It’s called anatomic because it’s fixed by anatomy and doesn’t change.Ībout a third of each normal breath we take is anatomic dead space, which means that a third of each breath is essentially wasted. It consists of conducting airways such as the trachea, bronchi, and bronchioles -structures that don’t have alveoli. Anatomic Dead SpaceĪnatomic deadspace consists of the parts of the respiratory tract that are ventilated but not perfused. They all impact how well a patient ventilates. There are three types of dead space: anatomic, physiologic, and that dead space belonging to any airway equipment being used to assist ventilation. Dead space is the portion of the respiratory system where tidal volume doesn’t participate in gas exchange: it is ventilated but not perfused. One important contributor to ventilation perfusion mismatch is dead space. It will help you understand how you can use these concepts to care for your patient. This article will describe how dead space is different from shunt. Physiologic dead space is ventilation of poor perfused alveoli. Depending on the disease condition, additional mechanisms that can contribute to an elevated physiological dead space measurement include shunt, a substantial increase in overall V'A/Q' ratio, diffusion impairment, and ventilation delivered to unperfused alveolar spaces.Shunt is perfusion of poorly ventilated alveoli. For the range of physiological abnormalities associated with an increased physiological dead space measurement, increased alveolar ventilation/perfusion ratio (V'A/Q') heterogeneity has been the most important pathophysiological mechanism. Although a frequently cited explanation for an elevated dead space measurement has been the development of alveolar regions receiving no perfusion, evidence for this mechanism is lacking in both of these disease settings. An elevated physiological dead space, calculated from measurements of arterial CO2 and mixed expired CO2, has proven to be a useful clinical marker of prognosis both for patients with acute respiratory distress syndrome and for patients with severe heart failure.
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