Pre-Operative Medications Modifications

Appropriate management of chronic medications before surgery is critical for maintaining hemodynamic stability, reducing perioperative complications, and ensuring safe anesthesia induction. Certain commonly prescribed medications—particularly antihypertensives and antidiabetic agents—require temporary discontinuation prior to surgery.

This article reviews key pre-operative medication modifications, with emphasis on ACE inhibitors, ARBs, GLP-1 receptor agonists, and metformin.

ACE Inhibitors and ARBs

ACE inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) should be held on the day of surgery.

Physiologic Rationale

During anesthesia induction, there is a loss of sympathetic tone that normally helps maintain blood pressure. When this sympathetic suppression is combined with renin–angiotensin system (RAS) blockade, patients are at increased risk for significant peri-induction hypotension.

Under these conditions:

• The vasopressin system becomes the primary remaining mechanism to maintain blood pressure

• Vasopressin release is slower and less responsive than the sympathetic nervous system

• Common intraoperative vasopressors such as ephedrine and phenylephrine may be less effective in patients with RAS blockade

This phenomenon explains why hypotension following induction may be refractory to standard pressors in patients who continue ACEIs or ARBs on the day of surgery.

Clinical Recommendation

• Hold ACE inhibitors and ARBs on the morning of surgery

• Resume postoperatively once the patient is hemodynamically stable

GLP-1 Receptor Agonists

GLP-1 receptor agonists should be held for a minimum of 1 week prior to surgery.

Rationale

GLP-1 medications significantly delay gastric emptying, increasing the risk of:

• Residual gastric contents

• Aspiration during anesthesia induction

• Nausea and vomiting in the perioperative period

This risk persists even when standard NPO guidelines are followed, making extended discontinuation necessary.

Clinical Recommendation

• Hold GLP-1 receptor agonists at least 7 days pre-operatively

• This applies to both daily and weekly formulations

Metformin

Metformin should not be taken on the day of surgery.

Rationale

Metformin is associated with a rare but serious risk of lactic acidosis, particularly in settings of:

• Perioperative hypoperfusion

• Renal dysfunction

• Hypoxia or contrast exposure

Holding metformin reduces metabolic risk during periods of physiologic stress.

Clinical Recommendation

• Hold metformin on the day of surgery

• Resume postoperatively once renal function and oral intake are stable

Clinical Importance

Failure to appropriately modify these medications can result in:

• Severe intraoperative hypotension

• Pressor-resistant shock

• Increased aspiration risk

• Metabolic complications

Medication reconciliation should be part of every pre-anesthetic evaluation, particularly in office-based anesthesia and outpatient surgical settings.

Quick Reference Summary

• ACE inhibitors / ARBs → Hold day of surgery

• GLP-1 receptor agonists → Hold ≥ 1 week pre-op

• Metformin → Hold day of surgery

Board and Exam Pearls

• ACEI/ARB-associated hypotension may be refractory to ephedrine and phenylephrine

• Vasopressin is often required for ACEI/ARB-induced hypotension

• GLP-1 agents delay gastric emptying → aspiration risk

• Metformin + hypoperfusion = lactic acidosis risk

Conclusion

Pre-operative medication modification is a critical component of safe anesthetic care. Holding ACE inhibitors, ARBs, GLP-1 receptor agonists, and metformin at appropriate intervals helps prevent hemodynamic instability, aspiration, and metabolic complications during surgery.