Our latest Guest Blog is by Dr Michael Wong, Director of the Singapore Urology, Fertility and Gynaecology Centre. He is a US Fellowship Trained Urologist, and previous President of the Singapore Urology Association. Michael gives an up to date and comprehensive account of Infective Complications in the Surgical Management of Urinary Stones.
Infective Complications in the Surgical Management of Urinary Stones
Despite the significant advancements in the surgical management of urinary stones, morbidity and even mortality are still being reported. Krambeck reported in the Journal of Urology in 2013 that deaths still occur after surgery, particularly in the elderly population as their immunity is lower and there could be delay in diagnosis due to lack of classical symptoms. The importance of appropriate antibiotic prophylaxis and assessment of risk factors prior to treatment cannot be underestimated.
Infective Issues with Percutaneous Nephrolithotomy (PCNL)
PCNL is most appropriate for large renal stones. One of the feared complications of PCNL is urosepsis. A common composition for staghorn stones is struvite,5 which results from the presence of urea-splitting organisms, and non-struvite stones may also harbor bacteria. There is therefore an increased risk for sepsis during the procedure. Further, PCNL utilizes large volumes of irrigation relative to ureteroscopy, which may increase the risk of sepsis.
The practice of prophylaxis for PCNL is not for debate. David Tolley reported that the rate of UTI reduces 3 fold when using prophylaxis for PCNL. Recently, the CROES group reported a series of 162 patients from multiple institutions who underwent PCNL without pre-operative antibiotics and matched them to patients who did receive antibiotics6 All patients had negative pre-operative urine cultures and matching was based on infectious risk factors such as diabetes, nephrostomy tubes and staghorn stones. They found that antibiotic prophylaxis led to fewer fevers (2.5% vs. 7.4%) and other complications (1.9% vs. 22%) and higher stone free rate (86.3% vs. 74%). The explanation for this finding may be that stones themselves may harbor bacteria that may not manifest in a voided urine culture.
Techniques to culture stones were described over 40 years ago. In a study examining infection rates in patients undergoing PCNL, 35% of patients had positive stone cultures, compared with 21% of upper tract and 11% of bladder urine cultures. Stone manipulation and lithotripsy can result in the release of bacteria and contamination of urine with possible systemic transudation resulting in sepsis or systemic inflammatory response syndrome (SIRS). Stone cultures have been shown to be a better predictor of sepsis and SIRS than voided cultures. Mariappan showed a positive stone culture to have over 80% sensitivity and a positive predictive value of 70% in predicting SIRS.7 Overall, positive stone cultures increased the risk of SIRS 4-fold. Along with bacteria, stones contain endotoxins that can potentially result in a systemic immune response clinically similar to sepsis.
The greatest limitation of stone cultures is that they are only available after a procedure with some days to allow bacteria culture and so cannot influence immediate peri-operative treatment. The utility of obtaining stone cultures in clinical practice is to guide antibiotic choice in the event of sepsis following ureteroscopy or PCNL rather than predicting it. Having said this, it is reassuring to routinely collect stone cultures intraoperatively from patients undergoing PCNL.
Understanding the Risk factors for Urosepsis during PCNL
Many groups have reviewed their experience with PCNL in an attempt to identify risk factors for post-operative fever, sepsis or SIRS. A positive pre-operative urine culture was associated with increased infectious risk (OR 2.2 -16.7), as were positive pelvic urine (OR 10.2 – 24.1) and stone cultures (4.88 – 25.6). Other factors such as female sex, hydroureteronephrosis, pre-operative nephrostomy tube, large or complex stone burden, and diabetes have all been associated with an increased risk of post-operative fever or sepsis.
Korets and colleagues showed that an increased number of access tracts increased the risk of SIRS (HR 4.8) when controlling for patient sex, stone culture and composition, while several other groups have found increased operative time to be a risk factor for fever. Dogan also showed volume of irrigation fluid required was a significant predictor. These three factors are likely all surrogates for stone size and complexity, resulting in a prolonged procedure.
Infective Issues with Ureteroscopy
A 2003 RCT by Knopf et al. that included 113 patients found a single prophylactic oral dose of fluoroquinolone prior to ureteroscopy reduced the incidence of post-operative bacteriuria (1.8% vs. 12.5%, p=0.02). There were, however, no incidences of symptomatic UTI. This study guided the AUA Best Practice Policy in recommending antibiotic prophylaxis prior to ureteroscopy for the management of stone disease.3 The guideline committee states that the potential risk of bacteriuria is 30% and UTI ranges from 4% - 25% without prophylaxis. There is no difference in efficacy between oral fluoroquinolone and intravenous cefazolin.
A Korean group reviewed their experience of infectious complications following ureteroscopy and identified several risk factors.4 They noted an overall UTI rate of 3.8%. Furthermore, they found hydronephrosis, bacteriuria, and an indwelling ureteral stent or nephrostomy tube was associated with an increased risk of post-procedural fever. Administration of antibiotics after the procedure was not as effective as pre-procedural prophylaxis.
