Can transcutaneous C[O.sub.2] tension be used to calculate ventilatory dead space? A pilot study

• Published in: Critical care research and practice 2016-01
• Main Authors: Lakshminarayana, Pradeep H, Geeti, Adiba A, Darr, Umer M, Kaufman, David A
• Format: Article
• Language: English
• Subjects: Analysis; Artificial respiration; Blood gases; Capnography; Intensive care units; Management
• ISSN: 2090-1305
• DOI: 10.1155/2016/9874150

Dead space fraction ([V.sub.d]/[V.sub.t]) measurement performed using volumetric capnography requires arterial blood gas (ABG) sampling to estimate the partial pressure of carbon dioxide ([P.sub.a]C[O.sub.2]). In recent years, transcutaneous capnography ([P.sub.tc]C[O.sub.2]) has emerged as a noninvasive method of estimating [P.sub.a]C[O.sub.2]. We hypothesized that [P.sub.tc]C[O.sub.2] can be used as a substitute for [P.sub.a]C[O.sub.2] in the calculation of [V.sub.d]/[V.sub.t] In this prospective pilot comparison study, 30 consecutive postcardiac surgery mechanically ventilated patients had [V.sub.d]/[V.sub.t] calculated separately using volumetric capnography by substituting [P.sub.tc]C[O.sub.2] for [P.sub.a]C[O.sub.2]. The mean [V.sub.d]/[V.sub.t] calculated using [P.sub.a]C[O.sub.2] and [P.sub.tc]C[O.sub.2] was 0.48 [+ or -] 0.09 and 0.53 [+ or -] 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.sub.tc]C[O.sub.2] measurements can provide a noninvasive means to measure [V.sub.d]/[V.sub.t], thus accessing important physiologic information and prognostic assessment in patients receiving mechanical ventilation.