Encrustations on Indwelling Urinary Catheters
by K.N. Moore, RN, PhD
(2003) Infection Control Resource, 2 (2): 2-7. http://www.infectioncontrolresource....ssue6/2V2.html
Indwelling catheters are associated with chronic recurrent urinary tract infections, urinary calculi, urethral strictures, epididymitis, orchitis, leakage, and blockage. At the root of catheter-associated complications are bacteriuria and alkaline urine. The catheter is itself a nidus for infection. Catheter care practices to prevent or delay the onset of bacteriuria include aseptic technique for insertion, early removal of the catheter, maintaining a closed drainage system and dependent drainage, securing the catheter to the body, washing hands and wearing gloves between patients, and separating catheterized patients, but none of these strategies has been completely effective in patients catheterized long-term.1,2
There are few randomized controlled trials on which to base practice, and healthcare practitioners are often challenged by the common catheter-care issues that arise. These include questions about how often to change the catheter, when to treat urinary tract infections, catheter size, and preventing encrustations and blockage.3,4 Adding to the confusion is the choice of catheter product; currently available models include silicone, latex, silicone- and TEFLONÂ®-coated latex, hydrophilic gel, and antiseptic- and antimicrobial-impregnated catheters. At present, all-silicone catheters appear to be the best choice for reducing allergic reactions, urethritis, infections, strictures, and encrustation.
Urinary tract infections/colonization
Colonization by gram-negative organisms occurs as soon as 3 days and as late as 30 days after catheterization; it affects all patients and is usually asymptomatic and uncomplicated.5 In the short-term catheterized surgical patient, colonization is usually treated with a fluroquinolone or TMP-SMX (trimethoprim-sulfamethoxazole) after catheter removal. In the asymptomatic long-term catheterized patient, antibiotic treatment is unnecessary and potentially harmful if resistant organisms develop. Unfortunately, up to 30% of long-term catheterized patients will become symptomatic and require some intervention.6 If symptomatic infection persists, potential complications include prostatitis, epididymitis, cystitis, pyelonephritis, and, rarely, bacteremia.2 Numerous strategies, all ineffective in preventing bacteriuria in catheterized patients, have been tried. For example, antibiotic ointments at the meatus, bladder irrigations with antibiotic solutions, antiseptic solutions in the catheter drainage bags, and oral antibiotics have not decreased bacteriuria and bacteremia.
Indications for urine culture
Historically, management of catheterized patients included routine urine cultures. This practice is no longer supported and should be done only if the patient is symptomatic as evidenced by hematuria, fever, flank or low back pain, urinary urgency, or delirium or cognitive or behavioral changes. Treatment of symptomatic bacteriuria includes obtaining a valid urine sample to culture using a sterile catheter (polymicrobial bacterial biofilms on the lumen of the in-situ catheter will otherwise contaminate the specimen), removing the catheter, and treating the patient with appropriate antibiotics or, if necessary, replacing the catheter and then treating the patient. In one randomized controlled trial to assess the impact of catheter removal and replacement versus no removal in symptomatic patients, subjects in the replacement group achieved bacteria-free status more quickly and were more likely to remain bacteria-free than the non-change group.7
If symptoms do not resolve after one course of appropriate antibiotic, patients should be referred to a urologist to rule out pathologic conditions such tumor, abscess, upper urinary tract damage, or bladder calculi.8 By far the most common cause of unresolved catheter-associated infection is calculi, which begin as small encrustations on the catheter.
Bacterial biofilms and encrustation
Catheter encrustations are due to gram-negative organisms that proliferate in alkaline urine (pH >6.5) leading to formation of calcium oxalate or struvite (magnesium ammonium phosphate) crystals. Attempts to acidify the urine with oral intake of ascorbic acid have been equivocal and non-confirmatory.9-11 Encrustations can collect in the bladder and form bladder stones that continue the cycle of bacterial growth and bladder spasms.3,12 Understanding encrustations depends on an understanding of the bacterial biofilms that develop on the catheter.
Bacterial colonization, biofilm development, and subsequent encrustation formation is complex (refer to table 1). In the presence of the indwelling catheter, a biofilm is formed when bacteria with a planktonic phenotype adhere to and colonize the catheter.13 An organic film supports rapid multiplication of the organisms, and they quickly cover the catheter's internal lumen, external walls, and drainage eyes.14,15 Bacteria are linked via changes in gene expression stimulated by acetyl homoserine lactones (AHL), and these alterations lead to the formation of a sophisticated, complex structure of multiple clusters of bacteria and a primitive circulatory system. A bacterial extracellular polysaccharide matrix further shields the bacteria from mechanical dislodgement, from endogenous host defenses such as phagocytic activity, and from exogenous attack via oral or parenteral antibiotic therapy. The near-impenetrable biofilm contains proteins, glycoproteins, electrolytes, and carbohydrates and has a net negative charge that attracts more molecules.16
The pH of the urine and biofilm matrix rises by the action of urease on urea, especially in the presence of urease-producing bacteria, particularly Proteus mirabilis, Proteus vulgaris, and Providencia rettgeri.17 The breakdown of urea to ammonia raises the pH above 6.8, and the alkaline urine in turn encourages the growth of organisms. Encrustation occurs when struvite (magnesium ammonium phosphate) and calcium phosphate crystals precipitate and agglomerate onto the catheter surface and biofilm.13,15,18 The process of encrustation reaches clinical significance when it obstructs urine outflow through the catheter.
