Central venous to mixed venous blood oxygen and lactate gradients are associated with outcome in critically ill patients.

OBJECTIVE: Blood O(2) saturation and lactate concentration gradients from superior vena cava (SVC) to pulmonary artery (PA) occur in critically ill patients. These gradients (DeltaSO(2) and Delta[Lac]) may be positive or negative. We tested the hypothesis that positive DeltaSO(2) and Delta[Lac] are associated with improved survival in critically ill patients. DESIGN AND
SETTING: Multinational, prospective observational study conducted in six medical and surgical ICUs. PATIENTS: Consecutive sample of 106 adults requiring insertion of a pulmonary artery catheter (PAC). Average age was 59.5 +/- 15.5 years, APACHE II score was 15.5 +/- 6.7 (mean +/- SD). Main outcome measure was 28-day mortality.
INTERVENTIONS: None. MEASUREMENTS AND
RESULTS: We drew blood samples from the proximal and distal ports of PACs every 6 h from the time of PAC insertion (Initial measurement) until its removal (Final measurement). Samples were analyzed for SO(2), [Lac], glucose concentration and blood gases. Hemodynamic measurements were obtained after blood samples. We monitored patients for 30.9 +/- 11.0 h. Overall mortality rate was 25.5%. More survivors had mean and final DeltaSO(2) > or = 0 and Delta[Lac] > or = 0 than decedents (p < 0.01; p < 0.05 respectively). On the average, DeltaSO(2) and Delta[Lac] were positive in survivors and negative in decedents. Survival odds ratios for final measurements of DeltaSO(2) > or = 0 and Delta[Lac] > or = 0 were 19.22 and 7.70, respectively (p < 0.05).
CONCLUSIONS: A strong association exists between positive DeltaSO(2) and Delta[Lac] and survival in critically ill patients. Whether therapy aimed at increasing DeltaSO(2) and Delta[Lac] results in improved ICU survival remains to be determined.