Fig 1.
Components of dead space and volumetric capnography.
The expired tidal volume on the Y axis is plotted against the partial pressure of expired CO2 on the X axis in order to express the curve of ‘Volume = VCO2/FCO2’. Phase I represents CO2-free and pure dead space, phase II represents the transition between airway and alveolar gas, and phase III represents alveolar gas. Phase II ends at the inner square area maximum point. The VDaw is determined by applying Fowler’s equal area method (area A equals to B). The volume from the start of expiration to the partial pressure of mixed expired CO2 point on the Y axis is defined as respiratory dead space (VDresp). Thus, alveolar dead space (VDalv) is calculated as VDresp−VDaw, shunt dead space (VDshunt) is calculated as VDphys−VDresp. Abbreviations: VDphys, physiological dead space; VDaw, airway dead space; VDalv, alveolar dead space; VDshunt, shunt dead space; VTE, expired tidal volume; VCO2, expired tidal volume of CO2; FCO2, fractional concentration of CO2 [FCO2 = PCO2 (PB–PH2O)-1 = PCO2 (760–47)-1; PB, barometric pressure; PH2O, water vapor pressure at 37°C]; PECO2, mixed expired partial pressure of CO2; PETCO2, end-tidal partial pressure of CO2; PACO2, alveolar partial pressure of CO2; and PaCO2, arterial partial pressure of CO2 are expressed as FCO2 in this figure.
Table 1.
Interpretation of dead space components.
Fig 2.
CONSORT diagram of patient recruitment for the comparison of volume-controlled ventilation and pressure-controlled inverse ratio ventilation.
Table 2.
Patient and surgical characteristics, and the respiratory and hemodynamic parameters at TBaseline (20 min after the initial setting).
Table 3.
Respiratory and hemodynamic parameters during intervention.
Fig 3.
Correlation between static compliance and shunt dead space ratio (shunt dead space/expired tidal volume).
The correlation between static compliance and shunt dead space ratio was evaluated using Spearman’s rank correlation at T20min (open circle) and T2h (closed circle) in the volume-controlled ventilation (A) and pressure-controlled inverse ratio ventilation (B) groups.