![]() Since it is not perfused, oxygen can’t be absorbed and carbon dioxide cannot be eliminated- that air here is wasted breath. It consists of conducting airways such as the trachea, bronchi, and bronchioles -structures that don’t have alveoli. Types of Dead Space Anatomic Dead SpaceĪnatomic dead space consists of the fixed parts of the respiratory tract that are ventilated but not perfused. There are three types of dead space: anatomic, physiologic, and the dead space belonging to any airway equipment being used to assist ventilation. What Is Dead Space?ĭead space is the portion of the respiratory system where tidal volume doesn’t participate in gas exchange. This article discusses the concept of dead space and it’s clinical use in recognizing hypoventilation and preventing hypoxia and hypercarbia. ![]() Having a tidal volume close to, or smaller than the patient’s dead space can lead to significant hypercarbia, hypoxia, and respiratory failure. A more subtle sign is that tidal volume becomes shallower. The most obvious sign is slowing of the rate of breathing. ![]() Hypoventilation from sedation, pain medications, anesthesia in the immediate postoperative period is common. 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.Understanding anatomic dead space is important to recognizing subtle hypoventilation. 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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