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Figure 1.
Study Identification and Selection Process Used in the Systematic Review
Study Identification and Selection Process Used in the Systematic Review

aNonduplicate references from other sources included review articles.3,108110 See eMethods 1 in the Supplement for further details of search strategy.

bRefers to records that were excluded after reference screening of full text articles. The screening criteria for full text inclusion were reporting of all case sepsis epidemiology in adult populations without specific assessment of interventions. The qualitative review assessed sepsis and septic shock definitions and criteria. The records included in the qualitative review (92 studies57,19107) are presented in eTable 2 in the Supplement. The quantitative review assessed septic shock criteria and mortality.

cRefers to the records included for quantitative assessment of septic shock mortality and the heterogeneity by criteria using random-effects meta-analysis (44 studies57,1959) (eTable 2 in the Supplement).

Figure 2.
Random-Effects Meta-analysis of Studies Identified in the Systematic Review, Reporting Septic Shock Mortality
Random-Effects Meta-analysis of Studies Identified in the Systematic Review, Reporting Septic Shock Mortality

Forty-four studies report septic shock–associated mortality57,1959 and were included in the quantitative synthesis using random-effects meta-analysis. The Surviving Sepsis Campaign (SSC) database analyses with similar data are reported in 2 studies6,29; therefore, only one of these was used in the meta-analysis reported.6 Levy et al report 3 septic shock subsets,6 Klein Klowenberg et al report 2 (restrictive and liberal),7 Zahar et al report 3 (community-acquired, ICU-acquired, and nosocomial infection–associated septic shock),30 and Phua et al report 2 groups,32 which were treated as separate data points in the meta-analysis. Studies under “consensus definition” cite the Sepsis Consensus Definitions.1,2 The categorization used to assess heterogeneity does not fully account for septic shock details in individual studies.

SI conversion factor: To convert serum lactate values to mg/dL, divide by 0.111.

aData obtained from GiViTI database provided by Bertolini et al (published 20158).

bThe mortality data of Group 1 patients (new septic shock population) and the overall potential septic shock patient populations (n = 18 840) described in the manuscript from the current study using the Surviving SSC database are also included in the meta-analysis. Septic shock–specific data were obtained from Australian & New Zealand Intensive Care Society Adult Patient Database (ANZICS), from a previously published report.22 This results in 52 data points for random-effects meta-analysis.

Figure 3.
Selection of Surviving Sepsis Campaign Database Cohort
Selection of Surviving Sepsis Campaign Database Cohort

Hypotension was defined as mean arterial pressure less than 65 mm Hg. Vasopressor therapy to maintain mean arterial pressure of 65 mm Hg or higher is treated as a binary variable. Serum lactate level greater than 2 mmol/L (18 mg/dL) is considered abnormal. The “after fluids” field in the Surviving Sepsis Campaign (SSC) database was considered equivalent to adequate fluid resuscitation. “Before fluids” refers to patients who did not receive fluid resuscitation. Serum lactate level greater than 2 mmol/L after fluid resuscitation but without hypotension or need for vasopressor therapy (group 4) is defined as “cryptic shock.” Missing serum lactate level measurements (n = 4419 [15.7%]) and patients with serum lactate levels greater than 4 mmol/L (36 mg/dL) who did not receive fluids as per SSC guidelines (n = 790 [2.8%]) were excluded from full case analysis. Of the 22 941 patients, 4101 who were coded as having severe sepsis were excluded. Thus, the remaining 18 840 patients were categorized within septic shock groups 1 to 6.

aPatients with screening serum lactate levels coded as greater than 2 mmol/L (n=3342) were included in the missing-data analysis.

Figure 4.
Serum Lactate Level Analysis
Serum Lactate Level Analysis

Adjusted odds ratio for actual serum lactate levels for the entire septic shock cohort (N = 18 840). The covariates used in the regression model include region (United States and Europe), location where sepsis was suspected (emergency department, ward, or critical care unit), antibiotic administration, steroid use, organ failures (pulmonary, renal, hepatic, and acutely altered mental state), infection source (pneumonia, urinary tract infection, abdominal, meningitis, and other), hyperthermia (>38.3°C), hypothermia (<36°C), chills with rigor, tachypnea (>20/min), leukopenia (<4000 cells/µL), hyperglycemia (plasma glucose >120 mg/dL [6.7 mmol/L]), platelet count <100 ×103/μL, and coagulopathy (eMethods 3 in the Supplement). The adjusted odds ratio (OR) for the 6 groups presented in eTable 7 in the Supplement and the adjusted OR for the individual variables (lactate, vasopressor therapy, and fluids) are reported in eTable 8 in the Supplement. To convert serum lactate values to mg/dL, divide by 0.111.

