Capnography

Capnography

Capnography CO2 mixing

Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO2) in respiratory gases. It is a vital tool in the field of anesthesiology, emergency medicine, and intensive care medicine. Capnography provides a rapid and reliable method to detect life-threatening conditions such as hypoventilation, esophageal intubation, and circulatory failure.

Principles of Capnography

Capnography is based on the principle that CO2 absorbs infrared radiation. A capnometer measures the amount of infrared light absorbed by CO2 molecules in a sample of exhaled air. The resulting data is displayed as a waveform known as a capnogram.

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Capnogram

A typical capnogram consists of four phases:

1. Phase I (Baseline): This phase represents the beginning of exhalation, where the air from the anatomical dead space is exhaled, containing little to no CO2. 2. Phase II (Ascending Phase): This phase shows the rapid rise in CO2 concentration as alveolar gas begins to mix with dead space gas. 3. Phase III (Alveolar Plateau): This phase represents the exhalation of alveolar gas, where the CO2 concentration reaches a plateau. 4. Phase IV (Descending Phase): This phase occurs during inhalation, where the CO2 concentration rapidly falls back to baseline.

Clinical Applications

Capnography is used in various clinical settings:

• Verification of Endotracheal Tube Placement: Capnography is the gold standard for confirming the correct placement of an endotracheal tube. A continuous capnogram indicates that the tube is in the trachea, not the esophagus.
• Monitoring Ventilation: Capnography provides real-time feedback on a patient's ventilatory status, allowing for the detection of hypoventilation or hyperventilation.
• Assessment of Circulatory Status: Changes in the capnogram can indicate alterations in cardiac output and perfusion, useful in cardiopulmonary resuscitation (CPR).

Types of Capnography

Capnometer schema

There are two main types of capnography:

• Mainstream Capnography: The sensor is placed directly in the breathing circuit, providing real-time measurements. It is commonly used in operating rooms.
• Sidestream Capnography: A small sample of exhaled gas is diverted to a sensor located away from the breathing circuit. This method is often used in non-intubated patients.

Capnometry vs. Capnography

Capnometry parts together

While capnography refers to the graphical representation of CO2 levels, capnometry refers to the numerical measurement of CO2 concentration. Both are essential in monitoring respiratory status, but capnography provides more detailed information through waveform analysis.

Related Pages

• Anesthesia
• Respiratory monitoring
• End-tidal CO2
• Pulse oximetry