What Solution Should You Use to Flush a Foley Catheter?

Normal saline, which is sterile 0.9% sodium chloride solution, is the standard and most widely recommended fluid for flushing a Foley catheter. It matches the body’s natural salt concentration, so it does not irritate the bladder lining, and it is effective at dislodging soft clots and sediment that cause most everyday blockages. For tougher problems like mineral encrustation, healthcare providers sometimes turn to acidic solutions such as citric acid, but these come with trade-offs that make them unsuitable for routine use. The choice of solution depends on what is actually blocking the catheter and how urgently flow needs to be restored.

Why Foley Catheters Get Blocked

Understanding why a catheter stops draining helps explain why different solutions exist. The simplest cause is a kink in the tubing or the catheter tip sitting against the bladder wall, and no flushing solution fixes a mechanical problem. But when the blockage is inside the catheter itself, it usually falls into one of two categories: blood clots and mucus, or mineral encrustation.

Blood clots and mucus plugs are common after urological surgery or in people with bladder inflammation. These are relatively soft obstructions, and a gentle flush with normal saline is usually enough to clear them. Mineral encrustation is a different beast. Certain bacteria, especially Proteus mirabilis, produce an enzyme called urease that breaks down urea in urine into ammonia. The ammonia raises the urine’s pH, making it more alkaline, which causes calcium and magnesium minerals to crystallize out of solution and deposit on the catheter surface.¹ These crystalline biofilms build up progressively, narrowing the catheter’s drainage channel until urine can no longer pass through.² When that happens, urine backs up into the bladder, which can lead to pain, bladder distension, and ascending urinary tract infections.

The type of blockage dictates the solution. Soft obstructions respond to saline. Crystalline encrustations made of calcium and magnesium phosphate require something that can dissolve minerals, which is where acidic solutions enter the picture.

Normal Saline for Routine Flushing

For the vast majority of catheter flushes, sterile normal saline is the right choice. It is isotonic, meaning it will not cause the bladder cells to swell or shrink the way plain water or a highly concentrated solution would. It is chemically inert with respect to catheter materials, so it will not degrade silicone or latex. And it is cheap, widely available, and safe enough that nurses can use it without special precautions beyond standard sterile technique.

A typical flush involves drawing up 30 to 60 milliliters of sterile saline into a catheter-tip syringe, disconnecting the catheter from the drainage bag at the appropriate port, and gently instilling the fluid. The key word is gently. Forcing fluid under high pressure risks damaging the bladder wall or pushing debris further into the urinary tract. If the saline meets resistance, pulling back on the syringe to aspirate can help dislodge small clots or sediment. In emergency settings, when a catheter has stopped draining and the bladder appears full on ultrasound, a saline flush is typically the first intervention tried before considering catheter replacement.³

Normal saline does have a limitation: it cannot dissolve mineral deposits. If you flush saline through an encrusted catheter and the blockage does not budge, repeating the flush harder is not the answer. The catheter either needs a different solution or, more often, it needs to be replaced entirely.

Citric Acid Solutions for Encrustation

When crystalline deposits are the problem, citric acid-based solutions are the main alternative to saline. The most well-known formulation is Suby G, a citric acid solution that has been used in catheter care for decades. The acid works by lowering the pH around the mineral deposits, dissolving the calcium and magnesium crystals that make up the encrustation. In laboratory testing, regular irrigation with citric acid solution dissolved roughly 70% of encrustation and restored free flow through blocked catheters.⁴

That sounds impressive, and it is, but it comes with important caveats. These results were achieved under controlled lab conditions with precise timing and consistent irrigation schedules. In real patients, the situation is messier. The encrustation may be mixed with biofilm that shields the minerals from the acid, and the solution does not stay in contact with the deposits for as long as researchers can manage in a laboratory setup. Still, citric acid solutions remain the most commonly used catheter maintenance solution for people who are known “blockers,” the patients whose catheters repeatedly crust over and fail.

Citric acid flushes are not something you would do on your own without medical guidance. The concentration matters, the dwell time matters, and the frequency needs to be individualized based on how quickly a particular patient’s catheter tends to encrust. Some catheter care protocols call for scheduled citric acid instillations, say twice a week, specifically to prevent full blockage from developing between catheter changes.

