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Tag: Lung mechanics

Monitoring during mechanical ventilation: MECHANICS DURING MECHANICAL VENTILATION (5)

From measurements of pressure and VT, it is possible to calculate mean airway pressure (P aw), resistance, compliance and work of breathing (Table 1). Many of the desired and deleterious effects of mechanical ventilation are determined by P aw. Factors Read More

Monitoring during mechanical ventilation: MECHANICS DURING MECHANICAL VENTILATION (4)

Evaluation of the static pressure-volume (P-V) curve may be useful for patients with acute respiratory distress syndrome (ARDS). In such patients, the P-V curve typically has a sigmoidal shape with an inflection point at low lung volume (lower Pflex) and Read More

Monitoring during mechanical ventilation: MECHANICS DURING MECHANICAL VENTILATION (3)

An end-expiratory pause can be used to determine autoPEEP. This method is only valid if the patient is not actively breathing and there are no system leaks (eg, circuit leak or bronchopleural fistula). For patients who are actively breathing, an Read More

Monitoring during mechanical ventilation: MECHANICS DURING MECHANICAL VENTILATION (2)

During pressure ventilation, PIP and Pplat may be equal. This is due to the flow waveform that occurs during this mode of ventilation. With pressure ventilation, flow decreases during inspiration and is often followed by a period of zero-flow at Read More

Monitoring during mechanical ventilation: MECHANICS DURING MECHANICAL VENTILATION (1)

With volume ventilation, airway pressure increases during inspiration as volume is delivered. The peak inspiratory pressure (PIP) varies directly with resistance, end-inspiratory flow, VT and elastance (ie, inversely with compliance). An end-inspiratory pause of sufficient duration (0.5 to 2.0 s) Read More

Monitoring during mechanical ventilation: INDIRECT CALORIMETRY (4)

The breath-by-breath calorimeter analyzes FiO2, fractional concentration of oxygen in expired gas (F E O2), F E CO2 and VT with each breath. This obviates the need for a mixing chamber. The system uses the same gas analysis and volume Read More

Monitoring during mechanical ventilation: INDIRECT CALORIMETRY (3)

The closed circuit calorimeter uses a volumetric spirometer, a mixing chamber, a carbon dioxide analyzer and a carbon dioxide absorber. The spirometer is filled with a known volume of oxygen. As the patient rebreathes, oxygen is consumed and carbon dioxide Read More

Monitoring during mechanical ventilation: INDIRECT CALORIMETRY (2)

Exhaled gas from the patient is directed into a mixing chamber. At the end of the mixing chamber, a vacuum pump aspirates a small sample of gas for measurement of oxygen and carbon dioxide. The entire volume of gas then Read More

Monitoring during mechanical ventilation: MIXED VENOUS OXYGENATION (2)

C v O2 (and its components P v O2 and mixed venous oxygen saturation [Sv O2]) is decreased with decreases in CaO2 (ie, PaO2, SaO2 or hemoglobin), decreases in Q or increases in V O2. Note that an increase in Read More

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