Ventilation/Perfusion Changes During Mechanical Ventilation

¹ Associate Professor, Anesthesiology

Changes in arterial blood gases occurring during mechanical ventilation of a patient with extensive pulmonary disease have been presented. The Pa₀₂ and A-aDO₂ values observed in this patient demonstrate that various areas of V_A/Q imbalance exist simultaneously in the diseased lung. By altering the tidal volume and the pressure transmitted to the pulmonary capillary bed, the proportion of various types of V_A/Q match or mismatch can be changed almost instantaneously. These findings suggest that single determinations of arterial oxygen tension cannot be used to predict what will happen from moment to moment nor at changing patterns of ventilation. Considerable thought and effort should be given to the feasibility of continuous monitoring and recording of arterial oxygen tension.