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Monitoring Ventilation with Capnography
Rafael Ortega, M.D., Christopher Connor, M.D., Ph.D., Sora Kim, B.S., Robin Djang, M.A., and Kunal Patel, M.D.
The following text summarizes information provided in the video. Overview

Carbon dioxide is generated in the body as a metabolicbyproduct. It dissolves in the blood and is transported in the bloodstream until it reaches the lungs, where it diffuses into the alveoli. The alveoli are ventilated through an open tracheobronchial tree and a patent upper airway. Carbon dioxide can then be detected in the patient’s expired breath. The measurement of expired carbon dioxide is useful because it can provide insight into importantlife-sustaining processes, including metabolic, circulatory, and respiratory activity. When satisfactory measurements of carbon dioxide cannot be made during patient exhalation, medically significant impairment of one or more of these processes may be present. Capnography is the standard of care for monitoring the adequacy of ventilation in patients receiving general anesthesia.1 It is also used tomonitor ventilation during procedures performed while the patient is under moderate or deep sedation. Capnography is increasingly being used to monitor patients who are receiving mechanical ventilation in intensive care units and to aid in the assessment and treatment of patients in cardiac arrest. Before capnography was available, physicians relied on noninvasive procedures, such asauscultation of the chest, to assess the adequacy of ventilation and the proper placement of endotracheal tubes, and on arterial blood gas analysis to determine the partial pressure of carbon dioxide. Capnography allows for noninvasive and continuous monitoring of carbon dioxide levels and can provide valuable information regarding the metabolic and respiratory condition of a patient. Although capnographyis not complicated, the clinician must understand the principles of capnography and the way in which the equipment works in order to interpret the information it provides.
Definitions

From Boston Medical Center, Boston. Address reprint requests to Dr. Ortega at the Department of Anesthesiology, Boston Medical Center, 88 E. Newton St., Boston, MA 02118, or at rafael.ortega@ bmc.org.
N Engl JMed 2012;367:e27. DOI: 10.1056/NEJMvcm1105237
Copyright © 2012 Massachusetts Medical Society.

Capnometry refers to the measurement and numerical display of carbon dioxide concentrations. Capnography refers to the graphic display of the concentration of exhaled and inhaled carbon dioxide plotted against time.2 Colorimetric capnography is a qualitative method of determining the presence ofcarbon dioxide using a pH-sensitive filter that changes color from purple to yellow when carbon dioxide is detected (Fig. 1). Paco2 denotes the partial pressure of carbon dioxide in arterial blood. Endtidal carbon dioxide (ETco2) is the percentage concentration, or partial pressure, of carbon dioxide at the end of exhalation. It is normally 5% of atmospheric pres- Figure 1. Colorimetric Carbon Dioxidesure, or approximately 38 mm Hg at sea level. Hypercapnia and hypercarbia refer Detector. to a greater-than-normal Paco2 in blood. Hypocapnia and hypocarbia refer to a lower-than-normal Paco2.

n engl j med 367;19

nejm.org

november 8, 2012

e27(1)

The New England Journal of Medicine Downloaded from nejm.org on December 6, 2012. For personal use only. No other uses withoutpermission. Copyright © 2012 Massachusetts Medical Society. All rights reserved.

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Indications

Capnography is used in the operating room to aid in the proper placement of endotracheal tubes and to monitor ventilation. Capnography is increasingly being used to assess the adequacy of ventilation and to monitor patients for hypercapnia or...