We have described the rates of sepsis and the associated mortality for a variety of hospital based surgical procedures. Esophageal, pancreatic, and gastric procedures represented the greatest risk for the development of sepsis, but mortality for patients developing sepsis was found to be the greatest following thoracic, adrenal, and hepatic procedures. Furthermore, we have demonstrated that older patients, men, and non-whites were more likely to develop sepsis as a complication after elective surgery. Our analysis further demonstrates that sepsis is an extremely costly complication to the health care system. Based on the frequency of cases performed, decreasing septic complications after cardiac and colorectal procedures may be the most cost advantageous to the health care system. To our knowledge, this is the largest population-based analysis evaluating the rates, risk factors, mortality, and cost associated with postoperative sepsis following elective surgery.
Previous studies evaluating postoperative sepsis may have limited generalizability due to small study size, single institution experiences, and small geographic regions.21-27
The incidence of sepsis has increased significantly in the United States over the last decade and has been accompanied by an increase in the severity of sepsis.1, 28-29
In the year 2002, The National Healthcare Quality Reports estimated 11.6 cases of post-operative sepsis per 1,000 elective surgery discharges with a hospital length of stay longer than 3 days.2
More than 40 million surgical procedures are performed annually in the United States, and despite a reduction in the disease case fatality over time, sepsis remains one of the leading causes of death in the United States.1, 4, 29-34
Our analysis has demonstrated that elective surgical procedures with the highest likelihood of developing sepsis do not necessarily have the greatest mortality. Among elective surgical cases, those with the greatest risk were esophageal, pancreatic, small bowel, and biliary procedures. Of note was the higher than expected rate of septic complications associated with gastric and small bowel cases, even though these procedures have been previously reported as having low septic complications from other large data series.35
Our analysis demonstrates that gastric and small bowel procedures appear to pose a significant risk for the development of postoperative sepsis which may be secondary to disease processes not analyzed in this study. After case-mix adjustment, thoracic, adrenal, and hepatic procedures ranked among the top procedures associated with the highest mortality if sepsis developed. The mortality rates for these procedures were higher than after esophageal and pancreatic procedures. In accordance with our findings, a population level analysis from the UK concluded that the greatest mortality rates were associated with general abdominal procedures.36
Beyond procedure type, we have defined the sociodemographics of postoperative sepsis after elective surgery. Previous large population analyses have evaluated global sepsis rates (medical and surgical combined) and have demonstrated that the incidence of sepsis disproportionately increased in elderly adults, and age was an independent predictor of mortality.37
After adjustment of this cohort for comorbidities, the aged still remained more likely to develop sepsis and had increased mortality after developing sepsis than younger patients. In addition, gender disparities in the occurrence of postoperative sepsis were demonstrated. Women were found to be less likely to develop post operative cases in the total surgical cohort. Multiple studies have evaluated the correlation of gender to the development of sepsis.38-41
Mechanistic reasons for this gender disparity remain unclear, but further analyses from a population level may provide insight into comorbidities and other factors increasing the likelihood of developing post-operative sepsis.
We have also demonstrated that ethnicity and income have a significant impact on the development of postoperative sepsis. Previous population level investigations have demonstrated a substantial relationship of race and income on mortality and use of services among Medicare beneficiaries.42-43
In our adjusted model, we have demonstrated that white race and greater income lessened the likelihood for the development of postoperative sepsis. Reasons for this finding remain unclear, but authors have suggested this may be secondary to educational level, access to care, or the extent of disease when treated.44
As well, other authors have demonstrated increased PSI rates in minorities and have suggested that patient race may influence the risk of experiencing a patient safety event. The authors suggested patient risk factors or the organizational characteristics of hospitals may affect quality of care and the occurrence of PSIs.45
We have also described institutional characteristics associated with the development of postoperative sepsis after elective surgery. Hospital quality has been previously shown to vary by geographic region and hospital characteristics.46
We determined that patients in larger hospitals were more likely to develop sepsis than in smaller hospitals. We also found that elective surgical procedures in urban and non-teaching hospitals were more likely to be complicated by postoperative sepsis. These findings suggest that factors contained within healthcare delivery systems may be associated with the development of postoperative sepsis. Others have suggested that improved outcomes at teaching hospitals may be secondary to increased teaching intensity and better rescue after complications develop, rather than fewer overall complications.47
Importantly, the structure and process of care within hospitals have been found to have a significant association with the prevention of surgical site infections.48
Khuri et al. has also noted the importance of complications utilizing the National Surgical Quality Improvement Program (NSQIP) database. The occurrence of 30-day postoperative complications were more important than preoperative patient risk and intraoperative factors in determining the survival after major surgery. This suggests that process improvements should be directed toward the prevention of postoperative complications.49
Finally, comparison of our findings utilizing the NIS to other large data other large data sets show similar rates of sepsis as a complication of elective procedures. Fowler et al. evaluated the Society of Thoracic Surgeons National Cardiac Database to evaluate clinical predictors of major infections after cardiac surgery.50
This study reported a postoperative septicemia rate of approximately 1.23% which was a subset of cardiac patients in which major infection occurred. This rate appears similar to the risk adjusted rate of sepsis of 1.11% found in this analysis. Based upon our analysis, cardiac and colorectal surgery may be future targets for intervention as the frequency of these procedures and the associated cost of sepsis may have a larger impact on limiting cost and expenditure associated with sepsis as a complication.
This study has several limitations. Administrative data originally were intended primarily for reimbursement, although multiple studies have validated the use of administrative data for research purposes.1, 51
The potential for inclusion bias based on limited coding schemes for the many clinical entities cannot be entirely excluded as well as the differentiation of comorbidities from chronic illnesses. It is possible that changes in rates of sepsis results may have occurred over time secondary to more complete capturing of codes by institutions based upon reimbursement. An inherent weakness of the study is the reliance upon ICD-9 discharge coding which may vary from institution to institution and within the same institution. Although the code scheme remained constant throughout the study, there may be coding variations between institutions and this cannot be evaluated from the data set. There may also be a bias in the definition of sepsis as a revised consensus sepsis definitions have been published during the study period which may lead to variation in the severity and classification of sepsis.52
There is also an inherent limitation by selecting patients having procedures performed within the first two days of admission, but this was performed to ensure that patients had elective admissions as well as elective procedures. There are limitations using administrative data on millions of patients compared to the use of smaller cohorts with more refined clinical information, but we propose that the present data from an epidemiological standpoint is valuable for future interventions and analysis.
In conclusion, we have identified several elective surgical procedures that demonstrate a greater risk for the development of postoperative sepsis. We have further defined procedures associated with the greater mortality after sepsis develops. We have also noted disparities in the occurrence of sepsis on a population level with regard to patient demographics and institutional characteristics. We have identified opportunities among several high-volume elective procedures where both improved clinical outcome and reduced costs could provide societal benefits. Further focused studies and root cause analyses will be required to decrease the rates of postoperative sepsis and delineate targets for process level improvements.