1. Why is this topic important? Detection and risk stratification of emergency department (ED) patients with infection and sepsis is necessary to optimize treatment and disposition. While high lactate has been traditionally useful for identification of patients with evidence of shock at risk of 28-day mortality, it is unclear how well lactate risk stratifies patients who are initially stable, and whether low lactate levels are adequate to rule out future short-term deterioration. This prospective cohort study aimed to identify the role of initial serum lactate in the prediction of short-term deterioration among patients presenting to the ED and not requiring critical care interventions within the first hour. Both admitted and discharged patients were included. While an initial lactate ≥ 4.0 mmol/L was highly predictive of short-term deterioration (specificity of 97%; positive likelihood ratio of 10.7), a lactate ≥ 2.0 mmol/L did not adequately capture patients at risk of deterioration (sensitivity of 67%; negative likelihood ratio of 0.5). Emergency physicians will often encounter septic patients who are hemodynamically stable, and must appropriately risk stratify and disposition them, based on their risk of short-term deterioration. While a lactate ≥ 4.0 mmol/L suitably identifies patients at high risk of short-term deterioration (and thereby necessitating disposition to a highly monitored setting), a lactate < 2.0 mmol/L does not reliably rule out short-term deterioration in these patients.
2. What does this study attempt to show?
3. What are the key findings?
4. How is patient care affected?
Original ContributionsHelpful Only When Elevated: Initial Serum Lactate in Stable Emergency Department Patients with Sepsis Is Specific, but Not Sensitive for Future Deterioration
Introduction
In the emergency department (ED), identification of patients with sepsis is critical, as it allows for the prompt initiation of appropriate resuscitation, including fluids and antibiotics (1). Once diagnosis is made and treatment is initiated, risk stratification (i.e., determining risk of future deterioration) of this patient population is difficult and ultimately paramount in determining the disposition of the patient (2). While many patients with severe sepsis or septic shock will require critical care in the intensive care unit (ICU), some patients are stable enough for management on the wards. However, patients who subsequently deteriorate on the wards and then require ICU admission have worse outcomes than those who are admitted directly to the ICU from the ED 3, 4, 5. It is therefore important to identify patients at risk of short-term deterioration at an early stage (6). Recent work in this area has focused on the utility of early warnings scores, and decision tools, such as the quick Sequential Organ Failure Assessment (qSOFA) (7). Unfortunately, the early data show that such tools have variable accuracy when tested in the ED setting, both prospectively and retrospectively, and include variables that are already suggestive of deterioration, such as hypotension 8, 9, 10, 11.
Serum biomarkers present an interesting avenue for investigation in risk stratification of ED patients with sepsis and, to date, > 180 different biomarkers have been linked with this disease process (12). Perhaps the biomarker of greatest interest to emergency physicians is serum lactate 13, 14. In the septic ED patient, lactate elevation occurs for several reasons, but the most common is inadequate tissue oxygenation (15). Most of the evidence surrounding the utilization of lactate in ED septic patients comes from patients admitted to hospital, where a lactate level ≥ 4.0 mmol/L is highly specific for in-hospital mortality (16). Hyperlactatemia is also a poor prognostic sign in these admitted patients, independent of evidence of organ hypoperfusion or shock, and regardless of the presumed etiology 14, 17, 18, 19. Furthermore, improved outcomes in patients with septic shock have been associated with clearance of lactate 20, 21. However, little is known regarding the use of lactate in risk stratification of ED patients not admitted to hospital, or about the ability of this biomarker to predict short-term deterioration (an important decision for the ED clinician in determining disposition). Furthermore, there are few published data on low lactate levels (i.e., < 2.0 mmol/L) and the prognostic value of a low lactate level in ruling out deterioration in ED patients with sepsis. Several studies have espoused the idea of cryptic shock, suggesting that patients who are hemodynamically stable, yet with evidence of hyperlactatemia, may in fact be in true shock, despite what would appear to be blood pressure capable of providing adequate organ perfusion 22, 23. Given this, we aimed to test the ability of initial ED serum lactate in predicting future deterioration among initially stable ED patients (defined as those not requiring endotracheal intubation, initiation of vasopressors or inotropes, or ICU admission, within the first hour following ED arrival). Additionally, with regard to patients with intermediate lactate levels (2.0–3.9 mmol/L), we sought to determine any differences between those who deteriorated and those who did not, as patients in this group are often the most difficult to prognosticate, and up to one-quarter may progress to septic shock (24).
Section snippets
Materials and Methods
This study was approved by the Albert Einstein College of Medicine Institutional Review Board.
Study Design
This was a prospective observational cohort study of adult ED patients satisfying the 1992 Society of Critical Care Medicine (SCCM)/American College of Chest Physicians (ACCP) criteria for diagnosis of sepsis, and performed in the EDs of the Montefiore Medical Center (Moses and Einstein campuses), both urban, academic EDs in Bronx, NY, with a combined annual adult census of > 190,000 visits per year (25). Salaried, trained, fluently bilingual (English and Spanish) ED research associates
Results
A total of 985 patients meeting the 1992 SCCM/ACCP criteria for diagnosis of sepsis were enrolled in the study. Selection of patients is depicted in Figure 1. Patients were stratified by initial serum lactate level into the following groups: < 2.0 mmol/L (n = 623), 2.0–3.9 mmol/L (n = 323), and ≥ 4.0 mmol/L (n = 39). Baseline characteristics are depicted in Table 1. Altogether, 84 patients (8.5%) met the primary outcome. Of these, 39 (46.4%) met the primary outcome while in the ED. Of the 66
Discussion
Risk stratification (i.e., determining risk of future deterioration) of patients presenting to the ED with infection remains of paramount importance in optimizing disposition and outcomes (26). Although promising, existing tools for risk stratification, such as the qSOFA, have shown varying accuracy when prospectively and retrospectively applied to ED patients with suspected infection 8, 9, 10, 11, 27. Biomarkers (particularly serum lactate) represent an important potential avenue for risk
Conclusions
In keeping with existing research, we found that significant hyperlactatemia (i.e., ≥ 4.0 mmol/L) was highly predictive of future deterioration in this population. However, we found that low serum lactate (i.e., < 2.0 mmol/L) was poorly sensitive for detecting patients at risk for future deterioration. Therefore, while a high lactate level is concerning, a low lactate level is not useful in ruling out future deterioration, and ED clinicians should not be reassured by a low lactate level.
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2020, Journal of Thoracic Disease
Andrew J. E. Seely holds patents related to multi-organ variability analysis, and has shares in Therapeutic Monitoring Systems Inc., a company whose mission is to help deliver waveform-based, variability-directed clinical decision support products to the bedside to improve care.
This work was presented at the 2017 annual meeting of the Canadian Association of Emergency Physicians in Whistler, British Columbia, Canada, where it was the “Top Resident Research Abstract” (to Shannon M. Fernando). It was presented in the plenary session entitled “The Top 4: The Best of Canadian EM Research” on June 6, 2017.