Extracorporeal Shockwave Lithotripsy in Elderly: Impact of Age and Comorbidity on Stone-Free Rate and Complications

Introduction

F ollowing the first ever successful treatment of the patient with recurrent nephrolithiasis, the initial clinical results of extracorporeal shockwave lithotripsy (SWL) were published by Chaussy and coworkers ¹ in 1980 and have forever revolutionized the treatment of urolithiasis. Since then, SWL has gained worldwide acceptance as a safe treatment modality for urinary calculi, with its noninvasive nature, fast patient recovery, and low complication rate in the general population.

Despite the early reports on effectiveness and safety of SWL in geriatric patients, ^2,3 recent studies reported less-favorable outcome regarding stone-free rate (SFR) in that particular population. ^4,5 Alternative stone removal procedures, such as ureterorenoscopy (URS) or percutaneous nephrolithotripsy (PCNL), are generally associated with greater morbidity because they require regional or general anesthesia and thus, in most cases, are not feasible as the first-line treatment option for elderly patients, because of their comorbidities and polypragmasia. However, if stone disintegration is not achieved by initial session, SWL sets a need for repeated treatments and thus increases the risk of complications in comorbid patients.

With the recent advancement in endourological management of stone disease the scientific interest is also focused on broadening the populations eligible for SWL. Studies on pediatric patients ⁶ showed good results, with low complication rates and SFRs comparable to those of adults. The aim of this study was to investigate success and complication rates of SWL in three cohorts of patients older than 60 years. We hypothesized that good SFR and low rate of complications could be achieved with proper patient selection for SWL, despite present comorbidities and regardless of patient's age.

Patients and Methods

This study was conducted at the Department of Urology, University Hospital Osijek, which is the Reference Center for Urolythiasis of Croatian Ministry of Health. We started the SWL treatment program in 1987 and since then we annually perform about 300 SWL sessions, with other treatment modalities for urinary calculi, such as PCNL or URS also available when indicated. Ever since the introduction of endoscopic procedures and SWL, open surgery for removing kidney stones has been almost abandoned.

The study included 444 patients older than 60 years with radiologic evidence of urinary stones between May 2001 and May 2008. During that period the patients were treated with Siemens Lithostar Plus lithotripter (Siemens, Erlangen, Germany). All studied patients were treated with this second-generation lithotripter and those treated with previous devices were not included in the analysis.

Before the procedure we collected records from patients for whom SWL treatment was indicated and these data included detailed medical history, physical examination, blood and urine analysis, renal functional tests, and renal ultrasonography. Plain abdominal film was used to confirm the diagnosis, with intravenous urography used for proper treatment planning and for detecting radiolucent stones. The patients were treated by stepwise SWL. Only pretreatment intramuscular analgesia (diclofenac sodium 75 mg) was given, with no additional use of opioids. No electrocardiography (EKG) triggering of the shockwaves was used, with respiratory triggering used only when indicated. The first follow-up was at 1 month post-SWL and SFR was assessed after 3 months. SFR was determined as complete absence of stone fragments on plain abdominal film and ultrasonography. Stone composition analysis with infrared spectroscopy was performed at the Department of Medical Biochemistry, University Hospital Osijek.

Three groups were formed: group I (60–65 years old), group II (66–70), and group III (>70). Demographic data, comorbidities, kidney function, stone characteristics, treatment details, complications (pain, bleeding, ureteric obstruction, etc.), and SFR were analyzed.

Descriptive statistical analysis was performed with SPSS 10.0 statistical program (SPSS, Chicago, IL), using analysis of variance between groups and Fisher exact and Kolmogorov–Smirnov test for comparing different variables between groups. A p-value of <0.05 was considered statistically significant.

Results

There were 444 patients older than 60 years and they represented 21.5% of the total of 2067 patients treated with SWL during the 7-year period. There were 175, 151, and 118 patients in group I (60–65 years old), II (66–70), and III (>70), respectively. Mean age of the patients was 67.7 ± 5.4 years (age ± standard deviation), with a maximum of 84 years and female-to-male ratio of 0.94. Each patient underwent a mean number of 1.7 ± 1.12 sessions (a maximum of eight sessions). The patients received 3166 ± 571.3 impulses per session (range: 1000–5000), with a mean energy of 18.78 ± 0.64 kV. Mean stone size for all locations was 12.18 ± 6.8 mm. In 26.8% of the patients, Double-J stent placement was required prior to SWL session. Complications were noted in 6% of the patients. URS or PCNL was needed in 4.73% of the patients as an adjunctive after SWL stone removal procedure. Mean creatinine level before the procedure was 91.39 ± 31.49 μmol/L. Data concerning age, sex, treatment details, and kidney function for the three studied groups are listed in Table 1. For number of SWL sessions (p = 0.78), number of impulses (p = 0.34), energy level (p = 0.5), stone size (p = 0.3), and pretreatment creatinine level (p = 0.88), we found no statistically significant difference between the studied groups.

