Continuation of metformin till night before surgery and lactate levels in patients undergoing coronary artery bypass graft surgery

Abstract

Background: Lactic acidosis is a rare but serious complication associated with metformin therapy in certain high-risk patients. NICE guidelines and the British National Formulary advise the discontinuation of metformin before surgery. The drug manufacturer's datasheet advises the withdrawal of metformin 48 h before surgery. However, the data regarding perioperative use of metformin is scarce. Aims: To evaluate the effect of continuation of metformin till night before surgery on lactate levels in patients undergoing coronary artery bypass graft (CABG) surgery. Materials and Methods: In this prospective cohort study, 1,800 consecutive patients who underwent CABG between 1st November 2015 and 31st October 2016 were enrolled. Following exclusion criteria, a total of 790 subjects were included for final analysis. Three-hundred and eight seven (48.9%) patients with diabetes received metformin till night before surgery (Met group), 239 (30.3%) patients with diabetes were non-metformin users (Non-Met group), and 164 (20.8%) patients were having no diabetes (Non-Diab group). Lactate levels and arterial pH were measured using arterial blood gas machine. Postoperative morbidity outcome data were obtained by collecting clinical data, routine biochemistry, and chest imaging. Results: The mean metformin dose was 1,124.6 mg/day (SD: 509.3; range: 500-2,500 mg/day). Mean postoperative lactate levels were 1.91 ± 0.7 in Met group, 2.04 ± 0.79 in Non-Met group, and 2.07 ± 0.78 in Non-Diab group. Lactic acidosis occurred in 41 patients and there was no difference among the groups [Met group = 18 (4.7%); Non-Met group = 14 (5.9%)]. Among secondary outcome measures, acute renal failure occurred more frequently in diabetic patients [Met group = 46 (11.9%) and Non-Met group = 32 (13.4%)] as compared with non-diabetic patients. There were no differences with regard to pneumonia, length of ICU stay, and duration of ventilatory support among the three groups. Conclusions: Continuation of metformin till night before surgery is not associated with significant changes in lactate levels in patients undergoing CABG.