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<\/a><\/figure>\n\n\n\nSingle breath CO2 analysis: insight into the patient\u2018s lung condition<\/h3>\n\n\n\n
The volumetric capnogram can also be divided into three areas:<\/p>\n\n\n\n
- \n
- Area X \u2011 CO2 elimination<\/li>\n\n\n\n
- Area Y \u2011 Alveolar dead space<\/li>\n\n\n\n
- Area Z \u2011 Anatomical dead space<\/li>\n<\/ul>\n\n\n\n
The size of the areas, as well as the form of the curve, can give you more insight into the patient\u2018s lung condition regarding:<\/p>\n\n\n\n
- \n
- Dead space fraction \u2011 VDaw \/VTE<\/li>\n\n\n\n
- Alveolar minute ventilation \u2011 V\u2018alv<\/li>\n<\/ul>\n\n\n\n
In the illustration (Figure 1) you can see:<\/p>\n\n\n\n
- \n
- Slope of Phase III<\/li>\n\n\n\n
- Slope of Phase II<\/li>\n\n\n\n
- The intersection of lines 1 and 2 defines the limit between Phases II and III<\/li>\n\n\n\n
- A perpendicular line is projected onto the X\u2011axis and its position is adjusted until the areas p and q on both sides become equal<\/li>\n<\/ol>\n\n\n\n
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<\/a><\/figure>\n\n\n\nFigure 1: The three areas of the volumetric capnogram<\/sup><\/p>\n\n\n\n
<\/h3>\n\n\n\n
Area X \u2011 CO2 elimination (V\u2018CO2)<\/h3>\n\n\n\n
Area X represents the actual volume of CO2 exhaled in one breath (VeCO2). Adding up all of the single breaths in one minute gives you the total elimination of CO2 per minute (V\u2018CO2). If cardiac output, lung perfusion, and ventilation are stable, this is an assessment of the production of CO2 called V\u2018CO2. The V\u2018CO2 value displayed on the ventilator can be affected by any change in CO2 production, cardiac output, lung perfusion, and ventilation. It indicates instantly how the patient\u2019s gas exchange responds to a change in ventilator settings. Monitoring trends allows for detection of sudden and rapid changes in V\u2018CO2<\/a> (Figure 2).<\/p>\n\n\n\n
Good to know:<\/strong><\/p>\n\n\n\n
Decreasing V\u2018CO2: Hypothermia, deep sedation, hypothyroidism, paralysis, and brain death decrease CO2 production and induce a decrease in V\u2018CO2. Decreasing V\u2018CO2 can also be due to a decrease in cardiac output or blood loss, and may also suggest a change in blood flow to the lung areas. Pulmonary embolism, for example, exhibits V\u2018CO2 reduction and a slope reduction in Phase II.<\/p>\n\n\n\n
Increase in V\u2018CO2: An increase in V'CO2 is usually due to bicarbonate infusion or an increase in CO2 production that can be caused by:<\/p>\n\n\n\n
- \n
- Fever<\/li>\n\n\n\n
- Sepsis<\/li>\n\n\n\n
- Seizures<\/li>\n\n\n\n
- Hyperthyroidism<\/li>\n\n\n\n
- Insulin therapy<\/li>\n<\/ul>\n\n\n\n
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<\/a><\/figure>\n\n\n\nFigure 2: Area X of the volumetric capnogram<\/sup><\/p>\n\n\n\n
<\/h3>\n\n\n\n
Area Y \u2011 Alveolar dead space<\/h3>\n\n\n\n
Area Y represents the amount of CO2 that is not eliminated due to alveolar dead space (Figure 3).<\/p>\n\n\n\n
Good to know:<\/strong><\/p>\n\n\n\n
Increase: Alveolar dead space is increased in cases of lung emphysema, lung overdistension, pulmonary embolism, pulmonary hypertension, and cardiac output compromise.<\/p>\n\n\n\n
Decrease:\u00a0If the above mentioned conditions improve due to successful therapy, the alveolar dead space decreases.<\/p>\n\n\n\n
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<\/a><\/figure>\n\n\n\nFigure 3: Area Y of the volumetric capnogram<\/sup><\/p>\n\n\n\n
<\/h3>\n\n\n\n
Area Z \u2011 Anatomical dead space<\/h3>\n\n\n\n
