Can Transcutaneous CO2 Tension Be Used to Calculate Ventilatory Dead Space? A Pilot Study

Dead space fraction () measurement performed using volumetric capnography requires arterial blood gas (ABG) sampling to estimate the partial pressure of carbon dioxide (). In recent years, transcutaneous capnography () has emerged as a noninvasive method of estimating . We hypothesized that CO2 can be used as a substitute for in the calculation of . In this prospective pilot comparison study, 30 consecutive postcardiac surgery mechanically ventilated patients had calculated separately using volumetric capnography by substituting CO2 for . The mean calculated using and CO2 was 0.48 ± 0.09 and 0.53 ± 0.08, respectively, with a strong positive correlation between the two methods of calculation (Pearson’s correlation = 0.87, ). Bland-Altman analysis showed a mean difference of −0.05 (95% CI: −0.01 to −0.09) between the two methods. CO2 measurements can provide a noninvasive means to measure , thus accessing important physiologic information and prognostic assessment in patients receiving mechanical ventilation.