Abstract
Obesity has quickly become a major worldwide medical problem, associated with significant comorbidity, including diabetes, cardiovascular disease, and several malignancies. Obesity has an important impact on the urologic patient in terms of both disease risk as well as its surgical and medical treatment. Urologic conditions associated with obesity include kidney cancer, aggressive prostate cancer, and urolithiasis. Importantly, obese patients may be at risk for worse outcomes following some urologic surgeries, including radical prostatectomy, stone surgery, and benign prostatic surgery. In addition to influence on specific procedures in urology, there are a number of important risks and challenges inherent in surgery of the obese patient. Preoperatively, the assessment of a patient that may have several comorbidities becomes particularly important. Intraoperatively, the positioning of a large patient introduces challenges and unique risks. Postoperatively, obese patients may be at increased risk of thromboembolic, cardiovascular, and pulmonary complications.
Keywords
Obesity, Adiposity, BMI, Prostate cancer, Kidney cancer, Urolithiasis, Complications
Key Points
- 1.
Obesity is a substantial, growing problem with broad medical impact.
- 2.
Obesity has and important pathophysiologic impact on many urologic diseases.
- 3.
Surgery in obese patients introduces unique issues which should be addressed to optimize outcomes.
In the decades obesity has quickly become a major worldwide problem. Worldwide, obesity has more than doubled since 1980, with estimates of nearly 2 billion people being at least overweight. In the United States, it is estimated that more than one-third of adults are obese and a staggering two-thirds of adults are at least overweight. Some estimates suggest that nearly 1 in 5 deaths in the United States can be attributed to obesity. The incidence of obesity has nearly tripled in just over 50 years and continues to increase. Fig. 16.1 illustrates the actual and predicted prevalence of obesity through 2030. It has been suggested that if the prevalence of obesity continues to rise at the current pace it could ultimately lead to a decline in life expectancy, which has not taken place in the last 2 centuries.
The health implications of obesity are enormous, as obesity is a well-established risk factor for a number of chronic conditions, including type 2 diabetes and cardiovascular disease. In addition, obesity contributes to the increased incidence of death from several malignancies. Largely as a result of these multiple comorbid conditions, medical care comes at a significantly increased economic cost for the obese. In 2006, medical costs for an obese patient were $1429 higher, or 42% more, than that of a normal-weight patient.
The World Health Organization (WHO) defines the terms overweight and obese as excessive fat accumulation presenting a risk to health. The most commonly used anthropometric measure of obesity is body mass index (BMI), which is a weight (in kilograms) divided by the square of height (in meters). The assumption of BMI is that adiposity is not reliant on height. The WHO has defined a BMI greater than 25 as overweight and greater than 30 as obese. The WHO classification of BMI is listed in Table 16.1 . The validity of BMI has been supported by multiple studies that have shown correlation to densitometry estimates of body fat composition. BMI may be a less reliable measure of central obesity, and as a result measures of waist-to-hip ratio and waist circumference have been used in several epidemiologic studies. Using BMI as a measure of obesity is certainly not perfect, but it is easily calculated and by far the most commonly used standard.
| Classification | BMI(kg/m 2 ) |
|---|---|
| Underweight | <18.50 |
| Severe thinness | <16.00 |
| Moderate thinness | 16.00–16.99 |
| Mild thinness | 17.00–18.49 |
| Normal range | 18.50–24.99 |
| Overweight | ≥25.00 |
| Pre-obese | 25.00–29.99 |
| Obese | ≥30.00 |
| Obese Class 1 | 30.00–34.99 |
| Obese Class 2 | 35.00–39.99 |
| Obese Class 3 | ≥40.00 |
As the prevalence of obese patients continues to increase, so will the number of obese patients seeking urologic care. Compounding the issue is that obesity can increase the risks of several urologic diseases, including kidney cancer, aggressive prostate cancer, urolithiasis, and lower urinary tract symptoms (LUTS). More now than ever urologists must be aware of the challenges associated with caring for and operating on overweight and obese patients.
