Abstract
Introduction
Early detection and treatment of sepsis improves chances of survival; however, sepsis is often difficult to diagnose initially. This is especially true in the prehospital setting, where resources are scarce, yet time is of great significance. Early warning scores (EWS) based on vital signs were originally developed to guide medical practitioners in determining the degree of illness of a patient in the in-patient setting. These EWS were adapted for use in the prehospital setting to predict critical illness and sepsis. We performed a scoping review to evaluate the existing evidence for use of validated EWS to identify prehospital sepsis.
Methods
We performed a systematic search using the CINAHL, Embase, Ovid-MEDLINE, and PubMed databases on September 1, 2022. Articles that examined the use of EWS to identify prehospital sepsis were included and assessed.
Results
Twenty-three studies were included in this review: one validation study, two prospective studies, two systematic reviews, and 18 retrospective studies. Study characteristics, classification statistics, and primary conclusions of each article were extracted and tabulated. Classification statistics varied markedly for prehospital sepsis identification across all included EWS: sensitivities ranged from 0.02–1.00, specificities from 0.07–1.00, and PPV and NPV from 0.19–0.98 and 0.32–1.00, respectively.
Conclusions
All studies demonstrated inconsistency for the identification of prehospital sepsis. The variety of available EWS and study design heterogeneity suggest it is unlikely that new research can identify a single gold standard score. Based on our findings in this scoping review, we recommend future efforts focus on combining standardized prehospital care with clinical judgment to provide timely interventions for unstable patients where infection is considered a likely etiology, in addition to improving sepsis education for prehospital clinicians. At most, EWS can be used as an adjunct to these efforts, but they should not be relied on alone for prehospital sepsis identification.
Introduction
Sepsis remains an immense diagnostic challenge for clinicians and public health professionals. It is the leading cause of death in the United States, the most common cause of death in critically ill patients within intensive care units (ICUs), and a large contributor to hospital readmissions (Citation1, Citation2). Early identification of sepsis is critical for survival yet remains a major challenge in patient management. Prehospital identification of acute and critical illness is a crucial component in health care as early treatment can reduce the risk of mortality and morbidity in a range of emergent conditions including sepsis (Citation3, Citation4). Patients arriving in the emergency department (ED) via emergency medical services (EMS) for sepsis are often sicker than those who arrive by private vehicle, resulting in higher rates of hospital and ICU admission (Citation5, Citation6). Therefore, the prehospital setting can play a major role in early detection of severe sepsis and septic shock, including alerting hospital staff to the concern (similar to prehospital activation for ST-segment elevation myocardial infarction or activation for stroke) and commencing early in-field treatment. Retrospective studies, for example, have shown that prehospital fluid administration is associated with increased chances of survival (Citation7).
It is imperative that septic patients at risk for deterioration receive proper intervention as soon as clinically relevant, as this increases their chances of survival and decreases their risk of new morbidity (Citation8). EMS clinicians transport about half of all sepsis cases, yet only around 61% of EMS clinicians are aware of all sepsis indicators (Citation4, Citation9). A survey conducted by Seymour and colleagues also revealed that while most EMS personnel identify the term “sepsis” and can identify some of its associated signs, inadequate understanding of sepsis and how to recognize and treat it could be a barrier to proper prehospital care (Citation10). This is due to a variety of factors, including lack of focused education among EMS clinicians and heterogeneity among prehospital protocols for sepsis identification and treatment (Citation4, Citation9). Clinical guidelines for sepsis management can be developed by EMS medical directors, regional, or state-specific protocols (Citation4). Additional prehospital challenges include limited diagnostic tools and other resources to aid in recognizing sepsis or identifying factors that portend sepsis.
Early warning scores (EWS, sometimes called early warning system scores) are clinical prediction tools used by medical professionals to recognize signs of in-hospital critical illness and deterioration. These scores rely heavily on vital signs including heart rate, blood pressure, oxygen saturation, and respiratory rate. EWS were originally created for the inpatient setting; however, they have been applied in the prehospital setting to identify critically ill patients and predict patient outcomes at an earlier point in the care continuum (Citation8). Prior studies have suggested that prognostic accuracy is higher for some EWS than others and calls for the use of a combination of EWS and clinical judgment (Citation11). Currently, there is no consensus on EWS derivation and validation methodology (Citation8). Heterogeneity in study design methodology includes selection of validation dataset (i.e., using different populations to validate EWS), reported outcomes of interest (e.g., diagnosis of disease vs. ICU admission vs. mortality), sepsis case definitions, and handling of missing values (Citation11). Reported sensitivity and specificity for each EWS varies based on the authors’ methods for derivation and validation, and the stated intended use for each EWS (Citation12). Finally, although EWS are meant to be quick and simple to use, they can be difficult to perform in the resource-limited prehospital setting (Citation8). We performed a scoping review of the available literature regarding the usage of validated EWS to identify prehospital sepsis and herein summarize the classification statistics of these scores in confirming prehospital sepsis.
