Lasix: Taking a Diuretic After Surgery

What You Should Know About Lasix (Furosemide)

Urine specimen, urine sample, what urine looks like, urine
Urine Output Is Increased By Lasix.

What Is Lasix?

Lasix, also known as furosemide, is a diuretic and is a prescription medication commonly used after surgery.  It is given to increase urine output which in turn can decrease blood pressure, edema, fluid overload, and can stimulate the kidneys when they are not working properly.  

Lasix is used to decrease the amount of fluid in the body, particularly in the veins and arteries of the body.

  If the body is holding too much fluid, it can increase stress on the heart, cause fluid to build up in the lungs, and can also cause swelling--typically in the legs and feet.  Triggering the body to increase urine output can help treat these conditions.

Why Lasix is Used After Surgery

Lasix is used after surgery for a variety of reasons.  Patients who have congestive heart failure will be monitored closely for fluid overload after a procedure, and if the condition is worsening after surgery Lasix may be given to reduce the workload of the heart.  If congestive heart failure occurs, or large amounts of fluid are being retained, the lungs can also be affected.  If this extra fluid begins to build in the lungs, a serious condition called pulmonary edema may result, which can make it difficult to provide the body with enough oxygen.  Removing this extra fluid can improve heart and lung function.

Swelling, especially in the legs, can also be an issue after surgery.  Fluid retention is often a problem, especially if the patient is not getting up to walk or is receiving ICU level care.  Some surgeries require ample fluids to be provided during the procedure, especially open heart surgery that is done “on pump.”  For these patients, removing this extra fluid in the first days of recovery is helpful.


For some individuals, the kidneys may not work as well after surgery as they typically do, this may be due to receiving anesthesia.  For these individuals, a dose or even several doses of Lasix may help “kick start” the kidneys and help them return to full function.  The same is true after experiencing kidney failure, or even after a kidney transplant.

Some patients take Lasix routinely at home for a variety of kidney, liver and heart conditions.  For these individuals, the Lasix given in the hospital may be a continuation of their daily medications that help maintain the fluid balance in the body at a better level than their body could do without medication.  

How Lasix Works

Lasix prevents the kidneys from keeping as much salt in the blood stream as they normally do, which increases the amount of salt in urine.  Water is drawn into the urine along with the salt, which in turn increases the amount of water that leaves the body.  

How Lasix is Given

Lasix can be given as a pill, a syrup taken by mouth, an IV injection or a injection into the muscle.

  It is rarely given as an injection into muscle. In the hospital setting, it is typically given as a pill or an IV injection. It is a prescription medication.

Common Side Effects of Lasix

Taking Lasix can cause a decrease in blood pressure as fluid is removed from the body.  This is often a desired effect of the medication, but can result in dizziness if the blood pressure falls quickly or is too low.

Lasix change the electrolyte balance in the body, particularly salt and potassium. This can lead to cramping, diarrhea, nausea and vomiting.

This medication can worsen liver problems.

Nausea, vomiting and diarrhea is a side effect of most medications and are also common after surgery.

Risks of Lasix

Lasix is a category C medications, which means that pregnant women should only take this medication if the rewards outweigh the potential risks of not taking the medicine.  Pregnant women who take Lasix are known to have higher birth weight babies than they would otherwise.  This medication can also decrease breast milk production and can be passed to an infant through milk.

Lasix is known to be ototoxic, which means it can be damaging to the ears and the ability to hear.  This is typically only a problem when the medication is given in very large doses through an IV.  To prevent this type of damage, the medication is given slowly when prescribed as an IV medication, with even small doses being given “slow push” into an IV. 

Lasix works by removing salt from the bloodstream, which can result in a loss of too much salt, which can be serious in severe cases.

When taking Lasix, the loss of potassium is a known risk.  Potassium should be monitored and if you take Lasix for an extended period of time you may require a daily potassium supplement. 

Individuals with a severe allergy to sulfa medications should use notify their healthcare provider prior to taking a dose of Lasix. 

This medication should not be taken by individuals with pancreatitis, an often painful inflammation of the pancreas. 

This medication can worsen gout, or trigger a flare of gout. 


Furosemide Monograph.  Accessed February, 2016.

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