Table 1.  
Summary of Septic Shock Definitions and Criteria Reported in the Studies Identified by the Systematic Reviewa
Summary of Septic Shock Definitions and Criteria Reported in the Studies Identified by the Systematic Reviewa
Table 2.  
Random Effects Meta-Analysis by Septic Shock Criteria Groups
Random Effects Meta-Analysis by Septic Shock Criteria Groups
Table 3.  
Distribution of Septic Shock Cohorts and Crude Mortality From Surviving Sepsis Campaign Database (n = 18 840 patients)
Distribution of Septic Shock Cohorts and Crude Mortality From Surviving Sepsis Campaign Database (n = 18 840 patients)
Table 4.  
Characteristics of Serum Lactate Level Cutoff Values for Complete Case Analysis and Imputation Analysis Using Surviving Sepsis Campaign Database
Characteristics of Serum Lactate Level Cutoff Values for Complete Case Analysis and Imputation Analysis Using Surviving Sepsis Campaign Database
Table 5.  
Crude Mortality in Septic Shock Groups From UPMC and KPNC Data sets
Crude Mortality in Septic Shock Groups From UPMC and KPNC Data sets
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Original Investigation
Caring for the Critically Ill Patient
February 23, 2016

Developing a New Definition and Assessing New Clinical Criteria for Septic ShockFor the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)

Author Affiliations
  • 1Division of Asthma, Allergy, and Lung Biology, King’s College London, London, United Kingdom
  • 2Department of Critical Care Medicine, Guy’s and St Thomas’ NHS Foundation Trust, London SE17EH, United Kingdom
  • 3The Ohio State University College of Medicine, Department of Biomedical Informatics, Center for Biostatistics, Columbus
  • 4Rhode Island Hospital, Brown University School of Medicine, Providence, Rhode Island
  • 5Clinical Research, Investigation, and Systems Modeling of Acute Illness Center, Department of Critical Care and Emergency Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania
  • 6Division of Research, Kaiser Permanente, Oakland, California
  • 7Department of Pediatrics, Hofstra-North Shore-Long Island Jewish-Hofstra School of Medicine, Steven and Alexandra Cohen Children’s Medical Center, New Hyde Park, New York
  • 8Department of Molecular Medicine, Hofstra-North Shore-Long Island Jewish-Hofstra School of Medicine, Steven and Alexandra Cohen Children’s Medical Center, New Hyde Park, New York
  • 9Feinstein Institute for Medical Research, Manhasset, New York
  • 10Associate Editor, JAMA
  • 11Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Ontario, Canada
  • 12Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada
  • 13Bloomsbury Institute of Intensive Care Medicine, University College London, London, United Kingdom
JAMA. 2016;315(8):775-787. doi:10.1001/jama.2016.0289
Abstract

Importance  Septic shock currently refers to a state of acute circulatory failure associated with infection. Emerging biological insights and reported variation in epidemiology challenge the validity of this definition.

Objective  To develop a new definition and clinical criteria for identifying septic shock in adults.

Design, Setting, and Participants  The Society of Critical Care Medicine and the European Society of Intensive Care Medicine convened a task force (19 participants) to revise current sepsis/septic shock definitions. Three sets of studies were conducted: (1) a systematic review and meta-analysis of observational studies in adults published between January 1, 1992, and December 25, 2015, to determine clinical criteria currently reported to identify septic shock and inform the Delphi process; (2) a Delphi study among the task force comprising 3 surveys and discussions of results from the systematic review, surveys, and cohort studies to achieve consensus on a new septic shock definition and clinical criteria; and (3) cohort studies to test variables identified by the Delphi process using Surviving Sepsis Campaign (SSC) (2005-2010; n = 28 150), University of Pittsburgh Medical Center (UPMC) (2010-2012; n = 1 309 025), and Kaiser Permanente Northern California (KPNC) (2009-2013; n = 1 847 165) electronic health record (EHR) data sets.

Main Outcomes and Measures  Evidence for and agreement on septic shock definitions and criteria.

