Capnometer and Capnometry

CO2 MV 1.0 PROCEDURE:
Capnography comprises the continuous analysis and recording of carbon dioxide concentrations [CO2] in respiratory gases. Although the terms capnography and capnometry are sometimes considered synonymous, capnometry suggests measurement (ie, analysis alone) without a continuous written record or waveform.

CO2 MV 2.0 DESCRIPTION/DEFINITION:
For the purposes of this Guideline, capnography refers to the evaluation of the [CO2] in the respiratory gases of mechanically ventilated patients. A capnographic device incorporates one of two types of analyzers: mainstream or sidestream.(1,2) Mainstream analyzers insert a sampling window into the ventilator circuit for measurement of CO2, whereas a sidestream analyzer aspirates gas from the ventilator circuit, and the analysis occurs away from the ventilator circuit. Analyzers utilize infrared, mass or Raman spectra, or a photoacoustic spectra technology.(3,4)

CO2 MV 3.0 SETTING:
This procedure may be performed by trained health care personnel in any setting in which mechanically ventilated patients are found-for example, the hospital, the extended care facility, or during transport.

CO2 MV 4.0 INDICATIONS:
On the basis of available evidence, capnography should not be mandated for all patients receiving mechanical ventilatory support, but it may be indicated for

4.1 evaluation of the exhaled [CO2], especially end-tidal CO2, which is the maximum partial pressure of CO2 exhaled during a tidal breath (just prior to the beginning of inspiration) and is designated PetCO2;(5,6)

4.2 monitoring severity of pulmonary disease(5) and evaluating response to therapy, especially therapy intended to improve the ratio of dead space to tidal volume (VD/VT)(7,8) and the matching of ventilation to perfusion (V/Q),(9) and, possibly, to therapy intended to increase coronary blood flow;(5,10,11)

4.3 determining that tracheal rather than esophageal intubation has taken place (low or absent cardiac output may negate its use for this indication);(12-16)

4.4 continued monitoring of the integrity of the ventilatory circuit, including the artificial airway;(12,15)

4.5 evaluation of the efficiency of mechanical ventilatory support by determination of the difference between the arterial partial pressure for CO2 (PaCO2) and the PetCO2.(17,18)

4.6 reflecting CO2 elimination;(19)

4.7 monitoring adequacy of pulmonary and coronary blood flow;(10,11,20-22)

4.8 monitoring inspired CO2 when CO2 gas is being therapeutically administered;(23)

4.9 graphic evaluation of the ventilator-patient interface. Evaluation of the capnogram may be useful in detecting rebreathing of CO2, obstructive pulmonary disease, waning neuromuscular blockade ('curare cleft'), cardiogenic oscillations, esophageal intubation, cardiac arrest, and contamination of the monitor or sampling line with secretions or mucus.(24)

CO2 MV 5.0 CONTRAINDICATIONS:
There are no absolute contraindications to capnography in mechanically ventilated adults provided that the data obtained are evaluated with consideration given to the patient's clinical condition.

CO2 MV 6.0 HAZARDS/COMPLICATIONS:
Capnography with a clinically approved device is a safe, noninvasive test, associated with few hazards. With mainstream analyzers, the use of too large a sampling window may introduce an excessive amount of dead space into the ventilator circuit.(2,25) Care must be taken to minimize the amount of additional weight placed on the artificial airway by the addition of the sampling window or, in the case of a sidestream analyzer, the sampling line.

CO2 MV 7.0 LIMITATIONS OF PROCEDURE OR DEVICE:
Capnography, when performed using a device calibrated and operated as recommended by the manufacturer, has few limitations. It is important to note that although the capnograph provides valuable information about the efficiency of ventilation (as well as pulmonary and coronary perfusion), it is not a replacement or substitute for assessing the PaCO2.(17,24,26-28) The difference between PetCO2 and PaCO2 increases as dead-space volume increases. In fact, the difference between the PaCO2 and PetCO2 has been shown to vary within the same patient over time.(29-32)

Certain situations may affect the reliability of the capnogram. The extent to which the reliability is affected varies somewhat among types of devices (infrared,(33) photoacoustic, mass spectrometry, and Raman spectrometry). Limitations include

7.1 The composition of the respiratory gas mixture may affect the capnogram (depending on the measurement technology incorporated).

7.1.1 The infrared spectrum of CO2 has some similarities to the spectra for both oxygen and nitrous oxide.(33) High concentrations of either or both oxygen or nitrous oxide may affect the capnogram, and, therefore, a correction factor should be incorporated into the calibration of any capnograph used in such a setting.(34)

7.1.2 The reporting algorithm of some devices (primarily mass spectrometers) assumes that the only gases present in the sample are those that the device is capable of measuring.(35) When a gas that the mass spectrometer cannot detect (such as helium) is present, the reported values of CO2 are incorrectly elevated in proportion to the concentration of helium present.

