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Metformin is an old but still indispensable agent that remains the most widely prescribed first-line pharmacological therapy for type 2 diabetes mellitus (T2DM) worldwide [1]. Consequently, a substantial proportion of surgical patients continue to receive metformin preoperatively. Historically, perioperative considerations regarding metformin have been dominated by concerns about adverse metabolic events, particularly glucose levels or lactic acidosis [2]. Therefore, perioperative guidelines and institutional protocols have offered divergent recommendations, with some advocating withholding metformin on the day of surgery and others supporting its continuation [2]. However, perioperative clinical concerns regarding metformin have predominantly focused on biochemical safety, including plasma glucose and lactate levels, when the drug is continued until surgery [3]. Consequently, less attention has been paid to clinically meaningful outcomes such as postoperative mortality and major complications.
In this issue of the Korean Journal of Anesthesiology, Oh et al. [4] presented a study that reframes the long-standing perioperative debate over metformin discontinuation into an outcome-focused evaluation in a broad, real-world, non-cardiac surgical population. A total of 22 944 adult patients with T2DM undergoing non-cardiac surgery were retrospectively analyzed and classified according to preoperative metformin exposure at hospital admission. Using the inverse probability of treatment weighting to adjust for baseline differences, the authors evaluated postoperative mortality and major organ complications.
Some key strengths of this study were the scope and choice of endpoints. Large observational cohorts have previously reported an association between preoperative metformin use and improved short-term postoperative outcomes [5,6]. However, these studies were largely limited to in-hospital or 30-day outcomes, and did not address whether such associations persisted beyond the immediate postoperative period. In contrast, the current study extended the question of long-term survival in a broad non-cardiac surgical population and investigated the organ-specific complications that most often drive decisions to withhold metformin. After robust adjustment using inverse probability weighting, preoperative metformin use was associated with significantly lower mortality across all time periods (hazard ratios of approximately 0.47 at 30 days, 0.76 at 1 year, and 0.84 at 5 years).
The observed reductions in respiratory and renal complications are of interest given that concerns regarding hypoxia and renal clearance often influence perioperative metformin management. The dose-related analyses, showing that reductions in respiratory complications were more pronounced at higher daily doses of metformin, indicate that perioperative exposure may involve gradations rather than a simple binary (“stop” or “continue”) decision. These findings suggest that the potential benefits of preoperative metformin may extend beyond glycemic control in appropriately selected surgical patients, while emphasizing the need for cautious and individualized decision-making.
Despite residual confounding and the absence of detailed markers of metabolic severity, this study provides further evidence that preoperative metformin exposure is not associated with excessive perioperative harm, but is instead associated with lower mortality and fewer major respiratory and renal complications in patients with T2DM undergoing non-cardiac surgery who lack clear contraindications. Although these findings cannot fully resolve the bedside question of whether metformin should be administered on the day of surgery, they support a more nuanced, risk-stratified approach to perioperative metformin management rather than routine blanket discontinuation and may help inform future guideline development and clinical decision-making.
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