Results  The systematic review identified 44 studies reporting septic shock outcomes (total of 166 479 patients) from a total of 92 sepsis epidemiology studies reporting different cutoffs and combinations for blood pressure (BP), fluid resuscitation, vasopressors, serum lactate level, and base deficit to identify septic shock. The septic shock–associated crude mortality was 46.5% (95% CI, 42.7%-50.3%), with significant between-study statistical heterogeneity (I2 = 99.5%; τ2 = 182.5; P < .001). The Delphi process identified hypotension, serum lactate level, and vasopressor therapy as variables to test using cohort studies. Based on these 3 variables alone or in combination, 6 patient groups were generated. Examination of the SSC database demonstrated that the patient group requiring vasopressors to maintain mean BP 65 mm Hg or greater and having a serum lactate level greater than 2 mmol/L (18 mg/dL) after fluid resuscitation had a significantly higher mortality (42.3% [95% CI, 41.2%-43.3%]) in risk-adjusted comparisons with the other 5 groups derived using either serum lactate level greater than 2 mmol/L alone or combinations of hypotension, vasopressors, and serum lactate level 2 mmol/L or lower. These findings were validated in the UPMC and KPNC data sets.

Conclusions and Relevance  Based on a consensus process using results from a systematic review, surveys, and cohort studies, septic shock is defined as a subset of sepsis in which underlying circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than sepsis alone. Adult patients with septic shock can be identified using the clinical criteria of hypotension requiring vasopressor therapy to maintain mean BP 65 mm Hg or greater and having a serum lactate level greater than 2 mmol/L after adequate fluid resuscitation.

Introduction

Consensus definitions, generated in 19911 and revisited in 2001,2 describe septic shock as a state of cardiovascular dysfunction associated with infection and unexplained by other causes. The increasing availability of large electronic health record (EHR) data sets, registries, national case mix programs, trial data sets, and claims databases using International Classification of Diseases codes have since generated multiple observational studies reporting septic shock epidemiology. However, variable interpretation and application of the consensus definitions1,2 have contributed to variable estimates of both incidence and outcomes.38 It is unclear to what extent these variations represent true differences or an artifact attributable to inconsistent use of definitions.8,9 Furthermore, emerging insights into sepsis pathophysiology1013 warrant a review of the current septic shock definition and the criteria used to identify it clinically.

Against this background, the Society of Critical Care Medicine (SCCM) and the European Society of Intensive Care Med (ESICM) convened an international task force to review definitions of sepsis and septic shock in January 2014. To support the task force deliberations on redefining septic shock, a series of activities was performed: a systematic review and meta-analysis of criteria used in observational studies reporting sepsis epidemiology in adults; a Delphi study to achieve consensus; cohort studies using the Surviving Sepsis Campaign (SSC) registry; and subsequent testing of the applicability of the new criteria in patients with suspected infection from 2 large EHR-derived data sets. The aims of this study were to develop an updated septic shock definition and to derive clinical criteria for identifying patients with septic shock meeting this updated definition. Specifically, this updated definition and these criteria are intended to provide a standard classification to facilitate clinical care, future clinical research, and reporting.

Methods

In this article, “definition” refers to a description of septic shock and “clinical criteria” to variables used to identify adult patients with septic shock.

Task Force

The SCCM and ESICM each nominated cochairs of the task force and provided unrestricted funding support toward the work conducted. The 2 cochairs then selected 17 other task force participants based on their scientific expertise in sepsis epidemiology, clinical trials, and basic or translational research. Task force participants are listed at the end of the article. The task force retained complete autonomy for all decisions. ESICM and SCCM had no role in study design, conduct, or analysis but were consulted for peer review and endorsement of the manuscript.14

Systematic Review and Meta-analysis

The aims of the systematic review were to assess the different criteria used to identify adult patients with septic shock and whether these criteria were associated with differences in reported outcomes. MEDLINE was searched using search terms, MeSH headings, and combinations of sepsis, septic shock, and epidemiology and limits of human studies; adults 19 years or older; English-language publications; and publication dates between January 1, 1992 (1991 definitions1), and December 25, 2015. For full-text review, only noninterventional studies reporting sepsis epidemiology and all-cause mortality were included. Randomized clinical trials were excluded, because the additional inclusion and exclusion criteria might confound the effect of criteria on mortality (the study objective).8 To avoid variability in outcomes related to specific pathogens, specific patient groups, and interventional before-and-after studies, studies reporting these populations were also excluded. Data were extracted on cohort recruitment period, cohort characteristics, setting, criteria used to identify septic shock, and acute mortality. Detailed methods, including search strategy, are presented in eMethods 1 and eTable 1 in the Supplement.

