Bariatric and Metabolic Surgery

Anaesthesia concerns

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As it has been realised that western diagnosis criteria for obese and metabolic syndrome do not hold true for Asian patients, anaesthesia care providers should be completely aware of the pathphysiology, risks and difficulties encountered by obese patients during the bariatric surgeries.

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The word ‘bari’ is the plural of ‘baros’. In Greek, ‘baros’ means weight / burden / load or heaviness. From this stems ‘Baris’ referring to the obese or fat / heavy / overweight people.

Obesity has reached epidemic levels within a short span of time with an alarming rise in the number of Type 2 diabetics globally. Asia Pacific itself has seen an upsurge of more than 50 million Type 2 diabetics with no signs of regression. It has also been seen that specifically in Asia the comorbidities, especially diabetes and cardiovascular disease, develop at a lower BMI and develop significant complications leading to fatality at a low age.

Health effects of obesity

As per the WHO criteria, the prevalence of obesity in Asia Pacific region is lower than western regions. According to research studies, health hazards occur at a much lower BMI in the Asian region. It has been predicted that by 2010 the number of diabetics in Asia alone would constitute to 130 million of the total 236 million worldwide, thus constituting more than half of the world’s diabetics.

Treatment of obesity

Treatment of obesity includes various options outlined below as well as a team effort as obesity is multifactorial and needs a combined effort by various specialists like the physician, nutritionist, psychologist, physiotherapist and last, but not the least, surgical intervention and the anaesthesia care giver.

  • • Assessment of Weight
  • • Dietary Therapy
  • • Physical Activity
  • • Behaviour Therapy
  • • Drug Therapy
  • • Combined Therapy
  • • Surgery

It has been observed that a weight loss of even 10 per cent significantly lowers the comorbidities, which is significantly seen in case of obstructive sleep apnoea wherein a weight loss of even 10 per cent might decrease the sleep apnoea by 50 per cent. Because bariatric surgery has become common these days, it is imperative that anaesthesia care providers be knowledgeable about the pathophysiology, risks and difficulties encountered during their care. Problems include difficulties with intravenous access, tracheal intubation and extubation, appropriate use of narcotics, muscle relaxants and other drugs. Based on Body Mass Index (BMI), humans may be classified as non-obese, overweight, obese, morbidly obese and super-morbidly obese.

Cardiovascular system

With the onset and progression of obesity, patients develop hypertension, increased blood volume and dyslipidemia. Even when they are normotensive, there is echocardiographic evidence of a significantly larger internal diameter of ventricles, thicker end diastolic septum and posterior wall of the left ventricle. These changes are related to the increased amount of intra-abdominal fat deposition. The hypertension is mild to moderate in the majority but severe in 5 to 10 per cent. For every 10-kg gain in body weight, systolic blood pressure is reported to increase by 3 to 4 mm Hg and the diastolic increases 2 mm Hg. Obesity is also associated with Ischemic Heart Disease (IHD). This is because obese patients are prone to hypercholesterolemia, a reduced density of lipoprotein levels, hypertension and diabetes mellitus. The Framingham study noted a direct correlation between angina pectoris, sudden death and obesity. Obese patients are also prone to cardiac arrhythmias because of increased fat infiltration of the cardiac conduction system, the presence of cardiomyopathy and coronary artery disease. Extra-cardiac factors such as obstructive sleep apnoea with the associated hypoxia, hypercapnia and electrolyte imbalance along with an increase in circulating catecholamines increase this predisposition. Many obese patients are asymptomatic even though they have varying degrees of cardiovascular dysfunctions. The primary reason is limitation of mobility. As a result of this, they may not complain of symptoms such as angina on exertion or exertional dyspnea.

Respiratory system

Obesity exerts profound effects on the respiratory system. The anatomic changes result in Obstructive Sleep Apnoea (OSA) and Obstructive Hypoventilation Syndrome (OHS) because of a reduction in pharyngeal free space. This is because of deposition of adipose tissue into the pharyngeal walls including the uvula, tonsils, tongue and aryepiglottic folds. The compliance of the chest wall and difference between extraluminal and intraluminal pressures along with oropharyngeal muscle tone determines airway patency. In obese individuals, collapse of the soft walled oropharynx and obstruction of the airway occurs easily because the pharyngeal free space is markedly diminished and extraluminal pressure is increased.

As a single independent factor, obesity is responsible for OSA in 60–90 per cent of the population with this disorder. OHS is different from OSA in that there is no cessation of airflow. Both OSA and OHS repeatedly disrupt sleep due to increased ventilatory effort induced arousal and causes daytime sleepiness and cardiopulmonary dysfunction.

