Understanding capnography waveforms
MedEd Bytes
MedEd Bytes is a video series that offers a quick and digestible learning format that can help solidify your understanding of different therapies leveraged in patient monitoring and respiratory interventions. In this series, we’ll cover topics such as capnography waveforms, the technology behind pulse oximetry, modes of ventilation, and more. To stay up to date with the series, please subscribe to our YouTube channel or start watching the series below.
MedEd Bytes series:
Understanding capnography waveforms
Byte 1: Measuring capnography and pulse oximetry
Pulse oximetry monitors oxygenation while capnography monitors ventilation, and both monitoring systems provide important but different physiologic measurements.
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Byte 2: What is capnography?
Capnography monitors CO2 removal during breathing and provides a breath-by breath assessment of the patient’s ventilatory status. Although the numeric etCO2 value is important, the waveform is equally important.
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Byte 3: Technology overview
Traditional technologies such as colorimetric CO2 detectors, and mainstream and sidestream sampling lines have certain limitations that can contribute to inaccurate readings and can cause their use to be restricted with certain patient populations.
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Byte 4: Ventilation perfusion mismatching
The gradient, an indicator of V/Q status, is the difference between the arterial carbon dioxide partial pressure (PaCO2) and end-tidal carbon dioxide partial pressure (etCO2) values. We discuss the relationship between ventilation (V) and perfusion (Q), and what mismatching can look like.
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Byte 5: Normal capnography waveform
The capnography waveform depicts the concentration of CO2 in the breath and has a generally uniform square-like morphology with consistent frequency. In this video, we look at what normal respiratory rates and waveforms look like for healthy patients.
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Byte 6: Different phases in normal waveforms
We review the phases of a normal capnography waveform in detail: phase I, phase II, phase III, end-tidal CO2, and phase 0.
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Byte 7: Apnea
Apnea is defined as no breath for 10 seconds or longer. It is central in nature with no respiratory effort or obstruction respiratory effort. Learn what the capnography waveform can look like in this scenario.
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Byte 8: Hypoventilation
Hypoventilation occurs when there is build-up carbon dioxide because of insufficient elimination of the by-product. Learn what the capnography waveform can look like in this scenario.
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Byte 9: Hyperventilation
Hyperventilation occurs when there are low carbon dioxide levels resulting from excessive elimination through rapid, deep breathing or metabolic acidosis. Learn what the capnography waveform can look like in this scenario.
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Byte 10: Return of spontaneous circulation (ROSC)
During cardiorespiratory arrest, there is a massive systemic buildup of carbon dioxide. Return of spontaneous circulation results in a rapid and abrupt influx of CO2. Learn what the capnography waveform can look like in this scenario.
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Byte 11: Bradypnea with hypercarbia
During bradypnea or hypercarbia, there is the presence of an abnormally high carbon dioxide level in the circulating blood. Respiratory rate may vary but generally slow and below a rate of 12 breaths per minute, representing bradypnea. Learn what the capnography waveform can look like in this scenario.
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Byte 12: Rebreathing of CO2
During rebreathing of CO2, the breathing pattern or rhythm usually normal and occurs approximately once every 3 to 5 seconds. Learn what the capnography waveform can look like in this scenario.
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Byte 13: Hypopnea with bradypnea
Hypopnea is defined as shallow breathing less than 0.5 liters in an adult and bradypnea is defined as low respiratory rate less than 12 breaths per minute. Learn what the capnography waveform can look like in this scenario.
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Byte 14: Tachypnea with hypocarbia
In tachypnea, abnormally rapid breathing, with hypocarbia, reduced CO2, respiratory rate may vary but is generally rapid above a rate of 20 breathes per minute. Learn what the capnography waveform can look like in this scenario.
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Byte 15: Lower airway obstruction — bronchospasm
In cases of lower airway obstruction resulting from bronchospasm, respiratory rate may vary, but it is generally greater than 20 breaths per minute and is often accompanied by a reduced tidal volume. Learn what the capnography waveform can look like in this scenario.
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Byte 16: Asthma, COPD, and emphysema
With asthma, emphysema, or chronic obstructive pulmonary disease (COPD), respiratory rate may vary but is generally greater than 20 breaths per minute and often accompanied by a reduced tidal volume and wheezes or rhonchi may be present. Learn more about how these factors can impact capnography waveforms.
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Byte 17: Curare cleft
This capnogram is rarely seen, and it occurs in mechanically ventilated patients who make an effort to breath. Learn more about curare cleft and how it can impact capnography waveforms.
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The measurements provided through the RespArray™ patient monitor, including Nellcor™, Microstream™, and other vital signs, should not be used as the sole basis for diagnosis or therapy and are intended only as adjuncts to patient assessment.