Stone composition analysis data were available for 18.2% of the patients. Calcium oxalate monohydrate (COM) stones were the most common (68.4%, 73.1%, and 47.1% for the three groups, respectively), with only two cystine stones treated with SWL in our study population. Other types of stones included uric acid, calcium oxalate dihydrate, and struvite stones.

The most common stone sites were kidney pelvis (37.41%), lower calices (17.99%), and distal ureter (15.11%). Stones were the largest in kidney pelvis (16.15 ± 7.46 mm), upper calices (14 ± 10.87 mm), and lower calices (12.1 ± 5.65 mm). Stone location and stone size for all groups are listed in Tables 2 and 3, respectively.

Comorbidity was present in 55% of patients, with arterial hypertension (37.9%) and diabetes mellitus (15.7%) being the most common, as expected. Kidney cysts were found in 13.7%, benign prostatic hyperplasia in 11%, and malignancy in 7.2% of the cases. Almost every third patient had two or more comorbidities present. Comorbidities for all groups are listed in Table 4.

Complications were noted in 27 of 444 patients (6%), with no significant difference when comparing complication rates between the groups (group I vs. group II, group I vs. group III, and group II vs. group III, with p = 0.228, p = 0.149, and p = 0.458, respectively). Renal subcapsular hematoma developed in 0.7% of cases. Hematomas were monitored by ultrasonography and no surgical intervention was needed in later follow-up. Steinstrasse developed in 12 patients and required URS treatment in 1 patient. List of complications and complication rates are shown in Table 5.

An overall SFR of 67.98% was found. SFRs for groups I, II, and III were 66.4%, 67.4%, and 71.2%, respectively. We found no statistically significant difference when comparing SFRs between the studied groups. When patients were divided into those with renal and ureteral stones, the SFRs were 65.54% and 72.28% (p = 0.055), respectively. There was no significant difference in SFRs for renal and ureteral stones between the three studied age groups. Comparison of SFRs between the age groups is shown in Table 6.

Further, we analyzed SFRs according to the exact location of the stone. With an overall SFR of 66%, the lowest SWL success rate was for lower calices stone location. When comparing SFRs according to location of the stone, none of the locations revealed significant difference in SFRs between the groups (Table 7).

Table 8 shows the influence of different variables on SFRs of the studied groups. As expected, patients with smaller stones had better SFR, with p = 0.0001 for all patients. For the youngest group, age influenced SFR (p = 0.022), but when all patients were included in the analysis, age had no effect on SFR (p = 0.383).

The influence of comorbidity on SFR was nonsignificant, with p-values of 0.084, 0.308, and 0.214 for groups I, II, and III, respectively. Complications did not have an impact on overall SFR, with p = 0.208. The p-values for each group were 0.540, 0.518, and 0.117 for groups I, II, and III, respectively.

Discussion

SWL is generally accepted as a safe and effective method for treating urinary calculi and is considered as the first-line, minimally invasive treatment option for stones ≤20 mm ⁷ or even, by some authors, ≤30 mm. ⁸ Its ease of application and no need for anesthesia have popularized the use of SWL not only in the general population but also in high-risk and comorbid patients. Although SWL is a least-invasive treatment modality for urinary calculi, it is not free of complications, ⁹ which are usually related to residual stone fragments, infections, and effects on urinary, gastrointestinal, and cardiovascular tissues, among others. ¹⁰ Elderly population is especially sensitive to SWL-induced complications, because of patients' concomitant diseases and polypragmasia, so proper patient selection plays a crucial role in decreasing the morbidity of SWL in this population. Also, the improvements in lithotripter design and their effectiveness will result in higher success and lower complication rates of SWL. ¹¹ Thus, the current efforts are based on developing lithotripters with higher disintegrating capacity and focused energy, which produces little or no renal trauma.

