Ratio of carbon dioxide veno-arterial difference to oxygen arterial-venous difference is not associated with lactate decrease after fluid bolus in critically ill patients with hyperlactatemia: results from a prospective observational study

Background High ratio of the carbon dioxide veno-arterial difference to the oxygen arterial-venous difference (P va CO 2 /C av O 2 ) is associated with fluid bolus (FB) induced increase in oxygen consumption (VO 2 ). This study investigated whether P va CO 2 /C av O 2 was associated with decreases in blood-lactate levels FB in critically ill patients with hyperlactatemia. Methods This prospective observational study examined adult patients in the intensive care unit (ICU) with lactate levels > 1.5 mmol/L who received FBs. Blood-lactate levels were measured before and after FB under unchanged metabolic, respiratory, and hemodynamic conditions. The primary outcome was blood-lactate levels after FB. Significant decreases in blood-lactate levels were considered as blood-lactate levels < 1.5 mmol/L or a decrease of more than 10% compared to baseline. Results The study enrolled 40 critically ill patients, and their median concentration of blood lactate was 2.6 [IQR:1.9 − 3.8] mmol/L. There were 27 (68%) patients with P va CO 2 /C av O 2 ≥ 1.4 mmHg/ml, and 10 of them had an increase in oxygen consumption (dVO 2 ) ≥ 15% after FB, while 13 (32%) patients had P va CO 2 /C av O 2 < 1.4 mmHg/ml before FB, and none of them had dVO 2 ≥ 15% after FB. FB increased the cardiac index in patients with high and low preinfusion P va CO 2 /C av O 2 (13.4% [IQR: 8.3 − 20.2] vs. 8.8% [IQR: 2.9 − 17.4], p = 0.34). Baseline P va CO 2 /C av O 2 was not found to be associated with a decrease in blood lactate after FB (OR: 0.88 [95% CI: 0.39 − 1.98], p = 0.76). A positive correlation was observed between changes in blood lactate and baseline P va CO 2 /C av O 2 ( r = 0.35, p = 0.02). Conclusions In critically ill patients with hyperlactatemia, P va CO 2 /C av O 2 before FB cannot be used to predict decreases in blood-lactate levels after FB. Increased P va CO 2 /C av O 2 is associated with less decrease in blood-lactate levels.