Acetic Acid and Vinegar-Based Flushes

Dilute acetic acid, essentially vinegar diluted to about 0.25%, has been explored as both an antimicrobial and an anti-encrustation agent. The logic is straightforward: acetic acid is mildly acidic, which can help dissolve mineral deposits, and it has some activity against bacteria. One case report found that bladder irrigation with dilute vinegar decreased bacteriuria in a patient who self-catheterized, and when combined with oral medications that acidify the urine, the approach appeared to shift the bacteria from resistant strains to ones that respond to standard antibiotics.⁵

The evidence for acetic acid is thin, though. Most of the data comes from case reports and small studies rather than large trials. It is sometimes used as a last-resort option for patients dealing with recurrent infections caused by highly resistant organisms, particularly when other approaches have failed. Acetic acid is not a first-line flushing solution, and using household vinegar without diluting it to the correct concentration risks irritating or damaging the bladder lining.

Antibiotic Irrigations and Their Limits

The idea of flushing antibiotics directly into the bladder sounds appealing in theory. Catheter-associated urinary tract infections are among the most common hospital-acquired infections, and putting the antibiotic right where the bacteria live should work better than swallowing a pill, right? The reality is more complicated.

Some studies have shown benefits. In one study of patients with chronic catheters and recurrent infections, antibiotic bladder irrigation resolved symptoms in about two-thirds of patients and reduced the need for systemic antibiotics.⁶ Another study in intensive care patients found that irrigation with a neomycin-polymyxin solution significantly reduced catheter-associated infections compared to saline irrigation alone.⁷

But a landmark trial published in the New England Journal of Medicine found no meaningful difference in infection rates between patients who received antibiotic irrigation and those who did not. Roughly the same proportion of patients in each group developed infections. Worse, the organisms that did cause infections in the irrigated group were more antibiotic-resistant.⁸ This is the central concern with antibiotic irrigation: it can select for resistant bacteria, creating harder-to-treat infections down the line.

Because of this resistance risk, most current guidelines do not recommend routine antibiotic irrigation for catheter maintenance. It remains a tool for specific clinical situations, usually in patients with recurrent symptomatic infections who have limited other options, and always under the direction of a urologist or infectious disease specialist.

Solutions That Can Harm the Bladder

Not every solution that dissolves mineral deposits is safe for the tissue it touches. The bladder lining, called the urothelium, is a delicate barrier, and irrigating it with the wrong chemical can strip away protective cells and make infections more likely rather than less.

Research on bladder irrigation has shown that the process itself, regardless of the solution, increases shedding of urothelial cells. When those shed cells were examined under electron microscopy, they showed more disruption than cells from people without catheters. The finding suggests that irrigation may further damage an already compromised bladder lining, potentially increasing susceptibility to the very infections the irrigation is meant to prevent.⁹

One class of solutions that has been studied and largely abandoned is EDTA, a calcium-chelating agent. EDTA dissolves calcium-based encrustations effectively, but the same property that makes it good at dissolving crystals makes it toxic to tissue. Animal studies found that disodium EDTA caused significantly more urothelial injury than control solutions. When researchers pre-saturated the EDTA with calcium, which neutralizes its chelating ability, the tissue damage disappeared, confirming that the very mechanism of action is what causes the harm.¹⁰ Later studies comparing various dissolution agents found that EDTA consistently caused the most serious bladder injury, and researchers concluded that no EDTA formulation yet developed is safe enough for clinical use.¹¹

Citric acid solutions also cause some degree of urothelial damage when used for prolonged periods, though less than EDTA. This is why citric acid flushes are used on a scheduled, limited basis rather than as continuous irrigation, and why the concentration and dwell time need to be carefully controlled.

Continuous Bladder Irrigation Is a Different Procedure

It is worth distinguishing between a catheter flush and continuous bladder irrigation, because they sound similar but serve different purposes. A flush is a brief, manual procedure: you push a small volume of solution through the catheter to clear a blockage or check patency. Continuous bladder irrigation, by contrast, involves running large volumes of saline through a three-way catheter over hours or days. It is a standard procedure after transurethral surgery and for managing gross hematuria, where blood in the urine would otherwise form clots that block the catheter.¹²

Continuous irrigation always uses normal saline. The goal is dilution and washout, not chemical treatment. The saline runs in through one channel of the three-way catheter and drains out through another, keeping the bladder flushed of blood and debris. This is a hospital-based procedure managed by clinical staff who monitor the flow rate, the color of the drainage, and the patient’s comfort level. It is not something done at home, and it is not a treatment for encrustation.

