Risks and Complications of Bariatric Surgery

The risks and complications of surgical treatment of obesity are most often due to the obesity-related health problems. That is why we stress quitting smoking and losing weight prior to surgery to decrease these risks as much as possible. Also, complications can occur if instructions are not followed properly after surgery.

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The Risks in bariatric surgery include


The risk of death is less than 0.3% (1 per 300 patients). Death is usually due to a health problems such as heart or lung disease. Surgical causes of death can be related to pulmonary embolism (blood clots to the lungs) or a gastrointestinal tract leak. Patients with a very high BMI, male patients, and patients with severe medical conditions are at the highest risk, but death can occur in any patient.

Pulmonary Embolism

Pulmonary embolism occurs when a blood clot in the leg (deep venous thrombosis or DVT) breaks off and travels to the lungs. Sometimes pulmonary embolism causes sudden death, but most times, patients develop sudden shortness of breath and chest pain.

Pulmonary embolism occurs in fewer than 1% of cases (fewer than 1 per 100 patients). To help prevent pulmonary embolism, patients are put on blood thinner therapy (heparin) and given compression stockings while in the hospital. Patients are also encouraged to get out of bed and walk as soon as possible after surgery.

Patients on birth control pills or hormone replacement therapy should stop these medications 3 weeks prior to surgery. If birth control pills are stopped, another form of contraception should be used.

Patients who are at a higher risk of pulmonary embolism because they have had DVT in the past or are immobile may need to be checked before surgery by a hematologist.
Most patients with a previous history of DVT or pulmonary embolism will need 3 to 4 weeks of a daily blood thinner injection after they are discharged from the hospital.

Smoking increases the risk of pulmonary embolism so it is essential that patients quit at least 2 months before surgery, if not sooner.

Gastrointestinal Tract Leak

Leaks from the gastrointestinal tract can occur where the bowel and stomach are connected or stapled. If a complete seal does not form, bowel contents can leak into the abdomen, causing a serious infection. This occurs in about 5% of patients.

Leaks usually happen within the first 2 weeks after surgery. Symptoms of a leak can include fast heart rate, abdominal pain, fever, shortness of breath, or “just feeling sick”.

The severity of the leak and the infection that might develop vary from patient to patient. In case of small leak, a drain may be placed by X-ray. Patients receive nutrition through the vein or through the tube that is inserted in the stomach. Small leaks typically heal within 2 weeks.

Patients with sepsis (severe infection) due to a leak may need to be in the intensive care unit for an extended period of time. Some patients require emergency surgery (laparoscopic or open) to wash out the area of the leak and place drains.

Placement of a drain at the time of initial surgery does not prevent a leak.

Conversion to Open Procedure

In fewer than 1 in 100 patients, the surgery may need to be converted from the laparoscopic approach to the traditional open surgical approach. Reasons include bleeding, injury to other organs, excessive scar tissue from previous surgeries, or a very large liver.

Patients are encouraged to diet before surgery to help decrease the amount of fat in the abdomen and to increase the likelihood that surgery can be performed laparoscopically.

Bowel Obstruction

Bowel obstructions (blockages) can be caused by scar tissue in the abdomen or kinking of the bowel. This occurs in 1% to 3% of patients.

Bowel obstructions can happen early after surgery but also late (months to years) after surgery. Symptoms of bowel obstruction include severe abdominal pain, nausea, and vomiting. An emergency operation is typically necessary. It is important to call our office or come to the emergency room if you develop any of these symptoms.


Excessive scar tissue formation (stricture) can occur where the stomach pouch is connected to the bowel. This occurs in about 2% of patients.

Symptoms of stricture usually occur within the first 2 months after surgery, during the time of healing. Symptoms include vomiting and decreased tolerance to food, even liquids. Patients typically do not have any pain.

A stricture is corrected by a procedure which involves inserting a tube (endoscope) through the mouth into the stomach, passing a balloon down the tube to the area of stricture, and inflating the balloon to dilate (stretch) the scar tissue.

Usually 1 or 2 dilations are necessary, although some patients require more dilations or, rarely, surgery may be needed to revise the connection.

Another area of potential stricture is where the small intestine passes under the colon. These strictures are rare and occasionally require surgical treatment.


