Obesity and Kidney Stone Procedures
Nikhi P. Singh, BS,1 Carter J. Boyd, BS,1 William Poore, BS,1 Kyle Wood, MD,2 Dean G. Assimos, MD2
1University of Alabama-Birmingham School of Medicine, Birmingham, AL; 2Department of Urology, University of Alabama-Birmingham, Birmingham, AL
Obesity is a chronic disease that has increased in prevalence in the United States and is a risk factor for the development of nephrolithiasis. As with other medical conditions, obesity should be considered when optimizing surgical management and choosing kidney stone procedures for patients. In this review, we outline the various procedures available for treating stone disease and discuss any discrepancies in outcomes or complications for the obese cohort.
[Rev Urol. 2020;22(1):24–29]
© 2020 MedReviews®, LLC
Obesity is a complex, multifactorial chronic disease influenced by genetic, behavioral, dietary, socioeconomic, and environmental factors.1 Obesity is increasing in prevalence in the United States, with the current rate approaching 35%, and more than 5% of the population classified as morbidly obese.1-3 Cardiovascular disease, dyslipidemia, and hyperinsulinemia are strongly associated with obesity.4 Obesity is most commonly defined by body mass index (BMI), which is based on weight and height. An individual is considered obese if their BMI is ≥30 kg/m2, and morbidly obese when BMI ≥40 kg/m2.1 New metrics of abdominal adiposity may be better indicators of disease risk compared with BMI.1,4
Obese patients have higher rates of kidney stone formation than non-obese patients.3,5,6 Hypertension and hyperlipidemia, common comorbidities observed in obese patients, have been demonstrated to increase the rate of stone formation.1,7,8 The mechanism of stone formation in obese patients appears to be linked to insulin resistance, dietary indiscretions, and other metabolic factors that contribute to an increased lithogenic urinary profile.9 Duffey and associates found that in a cohort of 45 morbidly obese patients, 98% were found to have at least one lithogenic risk factor in a 24-hour urine collection, and 80% had 3 or more.10 Stones in obese patients are mainly composed of calcium oxalate and uric acid.11
Several procedures are utilized to treat patients requiring removal of kidney and/or ureteral stones. These include ureteroscopy (URS), shock wave lithotripsy (SWL), percutaneous nephrolithotomy (PCNL), and, rarely, laparoscopy, robotic-assisted laparoscopy, and open surgery.
Outcomes. SWL is preferred by many patients due to its limited invasiveness. However, results in obese patients are usually inferior.12-15 Delakas and associates found that, in a cohort 683 patients of which 102 were obese, obesity increases the risk of SWL failure by 1.9-fold.15 When skin-to-stone distance (SSD) is less than 9 cm, success rates were found to be 79% versus 59% when SSD was more than 9 cm.16 Pareek and associates found that although about 20% of stone formers have a SSD larger than 10 cm, 85% of patients with residual stone fragments had a SSD larger than 10 cm.17 These differential outcomes are likely secondary to a longer SSD in the obese cohort, the stone being further out from the second focal point of shock wave energy delivery, and less optimal stone imaging for shock wave targeting.5 Obese patients should be informed about the possibility of inferior results with SWL and, if this modality is chosen, they need to be aware that salvage procedures such as ureteroscopy or percutaneous nephrolithotomy may be necessary.5 Compared with adults, obesity may not have as much of a negative impact on SWL results in children.18
Technical Considerations. Different approaches can be taken to handle stone/shock wave mismatches.19 Use of the blast path technique (based on the shock wave energy profile surrounding F2) with the Dornier HM3 lithotripter was previously described.19,20 Success rates of 89%, 71.4%, and 64.3% were reported for blast path distances from F2 of <1 cm, 1 to 2 cm, and 2 to 3 cm, respectively.20 However, there are very few of these highly effective devices being used at this time as production was stopped many years ago.14,21 Externally applied abdominal/flank pressure to push the stone into a closer F2 vicinity has been reported.13,14,20,21 Third-generation lithotripters with varying focal lengths, including longer ones, may produce better results in the obese cohort.12,22
Complications. Complications with SWL are not different between obese and non-obese patients except for inferior fragmentation and stone-free results.20,23
Anesthesia. Patients undergoing SWL may be administered conscious sedation, general anesthesia, or regional anesthesia.24 Results with general anesthesia are reportedly better as respiratory rate and excursion can be controlled, resulting in better shock wave targeting and stone fragmentation.14,25 Obese patients undergoing general anesthesia may have more difficult airways to manage and are at higher risk for peri-operative complications due to associated medical co-morbidities.5,26 The latter can be minimized with proper preoperative assessment and planning.
