Anatomic dead space can be measured with the single breath method (see Chapter 18, Fig. Va = /R(Vt - Vd), where Va is alveolar ventilation, fR is respiratory frequency, Vt is tidal volume, and Vd is anatomic dead space. As described in Chapter 18, anatomic dead space reduces the fraction of the tidal volume that reaches the alveoli: Positive pressure ventilation (i.e.Ventilation is the first step in the O2 cascade, and the level of alveolar ventilation (Va) is the most important physiologic factor determining arterial Po2 for any given inspired Po2 and level of O2 demand (Vo2) in healthy lungs.Neck extension and jaw protrusion (can increase it twofold).General anesthesia – multifactorial, including loss of skeletal muscle tone and bronchoconstrictor tone.The ratio of physiologic dead space to tidal volume is usually about 1/3. ![]() Alveolar dead space is the volume of gas within unperfused alveoli (and thus not participating in gas exchange either) it is usually negligible in the healthy, awake patient. ![]() Anatomic dead space is the volume of gas within the conducting zone (as opposed to the transitional and respiratory zones) and includes the trachea, bronchus, bronchioles, and terminal bronchioles it is approximately 2 mL/kg in the upright position. Physiologic or total dead space is the sum of anatomic dead space and alveolar dead space. Dead space is the volume of a breath that does not participate in gas exchange.
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