ObjectiveTo investigate the feasibility and predictive value of sublingual PCO2(PSLCO2) measurements as a noninvasive and early indicator of systemic perfusion failure.DesignA prospective, criterion study.SettingEmergency department and medical and surgical intensive care units of an urban community medical center.Participants and PatientsFive normal human volunteers and 46 patients with acutely life-threatening illness or injuries.InterventionsIntra-arterial or automated cuff blood pressure and arterial blood lactate (LAC) were measured concurrently with PSLCO2.ResultsPSLCO22.5 mmol/L had a PSLCO2of 81 +/- 24 mm Hg. This contrasted with patients admitted without clinical signs of shock and LAC of <2.5 mmol/L who had a PSLCO2of 53 +/- 8 mm Hg (p < .001). The initial PSLCO2of 12 patients who died before recovery from shock was 93 +/- 27 mm Hg, and this contrasted with 58 +/- 11 mm Hg (p < .001) in hospital survivors. Increases in PSLCO2were correlated with increases in LAC (r2= .84; p < .001). When PSLCO (2) exceeded a threshold of 70 mm Hg, its positive predictive value for the presence of physical signs of circulatory shock was 1.00. When it was <70 mm Hg, it predicted survival with a predictive value of 0.93.ConclusionPSLCO2may serve as a technically simple and noninvasive clinical measurement for the diagnosis and estimation of the severity of circulatory shock states. (Crit Care Med 1999; 27:1225-1229)