Читать книгу Manual of Equine Anesthesia and Analgesia - Группа авторов - Страница 201

 The ratio of physiologic dead space to the tidal volume (VD/VT) can be calculated using Enghoff's modification of the Bohr equation, which substitutes alveolar CO2 (PACO2) with arterial CO2 (PaCO2):

 This measurement is based on the fact that all expired CO2 comes from perfused alveoli and none from dead space.PECO2 in this equation is the CO2 content in the mixed expired gas, which is obtained under experimental conditions by sampling a mixture of the expired gas collected from a large bag or through a device that measures of expired CO2 content and expired volume over time.In clinical practice, end‐tidal CO2 can be used to follow trends in the VD/VT ratio.

 An increase in dead‐space ventilation necessitates an increase in minute ventilation in order to maintain alveolar ventilation. This results in an increase in the work of breathing required to maintain normal gas exchange in a spontaneously breathing patient. In a mechanically ventilated patient, an increase in dead space requires an adjustment in minute ventilation by increasing the respiratory rate or tidal volume settings. In a hemodynamically compromised patient, the latter changes may have negative cardiovascular consequences.