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Updated: Mar 14, 2026

Expired CO2 Measurement in Intubated or Spontaneously Breathing Patients from the Emergency Department
Published on: January 29, 2011
Can Transcutaneous CO2 Tension Be Used to Calculate Ventilatory Dead Space? A Pilot Study
Pradeep H Lakshminarayana1, Adiba A Geeti1, Umer M Darr2
1Section of Pulmonary, Critical Care and Sleep Medicine, Bridgeport Hospital, Yale New Haven Health, 267 Grant Street, Bridgeport, CT 06610, USA.
Abstract:
Dead space fraction (V d/V t) measurement performed using volumetric capnography requires arterial blood gas (ABG) sampling to estimate the partial pressure of carbon dioxide (PaCO2). In recent years, transcutaneous capnography (PtcCO2) has emerged as a noninvasive method of estimating PaCO2. We hypothesized that PtcCO2 can be used as a substitute for PaCO2 in the calculation of V d/V t. In this prospective pilot comparison study, 30 consecutive postcardiac surgery mechanically ventilated patients had V d/V t calculated separately using volumetric capnography by substituting PtcCO2 for PaCO2. The mean V d/V t calculated using PaCO2 and PtcCO2 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, p < 0.05). Bland-Altman analysis showed a mean difference of -0.05 (95% CI: -0.01 to -0.09) between the two methods. PtcCO2 measurements can provide a noninvasive means to measure V d/V t, thus accessing important physiologic information and prognostic assessment in patients receiving mechanical ventilation.
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