Updated June 23, 2014
Evolution in EMS practice continues at an increasing pace. Assessing the level of exhaled carbon dioxide is a good example of such progress; from its first use for endotracheal tube placement confirmation, we have come to value the use of end tidal carbon dioxide (EtCO2) monitoring in EMS practice. We can anticipate an evolving role of CO2 monitoring in future clinical decision-making.
The American Society of Anesthesiology made continuous CO2 monitoring of sedated patients the standard of care in the early 1990s. With the expansion of the use of procedures requiring sedation outside of the operating room, the Joint Commission mandated the use of CO2 monitoring to ensure the safety of patients undergoing procedural sedation in 2001. Since 1995, EMS has experienced a variable acceptance of CO2 monitoring as the market responded to this evolving need (Levine, 1997).
Basic CO2 concepts
Carbon dioxide is a byproduct of metabolism. It is measured at its highest concentration at the end of an exhaled breath. This is called end-tidal CO2 (EtCO2). Exhaled CO2 values indirectly correlate with cardiac output. The normal concentration of CO2 is generally between 35–45 mmHg.
CO2 monitoring is effective at evaluating respiratory states associated with hypoventilation, hyperventilation, and bronchospasm. It has been shown to improve the determination of hypoxia (Coté et al., 1991).
An elevated exhaled CO2 level is usually an indication of hypoventilation or increased metabolic activity. A low exhaled CO2 level may be an indication of hyperventilation, decreased cardiac output or poor pulmonary perfusion, as often seen in shock.
Clinical applications in intubated patients
CO2 monitoring has become the gold standard in verifying endotracheal tube placement (Silvestri et al., 2005).
Using CO2 monitoring has become an invaluable clinical tool in evaluating patients in cardiac arrest. According to the 2010 American Heart Association (AHA) Guidelines for CPR and ECC, CO2 monitoring is important in:
- Determining the effectiveness of compressions during CPR. Decreasing CO2 values less than 10 mmHg may indicate that it is time to change the person providing compressions or that compressions are not hard and fast enough.
- Recognizing the return of spontaneous circulation (ROSC). A rapid rise in CO2 may indicate ROSC, while consistent values less than 10 mmHg despite effective compressions and ventilations can indicate clinical death. This can help prehospital providers determine when to cease resuscitative efforts (Levine, et al., 1997).
- Determining the effectiveness of ventilations with a BVM device or an advanced airway such as a combitube, laryngeal mask airway or a supraglottic airway.
The expanded uses of CO2 monitoring include clinical considerations in the treatment of diabetics, head injuries, COPD, asthma, CHF, pulmonary embolism, and return of spontaneous circulation (ROSC).
Monitoring CO2 in trauma
CO2 monitoring is useful in the ventilatory management of patients with chest wall injuries. Adjusting the rate and depth of ventilations to return exhaled CO2 levels to a normal range is the best method to ensure that patients are not being hyperventilated unnecessarily.
If indicated, hyperventilation may be acceptable for brief management periods in patients experiencing cerebral herniation. CO2 levels of 25 to 30 mmHg may be the preferred range for patients with herniation associated with acute neurologic deterioration (Brain Trauma Foundation, 2010).
It has been suggested that the use of capnography is beneficial in monitoring intubated major trauma patients for hypercapnia and hypoventilation (Hiller et al., 2010).
Assessing respiratory conditions with EtCO2
CO2 monitoring can be effectively used during the assessment and management of asthma and chronic obstructive pulmonary disease (COPD) patients to determine the next level of treatment. If CO2 levels remain above 45 mmHg despite ventilatory assistance and bronchodilators, CPAP or intubation may be needed.
Capnography levels of patients receiving CPAP treatment can be continually monitored through use of a special nasal cannula fitted with a CO2 sensor.
Other clinical applications
CO2 monitoring can be useful in determining if patients need ventilatory assistance after receiving sedation, prior to electrical therapy or during pain management. Rising CO2 values above 45 mmHg can indicate hypoventilation (Krauss & Hess, 2007).
CO2 monitoring can be a useful tool to determine the presence of DKA. The rapid and deep respirations often seen in diabetic ketoacidosis (DKA) can cause the CO2 levels to fall below 29 mmHg. A 2002 pediatric study demonstrated that among diabetic children who presented to the emergency department with an EtCO2 of less than 29 mmHg, 95% were in ketoacidosis, whereas if the EtCO2 was greater than 36 mmHg, no ketoacidosis was found (Fearon & Steele, 2002).
CO2 monitoring is rapidly becoming commonplace in EMS practice, Providers will find an increasing need for its use as more situations are evaluated for its effectiveness. It’s likely that EtCO2 monitoring will become a mainstay tool in the EMT or paramedic’s toolbox.
References
Brain Trauma Foundation. Guidelines for the Management of Severe Traumatic Brain Injury. http://www2.braintrauma.org
Coté CJ, Rolf N, Liu LM, et al. A single-blind study of combined pulse oximetry and capnography in children. Anesthesiology. 1991;74:980–987.
Fearon DM, Steele DW. End-tidal carbon dioxide predicts the presence and severity of acidosis in children with diabetes. Acad Emerg Med. 2002;9:1373–1378.
Krauss B, Hess D. Capnography for procedural sedation and analgesia in the emergency department. Ann Emerg Med. 2007;50:172–181.
Hiller J, Silvers A, McIliroy DR, et al. A retrospective observational study examining the admission arterial to end-tidal carbon dioxide gradient in intubated major trauma patients. Anaesth Intensive Care. 2010;38:302–306.
Levine RL, Wayne MA, Miller CC. End-tidal carbon dioxide and outcome of out-of-hospital cardiac arrest. N Engl J Med. 1997;337: 301–306.
Silvestri S, Ralls GA, Krauss B, et al. The effectiveness of out-of-hospital use of continuous end-tidal carbon dioxide monitoring on the rate of unrecognized misplaced intubation within a regional emergency medical services system. Ann Emerg Med. 2005;45:497–503.
