Original ContributionEnd-tidal carbon dioxide is associated with mortality and lactate in patients with suspected sepsis
Introduction
Severe sepsis and septic shock are responsible for significant morbidity and mortality among patients admitted to the emergency department (ED) [1]. Early identification and treatment of these disorders have been shown to improve survival [2], [3]. A hallmark of septic shock is hypoperfusion leading to end-organ damage and cardiovascular collapse [1], [4]. Lactic acidosis is a well-accepted marker for disease severity in this population [4], [5] and has been shown to predict mortality in ED patients with infection [6]. The physiologic response to metabolic acidosis is a compensatory respiratory alkalosis for maintenance of homeostasis. Capnography, a noninvasive, real-time method of determining exhaled end-tidal carbon dioxide (Etco2), has been shown to predict severe metabolic acidosis in diabetic ketoacidosis [7], [8] and gastroenteritis [9]. Recently, Etco2 levels were associated with lactic acidosis and organ dysfunction in febrile patients admitted to the ED [10].
Mortality rates have been shown to decrease as much as 16% when early goal-directed therapy is initiated [2]. A challenge in implementing early and aggressive therapy has been properly identifying appropriate patients because hemodynamic compensation may mask the severity of underlying disease. Although lactate levels provide a reliable insight into disease severity, they may not be rapidly or easily attainable. One group noted a period of up to 172 minutes from the time of ED triage for a whole blood lactate value to be obtained in patients with sepsis [11]. Such delay may prevent prompt initiation of treatment in a condition that is amenable to improved outcomes with early interventions. Faster, point-of-care lactate tests have shown promise in expediting this process but have not yet been widely implemented [11], [12]. A real-time, noninvasive marker of disease severity in patients with suspected sepsis may expedite recognition, triage, and therapeutic intervention in this patient population.
We examined a prospective cohort of patients presenting to a tertiary referral ED with suspected sepsis to investigate the association of Etco2 with both direct (mortality) and indirect (lactic acidosis) outcome measures. We hypothesized that lower Etco2 levels would be associated with mortality and that Etco2 levels would decline with more severe lactic acidosis.
Section snippets
Design and setting
We performed a prospective convenience sampling of ED patients presenting with suspected sepsis. Institutional review board at the participating hospital approved the study protocol. Written consent was waived by the institutional review board because capnography is considered standard of care for many circumstances in our ED. Patient enrollment occurred between January 1, 2009, and October 31, 2010.
The study was conducted in the ED of a large adult tertiary hospital with an annual census of
Results
For 22 months, we enrolled a total of 201 patients with a mean age of 65 years (range, 18-99 years). Across all subjects, the mean length of stay was 8.6 days (range, 1-54 days), in-hospital mortality was 14%, 36% were admitted to the ICU, 24% were put on vasopressors, and 31% were blood culture positive (see Table 1). As a group, nonsurviving patients presented with higher respiratory rates and lower systolic and diastolic blood pressures, as well as lower oxygen saturations (see Table 1).
Discussion
This study suggests that Etco2 concentration may perform similarly to lactate levels as a predictor for mortality in patients with suspected sepsis. This performance was comparable across sepsis categories, as well as in both spontaneously breathing patients and those who required emergent intubation upon presentation to the ED. Furthermore, when we controlled for potential predictors of mortality, such as age, use of pressors, admission to the ICU, mechanical ventilation, positive blood
Conclusions
In conclusion, in patients admitted to the hospital with suspected sepsis, a single Etco2 measurement in the ED may predict mortality. Capnography is fast, noninvasive, and relatively inexpensive. Further studies are necessary to determine if Etco2 can be used to decrease time to recognition and therapy of patients with sepsis, and if prehospital Etco2 levels can be used to expedite care.
Acknowledgments
We thank all members of the ED staff for their assistance.
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