.8 per cent for elective, urgent and ruptured AAA repair respectively. Elective AAA repair undertaken at high-volume hospitals showed volume-related improvements in mortality (P < 0.001). Patients were discharged from hospital earlier (P < 0.001). The critical volume threshold was 32 elective AAA repairs per year. For urgent repair, patients at high-volume hospitals had a reduced mortality rate (P = 0.017) with an increased length of stay (P = 0.041). There was no relationship between volume and outcome for ruptured AAA repairs. CONCLUSION: Increased annual volumes were associated with significant reductions in mortality for elective and urgent AAA repair, but not for repair of ruptured AAAs.

Development of a dedicated risk-adjustment scoring system for colorectal surgery (colorectal POSSUM).

BACKGROUND: The aim of the study was to develop a dedicated colorectal Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (CR-POSSUM) equation for predicting operative mortality, and to compare its performance with the Portsmouth (P)-POSSUM model. METHODS: Data were collected prospectively from 6883 patients undergoing colorectal surgery in 15 UK hospitals between 1993 and 2001. After excluding missing data and 93 patients who did not satisfy the inclusion criteria, 4632 patients (68.2 per cent) underwent elective surgery and 2107 had an emergency operation (31.0 per cent); 2437 operations (35.9 per cent) for malignant and 4267 (62.8 per cent) for non-malignant diseases were scored. Stepwise logistic regression analysis was used to develop an age-adjusted POSSUM model and a dedicated CR-POSSUM model. A 60:40 per cent split-sample validation technique was adopted for model development and testing. Observed and expected mortality rates were compared. RESULTS: The operative mortality rate for the series was 5.7 per cent (387 of 6790 patients) (elective operations 2.8 per cent; emergency surgery 12.0 per cent). The CR-POSSUM, age-adjusted POSSUM and P-POSSUM models had similar areas under the receiver-operator characteristic curves. Model calibration was similar for CR-POSSUM and age-adjusted POSSUM models, and superior to that for the P-POSSUM model. The CR-POSSUM model offered the best overall accuracy, with an observed : expected ratio of 1.000, 0.998 and 0.911 respectively (test population). CONCLUSION: The CR-POSSUM model provided an accurate predictor of operative mortality. External validation is required in hospitals different from those in which the model was developed.