Preventing Blockage Without Flushing

For people living with long-term indwelling catheters, the best strategy is preventing blockage in the first place rather than repeatedly flushing a catheter that keeps crusting over. Several practical measures can make a significant difference.

Fluid intake is the single most important modifiable factor. Research has found that maintaining a high and uniform rate of fluid intake is essential for patients prone to catheter blockage. The emphasis is on “uniform” because drinking a large amount at one time and then going hours without fluids creates periods of concentrated, alkaline urine that promote crystallization. Steady fluid intake throughout the day keeps urine dilute and flowing.¹³

Dietary factors also play a role. The same research identified several avoidable risk factors for encrustation:

Excess calcium: found in certain protein supplements and antacids
Excess magnesium: found in certain beverages and antacids
Alkali intake: from effervescent tablets that raise urine pH
Intermittent dehydration: commonly from alcohol consumption

There are also less controllable risk factors, including infection with urease-producing bacteria, calcium loss from prolonged immobility, and excessive sweating. But addressing the modifiable factors is a good starting point for anyone dealing with recurrent catheter blockage.

One surprisingly simple approach that has shown promise is drinking lemon juice mixed with water. A randomized crossover study found that increased fluid intake with lemon juice may be an effective strategy to control catheter encrustation.¹⁴ The citrate in lemon juice inhibits crystal formation in urine, and the extra fluid keeps things flowing. For patients who are chronic blockers and stone formers, strategies like increasing fluid intake with citrated drinks can help control the problem, particularly when antibiotic treatment is unlikely to work because bacteria embedded in crystalline biofilms are highly resistant to antibiotics.¹⁵

When to Flush and When to Replace

One of the most common misconceptions about catheter care is that flushing can extend the life of an encrusted catheter indefinitely. In practice, once a catheter is significantly encrusted, flushing may temporarily restore flow, but the underlying biofilm remains on the catheter surface and will continue producing new mineral deposits. For long-term catheter users, scheduled catheter changes on a regular timetable are generally more effective at preventing complete blockage than relying on flushes to keep a deteriorating catheter going.

Flushing is most useful in two scenarios. First, as an acute intervention when a catheter stops draining and you need to restore flow quickly, whether to relieve a distended bladder or to buy time before a new catheter can be placed. Second, as a scheduled maintenance strategy using citric acid in patients who are known to encrust quickly, with the goal of keeping the catheter functional between planned changes. In both cases, the flush is buying time, not solving the root problem.

If you are managing a Foley catheter at home and it stops draining, a saline flush is a reasonable first step if you have been trained on the technique. If the blockage does not clear, or if you notice signs of infection like fever, cloudy or foul-smelling urine, or pain in the lower abdomen or back, that is a signal to contact your healthcare provider rather than continuing to flush. And you should never instill anything other than normal saline into a catheter without explicit medical instructions. The acidic, antibiotic, and antiseptic solutions discussed here are clinical tools with real risks, not home remedies.

Sterile Water Versus Normal Saline

A point of confusion that comes up often is whether sterile water can substitute for normal saline when flushing a catheter. The short answer: for flushing the drainage lumen, normal saline is preferred because it is isotonic. Sterile water is hypotonic, which means it can be absorbed into cells and cause them to swell. In small volumes and brief contact times, the practical difference is minimal, but saline is the safer default and the one endorsed by nursing guidelines.

Where this distinction matters more is with the catheter’s retention balloon. The balloon that holds the catheter in the bladder is inflated with sterile water, not saline. Saline can crystallize inside the balloon channel over time, making it difficult or impossible to deflate the balloon when the catheter needs to come out. This is a separate issue from flushing the drainage channel, but it is a common source of confusion because both involve syringes and the same catheter. If you ever need to add or check the volume in a catheter balloon, always use sterile water. If you are flushing the catheter to restore urine flow, use normal saline.