What is end-tidal capnography?
End-tidal capnography or end-tidal CO2 (EtCO2) monitoring is a non-invasive technique that measures the partial pressure or maximal concentration of carbon dioxide (CO2) at the end of an exhaled breath. The normal values are 5-6% CO2, which is equivalent to 35-45 mmHg. When CO2 diffuses out of the lungs into the exhaled air, a device called a capnometer measures the partial pressure or maximal concentration of CO2 at the end of exhalation and depicts it graphically as a capnogram. It provides information on ventilation, perfusion, and metabolism, which is important for airway management.
What are the four phases of the capnogram?
Capnogram (measured by the capnometer) is used in airway management to monitor the respiration levels. Below are the four phases of capnography:
- Phase I: It is called the beginning of exhalation or baseline, and there is no carbon dioxide (CO2) present. In this phase, no gas exchange occurs; hence, it is usually called a dead space (air in tubing and bronchus).
- Phase II: In this phase, CO2 from the lungs reaches the upper airway and mixes with dead space air, which causes a rapid increase in CO2. Carbon is detected using capnogram in exhaled air. It is also called an ascending phase or early exhalation.
- Phase III: In this phase, there is CO2 recorded uniformly in the nose/mouth and lungs.
- Phase IV: It is called an end-tidal phase. It shows the start of inspiration. Normal end-tidal CO2 values are 35-45 mmHg. This phase is also called a descending phase because oxygen fills when inhalation begins and CO2 concentration decreases.
When is end-tidal capnography recommended?
Usually, end-tidal capnography is used by emergency physicians and paramedics to determine the respiration of the patient. End-tidal capnography can also be used in the following settings:
- General anesthesia administration
- Procedural sedation, including sedation with monitored anesthesia care
- Analysis of ventilation (e.g., in the intensive care unit [ICU])
- Monitoring patients with heart and breathing diseases
- Sleep studies for patients having sleep apnea (breathing problem during sleeping)
- Monitoring the position of an endotracheal tube (ETT) or a blind insertion airway device.
In which conditions end-tidal capnography readings are abnormal?
Patients with below conditions have abnormal end-tidal capnography readings:
- Abnormally high body temperature
- Shivering
- Severe infection conditions like sepsis
- Endocrine disease
- Slow breathing patients
- Low heart rate patients
- Blood clots in the lungs (pulmonary embolism)
Is capnography really useful?
Carbon dioxide (CO2) levels in the blood are incredibly important for proper oxygenation and metabolism, that’s why capnography is very useful. An irregular amount of CO2 in a patient’s breath and the degree of that irregularity can tell healthcare providers a great deal about the condition and treatment required. It can inform you about the human body’s functions in an emergency situation, and it can often do so before any other measurement. Because its utility expands beyond just hospitals into pre-hospital emergency settings, its advantages become increasingly clear, and it becomes easier to consider capnography as a valuable tool that it is for emergency medical services. It helps paramedics to help critically ill patient’s condition by giving readings during chest compressions and breathing assessments.
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