SGLT2 Inhibitors Before Surgery: DKA Risk

A preoperative glucose of 7.8 mmol/L (140 mg/dL) can look reassuring. In a patient taking a sodium–glucose cotransporter 2 (SGLT2) inhibitor, it does not exclude diabetic ketoacidosis (DKA). Fasting, illness and surgical stress can drive ketone production while glucose remains normal or only modestly raised.

That mismatch is the perioperative trap: do not use glucose alone to decide whether ketosis or acidosis is developing.

Why normal glucose can mislead

SGLT2 inhibitors increase glucose loss in the urine. During fasting, reduced carbohydrate availability and a shift in the insulin-to-glucagon balance can promote fat breakdown and ketone production. Surgical stress adds counter-regulatory hormones. Dehydration, infection, vomiting, bowel preparation, a low-carbohydrate diet or reduced insulin can add to the risk.

The result may be euglycemic DKA: ketosis and metabolic acidosis with glucose below 200 mg/dL (11.1 mmol/L). SGLT2 inhibitors are also prescribed for heart failure and chronic kidney disease, so the reason for treatment matters when you assess the whole perioperative risk.

How long should SGLT2 inhibitors be withheld?

For scheduled surgery in the United States, the American Diabetes Association Standards of Care and U.S. labeling recommend withholding canagliflozin, dapagliflozin and empagliflozin for at least 3 days, and ertugliflozin for at least 4 days. Other guidance takes a different approach.

These are different approaches, not intervals to combine. Follow the policy for your jurisdiction and institution. Withholding lowers risk but does not abolish it; postoperative ketoacidosis has been reported even after a longer interruption.

A very-low-energy or liver-reduction diet needs earlier planning. For a patient with diabetes taking an SGLT2 inhibitor, stop the drug when that diet begins rather than waiting for the routine preoperative interval. Keep this separate from insulin management: withholding an SGLT2 inhibitor does not remove the need for an appropriate basal-insulin plan.

If the last dose was too close to surgery

First establish which drug the patient takes, why it was prescribed and when the last dose was taken. Then assess symptoms, diabetes and insulin history, fasting duration, recent carbohydrate restriction or bowel preparation, the planned operation and how soon oral intake is likely to resume.

Do not use glucose alone to decide whether an elective case can proceed. Check blood ketones and acid–base status when symptoms or the clinical context raise concern. Active DKA requires treatment and deferral of surgery unless the operation is immediately life-, limb- or organ-saving. In a patient without DKA, the decision to proceed depends on the metabolic findings, urgency, expected fasting and surgical stress, and the local pathway; no single ketone result guarantees safety in every setting.

Urgency changes the balance. Do not delay necessary urgent surgery solely to complete the usual withholding interval. Stop the drug on admission, assess for metabolic derangement and plan perioperative and postoperative surveillance. In patients with diabetes taking an SGLT2 inhibitor, UK perioperative guidance recommends daily capillary blood-ketone measurement until normal eating and drinking resume, even when glucose is normal.

Imagine an adult with type 2 diabetes taking empagliflozin who develops nausea and deep, rapid breathing after surgery. Glucose is 142 mg/dL, blood β-hydroxybutyrate is 3.4 mmol/L, pH is 7.25 and bicarbonate is 15 mmol/L. The diabetes history, ketonaemia and acidosis meet DKA criteria. The glucose is no reason to dismiss the diagnosis.

Recognising euglycemic DKA

Consensus criteria require all three DKA components: diabetes or glucose at least 200 mg/dL (11.1 mmol/L); ketosis, usually blood β-hydroxybutyrate at least 3.0 mmol/L or urine ketones of 2+ or greater; and metabolic acidosis, with pH below 7.3 and/or bicarbonate below 18 mmol/L. A history of diabetes meets the first component even when current glucose is lower. In euglycemic DKA, glucose is below 200 mg/dL.

Perioperative clues include unexplained nausea, vomiting, abdominal pain, malaise, tachypnoea, dehydration, tachycardia or hypotension. Under anaesthesia, symptoms may be hidden; unexplained metabolic acidosis or a rising anion gap may be the first sign. The anion gap helps frame the assessment, but it does not replace blood ketones and acid–base testing, and it should not be used alone to judge DKA resolution.

Measure blood β-hydroxybutyrate when available. Urine ketone strips measure acetoacetate, not β-hydroxybutyrate, the main circulating ketoacid in DKA. Urine testing can underestimate ketonaemia early in the illness, so a negative result should not overrule a concerning clinical picture. Mild ketonaemia alone is not DKA: interpret it alongside pH, bicarbonate, hydration and the possibility of starvation ketosis.

Initial management: treat the ketones, not the glucose number

Stop the SGLT2 inhibitor and escalate promptly. Check glucose, electrolytes, renal function, blood β-hydroxybutyrate and a venous blood gas; assess volume status and look for triggers such as infection or ischaemia. Manage confirmed DKA using the local adult DKA protocol, with fluid resuscitation, insulin, electrolyte monitoring and treatment of the precipitating illness. Tailor fluid management to the patient’s volume status, particularly with heart or kidney failure.

Because glucose may already be low or normal, dextrose-containing fluid may be needed early so insulin can continue to suppress ketone production without causing hypoglycaemia. Do not stop insulin simply because glucose has normalised. During DKA treatment, check glucose every 1–2 hours and repeat electrolytes, β-hydroxybutyrate and venous pH about every 4 hours until resolution, following the local protocol.

When to restart after surgery

After routine surgery, restart only when the patient is clinically stable, eating and drinking normally, and has no ongoing ketosis or acidosis. For inpatients, UK multisociety guidance uses normal intake and capillary ketones below 0.6 mmol/L as restart criteria. After SGLT2-associated DKA, do not restart automatically: reassess the indication and risks with the diabetes or prescribing team.

In a viva, make the sequence clear: identify the drug and last dose, assess ketones and acid–base status when indicated, distinguish ketosis from DKA, then base timing on the metabolic state and urgency of surgery. Glucose is only one part of that assessment. Candidates can check exam format and syllabus in the anaesthesia exam guides and rehearse the clinical reasoning in the Final/Advanced Anesthesia Structured Oral Examination (SOE).