Sublingual capnometry versus traditional markers of tissue oxygenation in critically ill patients

Objective: The purpose of this study was to determine the prognostic value of sublingual PCO2 (PSLCO2), lactate concentration, and mixed venous oxygen saturation (SMVO2) in hemodynamically unstable intensive care patients and, additionally, to compare the temporal changes of these variables in response to treatment. Setting. Medical/surgical intensive care unit. Subjects., Fifty-four patients, mean age 58 +/- 8 yrs. Interventions: Oxyhemodynamic variables, arterial lactate concentration, and PSLCO2 were recorded in unselected sequential intensive care patients undergoing pulmonary artery catheterization. A data set was obtained immediately after insertion of the pulmonary artery catheter and repeated 4 and 8 hrs later. Measurements and Main Results: Twenty-one patients had severe sepsis or septic shock. Twenty-seven (50%) patients died. The initial PSLCO2-PaCO2 gradient (PSLCO2-diff) and the initial PSLCO2 were highly predictive of outcome (p = .0004 and p = .004, respectively); however, there was no difference in the arterial lactate concentration and SMVO2 between the survivors and nonsurvivors. The PSLCO2-diff had the best receiver operator characteristic characteristics (area under the curve, 0.75), with a PSLCO2- diff >25 mm Hg being the best discriminator of outcome. With treatment, the PSLCO2-diff decreased in both survivors and nonsurvivors; however, the lactate and SMVO2 remained relatively unchanged during the study period. Conclusions. The baseline PSLCO2-diff and PSLCO2 were better predictors of outcome than traditional markers of tissue hypoxia and were more responsive to therapeutic interventions. The PSLCO2-diff and/or PSLCO2 may prove to be a useful marker for goal-directed. therapy and for assessing the response to clinical interventions aimed at improving tissue oxygenation.