The success of SWL, as described with SFR, depends on the stone size and location, renal anatomy, stone composition, and the type of lithotripter used. Other factors including age, sex, nationality, stone nature (de novo or recurrent), and ureteric stenting seem to have no significant impact on SWL success rate. ¹² Recent publications report SFRs after SWL treatment of ureteral stones of more than 97% ¹³ and SFRs following SWL of nonstaghorn stones in the kidney from 41% to 99%. ⁷ In the study by Tailly and coworkers, ¹⁴ the SFRs (85%–88.8%) for urinary calculi remained unchanged over the course of 20 years, with consistent use of SWL. The success and SFRs in elderly, however, tends to be somewhat lower than in the general adult population. Depending on the studied population, age limit, number of treatments needed, the definition (complete resolution or presence of clinically insignificant residual fragments), and time of SFR assessment, the SFRs in elderly ranged from 37.6% ⁴ to 87.1%. ⁵

Here we set to determine whether success of SWL in treating urolithiasis in older patients depends on age alone and to compare the complication rates between the studied age groups. Our hypothesis was that SFRs and number of complications do not depend on age of the treated patient and that good results with low morbidity could be accomplished with well-selected patients.

The reason we studied a population over 60 years of age was the fact that, according to the Croatian National Central Bureau of Statistics, life expectancy at birth for men and women in 2006 was 72.5 and 79.3 years, respectively. Because the patients older than 60 years represent almost one-fourth of total number of our SWL-treated patients and because of their comorbidities it was interesting to analyze them as a study population. The work-life expectancy in Croatia is 60 to 65 years, which correlates with the age limit setting of our group I. It is possible to prolong the working capability period up to 70 years of age (group II); after that, retirement is obligatory (group III).

When comparing the three studied groups we found no significant difference in number of treatments (p = 0.78), number of impulses per session (p = 0.34), energy level (p = 0.5), stone size (p = 0.3), and pretreatment creatinine level (p = 0.88). Double-J stenting was performed in 26.8% of the patients prior to SWL session, considering that the most common stone site was kidney pelvis and that the stones were largest in that location (16.15 ± 7.46 mm). In presenting our departments experience in noninvasive treatment of urinary stones from 1988 to 2004, Kuvezdic ¹⁵ showed that, in general, 13.95% (773/5542) of the patients required pre-SWL stenting, which is a lot less than in this population. High number of pre-SWL stenting in these high-risk patients was also a measure of precaution, based on our experience, wanting to avoid or decrease the number of obstructive and infective complications after SWL of large renal stones. As we only used parenteral analgesia with nonsteroidal anti-inflammatory drugs (diclofenac sodium 75 mg) before stenting, there was no need for sedoanalgesia or anesthesia that would increase the risk of morbidity. It has been previously reported that diclofenac sodium given intramuscularly at 45 minutes prior to the SWL procedure has an opioid-sparing effect. ¹⁶ In this study, only pretreatment analgesia was given, with no additional use of opioids. The adverse effects of opioids are well known and include nausea, vomiting, respiratory depression, and oxygen desaturation, which are all of importance when dealing high-risk patients, especially if they have comorbidities of the respiratory, cardiovascular, or digestive system.

The patients were treated by stepwise SWL, which could result in better stone communition than that by the conventional shockwave delivery, ¹⁷ although a recent randomized, double-blind trial ¹⁸ suggested that the immediate voltage escalation could be more effective. During the first ever SWL patient treatment, shockwaves induced extrasystoles, ¹⁹ which were later avoided with EKG triggering of the shockwave impulse. In this study, no EKG triggering was used; we performed a pretreatment cardiological evaluation of the patients with a history of cardiovascular disease and later registered no SWL-induced cardiological complications.

SFR for the entire study population of 444 patients was 67.98%. In comparison, when analyzing the overall SWL success at our department from 1988 to 2004, Kuvezdic ¹⁵ presented an SFR of 80.95%, which is consistent with the previously mentioned lower SFR in elderly patients. The three studied groups had similar SWL success, with the oldest group having the best SFR of 71.2%. Nevertheless, when comparing SFRs between the studied groups we found no statistically significant difference in SFRs. When the patients were divided into those with renal and ureteral stones, the SFRs were 65.54% and 72.28%, respectively, and these data, although not statistically significant (p = 0.055), suggest a trend toward significance.

Ng and coworkers ⁴ investigated the effect of patient age on SFR after SWL of the groups aged ≤40, 41 to 60, and >60 years, where they used the first group as the reference category. They found that the SFR after SWL for renal stones, but not ureteric stones, was significantly lower in older patients. One of the suggested reasons for the lower SFR in older patients was the sclerotic changes in kidney parenchyma. In our study there was no significant difference in SFRs for renal and ureteral stones between the three studied age groups (Table 6), although the design of our study did not include patients younger than 60 years in the analysis. Also, in the aforementioned study the authors did not specify the mean age of each studied group and so the comparison with our study cannot be drawn.