7.2 The breathing frequency may affect the capnograph. High breathing frequencies may exceed the response capabilities of the capnograph.(36) In addition, the breathing frequency, above 10 breaths/min, has been shown to affect devices differently.(37)

7.3 The presence of Freon (used as a propellant in metered dose inhalers) in the respiratory gas has been shown to artificially increase the CO2 reading of mass spectrometers (ie, to show an apparent increase in [CO2]). A similar effect has not yet been demonstrated with Raman or infrared spectrometers.(38)

7.4 Contamination of the monitor or sampling system by secretions or condensate, a sample tube of excessive length, a sampling rate that is too high, or obstruction of the sampling chamber can lead to unreliable results.

CO2 MV 8.0 ASSESSMENT OF NEED:
Capnography is considered a standard of care during anesthesia.(12) The Society of Critical Care Medicine has suggested that capnography be available in every ICU.(39) Assessment of the need to use capnography with a specific patient should be guided by the clinical situation. The patient's primary cause of respiratory failure and the acuteness of his or her condition should be considered. Patients with severe dynamic disease, such as ARDS, should be considered candidates for capnography.(5,6)

CO2 MV 9.0 ASSESSMENT OF OUTCOME:
Results should reflect the patient's condition and should validate the basis for ordering the monitoring. Documentation of results (along with all ventilatory, and hemodynamic variables available), therapeutic interventions, and/or clinical decisions made based on the capnogram should be included in the patient's chart.

CO2 MV 10.0 RESOURCES:
10.1 Equipment: The capnograph and accessories (eg, airway adapter, sampling tube, depending on capnograph). The capnograph should be calibrated as recommended by the manufacturer, with calibration quality gases in the clinical range of [CO2].

10.2 Personnel: Licensed or credentialed respiratory care practitioners or individuals with similar credentials (eg, MD, RN) who have the necessary training and demonstrated skills to correctly calibrate and evaluate the capnograph, assess the patient and the patient-ventilator system, and the ability to exercise appropriate clinical judgment.

CO2 MV 11.0 MONITORING:
During capnography the following should be considered and monitored

11.1 ventilatory variables: tidal volume, respiratory rate, positive end-expiratory pressure, inspiratory-to-expiratory time ratio (I:E), peak airway pressure, and concentrations of respiratory gas mixture;(24,26)

11.2 hemodynamic variables: systemic and pulmonary blood pressures, cardiac output, shunt, and ventilation-perfusion imbalances.(24,26)

CO2 MV 12.0 FREQUENCY:
Capnography (or, at least, capnometry) should be available during endotracheal intubation.(12,13,15,26) Capnography is not indicated for every mechanically ventilated patient; however, when it is used, the measurement period should be long enough to allow determination of the PaCO2-PetCO2 difference, note changes in PaCO2-PetCO2 difference as a result of therapy, and allow interpretation of observed trends.

CO2 MV 13.0 INFECTION CONTROL:
No specific precautions are necessary although Universal Precautions (as described by the Centers for Disease Control & Prevention)(40) and precautions designed to limit the spread of tuberculosis(41) should always be implemented during patient care.

13.1 The sensor (the portion of the device contacting the patient's airway) should be subjected to high-level disinfection between patients, according to the manufacturer's recommendations.

13.2 The monitor (the portion not contacting the patient or the patient's airway) should be cleaned as needed according to manufacturer's recommendations.

Applications:

• bronchial asthma of light and middle heaviness in the period of remission;
• respiratory allergoses in the stage of remission;
• chronicle bronchitis with breathing deficiency of 1-2 degree in the stage of remission;
• unfollowed peptic ulcer of stomach and duodenum in the stage of cicatrizing or remission;
• period of convalescence after pneumonia;
• first stage hypertension without clinical or functional symptoms of coronary deficiency;
• neurocirculatory dystonia, vascular dystonia;
• hyperventilation syndrome;
• ischemia out of exacerbation without clinical and functional symptoms of coronary deficiency.

Contra-indications:

• exacerbation of main disease;
• Clinical or laboratory symptoms of endocrine disorder;
• coronary deficiency of the 2-3 stage;
• breath deficiency of the 3 stage;
• chronic pulmonary heart in the stage of sub- or decompensation;
• serious disorder of heart rhythms and conductivity;
• serious diseases of central nerve system or affective disorders.

Mechanical Ventilation Focus Group

• Robert S Campbell RRT, Chairman, Cincinnati OH
• Richard D Branson RRT, Cincinnati OH
• William "Chuck" Burke PhD RRT, Indianapolis
• Jack Covington RRT BA CPFT, San Francisco CA
• John Graybeal CRTT, Hershey PA

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