Methods
We systematically searched the CINAHL, Embase, Ovid-Medline, and PubMed libraries (). Inclusion and exclusion criteria were determined a priori (Supplementary Table S1). An initial search was conducted in July 2021, with subsequent searches in April 2022 and September 2022. Articles between January 1, 1990, and September 1, 2022, were included. Note that articles were restricted from 1990 to 2022 as major contemporary headways in sepsis research did not begin until the 1990s when the first ACCP/SCCM conference was held (Citation13). Articles were restricted to those pertaining to adult humans and the English language.
Table 1. Line-by-line search terms used to retrieve articles assessing prehospital identification of sepsis using EWS.
Eligible articles included original research studies or review articles either testing or validating EWS for identification of prehospital sepsis. Studies that included non-human and/or pediatric subjects, employed biomarkers in the identification of sepsis, or included an evaluation of treatment strategies were excluded. Pediatric populations were excluded since general prehospital management of pediatric patients often differs from that of adults. We excluded EWS that incorporated biomarkers to identify sepsis so that the EWS were generalizable and consistent with tools that are routinely available to EMS personnel. Although some EMS units do use a point of care (POC) lactate test, many EMS personnel lack access to the necessary tools to collect and report information about biomarkers (Supplementary Table S1).
The initial search yielded 943 results, 336 of which were duplicates that were excluded. The remaining 607 unique titles and abstracts were screened by two authors (RDO and TWHS) to determine relevancy to the research question and objective. A third reviewer (AW) adjudicated disagreements and 579 articles were excluded. The remaining 28 articles underwent a full-text evaluation, of which 23 were included in this review (). Abstracted data include EWS(s) assessed, study type, study population and sample size, year published, country, methods, EWS outcomes (e.g., sensitivity and specificity), and conclusions (Supplementary Table S2). Findings are presented in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews checklist (PRISMA-ScR; Supplementary Table S3).
Figure 1. Flowchart for selection of articles assessing validated EWS use to identify prehospital sepsis.
We consulted two prehospital emergency medicine experts via a virtual synchronous Zoom call in a semi-structured interview to gain clarity regarding current prehospital practices, to understand their perspectives and opinions on prehospital sepsis identification and management, and for their recommendations regarding future directions of research. Although an impressive body of sepsis research exists, there are relatively fewer studies regarding prehospital sepsis. These experts have key roles in emergency medical services, serving as chief of the division of EMS at an academic center, director of the EMS fellowship, and medical director of a large air ambulance service. Each expert has numerous publications regarding emergency management and treatment of the critically ill, prehospital medicine, and sepsis. Briefly, we asked for 1) their opinions on current prehospital sepsis practices and EWS scores, 2) what the current efforts are with regards to identifying or creating a superior EWS scoring tool, 3) what they considered to be gaps in this field, and 4) where to direct future prehospital sepsis research. This consultation was conducted in accordance with the framework set out by Arksey and O’Malley (Citation14).
Results
Of the 23 articles included in this review, one was a validation study (Citation15), two were prospective analyses (Citation16, Citation17), two were systematic reviews (Citation18, Citation19), and 18 were retrospective studies (Citation20–37). These studies were conducted internationally; two from Canada (Citation15, Citation30), six from France (Citation16, Citation25–29), one from Germany (Citation22), one from Saudi Arabia (Citation20), two from Sweden (Citation17, Citation37), one from Switzerland (Citation35), one from Turkey (Citation36), two from the UK (Citation33, Citation34), and seven from the USA (Citation18, Citation19, Citation21, Citation23, Citation24, Citation31, Citation32) (). Primary outcomes were largely (61%) based on comparisons of discriminatory ability for identification of prehospital sepsis among two or more EWS () (Citation15–23, Citation26, Citation31, Citation32, Citation35, Citation37). A wide variety of EWS were used, but the score most assessed was the qSOFA (Citation15, Citation16, Citation21, Citation23–26, Citation31–36), followed by the BAS 90-30-90 (Citation15, Citation18, Citation19, Citation22, Citation37), the Modified Early Warning Score (MEWS) (Citation15, Citation18, Citation22, Citation25, Citation36), the Prehospital Early Sepsis Detection (PRESEP) (Citation15, Citation18, Citation19, Citation22, Citation25), and the Robson (Citation15, Citation18, Citation19, Citation22, Citation36) tool. In addition, shows that no single statistic was reported in every study, limiting our statistical analysis for this review. Publication dates ranged from 2014 to 2022, with most (70%) studies published within the last four years (Citation15–17, Citation20, Citation21, Citation24–30, Citation32–34, Citation36).
