Carbon dioxide monitoring (capnography)
- Baruch Krauss, MD, EdM, FAAP
Baruch Krauss, MD, EdM, FAAP
- Associate Professor of Pediatrics
- Harvard Medical School
- Jay L Falk, MD
Jay L Falk, MD
- Clinical Professor of Medicine and Emergency Medicine
- University of Florida College of Medicine
- Section Editors
- Ron M Walls, MD, FRCPC, FAAEM
Ron M Walls, MD, FRCPC, FAAEM
- Editor-in-Chief — Adult and Pediatric Emergency Medicine
- Section Editor — Adult Resuscitation
- Neskey Family Professor of Emergency Medicine
- Harvard Medical School
- Brigham and Women's Hospital
- Susan B Torrey, MD
Susan B Torrey, MD
- Section Editor — Pediatric Resuscitation; Pediatric Trauma
- Director, Division of Pediatric Emergency Medicine
- Associate Professor of Emergency Medicine and Pediatrics (Clinical)
- NYU School of Medicine
- Deputy Editor
- Jonathan Grayzel, MD, FAAEM
Jonathan Grayzel, MD, FAAEM
- Senior Deputy Editor — UpToDate
- Deputy Editor — Emergency Medicine (Adult and Pediatric)
- Deputy Editor — Primary Care Sports Medicine (Adolescents and Adults)
- Assistant Professor of Emergency Medicine
- University of Massachusetts Medical School
The term capnography refers to the noninvasive measurement of the partial pressure of carbon dioxide (CO2) in exhaled breath expressed as the CO2 concentration over time. The relationship of CO2 concentration to time is graphically represented by the CO2 waveform, or capnogram (figure 1). Changes in the shape of the capnogram are diagnostic of disease conditions, while changes in end-tidal CO2 (EtCO2), the maximum CO2 concentration at the end of each tidal breath, can be used to assess disease severity and response to treatment. Capnography is also the most reliable indicator that an endotracheal tube is placed in the trachea after intubation.
Oxygenation and ventilation are distinct physiologic functions that must be assessed in both intubated and spontaneously breathing patients. Pulse oximetry provides instantaneous feedback about oxygenation. Capnography provides instantaneous information about ventilation (how effectively CO2 is being eliminated by the pulmonary system), perfusion (how effectively CO2 is being transported through the vascular system), and metabolism (how effectively CO2 is being produced by cellular metabolism).
Capnography became a routine part of anesthesia practice in Europe in the 1970s and in the United States in the 1980s. It is now part of the standard of care for all patients receiving general anesthesia and is an emerging standard of care in emergency medical services, emergency medicine, and intensive care.
This topic review will discuss the basic physiology and interpretation of capnography and its use in the emergency department.
PRINCIPLES OF OPERATION
Carbon dioxide (CO2) monitors measure gas concentration, or partial pressure, using one of two configurations: mainstream or sidestream. Mainstream devices measure respiratory gas (in this case CO2) directly from the airway, with the sensor located on the airway adapter at the hub of the endotracheal tube (ETT). Sidestream devices measure respiratory gas via nasal or nasal-oral cannula by aspirating a small sample from the exhaled breath through the cannula tubing to a sensor located inside the monitor (picture 1).
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- PRINCIPLES OF OPERATION
- CO2 WAVEFORM
- CLINICAL APPLICATIONS FOR INTUBATED PATIENTS
- Verification of ETT placement
- Monitoring ETT location during transport
- Effectiveness of CPR
- Return of spontaneous circulation
- Prognosis in cardiac arrest
- Cause of cardiac arrest
- Increased ICP and trauma prognosis
- CLINICAL APPLICATIONS FOR SPONTANEOUSLY BREATHING PATIENTS
- Critical illness and seizure
- Acute respiratory distress
- Procedural sedation
- Ventilation in obtunded or unconscious patients
- Detecting metabolic acidosis
- Prognosis in sepsis
- SUMMARY AND RECOMMENDATIONS