anatomical dead space physiological dead space

RADFORD EP., Jr Ventilation standards for use in artificial respiration.Effect of pulmonary artery occlusion upon end-tidal carbon dioxide tension. JULIAN DG, TRAVIS DM, ROBIN ED, CRUMP CH.Change in PaCO2 with mechanical dead space during artificial ventilation. Effects of changes in respiratory pattern on physiological dead space. Links to PubMed are also available for Selected References. Get a printable copy (PDF file) of the complete article (711K), or click on a page image below to browse page by page. Full textįull text is available as a scanned copy of the original print version. The second equation requires an estimated Vd an and is applicable when Pa CO 2 is not measured or does not plateau (as in exercise). This fraction is ( Pa CO 2/Pa CO 2) 2, where Pa CO 2 and Pa CO 2 are the mean partial pressures of expired alveolar and of arterial CO 2 in the other equation this fraction is 2 where Pe CO 2 is mixed expired Pco 2 and Vd an is anatomical dead space.

The fraction of Vd m subtracted from Vd n is the square of the ratio of effective alveolar to total alveolar ventilation and is never > 1. With only a small modification, these equations are suitable for routine clinical use and give Vd p/ Vt within 0.02 of that by the validated equations (32 of 33 comparisons). To make the proper correction for Vd m, two equations have been derived and validated with seven subjects having Vd p/ Vt from 0.29 to 0.87, using Vd m's from 120 to 322 ml. Under these conditions the traditional subtraction of Vd m from Vd n leads to underestimation of Vd p and can give a falsely small ratio of Vd p to tidal volume ( Vt) when, in fact, an abnormally large Vd p/ Vt exists. When physiological dead space ( Vd p) is calculated for a patient who has alveolar dead space, e.g., after pulmonary vascular occlusion, less than the full volume of attached mechanical dead space ( Vd m) appears in the measured dead space ( Vd n).

Anatomical dead space physiological dead space