Respiratory dead space is that portion of the respiratory system not involved in gas exchange. The percent of tidal volume involved in ventilation of dead space is a measure of respiratory efficiency.
Bohr equation of dead space
(dead space volume) / (tidal volume) =
= ((PACO2) - (PCO2 of expiratory gas sample)) / (PACO2)
Since PaCO2 approximates PACO2, this becomes:
Physiologic dead space
= ((PaCO2) - (PCO2 of expiratory gas sample)) / (PaCO2)
• The normal ((dead space volume) / (tidal volume)) ratio is 0.2 - 0.3.
• Increased dead space ventilation can be seen in patients with ventilation of distal air spaces with nonfunctioning alveoli or in patients on ventilators with high mean airway pressures
To read more or access our algorithms and calculators, please log in or register.