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Obesity and Anesthesia

By Dr Ananya Mandal, MD

Obesity is a condition leading to excessive body fat. This is mainly caused by an imbalance between energy intake and expenditure leading to the accumulation of the excessive fat in the body.

Obesity is a rapidly growing public health problem leading to several chronic ailments like heart disease, diabetes, stroke, high blood pressure and some cancers.

Body mass index (BMI)

The body mass index (BMI) is one of the most widely used measure for measuring obesity and overweight. It is a measure of the relationship between height and weight.

  • BMI of less than 25 kg/m2 is considered normal
  • BMI of 25–30 kg/m2 is considered overweight but at low risk of serious medical complications
  • BMI of over 30 (Obese), over 35 (morbidly obese) and over 55 (super morbidly obese) kg/m2 are considered obese and at risk of serious medical conditions. Over 30 BMI the risk of death rises sharply

Obesity and surgery

Obesity also raises the risk of surgical and anesthetic complications. Obese individuals thus fare worse than normal weight individuals in surgeries.

Anesthesia risks for obese individuals

Anesthesia may pose several risks for the obese individuals. Some of these include:-

  • Risks to the respiratory system

Obese individuals are at a risk of obstructive sleep apnea and several other respiratory problems. They may have airway obstruction as well. An anaesthetist should also assess the patient’s ability to breathe deeply, an action that would ensure a good ventilation and oxygenation while under anesthesia.

Because of the lack of space in the back of the throat, intubation with an endotracheal tube that helps in breathing and ventilation during surgery may be difficult for obese and morbidly obese individuals. Fibreoptic intubation is the safest course of action for these patients.

There is also a risk of lowered oxygenation among obese individuals during surgery. Obese patients are also at risk of lung infections and other lung complications after anesthesia.

Due to the problems with general anesthesia regional anaesthetic techniques, such as peripheral nerve blocks and epidural blockade may be preferred for obese individuals.

  • Risks to the cardiovascular system

The heart is under pressure in an obese individual. There is a higher risk of heart attacks, angina pain, and lack of oxygenation of the heart muscles, stroke and high blood pressure in obese individuals. Anesthesia may raise the risk of cardiovascular adverse events in the obese.

For example, mild to moderate hypertension is seen in 50–60% of obese patients and severe hypertension in 5–10% patients. In addition there may be insulin resistance as well. Total blood volume is increased in the obese but the blood flow to the brain and kidneys are normal.

Obese individuals are also at risk of developing cardiac rhythm abnormalities due to low oxygenation, electrolyte disturbance caused by diuretic therapy, coronary artery disease, obstructive sleep apnea, myocardial hypertrophy etc.

During anesthesia, each of these risk factors is aggravated. There may be ventricular impairment, heart failure or arrhythmias precipitated by anesthetic agents.

After inducing anesthesia workings of the heart may deteriorate in an obese individual, blood pressure regulation may be deranged and there may be a risk of heart attacks as well.

Prevention of anesthetic complications and practical considerations

  • Patient is usually advised to lose as much weight as possible before surgery.
  • Regional anesthesia and awake intubation is preferred over general anesthesia.
  • Opioid and sedative drugs may cause respiratory depression and should be avoided.
  • Aspiration pneumonia, due to the back flow of the stomach’s contents into the lungs, is a common lung complication among obese people. To prevent this there should be adequate measures like medications and keeping the patient on a completely empty stomach for at least 12 hours before surgery.
  • Risk of deep vein thrombosis after surgery is larger among obese individuals. This may be prevented by suitable blood clot dissolving medications like heparin.
  • Most operating tables are designed for patients of up to 120–140 kg in weight. For those who weigh more than this limit, specially designed tables may be needed.
  • Position should be maintained to prevent nerve compressions and pressure sores. Tilting or turning the patient to their right may compress large blood vessels like the inferior vena cava in the abdomen leading to complications - this needs to be avoided.
  • Getting an intravenous line in an obese patient may be difficult due to high amount of subcutaneous fat. In case a line cannot be established, a central venous line is considered.

Reviewed by , BA Hons (Cantab)

Further Reading

Last Updated: Apr 8, 2013

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