The prevalence of encrustation in catheters is reported to be 40% to 50%.19,20 Several reports have noted that some patients are likely to be "blockers" while others are not; the typical blocker is female and immobile.21 Obstruction can occur as frequently as every few days in blockers whereas, in non-blockers, catheters can be patent for many weeks.
Management of catheter encrustation and blockage
Prevention of encrustation and catheter blockage has been largely unsuccessful: hydration has not been effective in encrustation-prone patients;21 alternative materials for catheter construction, such as hydrogels, have not prevented colonization with urease-producing bacteria or subsequent encrustation in the laboratory or clinical setting;22,23 and antiseptic- or antimicrobial-impregnated catheters have not prevented blockage. Several investigators have noted that latex catheters, even those treated or coated with silicone, cause cytotoxicity and should be avoided.24,25
Irritation and inflammation of the urethra can result from catheterization and can lead to strictures or outright blockage. A 1985 controlled, randomized, prospective study showed that all-silicone catheters are less likely to cause urethritis or strictures.26 In the study, 100 men who underwent elective cardiac surgery were catheterized, with antibiotic cover, for 48 hours. Six months after surgery, 22% of those with latex catheters had developed urethritis, compared with 2% of those in the silicone catheter group (p <0.01).
Another contemporaneous study looked at men who underwent coronary artery bypass grafting.27 Latex catheters were used in 100 subjects, and after 15-24 months the incidence of urethral stricture was 5.2%. A separate group of 117 had silicone catheters, and after 12-28 months experienced no urethral strictures.
These two studies looked at short-term use of catheters. Kunin et al. studied encrustation or blockage in long-term use, especially in patients who are blockers.28 This crossover study used silicone, silicone-coated, TEFLON-coated, and latex catheters (18-F with 30-ml balloon) that were left in place for 14 days. Results published in 1987 revealed that nonblockers, who constituted about half the subjects, did well regardless of type of catheter material used. Blockers had significantly less formation of encrustations and blockage with silicone as compared with TEFLON-coated or latex catheters. Investigators noted that the more rapid flow time through silicone catheters appeared to be related to a larger bore.
In current clinical practice, only three strategies are effective in the management of catheter blockage: irrigation with an acidic solution, application or addition of antibacterial medications, and replacement of the catheter.18,29
Muncie and associates30 compared daily irrigations versus no irrigation of long-term indwelling catheters in 32 subjects. There were no differences between groups in the incidence of symptomatic urinary tract infection, encrustation, or obstruction when daily irrigation with saline was added to routine catheter management. In 1978, Bruun and Digranes31 compared twice-daily bladder irrigation with saline, acetic acid, chlorhexidine, and silver nitrate solutions in patients with indwelling catheters and known bacteriuria. Saline and acetic acid did not change the colony counts; chlorhexidine and silver nitrate solution both did. Silver nitrate, however, was painful for the patient, and the authors recommended further research on chlorhexidine irrigations. Unfortunately, later research on chlorhexidine solutions has shown that continuous long-term use does not confer any significant benefit and might, in fact, contribute to antibiotic-resistant organisms.32
In Europe, an accepted measure for managing blocked catheters is irrigation with an acetic acid solution.33 Although acetic acid alone does not reduce colony counts, a combined solution of 3.2% citrate, 0.38% light magnesium oxide, 0.7% sodium bicarbonate, and 0.01% disodium edetate does seem to effectively reduce Proteus infection and encrustation.34 A more concentrated solution has been used following lithotripsy to dissolve struvite stones, but the solution irritates the bladder mucosa and is not recommended as a bladder irrigation solution.
RENACIDINâ„¢, a solution of citric acid, glucono-delta-lactone, and magnesium carbonate is used for renal calculi and has been advertised as a preventive strategy for catheter encrustations; however, no research has been conducted on the product, and product information warns of potential adverse reactions, especially in patients with compromised renal function.35 MANDELIC acid can also reduce the colony count in the catheterized bladder but is less effective against Proteus mirabilis than the other solutions.32 Several other studies18,21,36,37 indicate a potential benefit of routine irrigation with a small volume of a washout solution in indwelling catheters, but clinical trials are needed to prove the efficacy of this management strategy.
Silver-alloy impregnated catheters might have modest benefit in controlling bacteriuria in short-term catheterized patients. To assess their effectiveness in the longer term, Verleyen et al38 randomly assigned 215 post-urologic-surgery patients to standard or silver-coated catheters. No difference in incidence of bacteriuria was found in a subgroup of men catheterized for approximately 14 days after radical prostatectomy; in a larger group, after a mean of only 5 days of catheterization, onset of bacteriuria was delayed. Thus there appears to be a protective factor of silver alloy in the first 5 days of catheterization, but this influence disappears by approximately 14 days after catheterization.