Delphi Study

To generate consensus on the septic shock definition and criteria, 3 face-to-face meetings, 3-round sequential pretested questionnaires, and email discussions among the task force participants were conducted. One task force member did not participate in these surveys because of lack of content expertise, and 1 did not respond to the first 2 surveys. Questionnaires were developed, refined, and administered consisting of single- and multiple-diagnosis questions, free-text comments, and a 5-point Likert agreement scale. For consensus discussions and noting agreement, the 5-point Likert agreement scales were grouped at the tails of the scale choices (ie, “strongly disagree” grouped with “disagree”; “strongly agree” grouped with “agree”). All outputs from the systematic review, surveys, and the results of cohort studies were made available to participants throughout the Delphi study.

In the first round (August 2014), using 26 questions in 4 domains, agreement and opinions were explored on (1) components of the new septic shock definition; (2) variables and their cutoffs identified by the systematic review; (3) definitions of, and criteria for, hypotension, persistent hypotension, adequacy of resuscitation, and resuscitation end points; and (4) septic shock severity scoring. In the second round (November 2014), 4 questions were used to generate statements for key terms (persistent hypotension, adequacy of resuscitation, and septic shock) and to reach agreement on test variables and outcomes for subsequent analysis of predictive validity. The objectives of the third round (January 2015) were to establish a consensus definition of septic shock and related clinical criteria. In the third survey, the task force members were given 4 choices for the septic shock updated criteria ([1] serum lactate level alone; [2] hypotension alone; [3] vasopressor-dependent hypotension or serum lactate level; [4] vasopressor-dependent hypotension and serum lactate level) and were asked to provide their first and second choices. The cumulative first or second choices were used to agree on the reported septic shock criteria.

Questionnaire items were accepted if agreement exceeded 65%. Choices for which agreement was less than 65% were rediscussed to achieve consensus or were eliminated, as appropriate to achieve the project aims. The survey questionnaires are presented in eMethods 2 in the Supplement.

Cohort Studies

The institutional review boards of Cooper University Hospital (Camden, New Jersey),15 University of Piitsburgh Medical Center (UPMC; a network of hospitals in western Pennsylvania), and Kaiser Permanente Northern California (KPNC)16 provided ethics approvals for research using the SSC and EHR data sets, respectively.

The SSC registry includes data collected from 218 hospitals in 18 countries on 28 150 patients with suspected infection who, despite adequate fluid resuscitation as judged by the collecting sites, still had 2 or more systemic inflammatory response syndrome criteria and 1 or more organ dysfunction criteria (eMethods 3 in the Supplement). The SSC database setup, inclusion, and reporting items are described in detail elsewhere.6,17 To select clinical criteria for the new septic shock definition, an analysis data set was created that included all patients with a serum lactate level measurement or a mean arterial pressure less than 65 mm Hg after fluids, or who received vasopressors.

For external validation, mortality was determined using the same clinical criteria in patients with suspected infection (cultures taken, antibiotics commenced) within 2 large EHR databases from UPMC (12 hospitals, 2010-2012, n = 1 309 025) and KPNC (20 hospitals, 2009-2013, n = 1 847 165). Three variables (hypotension, highest serum lactate level, and vasopressor therapy as a binary variable [yes/no]) were extracted from these 2 data sets during the 24-hour period after infection was suspected. Descriptive analyses, similar to those performed on the SSC data set, were then undertaken. Because of constraints on data availability, hypotension was considered present if systolic blood pressure was 100 mm Hg or less for any single measurement taken during the 24-hour period after infection was suspected. Serum lactate levels were measured in 9% of infected patients at UPMC and in 57% of those at KPNC after implementation of a sepsis quality improvement program.

Statistics
Meta-analysis

A random effects meta-analysis of septic shock mortality by study-specific septic shock criteria and sepsis definitions was performed. Two meta-regression models of septic shock mortality were tested with the covariates: sepsis definition, criteria for shock, mid–cohort-year of study population, single center or multicenter, and World Health Organization member state regions.18 These 2 models (with and without per capita intensive care unit beds) were generated to account for international cohorts and countries for which per capita intensive care unit bed data were unavailable (See eMethods 1 in the Supplement for details).

Cohort Studies

Hospital mortality was used as the primary outcome for derivation and descriptive validation analysis. Using the 3 dichotomous variables identified in round 2 of the Delphi process, the SSC cohort was divided into 6 groups and the variables tested either alone or in combination: (1) hypotension (mean arterial pressure <65 mm Hg) after fluid administration; (2) vasopressor therapy; and (3) serum lactate level greater than 2 mmol/L or 2 mmol/L or less (to convert serum lactate values to mg/dL, divide by 0.111). Hypotension was assumed when vasopressor therapy was being administered, generating 6 distinct potential septic shock patient groups using the 3 selected variables (eTable 5 in the Supplement). Analyses were performed using either the 6 groups or the 3 dichotomous variables as the risk factor. Subsequent analyses using the serum lactate level as a categorical variable were performed using a χ2 test of trend for mortality.

