Postoperative Blood Pressure Does Not Affect Lactate Clearance in Cardiac Surgery: A Retrospective Observational Cohort Study

Background: Tight blood pressure control is a cornerstone of postoperative cardiac surgery patients. In addition, plasma lactate levels are frequently monitored in this setting as it is a marker for malperfusion, with early elevated levels being associated with increased morbidity and mortality. Elevations from malperfusion may be due to decreased cardiac output, hypovolemia, or persistent post-bypass vasoplegic response. Here, we investigate whether lower blood pressures, significant changes from baseline, and cardiac perfusion pressures delay the clearance of lactate after cardiac surgery. Methods: This is a retrospective cohort observational study of patients who have undergone coronary artery bypass graft (CABG) and valve replacement or repair surgeries at NYU Langone Long Island Hospital over a 6-month period. Postoperative blood pressures and lactate levels were examined over the first 16 h of care. Primary outcome: The relationship between blood pressure parameters and lactate clearance. Secondary outcomes: ICU length of stay, hospital length of stay, and mortality. Results: A total of 81 patients met inclusion criteria. The average pre-operative mean arterial blood pressure (MAP) was 95.4 mmHg and the average MAP in the first 6 h post-operatively was 78.4 mmHg. The average change in MAP from baseline was a decrease of 16.7%. The average cleared lactate fraction by 16 h postoperatively was 85.9%. Lactate clearance was associated in a statistically significant way only with the need for inotropic support on postoperative day 1, p = 0.03. There was a slight trend toward a delay in lactate clearance in those with lower early systolic blood pressures, p = 0.14. Conclusions: Lactate clearance appears to occur largely independently of postoperative blood pressures in the first 16 h after surgery but may be delayed in those requiring inotropic support through the morning or postoperative day one.