Bleeding can occur anywhere a stapling device was used. This includes the following:

  • Where the bowel and stomach are connected,
  • Where the intestines are connected,
  • At the stapled stomach,
  • Where scar tissue is ‘cut’,
  • Within the gastrointestinal (GI) tract (symptoms are vomiting blood or passing blood clots with bowel movements), or
  • Inside the abdominal cavity.

Bleeding occurs in about 2% of patients. In most cases, bleeding stops with stopping of the medication (heparin) used to prevent blood clotting and pulmonary embolism. In rare cases, an endoscopic exam or surgery may be needed to stop the bleeding.


An ulcer may develop in the area where the new stomach pouch is connected to the small bowel.

Symptoms of an ulcer include pain with eating, bleeding (noted as dark or bloody stools), vomiting blood, and nausea. An ulcer occurs in about 2 % of patients.

Ulcers are typically diagnosed by an upper endoscopy examination. They are treated by long-term use of an anti-ulcer medication.

Patients who smoke or take anti-inflammatory medications are also at increased risk.

Patients are discharged home from the hospital with a prescription for a strong antacid.


About 1 in 3 patients who follow a diet for rapid extreme weight loss will develop gallstones during the period of rapid weight loss. Symptoms of gallstones include pain under the ribs on the right side that spreads to the back, chest pain, nausea, or vomiting, especially after a meal high in fat.

About 7% of patients who undergo bariatric surgery need to have their gallbladders removed at a later.


Patients have a very low risk of developing infections.

  • Pneumonia is very rare (<1% of patients) if patients do breathing exercises and get back to normal activity soon after surgery. Patients who smoke are at increased risk of breathing problems and complications after surgery and need to quit smoking at least 6-8 weeks prior to surgery.
  • Abscess (pus collection) formation in the abdomen is also very rare (<1%). This can usually be drained without the need for an operation.
  • Urinary catheter insertion at the time of surgery poses a risk for a urinary tract infection. This is uncommon and usually can be readily eradicated with antibiotic treatment without any additional hospital stay.
    where scar tissue is ‘cut’,
  • Wound infections are uncommon as the small incisions heal well. The skin stitches are usually absorbed by the body, but occasionally the wound “spits it out”. Any wound infection that does occur is similar to a big pimple and is usually treated by opening the wound.

Chronic Nutritional Problems

Protein deficiency or vitamin and mineral deficiency can occur after gastric bypass surgery. More information about each type of deficiency follows:

Protein Deficiency

Protein is an essential nutrient for the body. Patients need to eat about 4 ounces (60 to 80 grams) or more of protein each day to maintain healthy organ function. If protein is eaten in 2 meals a day, a deficiency is very unlikely to occur. Protein supplements (shakes, bars, etc.) are usually not necessary as long as your dietary protein intake is adequate. Simply remember, protein first at mealtimes.

Vitamin and Mineral Deficiency

After a gastric bypass, adequate amounts of vitamins and minerals may not be consumed. Also, certain vitamins and minerals are not absorbed as easily. Therefore, after surgery, patients need to take the following supplements:

  • Multivitamins (2 times a day)
  • Abscess (pus collection) formation in the abdomen is also very rare (<1%). This can usually be drained without the need for an operation.
  • Iron supplement (once a day) – (in addition to the iron in multivitamins with iron)
    Calcium with vitamin D supplement (2 times a day).
  • Vitamin B12 (once-a-day pill or daily/weekly B12 lozenges that dissolve under your tongue or once a month injection)

Following is information about why these supplements are needed

  • Iron. Iron deficiency or anemia occurs in about 15% of patients after gastric bypass surgery. The amount of iron included in a multivitamin is usually not enough to prevent iron deficiency – a daily iron supplement is needed to prevent iron deficiency. The addition of vitamin C to iron supplements may help iron absorption.
    Rarely, patients who develop iron deficiency anemia that does not respond to iron by mouth may require injectable iron. Young women of child-bearing age will develop iron deficiency anemia, causing fatigue, if they do not take iron.
  • Calcium and Vitamin D. Vitamin D deficiency is very common in Australia. Vitamin D is needed to help absorb calcium. Malabsorption of calcium can lead to osteoporosis
    Women are already at increased risk for osteoporosis after menopause.
    We recommend that patients take 1000 to 2000 mg of calcium with vitamin D (1000 IU) every day. It is important to take the calcium and iron supplements at different times of day, because if taken together, less of each is absorbed.
  • Vitamin B12. Vitamin B12 deficiency occurs in 25% to 75% of gastric bypass patients after surgery we recommend B12 supplementation in all patients. B12 can be supplemented with a monthly shot or by mouth (on a daily or weekly base).
  • Folic acid (folate). For most patients, taking a daily multivitamin is enough to prevent folic acid deficiency. However, taking a folic acid supplement (1 mg per day) may be advised for pregnant women or women expressing a desire to become pregnant.
  • Thiamine. To avoid thiamine deficiency, patients are advised to take a multivitamin supplement daily.
  • Patients who need to be admitted to the hospital due to frequent vomiting will be given vitamins and thiamine through an IV.