Currently, there are no gold standard septic shock criteria for predictive validity comparisons.8 Thus, these analyses aimed to identify a patient population that has the attributes of the newly proposed definition, which includes higher mortality compared with other patient populations commonly reported as having septic shock in the literature identified by the systematic review. Therefore, the independent relationship between the 3 potential criterion variables (hypotension, serum lactate level, and vasopressor therapy) agreed on the second round of the Delphi process and a future outcome (hospital mortality) was tested using 2 generalized estimating equation population-averaged logistic regression models with exchangeable correlation structure, where hospital site was the panel variable.

The first model used the potential septic shock groups 1 to 6 derived from these variables (eTable 5 in the Supplement), with group 1 as the referent group and adjusted for other covariates to assess true mortality difference between these groups. The second model assessed the independent association of these 3 potential criterion variables on hospital mortality adjusted for other covariates. These models also included an a priori adjustment variable for covariates including region (United States and Europe), location where sepsis was suspected (emergency department, ward, or critical care unit), antibiotic administration, steroid use, organ dysfunction (pulmonary, renal, hepatic, and acutely altered mental state), infection source (pneumonia, urinary tract infection, abdominal, meningitis and other), hyperthermia (>38.3°C), hypothermia (<36°C), chills with rigor, tachypnea (>20/min), leukopenia (<4000 cells/µL), hyperglycemia (plasma glucose level >120 mg/dL [6.7 mmol/L), platelet count <100 ×103/μL, and coagulopathy.

These models were used to estimate acute hospital mortality odds ratios (ORs) and adjusted ORs for mortality per-unit increase in the serum lactate level using continuous natural log–transformed serum lactate level. The operating characteristics (sensitivity/specificity over hospital mortality curves; positive and negative predictive values) of different serum lactate cutpoints (2, 3, and 4 mmol/L) were also tested using the logistic regression model. Multiple imputations (n = 20) were used to assess the statistical effect of missing serum lactate values.

P < .05 (2-sided) was considered statistically significant. All analyses were performed using Stata version 13.1 (StataCorp).

Results
Systematic Review and Meta-analysis

The systematic review identified 44 studies (166 479 patients) reporting septic shock mortality57,1959 from a total of 92 studies reporting sepsis cohorts between 1987 and 201557,19107 (Figure 1; eTable 2 in the Supplement). Different shock criteria were used for systolic blood pressure (<90 mm Hg; <100 mm Hg; decrease >40 mm Hg; or decrease >50% of baseline value if hypertensive), mean arterial pressure (<70; <65; <60 mm Hg), serum lactate level (>4, >2.5, >2, >1 mmol/L) and base deficit (−5 mmol/L) (Table 1; eTable 2 in the Supplement). Temporal relationships between resuscitation status and end points to shock diagnosis were seldom reported. The studies differed in the description of resuscitation, persistent hypotension, and in their vasopressor definitions when using the cardiovascular Sequential [Sepsis-related] Organ Failure Assessment (SOFA) score categories.113 Diverse infection and organ dysfunction codes were also used in the International Classification of Diseases–based derivations.63,70,79,90 Variables highlighted in Table 1 and in eTable 2 in the Supplement informed the Delphi survey questions.

The random-effects meta-analysis showed significant heterogeneity in septic shock mortality (mean mortality, 46.5% [95% CI, 42.7%-50.3%], with a near 4-fold variation from 23.0% to 81.8%; I2 = 99.5%; τ2 = 182.5; and P < .001) (Figure 2). Statistically significant heterogeneity was also observed in random-effects meta-analysis by clinical criteria reported for septic shock case definition in studies (Table 2). The meta-regression models described could not explain this heterogeneity (eTable 3A and eTable 3B in the Supplement).

Delphi Study

In the first round, informed by the systematic review, 15 task force members (88%) voted to include persistent hypotension, vasopressor therapy, and hyperlactatemia in the updated criteria. There was no agreement on the lower cutoff for serum lactate level in this round. Eleven members (65%) voted that including fluid resuscitation would improve the criteria. The task force determined that neither a severity grading for septic shock nor criteria for either adequacy of fluid resuscitation or persistent hypotension should be proposed because of the nonstandardized use of hemodynamic monitoring, resuscitation protocols, and vasopressor dosing in clinical practice. (Other results are reported in eTable 4 in the Supplement.)

