10/12/2023 0 Comments Alveolar dead space ardsIt is accepted that positive-pressure ventilation increases (V D aw and (V D alv by dilating the conducting airways and by decreasing pulmonary capillary perfusion at the alveolar–capillary membrane, respectively. 8 Therefore, Bohr dead space ((V D Bohr) and its subcomponents of airway dead space ((V D aw) and alveolar dead space ((V D alv) have become available at the bedside on a breath-by-breath basis. 7 Today, true dead space according to Bohr's formula can be estimated because modern volumetric capnography can measure mean alveolar P CO 2 in a noninvasive way. Because this P aCO 2-based apparent dead space does not represents any real volume, it is also called fictitious dead space. 4 In the clinical field, V d is commonly estimated applying the Enghoff modification of Bohr's original formula, replacing the alveolar P CO 2 value with the arterial value (P aCO 2) 5, 6 This approach, however, contaminates the true dead space in which alveoli are ventilated but not perfused by the effect of shunting blood through non-ventilated lung areas. 1– 3 Using expired CO 2 as a tracer, volumetric capnography estimates dead space (V d) based on the mass balance equation originally described by Bohr. Volumetric capnography is a bedside tool to assess lung function and to adjust ventilatory settings in mechanically ventilated patients.
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