Oxygen metabolism can be impaired in at least two ways in septic patients. Patients can have either low central venous oxygen saturation (ScvO2) levels which reflect inadequate oxygen delivery, or normal or high ScvO2 levels which reflect depressed cellular oxygen consumption despite normal or high oxygen delivery.
Lactate levels and cardiac function are different between septic patients with different ScvO2 levels.
A retrospective analysis was performed on septic patients admitted to 9 ICU’s in 2 university hospitals between September 2009 to May 2012 meeting all of the following criteria: (i) initial lactate levels?2mmol/L, (ii) early goal-directed therapy (EGDT) was implemented, and (iii) lactate levels were measured every 6 hours during the first 24 hours. Patients were stratified into three groups according to ScvO2 values: low ScvO2 (<70%); normal ScvO2 (70-80%), and high ScvO2 (?80%). Clinical data, cardiac function and survival were compared among the 3 groups.
There were 305 patients who met criteria (low ScvO2 n=119, normal ScvO2 n=108, high ScvO2 n=78). There were no significant differences in age, gender, hemoglobin and lactate levels at the start of EGDT among the 3 groups. The incidence of cardiac disease history was significantly higher in the low ScvO2 (38.7%) group compared to normal (25.0%) or high ScvO2 (16.7%) groups (p<0.01). Left ventricular ejection fraction measured by ultrasonography was significantly lower in the low ScvO2 group compared to other 2 groups (p<0.05). In the low ScvO2 group, lactate levels remained consistently elevated during the first 24 hours while lactate levels continuously decreased in both normal and high ScvO2 groups (p<0.05). Inhospital mortality was higher in the low ScvO2 (41.2%) group than in normal (24.1%) and high ScvO2 (30.8%) groups (p<0.05).
Septic patients with low ScvO2 have worsened cardiac function compared to septic patients with normal or high ScvO2. Cardiac dysfunction in septic patients with low ScvO2 may play a role in the persistent hyperlactatemia and higher mortality. Other cardiac support in addition to EGDT may potentially improve outcomes in septic patients with low ScvO2.