Sublingual Capnography

Objective To compare sublingual Pco2 (Pslco2) measurements with gastric intramucosal Pco2 (Pimco2) as well as with the traditional indexes of tissue oxygenation in hemodynamically unstable ICU patients. Design A prospective, validation study. Setting The medical and coronary ICUs of a community teaching hospital. Patients Consecutive patients with severe sepsis, septic shock, or cardiogenic shock requiring pulmonary artery catheterization for hemodynamic management. Interventions During the first 24 h of ICU admission, the Pslco2, Pimco2, and blood lactate concentrations as well conventional hemodynamic and oxygenation parameters were recorded every 4 to 6 h. The Pslco2-Paco2 and Pimco2-Paco2 differences were used as indexes of tissue dysoxia. These variables were correlated with each other as well as with the traditional markers of tissue oxygenation. Results Seventy-six data sets were obtained on 22 patients. Fifteen patients had severe sepsis/septic shock, and 7 patients did not have sepsis. A patient with ischemic bowel who had a large Pimco2-Pslco2 difference (60.2 mm Hg) was excluded. The initial Pslco2 and Pimco2 measurements were 43.5 ± 10.4 mm Hg and 42.8 ± 10.9 mm Hg, respectively (correlation coefficient [r] of 0.86; p < 0.001). The mean Pslco2 and Pimco2 for the entire data set were 48.0 ± 13.4 mm Hg and 46.1 ± 12.3 mm Hg, respectively (r = 0.78; p < 0.001). Ten patients died. The initial Pslco2-Paco2 difference was 9.2 ± 5.0 mm Hg in the survivors and 17.8 ± 11.5 mm Hg in the nonsurvivors (p = 0.04). The initial Pimco2-Paco2 difference was 8.4 ± 4.8 mm Hg in the survivors and 16.1 ± 13.7 mm Hg in the nonsurvivors (p = 0.08, not significant). The initial Pslco2-Paco2 difference correlated with the initial mixed venous-arterial CO2 gradient (r = 0.66; p = 0.001), but correlated poorly with the initial blood lactate concentration (r = 0.38), mixed venous Po2 (r = 0.05), and systemic oxygen delivery (r = − 0.39). Conclusion In this study, sublingual capnometry yielded measurements that correlated well with those of gastric tonometry. Pslco2 may serve as a technically simple and noninvasive clinical measurement of tissue dysoxia in critically ill and injured patients.