Infected Urinary Stones, Endotoxins and Urosepsis. LPS. Lipopolysaccharide; SWL. Extracorporeal shock wave lithotripsy; SIRS. Systemic inflammatory response syndrome; MOF. Multiple organ failure.
Urinary tract infections (UTIs) and their complications represent one of the most common causes of medical consultation with high cost to medical services and high morbidity and mortality. Urinary stones are another medical challenge that represents an acute or chronic clinical setting for patients requiring most of the time active treatment, either as an invasive or as a non-invasive management, thus increasing costs and risks. The combination of both clinical scenarios —urinary tract infection and urinary stone— is common and can trigger a systemic inflammatory response syndrome (SIRS) before, during or after medical treatment (i.e. antibiotics) and/or surgical manipulation of infected urinary stones. It is believed that SIRS is due to the release of endotoxins from infected urinary stones, developing endotoxemia, bacteremia and urosepsis. If not controlled, multiple organ failure syndrome (MOF) and death of the patient may occur. Urologists are familiar with these scenarios where not only prevention and diagnosis but also an early and appropriated treatment is crucial. Unfortunately, the use of prophylactic antibiotics does not guarantee prevention of these fatalities. The aim of this chapter is to review the evidence of possible endotoxin release during invasive and non-invasive treatment of infected urinary stones as a trigger of SIRS and sepsis.
2. Urinary tract infections
Urinary tract infections are the second most frequent infections in developed countries and uropathogenic
2.1. Urinary bacterial epidemiology
Urinary tract infections in Western countries are mainly caused by
To invade hosts, bacteria use a variety of substances, some of them are essential for their survival. In Gram-negative bacteria, specific molecular patterns composed of lipid and sugar moieties represent some of the most toxic virulence factors of bacterial origin. Structurally classified as lipopolysaccharides (LPS), these substances have no chemical homologs among human cells, and are known as endotoxins, to denote their ability for causing fever, shock and organ injury when released in mammalian endothelial vessels (Beutler, 2000). The presence of endotoxins in the blood-stream is named endotoxemia and can trigger SIRS. LPS have specific structural motifs which are typical of different bacterial species. However, all of them are known to induce endotoxemia and sepsis (Bochud & Calandra, 2003). Endotoxins are known to be recognized by cell-surface proteins, the LPS receptors, which are widely distributed in animals as part of their immune systems (from insects to vertebrates). However, a strong inflammatory reaction after LPS recognition is restricted to a handful of species, including humans (Beutler, 2000). According to numerous studies in cellular and animal models, recognition of LPS by their receptors initiate a cascade of intracellular signals guiding the secretion of pro-inflammatory mediators (Beutler, 2000; Triantafilou & Triantafilou, 2005). An emerging concern is the toxicity of LPS after microbial death, especially in the context of hospital-acquired infections. In fact, released LPS keep their full toxic potential, unless inactivation processes take place in the host to degrade endotoxins (Munford et al., 2009).
3. Urinary stones
Urinary stones have been reported in human history since antiquity. Traditionally, stones have been classified according to their main mineral content. The etiology of urinary stones is wide, including chronic dehydration, urinary tract malformations, obstructed uropathy, metabolic diseases (i.e. hyperparathyroidism, gout, and obesity), foreign body inside urinary tract, infections, etc. The risk for stone disease in patients of developed countries is close to 10 % life-long. An increase in the incidence of stone disease related with changes in the life style, modifications on the diet, morbid obesity surgery syndrome and new drugs has been reported in Western countries in recent years. For example, in the United States, an increase of 37 % in stone disease was observed over the last 20 years (Straub & Hautmann, 2005). A variation in the frequency and in the composition of the minerals forming the urinary stones was also observed.
There is a large variety of urinary stone compositions. If the main component is more than 80 % of the total mass, the stone is named “pure”. If the main component is at least 50 % of the stone, it is named mixed. In Western countries, struvite stones used to represent 15-30 % of cases. Nowadays only 2 % of stones are struvite (McALeer et al., 2003; Kramer et al., 2000). The explanation of that decrease is unknown. In developing countries and Eastern countries there is a large variation among incidence, prevalence and stone composition. For example, in India a report including 1050 urinary calculi from surgically treated patients (900 renal and 150 ureteral) revealed 93.04 % oxalate calcium stones (80 % calcium oxalate monohydrate [COM] and 20 % calcium oxalate dihydrate [COD]), 1.92 % struvite stones, 1.48 % apatite stones, 0.95 % uric acid stones and 2.96 % mixed stones. Surprisingly, 89.98 % of the staghorn stones consisted of oxalates and only 4.2 % were struvite (Ansari et al., 2005). A study in Japan showed that the most common stone composition was struvite (32.1 %) and mixed calcium oxalate phosphate (22.2 %) (Akagashi et al., 2004). These differences could be explained by variations in ethnics, epigenetics, geographical area, diet, life-style, and different metabolism.
