3 The prognostic value of V D/V T has been linked to mortality risk in ARDS 4– 7 and to other important clinical indices. All conducting airways (anatomical and mechanical dead space), areas of pure shunt (pulmonary capillary perfusion with no ventilation), areas of pure dead space, and the presence of gas exchange units with any degree of inequality of ventilation in relation to perfusion, can contribute to the calculated dead-space ventilation.Īssessing V D/V T in critically ill patients during mechanical ventilation is important for several reasons. The definition of pure dead space is ventilation without perfusion, whereby alveolar gases do not contact blood flowing through the pulmonary capillaries. 2 Physiologic dead-space fraction (dead space divided by tidal volume ), as defined by Bohr and Enghoff, is the sum of anatomic or airway dead space (V D-anat) and alveolar dead space (V D-alv) divided by the V T. Dead-space ventilation, the portion of a tidal volume that does not contribute to gas exchange, was first described and calculated by the Bohr equation in 1891, 1 and later by the Enghoff modification of the Bohr equation in 1938.

Adding dead space to ventilator