ObjectiveTo compare the prognostic value of blood lactate concentrations, gastric intramucosal pH, and their combination in patients with severe sepsis.DesignProspective, noninterventional study.SettingMedical/surgical intensive care unit of a university hospital.Patients10 or <6 times 103cells/mm3), hypotension (systolic arterial pressure <90 mm Hg), and evidence of organ dysfunction (oliguria or deterioration of mental status).InterventionsArterial lactate concentration and intramucosal pH were measured at the time of study entry, and at 4 and 24 hrs later. Hemodynamic data and oxygen-derived variables were determined at the time of study entry and 24 hrs later. Arterial blood and balloon saline gases were also determined to obtain the pH gap (arterial pH - intramucosal pH) and the PCO2gap (intramural PCO2- PaCO2).Measurements and Main Results2 mEq/L) and 26 (74%) had a low intramucosal pH (<7.32). Initially, there were no significant differences in blood lactate concentrations between nonsurvivors and survivors (3.2 +/- 1.5 vs. 2.8 +/- 2.3 mEq/L). Lactate concentrations remained high in nonsurvivors and progressively decreased in survivors (4 hrs: 3.3 +/- 1.1 mEq/L in nonsurvivors vs. 2.2 +/- 0.9 mEq/L in survivors [p < .01]; 24 hrs: 3.5 +/- 2.0 mEq/L in nonsurvivors vs. 1.9 +/- 1.1 mEq/L in survivors [p < .05]). Intramucosal pH was lower in the nonsurvivors than in the survivors initially (7.19 +/- 0.15 in nonsurvivors vs. 7.30 +/- 0.14 in survivors [p < .05]), at 4 hrs (7.18 +/- 0.17 in nonsurvivors vs. 7.29 +/- 0.13 in survivors [p = .06]), and at 24 hrs (7.19 +/- 0.31 in nonsurvivors vs. 7.30 +/- 0.17 in survivors [p < .05]). Of the 23 patients with initially high lactate concentrations, 12 (60%) of the 20 patients with low intramucosal pH died, as compared with one (33%) of the three patients with normal intramucosal pH (p = .052). Of the 14 patients with persistently high lactate concentrations at 24 hrs, all nine (100%) patients with low intramucosal pH, but only two (40%) of five patients with normal intramucosal pH died (p < .001). No significant relationship was found between lactate or intramucosal pH and oxygen-derived variables. Intramucosal pH correlated better with gastric intramural PCO2(r2= .58) than with arterial bicarbonate or base deficit/excess. Intramural PCO2was a more specific predictor of mortality than intramucosal pH. When compared with patients with normal lactate concentrations, those patients with high lactate concentrations had a higher pH gap (0.22 +/- 0.22 vs. 0.07 +/- 0.13 [p < .01]) and PCO2gap [21.0 +/- 33.9 vs. 1.8 +/- 9.8 torr [2.79 +/- 4.5 vs. 0.24 +/- 1.34 kPa]; p < .01).ConclusionsBoth lactate concentrations and intramucosal pH represent reliable prognostic indicators in severe sepsis, and their combination improves the prognostic assessment in these patients. Both variables are better prognostic indicators than oxygenderived variables. Intramural PCO2appears to be a more specific variable than intramucosal pH, which partially reflects systemic metabolic acidosis. Combined determinations of blood lactate concentrations and intramucosal pH or intramural PCO2may help to predict outcome from severe sepsis.(Crit Care Med 1995; 23:1184-1193)