Serum lactate - A prognostic marker of early post-operative outcome after off pump coronary artery bypass surgery: A propensity matched study

Abstract

Objectives: Elevated blood lactate levels after on pump coronary artery bypass grafting is known to be an adverse prognostic marker. We proposed to assess the association between hyperlactatemia and early post-operative outcome after off pump coronary artery bypass (OPCAB) surgery. Materials and Methods: 350 consecutive patients undergoing OPCAB surgery were studied retrospectively. Early postoperative serum lactate level was measured in all patients, upon shifting the patient to the ICU (0 hours), at 6 hours and 12 hours. The primary outcome was a composite of 30day all-cause mortality and severe morbidity. A propensity model was constructed to overcome the baseline differences between the group with and without complications. Results: 32 (9.14%) patients had at least 1 complication, which was associated with significantly prolonged mechanical ventilation (38.6 h vs 12.8 h; p<0.001), and longer length of ICU stay (7.2 days vs 3.8 days; p<0.001).Propensity score matching yielded 23 pairs of cohorts with and without complications. Patients who developed complications, had higher serum lactate levels immediately after being shifted to the ICU (4.8 ± 0.6 Vs 2.9 ± 0.5; p < 0.001), at 6 hours (4.1 ± 0.5 Vs 2.3 ± 0.4; p < 0.001) and 12 hours (3.2 ± 0.5 Vs 1.8 ± 0.4; p < 0.001). Lactate levels of ≥ 3.65 mmol/L at 0 hours, ≥ 2.75 mmol/L at 6 hours and ≥ 2.25 mmol/L at 12 hours of ICU stay were associated with major post-operative complications. Amongst other intra- and postoperative variables, the rate of RBC transfusion was significantly higher in propensity matched cohort with complications (1.9 ± 0.3 Vs 1.1 ± 0.2; p < 0.001). Conclusion: Hyperlactatemia is associated with worse outcomes after OPCAB surgery. Its detection, therefore, is an early and a very cost-effective marker in identifying patients at higher risk for adverse events.