What do dead-space measurements tell us about the lung with acute respiratory distress syndrome?

In this issue of RESPIRATORY CARE, Kallet et al1 describe the prognostic value of sequential dead-space measurements in patients with acute respiratory distress syndrome (ARDS). The simple calculation using arterial and mixed expired partial pressures of carbon dioxide (the Enghoff modification of the Bohr dead-space equation: physiologic dead-space volume divided by tidal volume [VD/VT]) is more convenient to acquire the data for, and simpler than the calculation of shunt or venous admixture. The data from Kallet et al1 show that dead space is a useful index of lung dysfunction and a predictor of survival.