Neurosurgery has evolved in response to such forces as technological advances (both inside and outside of the specialty), innovation, changing patterns of disease, and shifting patient populations. For example, many neurosurgeons can readily recall the advent of first CT and then MRI scans and their impact on practice. Similarly, degenerative spine disorders have come to be treated by neurosurgeons primarily in developed countries, while in other countries neurosurgical practice frequently is devoted to intracranial manifestations of infectious diseases such as tuberculosis.
Developments such as these accentuate the need to anticipate changes that may impact neurosurgery in the future. A trend with significant potential to impact medicine in general and neurosurgery specifically is the increase in obesity, not only in the U.S. but also worldwide. The increase in obesity is probably the foremost demographic change and epidemiological health challenge of the 21st century. Recent headlines highlight that obesity is now more costly to the U.S. economy than either smoking or alcoholism. Obesity carries a 10 percent to 50 percent increased risk of death, primarily because of the increased risk of medical comorbidities such as heart disease, diabetes, hypertension and sleep apnea. It is obvious that the primary care field is significantly impacted by the legions of patients who are overweight and obese. For neurosurgery, it is expected that the incidence and prevalence of many neurosurgical diseases will change, the risk-benefit analysis of surgical interventions will be altered and intriguing opportunities for functional intervention as a means of treating or curing refractory obesity will come to light.
Economically, obesity is associated with a 36 percent increase in healthcare spending and accounts for nearly 10 percent of all direct medical expenditures, a price tag topping $100 billion a year. The loss of productivity alone costs nearly $4 billion a year. Obesity is now so common that in most countries it outstrips both malnutrition and infectious disease as the number one contributor to ill health.
In the U.S., as recently as 1990 not a single state had an obesity prevalence greater than 15 percent, while in 2006 only four states could boast prevalence rates below 20 percent. Today nearly two-thirds of all Americans (140 million) are obese or overweight, a figure that has doubled since 1970 and continues to increase. More than 60 million adults over age 20 are obese. Contributing to this epidemic is the inactive lifestyle of most Americans. In 2006, only 26 percent of Americans engaged in vigorous physical activity at least three times per week while nearly 60 percent engaged in no substantial fitness at all.
Overweight children are also a serious health concern. In all age groups, rates have tripled in the last two decades. Even among 2- to 5-year-olds an astounding 14 percent are already seriously overweight. Studies clearly demonstrate that weight problems in children typically translate into obesity in adult life.
Impact of Obesity on Surgical Outcome
Perhaps of greatest importance to neurosurgeons is the potential impact of
obesity on surgical outcome. Nearly every aspect of surgery and postoperative
care is complicated by excess weight. Consider a relatively straightforward
case of a five-foot-10, 300-pound male with a drop foot resulting from an
L4-L5 herniated disc that is unresponsive to the usual medical interventions.
In contrast to a rapid, minimally invasive, highly successful outpatient
procedure, this surgery for obese patients can present significant challenges
for anesthesia and positioning, a potentially prolonged surgical approach
with commensurate related postoperative issues—hypoventilation syndrome,
medical and wound healing complications, andlikely at least an overnight
hospitalization. While the absolute risks may be difficult to quantify given
all variables involved, the appreciation of surgical complications in obese
patients has led some spine surgeons to refuse surgical intervention for
any patient with a body mass index, or BMI, greater than 30.
What are the known additional risks of surgery in patients who are overweight? The first consideration is the associated medical problems including diabetes, end-stage renal disease, osteoarthritis, systemic and pulmonary hypertension, ischemic heart disease, arrhythmias, heart failure, restrictive ventilatory dysfunction and hypoxemia, obesity-hypoventilation syndrome, liver disease, and increased risk of aspiration related to delayed gastric emptying. Positioning also can be problematic and even hazardous in these patients. While most operating tables have a weight capacity of 200 kg (441 pounds), the prone positions used for many spinal procedures can be treacherous, particularly for patients with protuberant truncal obesity. Even supine positioning can have problems related to aortic and inferior vena caval compression and ventilatory impairment. In one study, obese patients had a greater than 30 percent incidence of surgically induced ulnar neuropathy compared with only 1.0 percent in controls. Other compression injuries and even rhabdomyolysis have been reported in prolonged neurosurgical procedures. Rehabilitation after spinal procedures also may be negatively affected by the poor muscle conditioning so prevalent in this underactive group of patients.