Table 2. Study characteristics.
Table 3. Summary of primary conclusions.
Table 4. Summary of classification statistics outcomes.
Disease screening statistics were tabulated from each study (). Most studies reported sensitivities ranging from 0.02–1.00, and some went on to include specificities (ranging from 0.07–1.00), positive predictive values (PPV, ranging from 0.19–0.98), and negative predictive values (NPV, ranging from 0.32–1.00). A few studies also listed an area under the receiver operating characteristic curve for their derivation and/or validation data sets. outlines the interview questions and quoted answers from our expert consultation. A full transcription of the interview is available in Supplementary Table S4. Our experts agreed that identifying prehospital sepsis with an EWS alone would be challenging given the external noise produced as a result of using an EWS with less-than-ideal classification statistics (e.g., a low PPV).
Table 5. Expert consultation questions and answers.
Discussion
We performed a scoping review to assess the available evidence for use of EWS tools, reliant solely on vital signs and without inclusion of laboratory biomarkers, for prehospital identification of sepsis. Based on our eligibility criteria, we included 23 studies that demonstrated EWS generally performed poorly and inconsistently for prehospital sepsis identification. Some EWS were overly specific and not sensitive (Citation19, Citation22, Citation26, Citation28, Citation36), some were overly sensitive (Citation15, Citation23, Citation32, Citation35), and some reported both poor sensitivities and specificities (Citation15, Citation24, Citation26). EWS that were evaluated across multiple studies (e.g., qSOFA and MEWS) performed inconsistently while EWS that were evaluated once across all 23 studies performed well in some areas but not others (e.g., demonstrated only high sensitivity or only high specificity). In addition, no single EWS tool performed better or worse than any other. Overall, the studies included in this review do not provide sufficient evidence for relying only on EWS for prehospital sepsis identification. A few studies regarded some scores as valuable tools to use in the prehospital setting due to their high sensitivity and/or specificity, but other studies reported contradicting results of lower sensitivity and/or specificity for the same EWS; this would result in many missed sepsis cases and/or a waste of resources. For those EWS that were evaluated numerous times, this review has demonstrated that despite repeated attempts to apply these scores, these EWS consistently performed poorly for prehospital sepsis identification (e.g., MEWS, PRESEP, qSOFA, Robson scores).
There are a few possibilities that could explain the variation in results. First, EWS were originally developed to train clinicians to identify deterioration in the inpatient clinical setting, where many more resources and tools are available for calculating these scores (Citation38). To apply EWS in the prehospital setting, changes were made to some scores so that EMS clinicians could properly deploy them with the available tools. For example, the qSOFA score was created by removing the laboratory tests from the SOFA score to create a quick and simple prompt for clinicians to identify potentially septic patients outside of the ICU (Citation19). Most EWS were also created with the intention of predicting clinical instability rather than precisely identifying sepsis (Citation8). It is reasonable to consider that applying EWS in an entirely different setting from the one in which it was originally derived and validated, and for identifying a different outcome, produces less than ideal results. Finally, heterogeneity in prehospital EWS validation could have resulted in reduced sensitivity or specificity. There was marked heterogeneity in patient populations and outcomes among the studies included in this review. Many validation papers for EWS use inpatient populations as ground truth, looking at outcomes of either ICU admission or in-hospital mortality, which could have biased the study results and classification statistics of the scores evaluated in this review.