In another randomized controlled trial of 1,309 patients requiring catheterization longer than 24 hours, there were no differences in the incidence of bacteriuria in the silver-alloy- or standard silicone-coated catheter groups.33 Of note was a significant increase in bacteriuria in the men randomized to the silver alloy group.
A 1997 study39 by Morris and colleagues compared the resistance of various types of indwelling urethral catheters to blockage by encrustation with mineralized Proteus mirabilis biofilms. In a simple laboratory model of the catheterized bladder, artificial urine was supplied to the bladder chamber at 0.5 mL/min. The bladder urine was inoculated with a clinical strain of P. mirabilis that had been isolated from an encrusted catheter. When a catheter blocked, atomic absorption spectrometry was used to assess the amounts of calcium and magnesium deposited on the catheters. Scanning electron microscopy was also used to locate and assess the degree of encrustation. None of the 18 types of catheter tested, including those coated with hydrogel or silver, was capable of resisting encrustation by P. mirabilis biofilm. Over all, the all-silicone catheters took longer to block than the TEFLON-, hydrogel-, or silicone-coated catheters.
A similar study reported a year later by Morris and Stickler produced similar results.40 The mean times to blockage were 17.7 hours (silver-coated latex), 34 hours (hydrogel-coated latex), 38 hours (silicone-coated latex), and 47 hours (all-silicone).
The results of these studies suggest that clinicians should consider carefully before recommending the use of the silver-alloy catheters. Work continues on introducing differing antibiotic agents within or on catheters that will either penetrate the biofilm, eradicate the organisms, or inhibit the crystallization process.16,41,42
Instillation of triclosan into the catheter balloon has recently been proposed as a way to prevent bacterial adherence and subsequent encrustation. In a laboratory controlled study, catheters inflated with triclosan solution and placed in an artificial bladder contaminated with Proteus mirabilis remained encrustation-free in a urine pH of 6.7 for more than 7 days.17 The control catheters became encrusted within 24 hours and urinary pH rose from 6.1 to 8.6.
Even aggressive antibiotic therapy does not obliterate biofilm formation.29 Once present, organisms survive antibiotic therapy and proliferate rapidly after discontinuation. At least three reasons are posed to explain the remarkable self-protective ability of the bacterial biofilm: the antibiotic might not completely penetrate the biofilm; some bacteria within the biofilm survive in a near-starvation mode and might not be killed by antibiotic treatment; or specific aspects of the biofilm mediated by gene expression might alter its sensitivity to antibiotics as soon as treatment is discontinued.12,43
Removal of the catheter eliminates the biofilm and any encrustation but also requires repeated and frequent re-catheterization with an increased risk of cost, infection, urethral trauma, and patient discomfort. Catheter changes should be based on catheter patency rather than according to fixed intervals.2 Assessment based on the catheter life of an individual patient, with pH and encrustation monitoring when the catheter is removed, is recommended to give both nurses and patients more control of catheter changes.44
The studies cited above show that all-silicone catheters may require fewer replacements, taking the longest time to become blocked.
Large catheters (>18 F) distend the urethra and can irreparably damage the urethra and bladder neck as well as contribute to bladder spasms and leakage.45 It is recommended that catheter size be no larger than 16 F with a 5-ml balloon inflated with 10 cc sterile water to ensure symmetry of the balloon.8 Larger catheters are indicated only after urologic procedures when hematuria and clots are anticipated.
All-silicone catheters offer an advantage in that their walls are thinner, thus providing a larger internal diameter than other types of the same French size. For instance, in the first study39 by Morris and colleagues cited above, the calcium and magnesium salts were mainly deposited on the 10 cm below the eye-holes of the catheters, and complete blockage generally occurred in the 2 cm immediately below the eye-hole. The investigators concluded that a catheter's internal diameter, not necessarily its composition, was a major factor in determining time to blockage. The second study, by Morris and Stickler,40 noted that the internal diameters of the latex catheters were only 1.5 mm compared with the 2.5 mm of the all-silicone catheters.
Occasionally, suprapubic catheters are recommended for long-term management to avoid urethritis, urethral erosion, prostatitis, and orchidoepididymitis, but there are no long-term research studies to support this practice.8
Encrustation and blockage of catheters is a perennial problem in catheterized patients and costs both the system and the patient. Current management of blocked catheters is either to replace the catheter before it blocks (depending on the "catheter life" of the patient) or to routinely irrigate.
Preventing catheter-associated complications is far easier than treating the problem once it has occurred. The judicious use of catheters in individual situations, use of a 14-F or 16-F catheter with a 5-ml balloon, and adequate fluid intake can go far to delay the onset of complications. All-silicone catheters might be the best choice because of their longer mean time to blockage; however, more clinical research studies are required to assist clinicians in managing catheter encrustations.
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