3.1. Infected stones
It has been suggested that urinary stones can be infected mainly in two ways. Stones develop due to several mechanisms which may or may not be associated to obstructive uropathy (i.e. hyperparathyroidism). The first way in which a stone can be infected is by ascending bacteria. Once the stone is formed, ascending bacteria may reach its surface, invade the interstice and become part of it (Takeuchi et al., 1984; Abrahams & Stoller, 2003). Adherence of new minerals could cover and paste bacteria layers. In this case, the stone acts as a reservoir for bacteria. Due to the poor penetration of drugs into the stone matrix the action of antibiotics is limited (Prabakharan et al., 1999). This phenomenon can be the reason of bacterial resistance, repeated, chronic or complicated UTIs in several patients, therefore increasing the risk of urosepsis. The most possible scenario according to the most frequent stone component and urinary bacteria in our Western world is a calcium stone infected with
The second scenario is that bacteria living inside the urinary tract and causing chronic UTIs produce the stones. These bacteria are named urea-splitting bacteria. Members of this group are
It has been suggested that some agents named nanobacteria could have a role in the development of calcium-based urinary stones (Kajander & Çiftçioglu, 1998); however, this is not yet well established (Kramer et al., 2000). A prevalence of nanobacteria in 0.5 % of 1000 stones was reported; but nanobacteria are still difficult to identify (Abrahams & Stoller, 2003).
3.1.1. Bacterial epidemiology of infected urinary stones
Urinary stone cultures from fragments retrieved during stone surgery were not a common practice until recently. Negative urine culture before urinary surgery was considered safe. In general urology it has been a routine to have a negative midstream urine culture before doing any endoscopic procedure. Recent studies suggest that voiding urine culture is not representative of upper urinary tract pelvis infection or pelvis infected stone bacteria (Mariappan & Loong, 2004; Mariappan et al., 2005a). A group of 73 patients with unilateral stone-obstructed ureter were treated with ureterorenoscopy and lithotripsy. Midstream urine (MSU) sample culture and sensitivity were performed the morning of the endoscopic surgery. During the procedure a pelvis urine sample and stone fragments were collected for culture and sensitivity with an aseptic technique in a retrograde approach. The authors reported that 25 (34.3 %) patients had positive stone culture, 43 (58.9 %) had positive pelvic urine and 21 (28.8 %) had positive MSU culture. The most common isolated bacterium was
Mariappan and colleagues (2005a) studied a group of 54 patients with renal stones who were candidates for percutaneous nephrolithotomy (PCNL). Various specimens were collected for culture and sensitivity, i.e., MSU sample, bladder urine sample, renal pelvic urine sample and crushed stone sample. The objective of the study was to identify the most predictive analysis of urosepsis. MSU culture was positive in 11.1 % of cases, stone culture was positive in 35.2 % and pelvic urine was positive in 20.4 % of cases. A wide variety of bacteria were isolated. In 37 % of the patients SIRS was developed and 5.5 % experienced septic shock. Pelvic urine culture predicted infected stones better than bladder urine culture. Patients with infected stones or pelvic urine were found to be at a relative risk for urosepsis that was at least four times greater (P = 0.0009). The authors concluded that positive stone and pelvic urine are better predictors of potential urosepsis than bladder urine and recommend routine collections of these specimens. Stone components were not analyzed. The bacterial epidemiology of infected urinary stones also depend on differences in geographic area, strains, bacterial resistance, bacterial virulence, exposure to some kind of antibiotics and environment.
4. Sepsis and urosepsis
Sepsis is an extreme health condition that threatens life of patients with a high cost for the healthcare systems. Reports from US and European surveys have estimated that severe sepsis accounts for 2–11 % of all admissions to hospitals or intensive care units. The most common microbes isolated from patients with severe sepsis and septic shock are Gram negative bacilli (mainly
5. Endotoxins and sepsis
Activation of local and systemic metabolic response to trauma and SIRS is mainly caused by activation of IL-1 and tumor necrosis factor-α (TNF-α). It is well established that after recognition by cognate receptors, LPS trigger the synthesis and release of pro-inflammatory cytokines (Triantafilou & Triantafilou, 2005). Once IL-1 and TNF are secreted, they activate several other reactions like complement factors, exacerbating the host inflammatory response. As a consequence, MOF or death may result.
6. Infected urinary stones and urosepsis
In a study on 700 patients, the prevalence of sepsis related with obstructed uropathy and urinary stones treated surgically was 1.28 %. These nine patients developed SIRS and sepsis during 6 hours postoperative. Although males and females were treated in roughly equal proportions, all of the patients who developed severe sepsis were females. There were six deaths accounting for 66 % mortality (O'Keeffe et al., 1993). Septic shock following urinary stone manipulation was reported with an incidence of 1 % and mortality up to 80 % (Rao et al., 1991).
