What is the recommended approach to diuretic therapy in postoperative patients?

Postoperative Diuretic Management

Diuretic management in postoperative patients must be tailored to the underlying indication: hypertensive patients should discontinue low-dose diuretics on the day of surgery and resume orally when possible, while heart failure patients must continue diuretics through the perioperative period with intravenous administration if needed to prevent volume overload and maintain hemodynamic stability. 1

Diuretics for Hypertension

For patients taking diuretics solely for hypertension management:

• Discontinue low-dose diuretics on the day of surgery to prevent volume depletion, hypotension, and electrolyte disturbances that increase perioperative risk 1, 2
• Diuretics cause hypokalaemia in up to 34% of surgical patients, which independently increases risk of ventricular arrhythmias and perioperative mortality in patients with cardiac disease 1
• Resume oral diuretics as soon as clinically possible postoperatively to maintain blood pressure control 1, 2
• If blood pressure reduction is required before oral therapy can be restarted, use alternative intravenous antihypertensive agents rather than diuretics 1

Diuretics for Heart Failure

For patients with heart failure requiring diuretics for volume control:

• Continue diuretics up to the day of surgery to prevent fluid retention and decompensation 1, 2
• Resume intravenously in the perioperative period if oral intake is not possible 1, 2
• Carefully monitor volume status throughout the perioperative period and adjust loop diuretics or fluids to optimize hemodynamics 1
• Increase dosage if signs of fluid retention develop; reduce dosage if hypovolemia, hypotension, or electrolyte disturbances occur 1
• Continue orally when possible to maintain optimal volume status 1

Electrolyte Management

Electrolyte disturbances must be corrected before elective surgery:

• Check potassium and magnesium levels preoperatively in all patients taking diuretics and those prone to arrhythmias 1
• Correct hypokalaemia and hypomagnesaemia before surgery to reduce risk of ventricular fibrillation and cardiac arrest 1
• Consider potassium- and magnesium-sparing diuretics (aldosterone antagonists like spironolactone or eplerenone) which reduce mortality in severe heart failure 1
• Provide dietary counseling to increase potassium and magnesium intake; reduce depleting drugs if possible; add supplementation as needed 1
• Minor, asymptomatic electrolyte disturbances should not delay acute surgery as acute preoperative repletion may carry more risks than benefits 1

Postoperative Diuretic Administration

When diuretics are needed postoperatively for volume overload:

• Loop diuretics (furosemide) are the primary agents for managing postoperative fluid overload 1
• Continuous infusion of furosemide (4-10 mg/hour after 20 mg loading dose) provides more sustained and less variable diuresis than bolus dosing in hemodynamically compromised patients 3, 4
• However, prophylactic furosemide does not prevent renal dysfunction in high-risk cardiac surgical patients and offers no advantage over placebo in patients with moderate postoperative renal impairment 5, 6
• Oliguria alone should not trigger diuretic therapy, as low urine output is a normal physiological response during surgery and anesthesia 1

Fluid Balance Targets

Postoperative fluid management should aim for near-zero to mildly positive balance:

• Discontinue intravenous fluids by postoperative day 1 at the latest 1
• Encourage oral intake within 4 hours after abdominal/pelvic surgery 1
• Aim for 1-2 L positive balance by end of surgery to protect kidney function, as zero-balance strategies increase acute kidney injury risk 1
• Use balanced crystalloids (Ringer's lactate) rather than 0.9% saline to avoid salt and fluid overload 1

Special Considerations for Cirrhosis

In cirrhotic patients with ascites (though typically not surgical candidates):

• Spironolactone monotherapy (100-400 mg) is reasonable for first presentation of moderate ascites 1
• Combination spironolactone (100-400 mg) plus furosemide (40-160 mg) is recommended for recurrent severe ascites or when faster diuresis is needed 1
• Monitor closely for adverse events, as nearly half require dose reduction or discontinuation 1

Critical Pitfalls to Avoid

• Do not routinely continue diuretics in hypertensive patients on the day of surgery, as this increases hypotension risk without benefit 1, 2
• Do not withhold diuretics in heart failure patients, as this risks volume overload and decompensation 1, 2
• Do not use diuretics prophylactically to prevent renal dysfunction, as evidence shows no benefit and potential harm 5, 6
• Do not treat oliguria reflexively with diuretics without investigating the underlying cause 1