Outcomes. PCNL is indicated for patients harboring large kidney stones (>20 mm).27,28 PCNL typically yields high stone-free rates and acceptable rates of complication.28 Non-obese and obese patients have similar stone-free rates and usually similar complication rates with PCNL.29,30,31 Sergeyev and associates, in a cohort of 85 patients, found that PCNL results are independent of BMI.30 Carson and associates, in a cohort of 44 obese and 226 non-obese patients who underwent PCNL, found that there were no differences in success rate and morbidity between the two cohorts.32 Koo and associates found in a cohort of 144 non-obese and 79 obese patients that no differences existed in PCNL outcomes.6,31 Zhou and associates, in a meta-analysis of 4962 patients, classified patients into non-obese, obese, and super-obese. They found that patients with a BMI ≥50 kg/m2 experienced no increase in complications but had longer PCNL operation times compared with non-obese patients. Surprisingly, obese individuals were found to have shorter hospitalizations than non-obese patients. This finding was thought to be confounded by a significantly higher number of staghorn calculi in the non-obese patients.29 Faerber and associates, in a cohort of 437 non-obese and 93 obese patients undergoing PCNL, found that stone-free rates were similar among the two groups; however, the complication rate was increased to 37% in the obese subjects compared with 16% for the non-obese cohort.33
Technical Considerations. Obese patients present several technical challenges including anesthesia, patient positioning, imaging for access, longer skin-to-collectingsystem distances, and nephrostomy tube dislodgement. Awake intubation and patient-assisted positioning should be strongly considered in patients with high BMIs. Use of a Jackson Spine Table may help with obese patients as the abdominal pannus is not compressed, which facilitates ventilation.34,35 Radiation exposure is greater in this cohort as the fluoroscopic devices typically increase the delivery of radiation to allow for adequate imaging.36,37 Thus, minimizing the amount of fluoroscopy is required. Pulsed fluoroscopic imaging may be utilized to limit radiation exposure in these cases.38 Extra-long needles, working sheaths, grasping devices, and rigid nephroscopes are frequently needed for these cases, and thus should be available.39 We strongly recommend a 2-guidewire technique that includes working and safety wires. There is an increased risk for working sheath excursion below the level of the skin. We suggest placing sutures in the sheath to allow extraction and repositioning of the working sheath above the skin level if the latter occurs. If the sutures break or were not placed, and working sheath displacement occurs, a Council catheter can be placed over the working guidewire and guided into the sheath, where it is inflated and gentle traction applied to bring the tube above the skin. If the latter does not solve this problem, a formal cut-down may be needed to extract and reposition the sheath.10,39 Nephrostomy tube dislodgement can also occur is obese patients.32 Certain measures can be taken to limit this occurrence. The nephrostomy tube can be positioned in the upper pole. When the tube is sutured to the skin, the point of fixation should be 3 to 4 cm above the skin to accommodate for inward migration. If more than one access is used during the case, a circle nephrostomy tube can be placed. In addition, an antegrade internalized ureteral stent can be inserted in cases where tube dislodgement is more likely to occur, such as in a patient with a diminutive renal pelvis. Some advocate a supine approach in obese patients thinking that respiratory physiology is optimized.40 However, the latter is debatable, and we have not found it to be necessary in this cohort.41,42 In addition, the working distance (skin to kidney/stone distance) is longer in the supine position which may be a disadvantage in obese subjects.43
Complications. The spectrum and rates of complications in the obese cohort is like that of nonobese patients.31,44
Outcomes. Ureterorenoscopy (URS) is a treatment option that can be used for most urinary tract stones and is now the most commonly performed stone removal procedure.45 URS has similar stone-free rates among non-obese and obese patients.45,46 Reported success rates of URS range from 57% to 97%.47 Because SWL is negatively impacted by obesity and URS stone-free rates are similar for obese and non-obese patients, URS may be the preferred method for treating the majority of obese patients requiring a stone removal procedure.5,48
Technical Considerations. A major advantage of URS over other stone removal procedures is that URS is less impacted by body habitus.49 Therefore, complex cases such as those seen in obese and morbidly obese patients may benefit from URS. The same techniques used for non-obese patients should be employed in this cohort, including utilization of safety guidewires, carefully performed stone fragmentation, and stone removal.45 Extreme morbid obesity can interfere with or preclude fluoroscopic monitoring and thus some of these cases may only be done under endoscopic guidance.50 Performance of URS in the dorsal lithotomy position may not be possible in high BMI patients. In this instance, URS can be performed with patients in the supine position.