In Delphi round 2, the task force was provided with a preliminary descriptive analysis from the SSC database. With agreement on the description of the septic shock illness concept, 3 test variables (hypotension after fluid resuscitation, vasopressor therapy, and serum lactate level) were agreed on for predictive validity analyses. The “after fluids” field in the SSC database was used as a proxy for resuscitation. The need for vasopressors was agreed as a proxy for persistent hypotension by 95% of the task force. Twelve members (71%) voted that a minimum vasopressor dose should not be proposed in view of the variability in blood pressure targets and resuscitation protocols identified by the systematic review, and because of variable sedation use. Vasopressor therapy was therefore treated as a binary variable within the analysis. To derive an optimal cutoff for serum lactate level, 13 task force members (77%) agreed on acute hospital mortality as the outcome variable. The test variables could be present either alone or in combinations, thus identifying 6 potential groups of patients with septic shock (Table 3; eTable 5 in the Supplement).

Prior to the final round of the Delphi process, all analyses from the SSC data set and the EHR data sets were provided. These findings generated the new definition—“septic shock is defined as a subset of sepsis in which underlying circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than sepsis alone”—and the clinical criteria described below.

Cohort Studies
SSC Database

Patients with serum lactate levels greater than 4 mmol/L who did not receive fluids as recommended by the SSC guidelines111 (n = 790 [2.8%]) were excluded. Patients without any serum lactate values measured were excluded initially for full case analysis (n = 4419 [15.7%]) but were reassessed in the missing data analysis. Of the 22 941 remaining patients, 4101 coded as having severe sepsis were excluded from this analysis, generating the analysis set of 18 840 patients who were either hypotensive after fluids or required vasopressors or had a serum lactate level measurement (Figure 3 and Table 3). Hypotension was reported in 83.1%, serum lactate level greater than 2 mmol/L in 78.1%, and receipt of vasopressors in 66.4%. Overall, crude hospital mortality was 34.7%. Cohort characteristics by setting are shown in eTable 6 in the Supplement.

Predictive Validity of Potential Septic Shock Groups

Of the 6 groups of potential patients with septic shock (Table 3), the most prevalent was group 1 (hypotension + vasopressor therapy + serum lactate level >2 mmol/L) (n = 8520); followed by groups 2 (n = 3985) and 4 (n = 3266). Crude hospital mortality rates in these 3 groups were 42.3%, 30.1%, and 25.7%, respectively. Statistically significant increasing trends in crude mortality were observed over increasing serum lactate level categories within groups (χ2 test of trend: P < .001 for groups 1 and 4, P = .04 for group 3). The adjusted OR for hospital mortality using group 1 for reference was significantly lower in all other groups (P < .01 for groups 2 to 6), suggesting that group 1 represents a distinct subpopulation with a significantly greater risk of death (eTable 7 in the Supplement). By a majority (cumulative first choice, 72.2%; second choice, 55.6%) (eTable 4 in the Supplement), the task force agreed that group 1 was most consistent with the proposed septic shock definition, thus generating the new septic shock criteria.

Derivation of Serum Lactate Cutoff Value and Missing Data Analysis

In the generalized estimating equation model (shown in eTable 8 in the Supplement), serum lactate level was associated with mortality, and the adjusted OR for hospital mortality increased linearly with increasing serum lactate level. An increase in serum lactate level from 2 to 10 mmol/L increased the adjusted OR for hospital mortality from 1.4 (95% CI, 1.35-1.45) to 3.03 (95% CI, 2.68-3.45) (referent lactate = 1; Figure 4). A serum lactate level greater than 2 mmol/L was chosen as the preferred cutoff value for the new septic shock criteria, the rationale being the trade-off between highest sensitivity (82.5% when using the n = 18 840 subset, and 74.9% when using patients in groups 1 and 2 combined [n = 12 475]), and the decision from the Delphi process to identify the lowest serum lactate level independently associated with a greater risk of death (OR of 1.4 at a lactate value of 2 mmol/L) (Table 4; eTable 9, eFigure 1, and eFigure 2 in the Supplement).