In an effort to predict septicemia following endourological manipulation for stones in the upper urinary tract, 117 patients were studied and classified according to the procedure performed (Rao et al., 1991): Percutaneous nephrolithotomy, push-back/push-bang procedure, double-J and extracorporeal shock wave lithotripsy (SWL), ureteroscopy, SWL alone and only cystoscopy. Blood samples for bacterial culture, endotoxin and tumor necrosis factor assay were collected before, at onset, at the end and one hour after completing the procedure. Preoperative bacteriuria was present in 35 % of the patients. The mean endotoxin level of the entire group —except the cystoscopy group— was 16.2 pg/mL (range 11 to 58.3 pg/mL). In the cystoscopy group the mean endotoxin level was 11.7 pg/mL (range 11 to 12.2 pg/mL). All patients (16) with preoperative endotoxemia had increased levels of endotoxin detected in subsequent samples (mean increase 15 pg/mL, range 0.5 to 64 pg/mL). The tumor necrosis factor was greater than 15 pg/mL in four cases preoperatively. Postoperatively there was elevation of the tumor necrosis factor only in 12 patients. The authors reported that in case of upper urinary tract manipulation, the risk of bacteremia was higher. The risk was greatest after performing the push-back method and least after cystoscopy. Combination of preoperative endotoxemia, bacteriuria and the type of procedure had 85 % of sensitivity, 84 % of specificity and a positive predictive value of 52 % for the development of postoperative bacteremia. A total of 41 patients had pyrexia and 17 patients had rigors and fever 2 to 3 hours after the end of the procedure. No patient suffered septic shock; however, this complication developed in a female patient one week after percutaneous nephrolithotomy. Serum endotoxin and tumor necrosis factor levels after admission of this patient to the intensive care unit were 67.7 pg/mL and 3,827.5 pg/mL, respectively (Rao et al., 1991).
Measurements of LPS were done in 34 renal stones, stored for several months and classified as infection stones (16), i.e., struvite and calcium apatite, and non-infection stones (18) composed of 50 % calcium oxalate monohydrate (McALeer et al., 2003). All stones were weighed, aseptically crushed and aliquots were tested for endotoxins. Four stones of each group were aseptically washed and crushed separately. Washed materials and crushed stones were processed in MacConkey agar culture to recover bacteria colonizing the stones. Mean endotoxin concentration in the infection group was 12,223 ng per gram of stone and 340.3 ng per gram of stone in the non-infection group. The difference was statistically significant (P = 0.001). These results reveal an almost 36 times higher concentration of endotoxins in the infection stones. No living bacteria were recovered on the MacConkey plates from crushed stones from neither group. The authors concluded that large amounts of endotoxins can be found in infected renal stones even months after they were removed from the body, and long after viable bacteria could be detected. Furthermore, endotoxin may remain after bacteria are no longer viable or have been killed with antibiotic therapy (Munford et al., 2009). Non-infectious stones can also contain endotoxin but in a lower amount (McALeer et al., 2003). McALeer et al. (2002) published a case report of an 8 year old boy with a left staghorn calculus treated with holmium laser percutaneous nephrolithotripsy (PCNL). Culture specific antibiotic were administered to the patient, both orally and intravenously, before, during and after surgery. Intraoperative fluid and pleural fluid cultures (urologists lost percutaneous access from lower pole calyx with intraperitoneal extravasation and pleural effusions) were obtained. A urine culture was performed before and after stone manipulation. All samples grew a few colonies of
There is not a general consensus on how to best prevent sepsis in patients undergoing surgical treatment of urinary stones. Pre-surgical, trans-surgical and post-surgical strategies have been proposed. The combination of multiple factors can prevent, trigger or worsen sepsis. For example, control of metabolic or cardiopulmonary diseases is important. Although antibiotic prophylaxis does not completely avoid the risk of developing sepsis, it is a recommendation for stone surgery according to the American Urological Association (AUA) and the European Association of Urology (EAU) guidelines on urinary tract infection (Grabe et al., 2011; Wolf et al., 2010). It is suggested to define an antibiotic prophylaxis according to local bacterial populations, resistance and antibiotic sensitivity patterns. In a prospective controlled trial, Mariappan et al. (2006) and Bag et al. (2011) reported the beneficial use of one week ciprofloxacin and nitrofurantoin regimen respectively, before percutaneous nephrolithotomy. Furthermore it has been found that renal stones larger than 20 mm are more likely to be culture positive (Mariappan et al., 2005a; 2005b). Mariappan and colleagues (2005a) suggested to obtain pelvic urine and stone samples for culture and sensitivity as a routine during surgical stone procedures, with the aim of administering proper antibiotic regimen if later urosepsis develops. If an unusual urine sample (i.e. turbidity, foully) is obtained, culture and sensitivity is a must. In this case, a nephrostomy tube should be left in place and the initial procedure rescheduled until sterile urine is confirmed.