While the impact of patient obesity on spine surgery may be obvious, studies also have demonstrated dramatic and statistically significant impact on craniotomies, surgery in children, and patients sustaining blunt trauma. In a series of elective thoracic and lumbar spinal fusions, complication rates increased directly with BMI (complication rates increased 14 percent for a BMI of 25, 20 percent for a BMI of 30, and 36 percent for a BMI of 40). Looking at morbidity following craniotomy for meningioma, readmission rates for complications were more than two-and-a-half times higher in the obese than in the nonobese population. A large study that evaluated all surgery on children saw higher rates of postoperative hypertension, diabetes mellitus and asthma in overweight patients. Also seen in the obese group were increased incidence of upper airway obstruction, difficult airways, prolonged stay in the postanesthesia care unit, and increased use of antiemetics. Obese patients admitted for blunt trauma also suffer more problems: While they seem to sustain somewhat fewer head injuries, they experience greater chest and extremity trauma, have higher complication rates (42 percent compared with 32 percent), and have higher mortality rates, as well as longer hospitalizations, stays in the ICU and days of mechanical ventilation.
The explosion in the number of obese people also will impact disease incidence and prevalence, affecting the spectrum of disorders exhibited by patients encountered in the neurosurgical office. Obesity is a known risk factor for pseudotumor cerebri (once a rare disorder); after treatment, shunt failures are extremely common, particularly in patients with classic android-type obesity (abdominal-truncal distribution of weight). Being overweight also increases the risk for many cancers. There is increased incidence of nearly all of the most common cancers, including colon and breast, in this population.
Not surprisingly, obesity is a major risk factor for development of osteoarthritis. A mere 10 additional pounds increases the force on a knee by 30-60 pounds with each step. One can imagine the additional stress on the spine and on spinal instrumentation in obese patients. Overall, osteoarthritis is four-to-five times more likely in obese patients while 66 percent of all patients diagnosed with osteoarthritis are either obese or overweight. Clearly obesity will increasingly influence the number of patients presenting to neurosurgeons with degenerative spine disorders.
Opportunity in Adversity
Adversity proverbially is the mother of invention, and with respect to the
obesity epidemic the invention, or opportunity, is the potential use of functional
neurosurgical intervention for the treatment of refractory obesity. If just
1.0 percent of the 70 million obese Americans were new neurosurgical patients,
this would represent more than 200 new cases for every practicing neurosurgeon.
It is already established that the brain and nervous system exert significant control over eating behavior. Studies using functional imaging have detected important differences between obese and normal- weight volunteers in brain activity related to eating. Classic neurophysiological doctrine describes a dual hypothalamic control mechanism for important endocrinological and functional control over eating and hunger involving the ventromedial nucleus and the lateral hypothalamic area. But these areas may represent just the final step in a complex neural pathway that may involve additional brain regions and a variety of neuropeptides. The pivotal concepts relate to the pathophysiology of satiety, a complex, interrelated network that involves the stomach and hypothalamus but may be coordinated or driven by another brain region. Clearly, satiety is not a physical phenomenon but rather the perceptual interpretation of some mechanical alteration such as stomach distention, and perception is almost certainly a cerebral (supratentorial) function. Indirect evidence for this principle comes from studies of gastric bypass patients who experience not only the expected rapid satiety from the reduced stomach volume but also reduced hunger and voluntary reduction in intake of calorie-dense foods. Functional imaging studies also indicate that the response of obese patients to eating is a more diffuse cerebral activation than the strong, prefrontal-focused activation catalogued in normal-weight volunteers. Fortunately, several neurosurgical centers are actively undertaking studies in this area, paving the way to a better understanding of the physiological mechanisms underpinning obesity and providing potential treatment for those in whom multiple other interventions have failed.
As the 21st century advances, neurosurgeons will be faced with different challenges than those which confronted the neurosurgeons who paved our way. Certainly, patient obesity will impact the diseases neurosurgeons treat as well as the outcomes expected for these patients, and we must strive to address this reality in the everyday practice of neurosurgery.
Deborah L. Benzil, MD, is associate professor at New York Medical College and a neurosurgeon at Westchester Spine and Brain Surgery PLLC, Hartsdale, N.Y. The author reported no conflicts for disclosure.
Acknowledgements: The author gratefully acknowledges the significant contributions to this article of Kathryn E. McGoldrick, MD, professor and chair of anesthesiology, New York Medical College; Joshua Rosenow, MD, associate professor, Northwestern University; Alon Mogilner, MD, PhD, North Shore Hospital; and Rebecca Newman, MD, a dedicated student who devoted a summer during medical school to understanding functional imaging and obesity.