Predicated on this understanding of the SSC database structure and the regression analyses completed (eTable 6, eTable 7, and eTable 8 in the Supplement), we assumed that data were missing at random; ie, any difference between observed values and missing values did not depend on unobserved data. Complete case analysis was therefore performed, followed by multiple imputation analysis to support the missing-at-random assumption.114 The ORs for mortality per unit increase in serum lactate level using complete case analysis (n = 18 840) and imputed analyses (n = 22 182) were similar (1.09 [95% CI, 1.08-1.10]; P < .001 vs 1.09 [95% CI, 1.08-1.09]; P < .001, respectively). The imputed and complete case analysis probabilities of hospital mortality were also similar (36.4% and 35.5%, respectively).

EHR Data Sets

The UPMC and KPNC EHRs included 148 907 and 321 380 adult patients with suspected infection, respectively (eTable 10 in the Supplement). Forty-six percent (n = 5984) of UPMC patients and 39% (n = 54 135) of KPNC patients with 1 or more SOFA score points and suspected infection fulfilled criteria for 1 of the 6 potential septic shock groups described. Patients meeting group 1 criteria (hypotension + vasopressor therapy + serum lactate level >2 mmol/L) comprised 5.3% (UPMC) and 14.9% (KPNC) of the EHR population of patients with suspected infection and had a mortality of 54% and 35%, respectively. Similar to the SSC database, crude mortality rates within each group were higher among those with higher serum lactate levels (Table 5).

Discussion

The systematic review illustrated the variability in criteria currently used to identify septic shock, whereas the meta-analysis demonstrated the heterogeneity in mortality. Informed by this systematic review, a Delphi process was used to reach a consensus definition of septic shock and related clinical criteria. Three large data sets were then used to determine the predictive validity of these criteria. Septic shock was defined as a subset of sepsis in which circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than sepsis alone. The clinical criteria representing this definition were the need for vasopressor therapy to maintain a MAP of 65 mm Hg or greater and having a serum lactate level greater than 2 mmol/L persisting after fluid resuscitation.

The proposed definition and criteria of septic shock differ from prior definitions1,2,111 in 2 respects: (1) the need for both a serum lactate level and vasopressor-dependent hypotension (ie, cardiovascular SOFA score ≥2) instead of either alone and (2) a lower serum lactate level cutoff of 2 mmol/L vs 4 mmol/L as currently used in the SSC definitions. In the new septic shock definition, an increase in serum lactate level is positioned as a proxy for a cellular metabolic abnormality, and as a variable independently associated with acute mortality (predictive validity), which is consistent with the published literature.115118 An elevated serum lactate level is not specific for cellular dysfunction in sepsis118,119 but has face validity given the lack of a superior yet readily available alternative. This present study identifies a lower serum lactate level cutoff as an independent prognostic variable when compared with a recent analysis of the entire SSC database. This disparity is explained by using a data set of 18 840 patients in the analysis in this study rather than the total 28 150-patient SSC data set used by Casserly et al.17 From this subpopulation 6 groups were identified and analyzed as risk strata within the generalized estimating equation model and performance-tested for various serum lactate level cutoffs. The group with a significantly greater risk of death was then selected. In contrast, Casserly et al17 reported the independent relationship of hypotension and serum lactate levels with mortality in severe sepsis.

The 6 potential septic shock patient groups analyzed in this study also provide an explanation for the heterogeneity in septic shock mortality highlighted by the meta-analysis. Depending on the group selected, septic shock mortality ranged from 12.8% to 51.2% within the SSC data set and from 7.0% to 64.0% in the EHR data sets. The KPNC EHR data set corroborated the consistent trends of higher mortality associated with a higher serum lactate level, even in a population with a wider range of illness severity captured by more prevalent measurement of serum lactate levels.

The key strengths of the present study are in the methodology used to arrive at the new definition and clinical criteria for septic shock, a clinical syndrome with a range of signs, symptoms, and biochemical abnormalities that are not pathognomonic. Furthermore, the supporting studies (systematic review, Delphi process, and analyses of the SSC and EHR cohorts) were iterative and concurrent with the consensus process, a significant step forward from previous definitions.

