![]() For patients that are already hypercarbic at baseline, drops in their alveolar ventilation will cause much higher changes in PaCO 2. Hypercapnia is usually caused when alveolar ventilation is low. Where k: unit correction constant of 0.863 Relationship is best defined by the equation: When the degree of hyperventilation is not enough to compensate, the patient’s PaCO 2 will rise. 48) and VDAnat is measured using Fowler’s method. VDPhys is measured using the Bohr equation (see p. As VDPhysVDAnat+VDAlv, the alveolar dead space can be calculated if VDPhys and VDAnat are known. With an increase in dead space, an increase in alveolar ventilation via hyperventilation is required to maintain PaCO 2. Alveolar dead space cannot be measured directly. This may be observed in patients with conditions that increase dead space such as obstructive lung disease. Changes in dead space, whether anatomic or physiologic, require changes in alveolar ventilation in order to maintain a constant PaCO 2. ![]() Therefore, alveolar ventilation, not minute ventilation, ultimately determines the elimination of CO 2 and thus PaCO 2. However, only a portion of what is inspired participates in gas exchange at the level of the alveoli and respiratory bronchioles and the rest remains as dead space. Holding V e RR V t constant, V a decreases with increasing RR (and corresponding decreasing V t). If all else is constant, V a increases with increasing RR and V t. Minute ventilation is determined by the product of tidal volume and respiratory rate. These forms of the dead space equation tell us three important things: If all else is constant, V a decreases with increasing V d. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |