Show Summary Details
Page of

A Breath of Fresh Air—Ventilation 

A Breath of Fresh Air—Ventilation
A Breath of Fresh Air—Ventilation

James R. Munis

Page of

PRINTED FROM OXFORD MEDICINE ONLINE ( © Oxford University Press, 2021. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single chapter of a title in Oxford Medicine Online for personal use (for details see Privacy Policy and Legal Notice).

date: 09 May 2021

The sine qua non of ventilation is arterial carbon dioxide. If you want to know about ventilation, just check the PaCO2. If it is low or normal, ventilation is fine, regardless of any other parameter, including respiratory rate, tidal volume, or dead space ratio. However, if PaCO2 is high, then alveolar ventilation (VA) is impaired (relative to the carbon dioxide load being presented to the lungs). In a conventional breathing circuit, dead space ends at the Y-shaped junction of the inspiratory and expiratory arms of the circuit and the endotracheal tube. On the machine side of that junction, the inspiratory and expiratory limbs see only fresh inspired or expired gas, respectively, but not both. You should know 2 other things about ventilation. One is the Bohr equation, which estimates the ratio of dead space to tidal volume. The anatomic dead space is estimated as the expired volume that coincides with half maximal nitrogen content. The second thing is the effect of gravity on the distribution of ventilation within the lung.

Access to the complete content on Oxford Medicine Online requires a subscription or purchase. Public users are able to search the site and view the abstracts for each book and chapter without a subscription.

Please subscribe or login to access full text content.

If you have purchased a print title that contains an access token, please see the token for information about how to register your code.

For questions on access or troubleshooting, please check our FAQs, and if you can't find the answer there, please contact us.