This study also has several limitations. First, the systematic review did not formally assess study quality and was restricted to MEDLINE publications, adult populations, and observational studies reporting epidemiology. Second, only the Delphi-derived variables were tested in multiple data sets to generate the proposed septic shock criteria. Other variables, including tissue perfusion markers (eg, base deficit, oliguria, acute alteration in mentation), blood pressure characteristics (eg, diastolic pressure), resuscitation end points (eg, central venous saturation, lactate clearance), and numerous biomarkers reported in the literature,17 could potentially improve on the proposed septic shock criteria but were not included. However, operationalizing the definition of septic shock with 3 commonly measured variables should increase both generalizability and clinical utility. Third, the lack of a gold standard diagnostic criteria for septic shock8 precludes comparative assessment of these proposed criteria. Fourth, all data sets had missing data that could potentially introduce a form of selection bias.120 In the primary data set (SSC database) this issue was addressed by demonstrating that full case analysis is an appropriate method (see “Derivation of Serum Lactate Cutoff Value and Missing Data Analysis”). Fifth, serum lactate measurements are not universally available, especially outside of a critical care setting or in resource-limited environments. Although feasibility is a quality indicator for a definition,8 identification of a critically ill patient would generally trigger obtaining a serum lactate measurement, both to stratify risk and to monitor the response to treatment.17 Sixth, although the proposed new definition and clinical criteria for sepsis are arbitrary, these do have predictive validity for mortality, alongside face and content validity.8

This study represents one step in an ongoing iterative process and provides a resourceful structure and a predictive validity standard for future investigations in this area. Prospective validation of the clinical criteria may improve on the variables and cutoffs proposed herein, and identification and validation of novel markers of organ dysfunction and shock may replace lactate level.8

Conclusions

Based on a consensus process using results from a systematic review, surveys, and cohort studies, septic shock is defined as a subset of sepsis in which underlying circulatory, cellular, and metabolic abnormalities are associated with a greater risk of mortality than sepsis alone. Adult patients with septic shock can be identified using the clinical criteria of hypotension requiring use of vasopressors to maintain mean blood pressure of 65 mm Hg or greater and having a serum lactate level greater than 2 mmol/L persisting after adequate fluid resuscitation.

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Article Information

Corresponding Author: Manu Shankar-Hari, MD, MSc, Department of Critical Care Medicine, Guy’s and St Thomas’ NHS Foundation Trust, London SE1 7EH, United Kingdom (manu.shankar-hari@kcl.ac.uk).

Author Contributions: Dr Shankar-Hari had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Shankar-Hari, Levy, Deutschman, Angus, Rubenfeld, Singer.

Acquisition, analysis, or interpretation of data: Shankar-Hari, Phillips, Levy, Seymour, Liu, Singer.

Drafting of the manuscript: Shankar-Hari, Phillips, Levy, Deutschman, Angus, Singer.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Shankar-Hari, Phillips, Seymour, Liu.

Obtained funding: Levy.

Administrative, technical, or material support: Shankar-Hari, Levy, Deutschman, Angus.

Study supervision: Seymour, Deutschman, Singer.

Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Drs Shankar-Hari and Singer reported receiving support from the UK NIHR Biomedical Research Centre schemes. Dr Levy reported receiving a grant from ImmuneExpress. Dr Seymour reported receiving personal fees from Beckman Coulter. Dr Liu reported receiving K grant support from the National Institutes of Health (K23GM112018). Dr Deutschman reported holding patents on materials not related to this work and receiving travel/accommodations and related expenses for participation in meetings paid by the Centers for Disease Control and Prevention, World Federation of Societies of Intensive and Critical Care, Pennsylvania Assembly of Critical Care Medicine/PA Chapter, Society of Critical Care Medicine (SCCM)/Penn State–Hershey Medical Center, Society of Critical Care Medicine, Northern Ireland Society of Critical Care Medicine, International Sepsis Forum, Department of Anesthesiology, Stanford University, Acute Dialysis Quality Initiative, and European Society of Intensive Care Medicine (ESICM). Dr Singer reported serving on advisory boards for Bayer and Biotest and that he is a recipient of a UK NIHR Senior Investigator Fellowship (2009-2017). No other disclosures were reported.

Members of the Sepsis Definitions Task Force and Delphi Study: Derek Angus, Djilalli Annane, Michael Bauer, Rinaldo Bellomo, Gordon Bernard, Jean-Daniel Chiche, Craig Coopersmith, Cliff Deutschman (cochair), Richard Hotchkiss, Mitchell Levy, John Marshall, Greg Martin, Steve Opal, Gordon Rubenfeld, Christopher Seymour (co-opted), Manu Shankar-Hari (co-opted), Mervyn Singer (cochair), Tom van der Poll, Jean-Louis Vincent.

Funding/Support: The Sepsis Definitions Task Force received unrestricted funding support from the European Society of Intensive Care Medicine and the Society of Critical Care Medicine (sponsors).

Role of the Funders/Sponsors: The funders/sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Disclaimer: Dr Angus, JAMA Associate Editor, had no role in the evaluation of or decision to publish this article.

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