Patient Care

Use End-tidal Carbon Dioxide to Diagnose Sepsis

Issue 3 and Volume 39.

Early identification of sepsis provides the best opportunity for aggressive goal-directed therapy that may improve survival. Screening tools, protocols and alert systems have been shown to improve guideline adherence for interventions such as antibiotics and fluid resuscitation. EMS personnel are caring for an increasing number of septic patients, and prehospital screening tools for severe sepsis have been developed to improve awareness.1

Most of these screening tools rely on the suspicion of infection, >- 2 systemic inflammatory response syndrome (SIRS) criteria, and point-of-care serum lactate levels. However, it’s possible to screen for severe sepsis without these costly devices and potentially time-consuming blood draws.

Capnography, the waveform measurement of exhaled end-tidal carbon dioxide (EtCO2), is a well-known tool in EMS. EtCO2 is a continuous variable determined by basal metabolic rate, cardiac output and ventilation. Thus, abnormal levels may reflect derangement in perfusion, metabolism or gas exchange. Capnography has multiple prehospital applications for confirmation and monitoring of proper endotracheal tube placement, and evaluating return of spontaneous circulation during cardiopulmonary arrest. However, it can be very effective when used on the conscious patient to detect conditions such as septic shock.

Severe sepsis is characterized by poor perfusion, leading to a buildup of serum lactate and resulting metabolic acidosis. EtCO2 levels decline in the setting of both poor perfusion and metabolic acidosis. To compensate for metabolic acidosis, patients increase their minute ventilation. This increased respiratory rate “blows off” carbon dioxide and lowers EtCO2. At the same time, poor tissue perfusion decreases the amount of blood flow to the alveoli of the lungs, reducing the amount of carbon dioxide that can be exhaled—the most dramatic demonstration of this process is during cardiac arrest. Therefore, EtCO2 is inversely proportional to lactate: As lactate levels rise in septic patients, EtCO2 levels drop.

Previous studies have shown that low EtCO2 levels correlate with elevated lactate levels and predict mortality in patients with suspected sepsis, severe sepsis and septic shock.2,3 In fact, low prehospital EtCO2 levels predict metabolic acidosis and mortality across a wide spectrum of patient complaints.4

In patients with >- 2 SIRS criteria, an EtCO2 measurement of -< 25 mmHg is strongly correlated with lactate levels > 4 mM/L and increased mortality.Capnography is fast, non-invasive and available on many ALS vehicles. An adequate screening for severe sepsis may be provided by utilizing capnography in addition to modified SIRS criteria in the setting of suspected infection. Furthermore, capnography can be monitored to assess the impact of therapies designed to improve perfusion.

The Orange County (Fla.) EMS System, with assistance from our regional hospitals, has developed a Sepsis Alert protocol utilizing low EtCO2 as an equivalent to elevated serum lactate. This has allowed our agency’s discretion to utilize their existing equipment rather than purchase approved lactate monitors. Prospective evaluation of this protocol is currently ongoing. 


1. Seymour CW, Rea TD, Khan JM, et al. Severe sepsis in prehospital emergency care: Analysis of incidence, care, and outcome. Am J Respir Crit Care Med. 2012;186(12):1264–1271.

2. Hunter CL, Silvestri S, Dean M, et al. End-tidal carbon dioxide is associated with lactate levels and mortality in emergency department patients with suspected sepsis.Am J Emerg Med. 2013;31(1): 64–71.

3. McGillicuddy DC, Tang A, Cataldo L, et al. Evaluation of end-tidal carbon dioxide role in predicting elevated SOFA scores and lactic acidosis. Intern Emerg Med. 2009;4(1):41–44.

4. Hunter CL, Silvestri S, Ralls G, et al. The sixth vital sign: Pre-hospital end tidal carbon dioxide predicts in-hospital mortality and metabolic disturbances. Am J Emerg Med. Nov. 6, 2013. [ePub ahead of print.]



Sepsis is a rapidly progressing, life-threatening condition due to systemic infection. Sepsis must be recognized early and treated aggressively to prevent progression to shock and death. Sepsis can be identified when the following markers of the SIRS are present in a patient with suspected infection:

>> Temperature > 38 degrees C (100.4 degrees F) OR < 36 degrees C (96.8 degrees F);

>> Respiratory rate > 20 breaths per min; and

>> Heart rate > 90 beats per min.

In addition to physiologic markers of SIRS, severe sepsis may cause hypoxia and inadequate organ perfusion, resulting in metabolic acidosis marked by elevated blood lactate levels and decreased EtCO2 levels (measured by capnography).


The purpose of a sepsis alert is to provide pre-arrival ED notification in order to facilitate rapid assessment and treatment of a suspected severe sepsis patient. A sepsis alert will be instituted for patients meeting the following three criteria:

1. Suspected infection;

2. Present with two or more markers of SIRS; and

3. EtCO2 -< 25 mmHg OR lactate > 4 mmol.


>> Supplemental 100% oxygen


>> Full ALS assessment and treatment

>> Notify hospital of incoming sepsis alert prior to arrival

>> IV 0.9% NaCl en route

  • Administer 250 mL boluses until systolic BP > 90 mmHg
  • Total amount of IVF should not exceed 2000 mL
  • Boluses may be given in rapid succession if systolic remains < 90 mmHg

>> If systolic BP remains < 90 mmHg after 4th fluid bolus (1000 mL):

  • Dopamine infusion at 5–20 mcg/kg/min titrated to maintain systolic BP > 90 mm Hg