Anatomical dead space measurement using a volumetric capnogram gives an effective, in\u2011vivo measure of volume lost in the conducting airway. This area represents a volume without CO2. It does not take part in the gas exchange and consists of the airway, endotracheal tube, and artificial accessories, such as a flextube positioned between the CO2 sensor and the patient (Figure 4).<\/p>\n\n\n\n
Good to know:<\/strong><\/p>\n\n\n\n
Expansion of Area Z: An expansion of Area Z can indicate an increase in anatomical dead space ventilation (VDaw). Consider a reduction in your artificial dead space volume.<\/p>\n\n\n\n
Diminution of Area Z:\u00a0A diminution of Area Z is seen when the artificial dead space volume is decreased and when excessive PEEP is decreased.<\/p>\n\n\n\n
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<\/a><\/figure>\n\n\n\nFigure 4: Area Z of the volumetric capnogram<\/sup><\/p>\n\n\n\n
<\/h3>\n\n\n\n
Alveolar minute ventilation \u2011 V\u2018alv<\/h3>\n\n\n\n
Phase III of the waveform represents the quantity of gas that comes from the alveoli and actively participates in gas exchange. V\u2018alv is calculated<\/a> by subtracting the anatomical dead space (VDaw) from the tidal volume (VTE) multiplied by the respiratory rate from the minute volume (MinVol): V\u2019alv =RR*Vtalv = RR*(VTE\u2011VDaw) (Figure 5).<\/p>\n\n\n\n
Good to know:<\/strong><\/p>\n\n\n\n
Increase: An increase in V\u2018alv is seen after an efficient recruitment maneuver and induces a transient increase in V\u2018CO2.<\/p>\n\n\n\n
Decrease:\u00a0A decrease in V\u2018alv can indicate that fewer alveoli are participating in the gas exchange, for example, due to pulmonary edema.<\/p>\n\n\n\n![\"\"](\"https:\/\/csccm.org.cn\/wp-content\/uploads\/2024\/03\/f0aa5100085caad10e28b91a8aa59fbcc8e42db9-1024x576.png\")
<\/a><\/figure>\n\n\n\nFigure 5: PetCO2 before and after recruitment<\/sup><\/p>\n\n\n\n
<\/h3>\n\n\n\n
Dead space ventilation \u2011 VDaw\/VTE ratio<\/h3>\n\n\n\n
The ratio of airway dead space (VDaw) to tidal volume (VTE) \u2011 the VDaw\/VTE ratio \u2011 gives you an insight into the effectiveness of ventilation<\/a> (Figure 6).<\/p>\n\n\n\n
Good to know:<\/strong> A rising VDaw\/VTE ratio can be a sign of ARDS.<\/p>\n\n\n\n
- \n
- In a normal lung, the VDaw\/VTE ratio is between 25% and 30%.<\/li>\n\n\n\n
- In early ARDS, it is between 58% and up to 83%.<\/li>\n<\/ul>\n\n\n\n
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<\/a><\/figure>\n\n\n\nFigure 6: Dead space ventilation<\/sup><\/p>\n\n\n\n
<\/h3>\n\n\n\n
Volumetric capnography on Hamilton Medical ventilators<\/h3>\n\n\n\n
All Hamilton Medical ventilators offer volumetric capnography<\/a> (All models except HAMILTON\u2011MR1A\u200b). It is available as an option on the HAMILTON\u2011C6, the HAMILTON\u2011G5, the HAMILTON\u2011C3, and the HAMILTON\u2011C1\/T1, and as a standard feature on the HAMILTON\u2011S1.<\/p>\n\n\n\n
Author: <\/strong>Karjaghli Munir, Respiratory Therapist, Hamilton Medical Clinical Application Specialist; Matthias Himmelstoss, ICU Nurse, MSc Physics, Product Manager<\/p>\n\n\n\n
Date of first publication: <\/strong>16.11.2023<\/p>\n\n\n\n
Source: Hamilton Medical<\/a><\/strong><\/p>\n\n\n\n
References:<\/strong><\/p>\n\n\n\n
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- Wolff G, X. B. J. , Weibel W., Bowes C.L. , Muchenberger R., Bertschmann W. (1989). Anatomical and series dead space volume: concept and measurement in clinical practice. Applied cardiopulmonary pathophysiology, 2, 299\u2011307.<\/li>\n<\/ol>\n\n\n\n
\u00ab\u00ab Cell-Based Therapies for ARDS <\/a><\/p>\n\n\n\n