Can Transcutaneous CO_2 Tension Be Used to Calculate Ventilatory Dead Space? A Pilot Study

• Published in: Critical Care Research and Practice 2016-12, Vol.2016, p.196-199
• Main Authors: Lakshminarayana, Pradeep H., Geeti, Adiba A., Darr, Umer M., Kaufman, David A.
• Format: Article
• Language: English
• ISSN: 2090-1305; 2090-1313
• DOI: 10.1155/2016/9874150

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 ( P a C O 2 ). In recent years, transcutaneous capnography ( P t c C O 2 ) has emerged as a noninvasive method of estimating P a C O 2 . We hypothesized that P t c CO 2 can be used as a substitute for P a C O 2 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 P t c CO 2 for P a C O 2 . The mean V d / V t calculated using P a C O 2 and P t c CO 2 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. P t c CO 2 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.