ObjectiveThe 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.SettingMedical/surgical intensive care unit.SubjectsFifty-four patients, mean age 58 ± 8 yrs.InterventionsOxyhemodynamic variables, arterial lactate concentration, and PSLco2were 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 ResultsTwenty-one patients had severe sepsis or septic shock. Twenty-seven (50%) patients died. The initial PSLco2–Paco2gradient (PSLco2-diff) and the initial PSLco2were highly predictive of outcome (p= .0004 andp= .004, respectively); however, there was no difference in the arterial lactate concentration and SMVo2between 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 SMVo2remained relatively unchanged during the study period.ConclusionsThe baseline PSLco2-diff and PSLco2were better predictors of outcome than traditional markers of tissue hypoxia and were more responsive to therapeutic interventions. The PSLco2-diff and/or PSLco2may prove to be a useful marker for goal-directed therapy and for assessing the response to clinical interventions aimed at improving tissue oxygenation.