Emergency department charges may be associated with mortality in patients with severe sepsis and septic shock: a cohort study

Administrative data sets are an increasingly important tool for conducting population-based and health services research as they contain detailed information about medical care and outcomes [1]. Administrative data sets allow for rapid identification of a large cohort of patients, and they facilitate study across medical centers and health systems [2]. While health services studies using administrative data in sepsis and critical care exist [3, 4], it has been challenging to perform rigorous analyses because no robust physiologic measure of illness severity is captured in hospital claims [5]. Therefore there remains a need for a validated method to adjust for severity of illness based on administrative data.

Sepsis is responsible for 17% of US in-hospital deaths, and nearly one-half of sepsis admissions are treated in the emergency department (ED) [6, 7]. Age, medical comorbidities, admission diagnosis, and surgical status impact morbidity and mortality significantly, so risk adjustment models are critical to compare outcomes across clinical sepsis studies [8]. Illness severity scores, such as the Acute Physiology and Chronic Health Evaluation, 2nd edition (APACHE-II) score [9], the Simplified Acute Physiology Score (SAPS), and the Sequential Organ Failure Assessment (SOFA) score are valid scoring systems for critically ill patients [10‐12], but the parameters used to calculate these scores are not captured in claims.

The objective of this study is to measure the concordance between ED charges and mortality in patients admitted with severe sepsis or septic shock, with a secondary objective of measuring the association between ED charges and APACHE-II score. We hypothesize that intensity of care is closely related to severity of illness, and that level of intensity could be approximated by ED charges. If validated, ED charges could be a useful covariate for claims-based health services analyses of acute care conditions like sepsis.

During the 2-year study period, 294 patients were included in the analysis, and 83 (28%) died. Table 1 shows the demographics, ED interventions, comorbidities and baseline vitals. The median APACHE-II score was 17 (rang 2 to 47), and the median ED charge was $3640 (IQR $2861 - $5234).

The ability to adjust for severity of illness is important in comparing clinical outcomes such as mortality and length-of-stay in observational health services analyses, but this adjustment has been elusive for administrative analyses of sepsis studies. The APACHE-II score is a robust and well-validated tool that can be used to predict mortality, and it is commonly used when comparing health care outcomes for critically ill patients [10]. Physiologic and laboratory data are often unavailable in health services analyses that are conducted using administrative claims data, which limits severity adjustment in these studies [15]. This study identifies ED charges as a potential surrogate measure, suggesting that it can be used as a covariate in outcomes-based sepsis studies using administrative claims, even when more robust physiologic severity of illness measures are not available.

ED charges are usually viewed as an outcome related to care provided, but they are also a reflection of the amount and type of care needed during an ED stay. In the United States, ED charges are generated from professional fees and facility fees, and charges performed during the study period were performed on a fee-for-service basis. These fees are based on the time that health care providers spend caring for a patient, separately billable procedures that are performed (e.g., central venous line placement, endotracheal intubation), and the medical complexity documented. All severity of illness indices are surrogate markers for the probability of death assessed at admission [9]. These markers are designed to allow for risk adjustment to measure the probability of death attributable to only conditions recognized at the time of hospital admission, and ED charges were hypothesized to function similarly. Patients who are more seriously ill (hypotensive, requiring intubation, or needing more time and resource-intensive care) also receive higher hospital bills, and that relationship was validated in our model.

In addition to finding that ED charges are related to mortality, however, the decreased mortality was found with higher charges. This finding might indicate that care delivered in the ED (measured by charges) may also be influencing outcomes. Early aggressive ED sepsis care has been shown to decrease mortality [16], and the higher ED charges may be capturing the impact of aggressive appropriate resuscitation. This finding suggests that ED charges may be included in studies of non-ED interventions on sepsis outcomes, because controlling for ED charges may capture both the effect of severity of illness and treatment effects of ED care.

This study introduces ED charges as a predictor of clinical outcomes when physiologic severity of illness scores are not available retrospectively for research purposes. There are many areas of acute care research that may benefit from adjusting for ED charges as a marker of disease severity. Studies of diseases where acute disease severity strongly influences outcomes, such as sepsis, acute respiratory failure, stroke, and trauma may benefit from such an adjustment. Although these data only inform the use of ED charges in sepsis studies, other future studies should consider ED charges for its predictive value. In this way, ED charges can be treated as a nuisance variable – a variable that may be associated with a potentially confounding variable, but where the magnitude of effect is irrelevant in itself. There may also be other non-critical care diseases where this adjustment may also be useful, such as asthma or congestive heart failure.

This study has several limitations. First, we used retrospectively collected data from a single site. Although this may limit the external validity of our finding, it reflects accurately the way that this tool may be used in actual observational analyses. For our data collection we looked at ED charges, not actual cost to the patient. Costs are challenging to estimate, so they often are estimated based on the cost-to-charge ratio, and use of this ratio would be expected to yield similar precision. As with all claims-based studies, there is a bias towards identifying patients with more severe illness [17]. The high mortality in this cohort, however, supports that severity was likely reflected accurately. Finally, as a single-center study, we have no data on the concordance between hospitals, which is an important consideration for this method to be used on a large scale. Additionally, the application of ED cost to predict mortality may not be applicable outside of the United States where charges are more variable. Fortunately, studies that propose to use this method can validate the association between ED charges and clinical outcomes within the study, so using ED charges as a covariate in a multivariable regression model will allow one to assess its contribution to model fit in each application independently.

This study also included only patients admitted to an intensive care unit. These inclusion criteria were intended to limit the study population to those with greater severity of illness, but it may limit the generalizability of the findings.

ED charges are a useful surrogate measure for severity of illness in sepsis studies based on administrative data. ED charges are inversely associated with mortality in severe sepsis and septic shock, and they predict hospital and ICU length-of-stay. ED charges may reflect both severity of illness and the contribution of ED care on clinical outcomes. Future work should focus on the applicability of comparing this covariate across hospital systems to adjust severity of illness in large administrative data sets, and to use it in other disease categories.