Most studies included in this review had small sample sizes and were subject to additional bias due to their retrospective natures. There are a variety of EWS that have been internationally developed (Citation16, Citation28) and the range of international EWS included in this review allowed us to evaluate a more robust dataset; however, it should be noted that prehospital care varies widely across different countries, limiting generalizability to US models of prehospital care. Because of the significant heterogeneity within the data, the results suggest that some EWS (e.g., NEWS, PRESEP, and SIGARC scores) could be valuable tools in prehospital management, but most EWS perform inadequately and should not be relied on as sole indicators of sepsis in the prehospital setting (i.e., qSOFA). Our results imply that identifying or creating a gold standard EWS given currently available prehospital diagnostic tools is not ideal and over-reliance on use of EWS can be misleading.
The available evidence and key points from our expert consultation suggest that a combination of standardized prehospital protocols focused on management of clinical instability paired with early identification of a possible infectious source for the etiology of clinical instability, supplemented by extensive sepsis education to bolster clinical judgment, may be most effective in enabling rapid prehospital identification of sepsis-induced clinical instability and subsequent higher quality prehospital care. They also noted that researchers could potentially shift their focus of future research to unexplored areas of sepsis, such as different vital signs or novel laboratory biomarkers, include linkage of more detailed outcomes to prehospital data rather than relying on administrative data, or prehospital identification of septic shock instead of overall sepsis.
For example, the incorporation of supplemental real-time, diagnostic modalities such as end-tidal carbon dioxide (EtCO2) monitoring may be of benefit to the identification of prehospital sepsis. Unlike laboratory biomarkers (e.g., lactate) that may be difficult to obtain in the resource-limited prehospital environment, various forms of EtCO2 monitoring such as capnography and capnometry are already widely available in EMS systems. The most current version of the National EMS Scope of Practice Model stipulates that application of EtCO2 monitoring and capnography is in the scope of practice for advanced emergency medical technicians and paramedics (Citation39). States such as Kentucky are permitting emergency medical technicians to use this tool due to its simple application, noninvasive nature, and presence in current educational standards (Citation40). Lactate is used as a marker of tissue hypoperfusion and organ dysfunction commonly associated with sepsis, and serum values greater than 2 mmol/L can be used to diagnose septic shock (Citation41, Citation42). Some studies have established a correlation between decreased EtCO2 and elevated lactate (Citation43–45). A more recent study further validated these findings in the hospital setting and described success of EtCO2 levels in predicting initial lactate levels. However, the authors did not find it to be a reliable indicator of an infectious source, unlike the SIRS criteria (Citation46). Heart rate variability is another instrument that could be used to identify patients at risk of decompensation, though studies in the prehospital setting are lacking at this time. Like our prior suggestions, EtCO2 monitoring or heart rate variability would likely be most effective when used as adjunctive tools in addition to clinical judgment, enhanced education, and standardized sepsis protocols.
There are several limitations to our review. It is possible that some relevant articles were not included in this review based on the database search criteria. Articles without English manuscripts were excluded due to lack of translation services. We were unable to perform a systematic review and meta-analysis because most studies were retrospective, many studies had limited high-quality data, and there was a lack of homogeneity across methodologies. Because of the limited high-quality data among our chosen studies, and since scoping reviews generally provide a broader synopsis of existing literature, we did not perform a bias assessment (Citation47). Missing data (as seen in ) limited the conclusions and generalizability of this review. In addition, missing and limited data precluded the use of diagrams such as forest and funnel plots for formal data visualization and analysis. Finally, the field of prehospital sepsis research remains relatively new, and the definition of sepsis is still being refined. Lack of homogeneity in how studies defined sepsis could have affected the methods and results of individual studies, which in turn could have affected the results and generalizability of this review.
Conclusion
We determined that there is limited evidence to support applying EWS tools as the primary or sole method to identify prehospital sepsis. We recommend that future efforts shift the focus from identifying a gold standard EWS for prehospital sepsis identification to standardizing prehospital care and subsequent interventions for acutely unstable patients where infection is considered a likely etiology, and improving sepsis education for prehospital clinicians. Providing EMS personnel with real-time data and instantaneous feedback is one method to improve prehospital clinical care for septic patients. Prospective modeling is needed to evaluate the effects of these interventions on outcomes such as identification of acute and rapid deterioration and patient-specific outcomes such as ICU admission, in hospital and 30-day mortality, and quality of life.
Supplemental Material
Download Zip (547.2 KB)Acknowledgments
Thank you to Dr. Francis X. Guyette and Dr. Christian Martin-Gill for their time, guidance, and support of this project.
Disclosure statement
Dr. Weissman has no direct conflicts of interest to report. Dr. Weissman is a consultant for Inflammatix Inc. unrelated to this work. All other authors report no conflict of interest.
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References
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