Condition-specific Considerations
Malignant Urologic Disease
Obesity as a risk factor for cancer first garnered attention as a result of a number of epidemiologic studies in the 1970s–1980s. Obesity has been linked to the development of a number of malignancies, most notably colon, breast (postmenopausal women), endometrial, esophageal, and kidney cancer. It has been estimated that 15–20% of all cancer deaths in the United States can be attributed to overweight and obesity.
The biologic mechanisms linking obesity to cancer are not well understood, but likely involve the alterations obesity causes in metabolism and endocrine activity, as well as to peptide and steroid hormone production. Insulin resistance and hyperinsulinemia resulting from increased circulating levels of free fatty acids may play an important role in the development of several cancers. Insulin promotes synthesis of the hormone insulin-like growth factor 1 (IGF1), which has been shown to promote cell proliferation and inhibit apoptosis. Additional support for hyperinsulinemia as a risk factor for cancer development lies in the association of many cancers with type 2 diabetes, which is typically associated with long-term insulin resistance and hyperinsulinemia.
Beyond the association with aggressive disease, obesity has a major influence on the surgical approach to urologic malignant disease. Commonly performed surgical procedures are found to be more difficult and complex among the obese, with an increased risk of perioperative complications, incomplete resection, and poor oncologic outcomes.
Prostate Cancer and Radical Prostatectomy
Obesity is a condition that can have a dramatic effect on sex hormones, specifically raising estrogen levels through increased aromatase activity and thus lowering testosterone levels. It is a logical step to think obesity may have an effect on the incidence of an androgen sensitive malignancy such as prostate cancer. Links between obesity and other sex hormone related malignancies, such as postmenopausal breast cancer and endometrial cancer, have been more clearly defined, but the data on prostate cancer and obesity are not as clear.
Several meta-analyses have been performed in regard to obesity and prostate cancer incidence with conflicting results. Some have found a weak positive correlation, while others have found no significant effect. As one might expect, the studies included in these analyses vary greatly in their findings, whether harmful or protective. Largely due to the heterogeneity of these findings and the lack of a consensus effect, prostate cancer has not typically been listed among malignancies in which obesity has a significant role.
While overall incidence of prostate cancer may not be associated with BMI, there is a growing body of evidence that obesity is linked to particularly aggressive prostate cancer. A meta-analysis by MacInnis et al. found obesity increased risk for advanced disease with a relative risk (RR) of 1.12 (95%, CI 1.01–1.23) for every 5-unit increase in BMI. Similarly, Discacciati et al. found an increased risk of advanced disease, RR = 1.09 (95%, CI 1.02–1.16), for every 5-unit increase in BMI while actually observing a protective effect in localized disease, RR = 0.94 (95%, CI 0.91–0.97). This dual effect on localized and aggressive disease may help explain why no obvious relationship has emerged in regard to total incidence. An elevated risk of aggressive disease, however, may help explain the association with increased risk of prostate cancer mortality in the obese. Calle et al. found a 34% increased risk of dying from prostate cancer with a BMI greater than 35 in a prospectively followed group of more than 900,000 people. Similarly, in a meta-analysis performed by Cao et al., each 5 kg/m 2 unit increase in BMI increased risk of death from prostate cancer by 15%.
Outcomes after radical prostatectomy seem to corroborate the notion that obesity may be associated with more aggressive disease. A multi-institutional review found obesity was associated with higher-grade tumors, a trend toward more positive surgical margins, and higher biochemical failure rates. Similarly, data from the CaPSURE database showed increasing BMI was associated with biochemical recurrence, with very obese patients 1.69 times more likely to recur than normal-weight patients. In addition, obese patients are less likely to regain urinary continence and sexual function after radical prostatectomy.
Technical Considerations
Obesity can compromise both open and robotic-assisted prostatectomy techniques. In the case of open surgery, the depth of the incision compromises visibility and manual dexterity and limits the ability to expose neurovascular structures and the membranous urethral complex. A number of techniques have been implemented to improve apical exposure, including pubic osteotomy, but in general, when performing prostatectomy on obese patients, a generous incision, use of a multi-bladed fixed retractor, and surgical magnification are useful.