An increase of pressure inside the urinary tract system generated by the irrigation fluid results in a potential bacterial and endotoxin translocation into the bloodstream. Auge et al. (2004) reported significant reduction in urinary tract pressures using ureteral access sheath if working both in distal ureter and inside the renal pelvis. Bacteria and likely endotoxins may emerge from several kinds of urinary stones and not exclusively from struvite stones (Hugosson et al., 1990; McALeer et al., 2003). In post-surgical stage, the most critical evidences of SIRS are during the first 6 hours post-procedure and seem to correlate with cytokines release into the bloodstream after endotoxin stimulus (Dandona et al., 1994; O'Keeffe et al., 1993; Rao et al., 1991; Taudorf et al., 2007). It has been suggested that if other causes of SIRS different than infection (i.e. cardiogenic or pulmonary events, atelectasis, hypovolemia and pain) have been ruled out and if SIRS persists, then sepsis could be the explanation (Monga, 2005). Close vital signs and symptoms monitoring and high suspicious index for sepsis is crucial at this stage. Once urosepsis is diagnosed, an early tissue oxygenation, appropriate initial antibiotic therapy, inotropic and nutritional support with invasive monitoring at intensive therapy unit is required. Empirical broad-spectrum antibiotics regimen is prescribed according to local bacteria, sensitivity and resistance patterns. If cultures were performed from bladder urine, pelvis urine or stone sample, direct therapy must be installed as soon as results are obtained (Mariappan et al., 2005b). Wagenlehner and his group (2007) reported that the treatment of urosepsis comprises four major aspects: Early goal-directed therapy, optimal pharmacodynamics exposure to antimicrobials both in blood and in the urinary tract, control of complicating factors in the urinary tract and specific sepsis therapy. They considered that interdisciplinary approach is necessary to achieve an optimal goal of treatment. At any of these stages, it is very important to act as soon as possible if any evidence of initial SIRS and urosepsis is addressed. It is necessary to instruct the patient and relatives once discharged from the hospital, that if SIRS develops, urgent evaluation in an emergency unit is crucial (Rao et al., 1991). There is no doubt that further research is required and that several other issues have to be considered; however, these do not fall within the scope of this chapter.
7. Research on bacterial suspensions and extracorporeal shock wave lithotripsy
Several articles report the bactericidal effect of shock waves
8. Research with stone models
Efforts to develop an ideal stone model have been done worldwide to perform
8.1. The bactericidal effect of intracorporeal lithotripters
Only a few authors report results on the interaction of infected urinary stones with intracorporeal lithotripters. Artificial kidney stones, infected with
Our group also studied the effect of the four above-mentioned intracorporeal lithotripters on the bacterial inactivation of artificial struvite stones inoculated with
In conclusion, it seems that the stone material plays a minor role regarding bacterial inactivation due to intracorporeal lithotripsy. Furthermore, according to our results, intracorporeal lithotripters are very harmful to bacteria; however, whether bacterial destruction is desirable or not is still unknown.
8.2. The bactericidal effect of extracorporeal lithotripters
A reduction in bacteriuria and resolution of urinary tract infection after SWL has been reported by several authors (Beck & Riehle, 1991; Gerdesmeyer et al., 2005; Michaels et al., 1988; Pode et al., 1988); however, it is not known if the stone protects bacteria or if other mechanisms, such as shear, contribute to the bactericidal effect of shock waves. To answer these questions, infected stones were exposed
Sepsis is a serious health condition with high mortality and cost. Advances in the manufacture of standardized infected stone models and
|During sepsis, a 25 - 50 pg/mL LPS concentration has been reported in the bloodstream.|
LPS concentrations of up to 285,600 pg per gram stone have been reported in a fatal case of urosepsis.
Release of LPS has been observed after
The bactericidal effect of both extra- and intracorporeal lithotripsy should be studied carefully due the possible release of large amounts of LPS.
Under certain circumstances, this initial evidence could explain triggering of SIRS, urosepsis and MOF.
The authors would like to thank Carmen Clapp, Carmen Wacher-Rodarte, Eduardo Fernández-Escartín, Concepción Arredondo, Olivia Vázquez, Marisol Moreno, Daniel Marín, Mauricio Díaz-Muñóz, Rodolfo Galeana, Arturo Méndez, and René Preza for important assistance. This research was supported by the PAPIIT-UNAM grant IN108410.