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B56. Morbid obesity, and bariatric surgery

Overweight and obesity are states of increased body weight due to excess adipose tissue. These are risk factors for severe disease, including cardiovascular disease, cerebrovascular disease, and cancer. Obesity (and to a lesser extent overweight) is a chronic disease which leads to significant excess morbidity and mortality. It’s also an epidemic that is rising for every year, and is associated with many diseases, including diabetes, hypertension and physical inactivity.

The Body Mass Index (BMI) is used to defined overweight and obesity, although it has its imperfections. It is closely correlated with body fat. However, the BMI will not be the right method to choose if you have a lot of muscle, as the density of muscle tissue is higher than that of fat.

Overweight is defined as a BMI of 25 – 30, while obesity is defined as a BMI > 30. BMI of more than 35 or 40 (depending on the source) is sometimes referred to as morbid obesity.

Overweight and obesity are preventable causes of morbidity, mortality, and healthcare costs. Overweight and obesity cause more deaths worldwide than underweight. 4 million people die every year due to disease caused by overweight or obesity. Around 4-8% of cancers are attributed to obesity.[1]

Etiology

Overweight and obesity is the result of a long-term positive energy balance (more calories in than calories burnt), but the cause of this is multifactorial. Many lifestyle factors, like physical inactivity, poor sleep, and poor diet, are associated with it. However, studies suggest than genetic predisposition accounts for 40 – 70% of the etiology contribution of overweight. Having one overweight parent increases the risk threefold, and having two overweight parents increases the risk tenfold. However, these genetics factors are not due to any single genes but rather many; the inheritence for obesity is polygenic. Research shows that twins who grow up separately with separate foster parents have a body composition more similar to their biological parents than their foster parents.

One theory is the following: The human body evolved to be in activity every day due to unpredictable lives where food was scarce and not readily available. The body is therefore not well adapted to environments where we have too much food and where physical activity is not necessary for survival. In the modern world, there is suddenly a lot of tasty food, but not enough activity.

Important to note that in many countries (like Norway), the prevalence of overweight and obesity has increased over a period during which the average person ate less and healthier, and worked out more.

Types

Obesity can be divided into central and peripheral obesity.

Central obesity

Central obesity, also known as visceral or abdominal obesity, is characterized by fat accumulating in the trunk and in the abdominal cavity around the organs and in the mesentery. Central obesity is more harmful than peripheral obesity, because visceral adipose tissue is more hormonally active than nonvisceral adipose tissue. People with central obesity have an increased waist circumference, which is a risk factor for other diseases independent of the BMI itself.

Peripheral obesity

Peripheral obesity is accumulation in subcutaneous tissue, as in the thighs, breasts and arms.

Pathology

Adipose tissue, especially visceral adipose tissue, is hormonally active and secretory organ, producing different hormones and molecules, including adiponectin, leptin, tumour necrosis factor, and interleukin 6, which cause chronic low-grade inflammation and disease. Increased mass of visceral adipose tissue causes excess release of free fatty acids, which leads to insulin resistance. The adipose tissue of lean people mainly secretes anti-inflammatory hormones and molecules, while the adipose tissue of overweight people mainly secretes pro-inflammatory ones.

Overnutrition makes the blood glucose level rise, so the insulin production increases to be able to lower the blood glucose. The insulin receptors will open up for glucose intake, making the cells store glucose as fat. This overnutrition makes the adipocytes full of fat and the muscles and liver full of sugar and glycogen, so they can’t handle any more glucose and shut down their insulin receptors. Pancreas try to produce more and more insulin to lower the sugar levels, but it will all result in hyperglycemia and hyperinsulinemia. High insulin levels prevent lipolysis and fat oxidation, but the patient is still hungry and tired. It becomes a viscous circle.

High levels of insulin may increase levels of Insulin-like-growth-factor-1, (IGF-1), which stimulates growth and survival of cancerous cells. This may explain some of the increased risk for cancer in obesity.

Obesity causes changes in leukocyte count and a switch from M2 (anti-inflammatory) to M1 (pro-inflammatory) macrophages.

Diagnosis and evaluation

Various anthropometric measurements can be used in the evaluation.

BMI

The body mass index (BMI) is defined as the weight (kg) divided by the height squared (m2). According to the BMI, obesity is classified as follows:

  • BMI < 18.5 – underweight
  • BMI 18.5 – 25 – normal range
  • BMI 25 – 30 – overweight (pre-obesity)
  • BMI 30 – 35 – obese (grade 1 obesity)
  • BMI 35 – 40 – severely obese (grade 2 obesity)
  • BMI > 40 – morbidly obese (grade 3 obesity)

BMI has been controversial lately, as some say that it's too imprecise to evaluate body composition and that muscular people can have a falsely elevated BMI. It's important to evaluate the patient as a whole and not focus solely on the BMI.