When comparing the success rates of SWL for ureteral stones between patients younger and older than 70 years, Halachmi and Meretyk ²⁰ found that age did not have an impact on the success rate of SWL. In that study, complications rates were 1% for older patients and 3.7% for the younger ones. However, when including renal stones, complication rates tend to be somewhat higher. In the report by Dhar and coworkers, ²¹ the probability of post-SWL hematoma increased with the patients' age and was 1.67 times greater for each 10-year increase in age. Despite almost every third patient in our study having two or more comorbidities, we noted complications in only 27 patients, with no significant difference when comparing complication rates between the groups. Somewhat higher incidence (0.7%) of renal subcapsular hematoma than that previously recorded for the general population ¹⁴ did not require any surgical intervention and thus the need for anesthesia was avoided. Further, two hematomas were recorded for group I, one for group II, and none for the oldest studied group, which is contrary to that previously described. Hematomas and other complications, as well as comorbidities, of our patients did not delay stone clearance and influence SFR, which all shows the safety and efficacy of SWL regardless of patients' age.

Consistent with previously published data, we found that the significant predictor of outcome was the location of the stone in lower calix, with the lowest SFR of 66%. When analyzing SFRs according to exact location of the stone, none of the compared locations revealed significant difference in SFR between the groups. Also, patients with smaller stones had better SFR, as expected. Although, in the youngest group, age seemed to have an impact on SFR (p = 0.022), SFR for all patients was not influenced and did not differ significantly in comparison with other age groups; therefore, age cannot be considered a factor that influences SFR. Number of impulses, energy level, and pretreatment creatinine level did not have an impact on SFR.

The outcome of SWL could also be influenced by stone composition: COM and cystine stones have a lower fragmentation coefficient than uric acid and calcium oxalate dihydrate stones. ⁷ In our study, the stone composition analysis data were available for only 81 of 444 (18.2%) patients. COM stones were the most common (68.4%, 73.1%, and 47.1% for the three groups, respectively), with only two cystine stones treated with SWL in our study population. As COM stones are among the hardest stones to fragment ²² and were most commonly represented here, we investigated whether there was difference in the proportion of COM stones between the three groups. We found no statistically significant difference between the studied groups (group I vs. group II, group I vs. group III, and group II vs. group III, with p = 0.204, p = 0.114, and p = 0.081, respectively) and concluded that the stone composition, although influencing fragmentation after SWL, did not interfere with the end result of our study, because the groups did not differ in the proportion of COM stones.

Although one would expect higher stone-free and lower complication rates in younger patients, our analysis of three subgroups of patients over 60 years of age showed that SWL is safe and effective as a primary treatment option for urinary calculi in these comorbid patients. None of the compared groups revealed any age dependency in complication or SFRs and the only significant predictors of lower SFR were size and location of the stone.

Other possible predictors of SWL failure, such as body mass index (BMI) and increased stone density on noncontrast computed tomography, ²³ were not recorded here. Intravenous urography was used for pre-SWL evaluation because it is still considered a standard procedure and because of the large number of patients coming to our SWL Reference Center from smaller hospitals where noncontrast computed tomography is not available. BMI was rarely measured here, although the patients weighing over lithotripter manufacturers' standards (120 kg) were not treated by SWL. Obesity, as expressed with BMI, is one of the important factors that can improve patient selection for SWL and thus will be incorporated in future assessments of patients with urinary stone disease.

Another shortcoming of our study is the lack of comparison of SWL results with other possible treatment modalities, such as PCNL, in the observed population with similar stone burden. One recent review ²⁴ emphasized that PCNL and URS in elderly have the same efficacy and safety as in adult population, but, in that same population, SWL results seem to be somewhat inferior compared with other treatment modalities. Sahin and coworkers ²⁵ have also shown good results of PCNL in elderly, with an SFR of 89% for patients older than 60 years. To compare success and complication rates of SWL and PCNL in these three cohorts of patients is beyond the scope of this study, but it would surely improve our future efforts in choosing the right treatment option, having in mind the stone burden and indications for both modalities.

In conclusion, we have shown that SWL is a safe, successful, and noninvasive method for treating urinary calculi even in high-risk, comorbid patients, regardless of patients' age. Good results with low rate of complications can be achieved by proper patient selection, where older age does not seem to be a significant predictor of SWL failure.