The NICO 2 provides a standard, expired single-breath C[O.sub.2] waveform that can be divided into three phases (Figure 1); Phase I represents C[O.sub.2]-free gas expired from the large airway and tracheal tube dead space, Phase H represents a mixture of gas from both the large airway dead space and alveolar dead space
and Phase III (or alveolar plateau) represents alveolar ventilation (13,14).
They vary from extremely low (bordering shunting) to exceptionally high (approaching alveolar dead space
Along the second axis, increased alveolar dead space
, commonly due to acute lung injury, volume overload, obstructive lung disease, hypovolemia, excess PEEP or pulmonary arterial occlusion, impairs the lung's CO2-exchanging efficiency.
Pulmonary embolism is a pulmonary vascular disease that is characterized by high [V.sub.A] [Q.sub.C] ratios and alveolar dead space
Similarly, alveoli receiving ventilation, but no perfusion have a [dot.V]/[dot.Q] ratio of [infinity], and are alveolar dead space