While robotic-assisted surgical techniques as compared to open surgery may allow better exposure of the deep pelvis and increased dexterity, obesity negatively impacts the technique as well. Obese patients are often unable to tolerate the steep Trendelenburg position due to increased airway pressure, diaphragmatic elevation, and difficulty with ventilation. Upon docking, arm movement can be made difficult by the presence of a large, protuberant abdomen, similarly limiting the reach of instruments to the deep pelvis. In these cases, careful port position selection, below the level of the most protuberant abdomen, can be helpful.
In approaching obese patients with prostate cancer, a recommendation for preoperative weight loss is reasonable, provided the patient’s disease risk is not deemed to be excessive, risking progression upon delaying surgery. In general, patients who would benefit from radical prostatectomy have time for consideration of weight loss. If weight loss cannot be achieved, then alternative therapeutic approaches might be considered.
Kidney Cancer, Nephrectomy, and Partial Nephrectomy
Kidney cancer, specifically renal cell carcinoma, is one of the malignancies more firmly established as being associated with increased risk in the obese. The majority of epidemiologic studies have identified obesity as increasing the risk of renal cancer in a directly proportionate manner. Some have shown a greater risk for cancer in obese women compared to men, while others have shown a similar effect regardless of sex. A meta-analysis in 2001 of 11 studies found a relative risk of 1.06 and 1.07 for men and women, respectively, for each unit increase in BMI. This corresponds to a relative risk of 1.84 for an obese patient compared to a normal-weight patient. In prospectively following more than 900,000 people, Calle et al. found that increased BMI correlated to an increased risk of death from kidney cancer of up to 70% in patients with BMIs greater than 35. Hypertension and diabetes, both of which are commonly associated with obesity, are also established risk factors for kidney cancer. Despite possible confounding factors, obesity has been shown to increase risk of kidney cancer independent of hypertension. With the majority of evidence showing a positive association, The International Agency for Research on Cancer, a part of the World Health Organization, has included kidney cancer among malignancies linked to obesity.
Like prostate cancer, obesity may have a large impact on how kidney cancer is surgically treated. This is an important point because more than half of patients undergoing surgery for kidney cancer will be at least overweight. The data are mixed on how obesity affects outcomes given the particular approaches for kidney surgery. Some data suggest obese patients have increased complications regardless of approach. In the advent of laparoscopic surgery, obese patients were reported to have increased complications and obesity was regarded as a relative contraindication to minimally invasive surgery. As experience increased, multiple reports showed similar outcomes among obese and nonobese patients. Romero et al. compared open and minimally invasive partial nephrectomy in obese and nonobese patients and found obese patients undergoing open surgery had longer operative times, more blood loss, longer clamp times, increased complications, and longer hospital stays than did nonobese patients. In contrast, obese patients undergoing laparoscopic surgery had similar outcomes compared to nonobese patients except for greater blood loss. A report using the National Surgical Quality Improvement Program from 2005 to 2012 showed patients undergoing laparoscopic partial nephrectomy had fewer overall complications than those undergoing open partial nephrectomy for all BMI categories, but the difference was largest for the morbidly obese, 22.2% versus 9.2%. Robotic surgery has lowered some of the technical hurdles of laparoscopic partial nephrectomy, and many regard robotic partial nephrectomy as the procedure of choice for small renal masses. Obese patients undergoing robotic partial nephrectomy have similar outcomes compared to nonobese patients with the exception again of greater blood loss.
Technical Considerations
In approaching the obese patient for renal tumor surgery, patient positioning is a critical consideration. Weight distribution during flank position can lead to increased risk of nerve injury, rhabdomyolysis, and compartment syndrome. Specific considerations for positioning are covered in Chapter 9 , Chapter 31 , Chapter 37 . In general, careful padding of the upper extremity; fixation of the arms, chest and pelvis; and avoidance of excessive flex can minimize positioning-related injuries. Elevation of the kidney rest should, likewise, be avoided to minimize pressure on the dependent muscles of the flank. In positioning the patient, either in full flank or semi-oblique positions, the pelvis should be sufficiently rotated to distribute weight on the hip rather than the gluteal or presacral muscle compartments.
