What are the implications of a furosemide (Lasix) challenge?

From the Guidelines

The Lasix challenge, also known as a furosemide stress test, has significant implications for patients with suspected heart failure or acute kidney injury, and it is crucial to approach this test with caution due to the potential risks of dehydration, electrolyte imbalances, and worsening renal function 1, 2.

Key Considerations

• The test involves administering a high dose of furosemide (40-80 mg intravenously) to assess the patient's renal response, and the initial dose can be adjusted according to renal function and history of chronic oral diuretic use 3.
• If the patient's urine output increases significantly (more than 200 mL over 2 hours) after the test, it may indicate that the kidneys are responsive to diuretic therapy and that heart failure is not the primary cause of their symptoms.
• However, if the patient's urine output does not increase, it may suggest that they have acute kidney injury or heart failure, and further evaluation and treatment are necessary.

Monitoring and Precautions

• It is essential to monitor the patient's vital signs, electrolyte levels, and urine output closely during and after the test, as the high dose of furosemide can cause dehydration, electrolyte imbalances, and other adverse effects 4, 1.
• The test should only be performed under the guidance of a qualified healthcare professional, and the results should be interpreted in the context of the patient's overall clinical presentation.
• Patients with chronic kidney disease or heart failure may require more frequent monitoring and dose adjustments to minimize the risk of worsening renal function 2.

Clinical Implications

• The Lasix challenge can help differentiate between heart failure and other causes of symptoms, such as acute kidney injury, and guide further treatment and management decisions 1, 3.
• The test results should be interpreted in conjunction with other clinical findings, such as echocardiography and renal function tests, to determine the best course of treatment for the patient.

From the FDA Drug Label

As with any effective diuretic, electrolyte depletion may occur during furosemide therapy, especially in patients receiving higher doses and a restricted salt intake Hypokalemia may develop with furosemide, especially with brisk diuresis, inadequate oral electrolyte intake, when cirrhosis is present, or during concomitant use of corticosteroids, ACTH, licorice in large amounts, or prolonged use of laxatives. Digitalis therapy may exaggerate metabolic effects of hypokalemia, especially myocardial effects All patients receiving furosemide therapy should be observed for these signs or symptoms of fluid or electrolyte imbalance

The implications of a furosemide challenge include:

• Electrolyte depletion: Furosemide therapy can cause electrolyte depletion, especially in patients receiving higher doses and a restricted salt intake.
• Hypokalemia: Furosemide can cause hypokalemia, which can be exacerbated by certain conditions or concomitant use of other medications.
• Fluid imbalance: Patients receiving furosemide therapy should be observed for signs or symptoms of fluid or electrolyte imbalance, including dryness of mouth, thirst, weakness, lethargy, and hypotension.
• Cardiac effects: Digitalis therapy may exaggerate the metabolic effects of hypokalemia, especially myocardial effects. 5

From the Research

Implications of a Furosemide Challenge

The implications of a furosemide challenge, also known as the furosemide stress test, are significant in the management of acute kidney injury (AKI). The test has been shown to:

• Predict the progression of AKI to more severe stages, such as Stage III AKI 6, 7, 8
• Identify patients at higher risk of AKI progression and the need for renal replacement therapy 6, 9
• Predict the cessation of continuous renal replacement therapy in patients with established AKI 6
• Evaluate the kidney function in critically ill patients, particularly in those with sepsis-associated AKI 10, 9

Clinical Utility

The furosemide stress test has been found to be a useful tool in the clinical management of AKI, with a number of studies demonstrating its predictive value. For example:

• A study published in the Journal of Critical Care found that a urinary flow rate of less than 200mls in the first 2 hours after the furosemide stress test was predictive of progression to Stage III AKI, with a sensitivity of 73.9% and specificity of 90.0% 7
• Another study published in Minerva Anestesiologica found that the response to the furosemide stress test and the Renal Index could be used as additional tools to evaluate kidney function in critically ill patients 10

Predictive Value

The predictive value of the furosemide stress test has been evaluated in a number of studies, with results showing that it can predict the progression of AKI and the need for renal replacement therapy. For example:

• A study published in Cureus found that the furosemide stress test and Renal Resistive Index could predict the severity of AKI in sepsis, with a sensitivity of 35.1% and specificity of 80.4% for predicting the need for renal replacement therapy 9
• A study published in Critical Care found that the furosemide stress test could predict the development of AKIN Stage-III in critically ill subjects with early AKI, with an area under the receiver operator characteristic curve of 0.87 8