Complications. No differences in overall complication rates have been found between obese and non-obese patients.51 Obese patients are more prone to developing compartment syndrome in the lithotomy position than the non-obese cohort.52 Therefore, prolonged URS procedures in this position should be avoided in this cohort. Performance of URS in the supine position should be considered in these instances.
Anesthetic Considerations. URS is commonly performed under general anesthesia. In some settings, regional anesthesia can be utilized. In the super-obese cohort, ventilation may be quite difficult in the dorsal lithotomy position. Performing flexible URS in the supine position under local anesthesia may be an option in this unique cohort.
Open surgery for the management of patients with kidney stones is rarely needed in today’s practice. It is now only considered in patients who are not candidates for less invasive surgical approaches or have failed such treatments. These patients typically have complex stone disease associated with abnormalities of ureteral and collecting system anatomy and or challenges of unique body habitus.50,53
Complications. Obese patients can prove challenging and present additional complications throughout the timeline of patient care in any open surgical procedure.54 These patients have increased risk of wound complications including infection, impaired wound healing, and incisional hernia.35,55
Very few patients require laparoscopic kidney stone removal. Desai and Assimos reported that this approach was only needed in approximately 1% of patients requiring a stone removal procedure in a tertiary referral practice.56 Outcomes of laparoscopic renal/ureteral stone removal procedures have not been distinctly characterized based on obesity. Therefore, information from other laparoscopic procedures will be extrapolated to profile some of the risks and benefits of this approach in obese patients. Laparoscopy with adapted surgical methods and anesthetic care appears to be safe for obese patients and may provide advantages over open surgery including reduced pain, fewer wound problems, and shorter hospitalization.54,57-59 Extra-long trocars and instruments and revised trocar placement may be helpful in obese patients.60 Ergonomic stress from laparoscopic procedures on surgeons has not been shown to be increased in cases with obese patients.61
Complications. Obese patients undergoing non-cardiac laparoscopic surgery may have increased risk of trocar site hernias/wound healing as well as acute kidney injury.62,63 The latter is likely related to associated medical comorbidity.62 Patients with high BMIs may not tolerate creation of a pneumoperitoneum due to underlying cardiovascular dysfunction and intraoperative compression of respiratory structures.64,65
Robotic stone surgery has similar indications to open and laparoscopic surgery and is becoming increasingly popular, with high stone clearance rates.66 However, success rates of robot-assisted surgery in obese patients are again not clearly defined. Information from other robotic surgeries in obese patients can be extrapolated to robotic stone surgery in obese patients. In robot-assisted radical prostatectomy, success outcomes for obese patients have been proven to be similar to non-obese rates; however, uncertainty of perioperative outcomes exists, and this may be due to variability in surgeon skill due to the learning curve of operating on obese patients.67 Complication rates have not been found to be increased in obese patients undergoing robotic partial nephrectomy.68 In a cohort of 168 endometrial cancer patients with BMIs ranging from 18.5 to 24.9 kg/m2 to ≥50 kg/m2 undergoing robotic surgery, outcomes and complication rates were similar.69 Conversion rate to open surgery in robotic-assisted surgery has been observed to be higher in obese patients.68,69 Some uncertainty exists about the benefits of robotassisted surgery over conventional approaches.70 However, Thomas and associates in a meta-analysis of 36 papers found that robot-assisted surgery has a favorable risk/benefit profile over traditional laparoscopy.71 Similar to laparoscopy, robotic-assisted laparoscopic surgery has reduced blood loss and shorter hospitalization than open surgery.72
Technical Considerations. Robotic surgery offers increased vision, accuracy, precision, ergonomics, and dexterity over laparoscopy in obese patients.60 Increased abdominal wall thickness reduces trocar range of motion and may call for adapted surgical methods.73
Complications. Obese patient may also be at risk for trocar site hernias, with 47.9% reported in robotic bariatric surgical procedures.63
Obesity is a risk factor for developing kidney stones. Fortunately, obese patients typically have similar outcomes with various stone removal procedures except for SWL. Overall the rate of complications is like the non-obese cohort except for higher risk for trocar site hernias in those subjected to laparoscopic/robotic surgery and wound-related problems including infection and hernia in those undergoing open surgery. Physicians need to be aware of some of the unique anatomic and physiologic challenges of this patient cohort and make the necessary adjustments to optimize treatment outcomes.
The authors have received funding for this article (K08DK115833 and P20DK119788) and report no conflicts of interest.