Mobilization of the kidney in the obese patient can present a unique challenge due to the abundance of perinephric fat and pericolic fat, as well as the depth of incision in the case of open surgery. Often fat surrounding the kidney can be inflamed, hypervascular, and adherent to the renal capsule. It is critical that the surgeon conduct the operation by first identifying critical anatomic structures surrounding the kidney, thereby minimizing the risk of inadvertent injury, and facilitating ultimate kidney mobilization for radical or partial excision. In the case of partial excision of the kidney, removal of excessive outer perinephric fat can aid in increasing mobility of the kidney during manipulation if partial nephrectomy is contemplated.
The decision for open versus laparoscopic renal surgery techniques is highly surgeon dependent. As in the case of other surgical procedures, open nephrectomy in the obese will likely require larger incisions, deeper exposure, and risk of perioperative morbidity as outlined below. Laparoscopic surgery should only be undertaken in the obese in the hands of experienced surgeons who can ensure that operative times are not excessive, in order to minimize the risk of positioning-related complications and pulmonary morbidity.
Bladder Cancer
There is a general lack of evidence for a link between obesity and the incidence of bladder cancer. Several large epidemiologic studies fail to show an association between the two, but there are limited data to support an association. Koebnick et al., using the NIH-AARP Diet and Health Study of nearly 500,00 people, found a positive correlation between BMI and bladder cancer with a relative risk of 1.28 (95%, CI 1.02–1.61) in those with the highest BMI. Additionally, a meta-analysis of 11 cohort studies found a modestly increased risk of bladder cancer in the obese with a relative risk of 1.09 when controlled for smoking. More recently, a systematic review of the literature by Cantiello concluded there is no consensus effect of BMI on the incidence of bladder cancer. Perhaps more importantly, Calle et al. found no association between obesity and the risk of dying from bladder cancer in a cohort of more than 900,000 people.
While there may not be consensus on whether obesity plays a role in the development of bladder cancer, there is evidence treatment is impacted in terms of outcomes and complications. In nonmuscle invasive bladder cancer, studies suggest obese patients have higher risks of recurrence, progression, and mortality. In patients undergoing radical cystectomy, the obese have higher readmission rates, increased blood loss, and more complications, specifically postoperative ileus and parastomal hernia. There are conflicting data regarding the impact of obesity on survival after radical cystectomy. In a multicenter review of over 4000 patients, Chromecki et al. found BMI >30 was associated with a higher risk of disease recurrence as well as disease-specific and overall mortality. Other reports found no association. Some reports suggest obese patients actually do better than normal-weight patients following radical cystectomy, consistent with the “obesity paradox,” or protective effect of obesity observed in a number of chronic conditions. Few would argue to advocate for increased levels of obesity for better outcomes after cystectomy; however, perhaps those with lower BMI, malnourishment, and lean muscle wasting are at greater risk. In a single institution series of patients undergoing radical cystectomy, Psutka et al. observed a protective effect in increased BMI, which was lost when adjusting for sarcopenia.
Technical Considerations
Considerations for cystectomy in the obese patient are similar to those for prostatectomy. Exposure through wide incision and adequate retraction is essential, as is identification of critical vascular structures in the pelvis, prior to bladder mobilization. Urinary diversion can be particularly challenging in obese patients, owing to a thick, fat mesentery with limited mobility. Wide mesenteric incisions, to maximize bowel mobility, along with careful selection of bowel segment are essential. In forming a stoma, the Turnbull loop technique can be utilized if the bowel does not reach skin easily, as discussed in Chapter 45 , but extending the distal mesenteric incision line may offer the most aid in lengthening of the segment.
Lower Urinary Tract Symptoms
Obesity is a well-established risk factor for development of benign prostatic hyperplasia (BPH) and LUTS. In a longitudinal study of VA patients in 1985, Glynn et al. noted only BMI was a significant predictor of BPH. More than a decade later, Hammarsten et al. found prostate size correlated with several components of metabolic syndrome, including not only obesity but also hyperinsulinemia, hypertension, and dyslipidemia. Additional data have suggested BPH may be a consequence of metabolic syndrome, specifically from increased insulin levels. Excess abdominal fat, or central obesity, is particularly recognized as a core component of metabolic syndrome. Correspondingly, Giovannucci et al. found that central obesity as measured by waist circumference was predictive of LUTS. Multiple additional studies confirm this association. In addition to being at higher risk for urinary symptoms, data suggest that patients with central obesity do worse following surgery for LUTS/BPH. Gacci et al. recently showed patients with a waist circumference greater than 102 cm are less likely to symptomatically improve, specifically in regard to storage symptoms after surgery.
