CO2 Pocket Guide [PDF]

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Use of Capnography During Intubation

Capnography is the sensing of exhaled CO2. Carbon dioxide is produced in the body as a by-product of metabolism and is eliminated by exhaling.

Carbon dioxide is eliminated from the lungs, but not from the stomach or esophagus (unless a carbonated beverage has been consumed). It is easy to determine when a tube, such as an endotracheal or nasogastric tube, has been placed in the trachea. When tracheal placement occurs, a capnogram shows exhaled CO2.

By measuring exhaled CO2, many types of pulmonary assessments can be made.

Capnogram after successful placement of endotracheal tube

CO2 Monitoring RN, DNS, CCRN, CS

If esophageal placement occurs, a flat line occurs or no CO2 is detected. Flat line indicating the endotracheal tube is not in the trachea or the patient has become disconnected from the ventilator

PETCO2 (or end-expiration)

Slow rise in CO2 with plateau at end-expiration

A supplement to CRITICAL CARE NURSE® Agilent #5968-9027E Printed in USA 2/00

Expiration

Beginning of inspiration

Detecting Disconnection from Mechanical Ventilation Capnography is the fastest way to determine if a patient has become disconnected from the ventilator. Capnography, unlike ventilator alarms, monitors the patient. Immediately upon disconnection from the ventilator, the waveform on the capnogram disappears and goes flat.

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Characteristics of a Normal Capnogram

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• Detecting esophageal placement of endotracheal tubes during intubation. • Detecting tracheal placement of nasogastric tubes. • Disconnection of the patient from mechanical ventilation. • Predicting survival in cardiopulmonay resuscitation. • Avoiding ABG analysis in selected clinical sitiuations. • Detecting changes in dead space (eg, pulmonary emboli). • Identifying end-expiration on hemodynamic waves. • Identifying alveolar emptying (eg, effectiveness of bronchodilator therapy). • Identifying attempts to breathe while paralyzed.

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By Tom Ahrens,

Applications of Capnography

HP Card.Capnography.pages

What Is Capnography?

Avoiding Unnecessary Arterial Blood Gas Testing

Predicting Survival in Cardiopulmonary Arrest

Normally, the PETCO2 level correlates closely with PaCO2. The PETCO2 is usually 1 to 5 mm Hg lower than the PaCO2. The difference between the PaCO2 and PETCO2 is called the PaCO2-PETCO2 gradient.

When the PaCO2-PETCO2 gradient is normal, the PaCO2 can be estimated from the PETCO2. It is important to note the gradient when results of ABG analysis are obtained.

Exhaled CO2, specifically PETCO2, is a noninvasive indicator of cardiac output. The lower the cardiac output, the lower the PETCO2. If PETCO2 is less than 10 mm Hg after 20 minutes of cardiopulmonary resuscitation, the code is almost always unsuccessful.

· VE 5 L/min PETCO2 40

· Q 5 L/min

2.5 2.5 46

5

5 40

– CO 2 Pw

Pa C

O2

C Pa

PaCO2 40 Pulmonary Capillaries

· VE 5 L/min PETCO2

· Q 5 L/min

· 5 Q · O2

Capnogram during cardiopulmonary arrest showing a PETCO2 of 21 mm Hg

Dip in the exhaled capnogram wave indicating a spontaneous breathing attempt

Exhaled air from the poorly perfused part of the lung contains a very small amount of CO2. This reduced CO2 level is detected by capnography.

End-Expiration in Hemodynamic Waveforms By locating the PETCO2 level, end-expiration is often easily identified through the use of capnography.

C Pa

40

O2

20

5

VE·

5

VE

O 2

C Pa

Pa C

Embolism

40

The higher the PETCO2, the more effective the resuscitation efforts.

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When a condition such as pulmonary embolism (PE) occurs, blood flow to a part of the lung is decreased.

In a patient who is paralyzed, one of the first indications of incomplete paralysis is movement of the diaphragm, which can be detected by noting a dip in the capnogram waveform.

Recognizing the Adequacy of Alveolar Emptying PaCO2 40

Two patients with shortness of breath and a potential diagnosis of pulmonary emboli Patient 1

Patient 2

PaCO2

36 mm Hg

39 mm Hg

PETCO2

32 mm Hg

21 mm Hg

Interpretation

No significant PE. Normal PaCO2-PETCO2 gradient.

PE should be considered. Widened PaCO2-PETCO2 gradient.

Abnormal capnogram waveform showing ineffective bronchodilator therapy.

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40

Capnogram during cardiopulmonary arrest showing a PETCO2 of 8 mm Hg

If the ªE has changed, it is probably unwise to estimate PaCO2 from the PETCO2.

Recognizing Spontaneous Breathing Attempts in a Patient Who Is Paralyzed

Alveoli

46

O 2

When using PETCO2 to estimate PaCO2, it is helpful to simultaneously measure expired ventilation (ªE). If the ªE and PETCO2 remain constant, then the PaCO2-PETCO2 gradient is unlikely to have changed.

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Normally, if the PaCO2 increases, so will the PETCO2. The relationship between the PaCO2 and PETCO2 is lost when the pulmonary dead space increases.

HP Card.Capnography.pages

Detecting Changes in Pulmonary Dead Space

End-expiration indicated by waves in the circle

Decrease in PETCO2 indicates where to locate end-expiration