Waist circumference

The waist circumference predicts mortality better than any other anthropometric measurement. The circumference is measured at the level of the umbilicus, rounded to nearest 0.5 cm. Two risk levels exist according to waist circumference:

  • Level 1 – males – circumference > 94 cm
  • Level 2 – males – circumference > 102 cm
  • Level 1 – females – circumference > 80 cm
  • Level 2 – females – circumference > 88 cm

Hip circumference

Hip circumference is measured at the point of greatest circumference around the hips, rounded to nearest 0.5 cm.

Waist/hip ratio

  • Waist circumference divided by hip circumference
  • Defined as central obesity if ratio > 0.95 in males or > 0.80 in females

Skinfold thickness

A skinfold caliper is a special tool which can be used to measure the thickness of a fold of skin, which can be used to estimate the body fat percentage. It's very cheap, not very accurate. Common sites to measure skin fold thickness:

  • Triceps
  • Abdomen
  • Frontal thigh
  • Chest

Hydrostatic weighing

By lowering a person into a pool of water and measuring how much water is displaced, we can find out the volume and therefore the density of the person. The density can be used to estimate the body fat percentage. It's expensive and time-consuming, but very accurate.

Bioelectrical impedance analysis

These machines usually double as weight scales. When standing on it, the machines weighs the person and measures the resistance (impedance) of the body and estimates the body fat percentage based on this. It's very fast, relatively expensive but not very accurate.

Complications

Obesity itself is a chronic disease which may lead to a number of other diseases:

Treatment

The old mantra was that obesity should be managed with lifestyle changes, and that medical therapy was a last-line option, to avoid treating a "lifestyle problem" with medication. Nowadays, the scientific community is shifting more towards a practice where obesity is treated in the same manner as another very common chronic disease, hypertension. Hypertension can also be managed with lifestyle therapy alone but most patients with hypertension also require medical therapy.

Treating obesity significantly decreases morbidity and mortality, and we should use those tools which we have available, especially with the introduction of newer, more efficacious anti-obesity drugs (GLP-1 analogues).

Patient compliance should be high and there should be no contraindications before drug therapy is initiated. The weight lost by these drugs is usually regained if they’re stopped. As such, lifelong treatment is often necessary. This is often deterring to patients and providers, but the same is the case for statin therapy, antihypertensive therapy, and antidiabetic therapy.

Pharmacological therapy

More and more options for pharmacological treatment of obesity are available. Buproption-naltrexone and GLP-1 analogues are the most commonly used ones. The former achieves an average of 5% weight loss while the latter achieves an average of 5-16%.

Bariatric surgery

Bariatric surgery is weight-loss surgery, that is, those surgical procedures aimed at causing weight loss. It must be combined with lifestyle modification.

Patients must meet the following criteria:

  • Persons with BMI > 40 OR persons with BMI 35 – 40 and a comorbidity:
    • Type 2 diabetes
    • Obstructive sleep apnoea
    • Hypertension
    • Obesity-hypoventilation syndrome
    • Nonalcoholic steatohepatitis
    • Impaired quality of life
    • Etc.
  • Failed dietary therapy
  • Psychiatrically stable without alcohol dependence or illegal drug use
  • Age 16 – 65

Preoperative assessment

Preoperative assessment is comprehensive and should be performed by a multidisciplinary team. The person’s psychology and cognitive abilities should be assessed for any psychiatric disorders and to determine whether the patient is able and willing to make the necessary lifestyle changes. Any newly diagnosed significant psychiatric disorders should be treated ahead of surgery.

A dietician should be involved to make nutritional plans for the patient before, during, and after bariatric surgery. A thorough medical assessment must be made to assess for any comorbidities which may contraindicate the surgery.

Patients should participate in lifestyle change programs before surgery to demonstrate their commitment to them. Pregnancy is discouraged for the first 2 years after surgery, so patients of childbearing should be encouraged to use birth control.

Obesity leads to physiological changes that impact perioperative anaesthesia, and so getting anaesthesia on board for evaluation is important.

Surgeries

Bariatric surgeries have a volume-restrictive and nutrient-malabsorptive effect, which is what drives the weight loss.

The possible bariatric surgeries include:

  • Sleeve gastrectomy
  • Roux-en-Y gastric bypass
  • Gastric banding
  • (Intragastric balloon)

Sleeve gastrectomy is a partial gastrectomy in which the majority of the greater curvature of the stomach is removed.

Roux-en-Y gastric bypass involves separating the stomach into two pouches, followed by gastrojejunostomy to connect the smallest pouch to the jejunum. The larger pouch is completely bypassed, hence the name.

Gastric banding refers to applying a band to the epigastric part of the stomach, which narrows it. It’s a much smaller procedure than bypass or sleeve, and is applied laparsoscopically. It’s a commonly used procedure nowadays due to its less invasive nature and reversibility.

Another option is an intragastric balloon. This balloon is placed in the stomach endoscopically and filled with 400 – 700 mL of saline. It occupies volume in the stomach, thereby promoting satiety. The balloon must be removed after six months, and so intragastric balloon is not a permanent solution. This method was not covered in the lecture.


References

  1. ↑ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9857053/