Erectile Dysfunction
Sexual function is generally negatively impacted in the obese, and erectile dysfunction (ED) is no exception. Obesity, and central obesity in particular, has been linked to ED in several studies. ED is known to be multifactorial in origin, with vascular-, neurologic-, and endocrine-related etiologies. Obesity can have profound effects on each of these factors so an association with ED is not particularly surprising. Diabetes, of which obesity is a risk factor, can lead to microvascular compromise as well as autonomic neuropathy. Obesity is known to lower levels of testosterone and increase estrogens. Overweight and obese patients have been estimated to have between a 1.5 and 3 times increased risk of developing ED. Treatment of ED in the obese may be particularly difficult, especially in diabetics because pharmacologic therapy in these patients is not as effective. In a randomized trial, Esposito et al. demonstrated lifestyle changes and weight loss improved sexual function in up to one-third of obese men with ED.
These observations are important when counseling men undergoing radical prostatectomy as the increased risk of ED in the obese population likely influences recovery of erections following surgery.
Urolithiasis
As the prevalence of obesity has dramatically increased in recent years, so has the prevalence of stone disease. Epidemiologic studies have increasingly linked the two conditions. Using data from the Nurses’ Health Study I and Health Professionals Follow-Up Study, Curhan et al. reported an increased risk of stone formation with higher BMI in women but not men. A later report using the same datasets, in addition to the Nurses Health Study II, found BMI was associated with increased risk of kidney stone formation in both men and women, with obese men having a 1.33 and obese women having a 1.9–2.09 times increased risk of those with BMIs from 21 to 22.9. Moreover, weight gain itself was associated with increased risk of kidney stone formation, as was central obesity measured by waist circumference. Reasons for increased risk of stones with obesity are likely multiple and associated with various components of metabolic syndrome. Hyperinsulinemia and resultant insulin resistance are associated with impairments in renal ammonium production, with obese and diabetic patients shown to form more acidic urine. Low urinary pH is an important risk factor for uric acid stones, but defects in renal acid handling may also lead to hypocitraturia. Hyperinsulinemia can lead to increased urinary calcium excretion, and both hypocitraturia and hyperinsulinemia increase the risk for calcium oxalate stones.
Obesity may further play an important role in which surgical treatment modality is chosen for stones. Current European Association of Urology guidelines state morbid obesity is an indication for open stone surgery, but few are eager to perform such procedures due to associated morbidity. Extracorporeal shock wave lithotripsy (ESWL) seems less effective in the obese. Issues with ESWL in the obese may include poor fluoroscopic targeting and increased skin to stone distance. In a systematic review of seven studies, Aboumarzouk et al. found a stone-free rate of 87.5% in patients with a mean BMI of 42.2 undergoing flexible ureteroscopy. In expert hands, percutaneous nephrolithotomy (PCNL) in the obese has similar stone-free rates (SFR) with minimal complications, although potentially with increased operative times and more radiation exposure. A prospective review of 5803 patients from the Clinical Research Office of the Endourological Society (CROES) database showed PCNL could be done safely in the obese but resulted in lower SFR and more repeat procedures. Several factors make PCNL challenging in the obese. From an anesthetic perspective, the prone position can compromise respiratory function and venous return, particularly in the obese. Standard instrumentation and techniques may need modification due to the anatomy of the obese patient and increased skin to stone distance. Several strategies are suggested to improve success, including use of extra-long nephroscopes, long access sheaths, or suture tails to allow burying of sheaths within the subcutaneous fat. Regardless of approach, surgical treatment of stones in the obese requires both surgeon experience and the thoughtful analysis of all available options ( Table 16.2 ).
Related posts:
Classification of Complications and Assessment of Quality of Care
Complications of Transurethral Resection of Bladder Tumors
Complications of Radical Cystectomy and Urinary Diversion
Complications of Extracorporeal Shock Wave Lithotripsy
Complications of Pediatric Urinary Diversions and Bladder Augmentation
Complications of Urethral Reconstruction
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