Perioperative use of metformin in cardiac surgery

Metformin is an oral antidiabetic agent, used to reduce blood glucose concentration in patients with non–insulin-dependent diabetes mellitus. Metformin was approved in Europe in 1957, and it is used for the treatment of non–insulin-dependent diabetes mellitus for more than 50 years. One of the most serious complications of the treatment with this drug is metformin-induced lactic acidosis. It is a rare but dangerous metabolic complication with a mortality rate of up to 50% that can result from the accumulation of lactates. Lactic acidosis is also associated with conditions such as diabetes mellitus, significant tissue hypoperfusion, and hypoxemia caused by lactic acid overproduction or underutilization. It is characterized by an increased serum lactate level (>5 mmol/L or >45 mg/dL), decreased blood pH (<7.35), and electrolyte imbalance with an increased anion gap. The rate of lactic acidosis in patients receiving metformin is not precisely known. The estimated incidence of this syndrome is 2–9 cases per 100 000 patients. However, in the majority of cases, lactic acidosis is diagnosed in patients with severe acute renal failure, which itself can cause lactic acidosis. Currently, there are no standardized guidelines for metformin administration during the perioperative period, and published data remain controversial. According to some investigators, metformin should be withdrawn before major surgery. Concerns have been raised for the use of metformin in patients with cardiovascular, renal, hepatic, and respiratory failure. The aim of the article is to overview the frequency of metformin-caused lactic acidosis and the latest recommendations for the use of metformin in the perioperative period proposed in recent years.