Pulmonary function tests may be necessary to note effects on lung capacities and airflow mechanics. Arterial blood gases will indicate if the patient is retaining carbon dioxide or has hypoxemia. The presence of polycythemia will suggest long-standing hypoxemia. A chest x-ray will evaluate the anatomical status of the lung and cardiac structures

Effects of obesity on the liver

Obesity predisposes patients to Non-Alcoholic Steatohepatitis (NASH) and cholelithiasis. However, metabolic function of the liver is not affected in the majority of obese patients. Diabetes mellitus predisposes obese patients to NASH.

Patients with NASH may have elevated liver enzymes, increase in triglycerides, hepatomegaly and cirrhosis.

Deep Vein Thrombosis (DVT)

Both polycythemia and venous stasis predispose obese individuals to DVT. Venous stasis results from increase in intra-abdominal pressure and accompanying immobilisation noted in obesity. Decreased fibrinolytic activity along with increase in fibrinogen concentrations has been observed in obese individuals.

The risk of DVT is doubled in obesity (48 per cent vs. 23 per cent) when compared to lean individuals during abdominal surgery. This automatically increases the likelihood of Pulmonary Embolus (PE) and is reported as being between 2.4-4.5 per cent following bariatric surgery. To reduce the risk of DVT and PE in obese patients, most surgical protocols favour the use of anticoagulant prophylaxis and pneumatic compression lower extremity stockings.

The morbidly and super-morbidly obese are particularly challenging patients because of their size. In addition to routine evaluation, areas of concern in this patient group are as follows:

Intravenous access – The presence of excessive subcutaneous tissue decreases the easy visibility of peripheral veins. Portable ultrasound equipment may be required for identification and cannulation of peripheral veins

Preoperative airway assessment – Obese patients are more difficult to mask ventilate and intubate. This is because of their size, presence of a neck that has a widened circumference, is shorter and the presence of excessive pharyngeal tissue with a tongue that has a large base. It is imperative that every obese patient be carefully examined for the feasibility of mask ventilation and intubation including aspiration risk. Neither obesity nor body mass index has been associated with difficult intubation. Large neck and Mallampati score are the only two predictors of potential intubation problems. Also, patients with a Mallampati score greater than or equal to three have increased difficulty with tracheal intubation. Other routine assessments namely, jaw and neck mobility, dental status, patency of nostrils, and inspection of oropharynx should be done prior to implementation of an anaesthesia care plan for obese patients.

Patients undergoing bariatric surgery are prone to slipping off the table, so they must be securely strapped to the table.

Anaesthetic pharmacology – The physiological changes associated with obesity lead to alterations in distribution, binding and elimination of many drugs. Many doses have to be calculated according to the ideal body weight or more accurately according to the lean body mass. In 20 to 40 per cent of obese individuals, ideal body weight and lean body mass are not identical. This is because increase in body weight may be due to an increase in lean body mass.

Extubation – Obese patients must be extubated when they are fully awake and after they have returned of motor power. It is less threatening to extubate those that were not difficult to mask ventilate and or intubate. Factors that play a role in determining successful extubation include the severity of obstructive sleep apnoea, duration and type of procedure. Either facemask, nasal Continuous Positive Airway Pressure (CPAP) or Bi-level Positive Airway Pressure (BiPAP) support with oxygen may be required in some patients following extubation. This is usually the case for those with a history of sleep apnoea or those using CPAP before surgery and supplemental oxygen is usually required.

Conclusion

Caring for obese patients remains a challenge for anaesthesia providers. Some patients require special care in a low-cost obesity care unit while others may need prolonged care in the intensive care unit.

The various associated health hazards

  • • Arthritis, Osteoarthritis (OA), Rheumatoid Arthritis (RA)
  • • Cancers, Breast Cancer, Cancers of the Esophagus and Gastric Cardiac, Colorectal Cancer, Endometrial Cancer (EC), Renal Cell Cancer
  • • Birth Defects
  • • Cardiovascular Disease (CVD), Stroke, Hypertension
  • • Carpal Tunnel Syndrome (CTS)
  • • Daytime Sleepiness, Sleep Apnoea
  • • Deep Vein Thrombosis (DVT), Chronic Venous Insufficiency (CVI)
  • • Diabetes (Type 2)
  • • End Stage Renal Disease (ESRD)
  • • Gallbladder Disease
  • • Gout
  • • Heat Disorders
  • • Impaired Immune Response
  • • Impaired Respiratory Function
  • • Liver Disease, Pancreatitis
  • • Low Back Pain
  • • Obstetric and Gynecologic Complications, Infertility
  • • Surgical Complications, Infections Following Wounds
  • • Urinary Stress Incontinence

Author Bio

Sunitha Goel is a Consultant Anaesthesiologist in Saifee Hospital, Dr L.H. Hiranandani Hospital, Cumbala Hill Hospital and Breach Candy Hospital. She was awarded Industry Leadership Award in 2004.

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