Eswara and colleagues retrospectively reviewed their experience with stone cultures in patients undergoing ureteroscopy (n=274) or PCNL (n=54). They found that while pre-operative urine cultures were only positive at some point in 7% of patients, stone cultures were positive in 29%. Their overall sepsis rate was about 3-4% for all patents. In patients with positive stone cultures, the sepsis rate was significantly higher at 8% compared to only 1% in those who had negative stone cultures. Ultimately, urine cultures had a sensitivity of 11% versus 64% in stone cultures and there was a concordance of 64% between the stone culture pathogen and the one causes sepsis compared to only 9% of pre-operative urine cultures. Despite the correlation of stone cultures and post-operative infection, their utilization in guiding clinical practice is limited in that it takes several days following the removal of the stone for cultures to results. They are most helpful following the development of UTI to help guide antibiotic choice.
Unfortunately we do not have a study showing the use of ureteric stent post URS reduces UTI as upper tract decompression using a stent would also play a part in reducing UTI.
Infective Issues in Extra-Corporeal Shock Wave Lithotripsy (ESWL)
In general, the incidence of urinary tract infection occurring after uncomplicated ESWL is less than 1%, rising to 2.7% for staghorn calculi. This risk of sepsis increases in the presence of bacteriuria prior to ESWL especially if there is distal obstruction.
Until recently, the practice of giving prophylactic antibiotics was controversial in patients undergoing ESWL with negative urine cultures. It has been reported that bacteriuria can develop in 5-6% of patients undergoing ESWL even in the presence of sterile urine prior to the procedure and the risk of clinical UTI can be seen in 2-3% subsequently.
The European Association of Urology guidelines on urological infections (updated in 2010) do not recommend prophylactic antibiotics in ESWL unless there are risk factors like ureteral stents, urinary catheters, nephrostomy tubes or infective stones1.
More recently, in a meta-analysis reported in the Journal of Urology in 2012 covering 9 randomized trials of 1364 patients undergoing ESWL for urinary stones with sterile urine cultures2, Lu et al reported no significant differences between the prophylactic group and the control group in terms of symptoms, rate of fever, rate of positive urine culture and the incidence of urinary tract infection. They suggested that antibiotic prophylaxis is not necessary for ESWL in low risk patients.
The American Urological Association guidelines3 were recently updated in Jan 2014 and currently do not recommend antibiotic prophylaxis for patients undergoing ESWL with negative urine culture. In the light of more recent publications, prophylactic antibiotics are recommended only in high risk stone groups with infective stones, recent instrumentation, nephrostomy tubes, positive urine cultures and a history of recent UTI or sepsis. In addition, special considerations should also be given to high risk patient groups which the AUA defines as advanced age, anatomical anomalies of the urinary tract, poor nutritional status, chronic smokers, chronic steroid users, immunodeficiency, externalized catheters and prolong hospitalisation.
In general, ESWL should only be performed if the urine is sterile and when there is no distal obstruction to minimise infective complication. Currently, prophylactic antibiotics should be considered only in high risk patients.
The current guidelines and practice patterns pertaining to stone surgery have evolved based on emerging clinical data. These recommendations in conjunction with patients’ individual risk factors and culture data should help guide ongoing practice patterns.
1. Wolf, J. S., Jr., Bennett, C.J., Dmochowski, R.R. et al. : Best practice policy statement on urologic surgery antimicrobial prophylaxis. J Urol, 179:1379,2008.
2. Grabe, M., Bjerklund-Johansen, T.E., Botto, H. et al.: Guidelines on Urological infections. European Association of Urology:79,2010.
3. Lu, Y., Tianyong, F., Ping, H. et al.: Antibiotic prophylaxis for shock wave lithotripsy in patients with sterile urine before treatment may be unnecessary: a systematic review and meta-analysis. J Urol, 188:441,2012.
4. Sohn, D. W., Kim, S. W., Hong, C. G. et al.: Risk factors of infectious complication after ureteroscopic procedures of the upper urinary tract. J Infect Chemother, 2013
5. Segura, J. W., Preminger, G. M., Assimos, D. G. et al.: Nephrolithiasis Clinical Guidelines Panel summary report on the management of staghorn calculi. The American Urological Association Nephrolithiasis Clinical Guidelines Panel. J Urol, 151: 1648, 1994
6. Gravas, S., Montanari, E., Geavlete, P. et al.: Postoperative infection rates in low risk patients undergoing percutaneous nephrolithotomy with and without antibiotic prophylaxis: a matched case control study. J Urol, 188: 843, 2012
7. Mariappan, P., Loong, C. W.: Midstream urine culture and sensitivity test is a poor predictor of infected urine proximal to the obstructing ureteral stone or infected stones: a prospective clinical study. J Urol, 171: 2142, 2004
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