The volumetric capnography loop displayed is from a passive patient ventilated in PC mode. What does its shape tell us?
Airway dead space seems to be in the normal range; it is calculated by the ventilator to be 114 ml.
The slope of Phase II is flatter than usual, suggesting an increase in airway resistance.
The slope of Phase III is increased, suggesting considerable heterogeneity in the lung with alveoli having a widely varying ventilation/perfusion ratio.
PetCO2 is low with a large gradient between PaCO2 and PetCO2, which confirms the severe ventilation/perfusion mismatching.
This is a patient with COPD with pneumonia ventilated with PEEP of 12 cmH2O. The PEEP setting may not have been appropriate in this case.
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