Failure of Weight Loss – Chronic Symptoms

Patients may have unrealistic expectations about weight loss after surgery. Counseling before surgery is essential to set realistic goals for health and weight loss after bariatric surgery.

About 1 in 10 patients fail to lose adequate weight (50% or more of excess body weight) after gastric bypass surgery (although health problems such as diabetes usually improve). Failure may be due to “not following all the rules” following the prescribed diet, exercise, activity, office follow-ups), or just to poor metabolism: some patients seem to be destined to be overweight no matter what they do.

Patients who “graze” on food all day or constantly eat to the point of stretching their pouch can gain weight again. Also, patients who do not exercise regularly may not achieve their goal weight.

Surgery is not a “quick fix” for weight loss. Patients must be motivated and committed to changing their lifestyle – the surgery is a tool to help them lose weight. It doesn’t work by magic and it does not work alone.

Many patients will start to gradually gain weight 2 to 3 years after their surgery for one or both of these reasons:

  • The gastric pouch may dilate (enlarge) over time, allowing patients to tolerate a larger meal.
  • The small intestine becomes more efficient in absorbing calories (less dumping syndrome).

The weight gain occurs in most cases when patients eat many small portions of high-calorie foods. Patients will gain weight after surgery if they don’t follow the rules for a healthy diet, exercise, etc. Patients often say that it is more difficult to lose the 10 to 30 lbs they regain than the 150 lbs they initially lost with surgery.

Morbid obesity is a complex problem that is not easily fixed, even when surgery is technically successful. It is vital that patients obtain nutrition counselling, psychological counselling, and expert opinion about bariatric surgery.

Too Much Weight Loss – Chronic Nausea, Vomiting, Abdominal Pain

Rarely, excessive weight loss (BMI less than 19 kg/m2) occurs after bariatric surgery.

Each patient’s metabolism is different, so post-surgery weight loss varies from patient to patient. In the great majority of patients, metabolism reaches equilibrium at the end of the first year and they stop losing weight

This may be due to one or more of the following:

  • Depression
  • Food fear
  • Anorexia
  • Chronic abdominal pain
  • Chronic nausea
  • Untreated chronic stricture

About 1 in 200 patients (0.5%) develop chronic abdominal pain or nausea after surgery.

Body Image – Emotional Loss – Depression

Patients may experience psychological turmoil the first year after surgery.

Rapid weight loss may cause body image distortion, in which patients have a hard time adjusting to their new body image and develop anxiety or depression.

About 1% of patients find that they are depressed after surgery, even though they have good weight loss and have not suffered any complications.

Surgical weight loss may affect personal relationships for the better or worse.

Nerve Problems

Nerve problems (neuropathy) may occur during the hospital stay or at the time of surgery. This occurs in fewer than 1 in 200 obese patients.

Another cause of nerve problems is low levels of the vitamin thiamine.

Low Blood Sugars (Hypoglycemia)

Low blood sugar (hypoglycemia) can occur after weight loss surgery. Symptoms can include shakiness, nervousness, tremor, palpitations, tachycardia, sweating, clamminess, nausea, vomiting, abdominal discomfort, abnormal thinking, confusion, fainting, and seizures.

Low blood sugars can occur if the patient has not eaten for a few hours. It may be a signal that it’s time to eat.

“Late dumping syndrome” can cause hyperglycemia. This typically occurs about 1 hour or so after a meal if starches (bread, potatoes, pasta) were consumed. The starch is digested, turned to sugar, and causes an initial high blood sugar. The pancreas then releases too much insulin, resulting in the episode of hypoglycemia. Patients should keep a diary of their foods, meal times, and time of symptoms. If this is the case, starches should be avoided.

Rarely, some patients may need to eat a little sugar or glucose tablet to treat these episodes, but have to be careful not to eat too much as to regain weight.

Kidney Problems

Kidney failure or kidney stones may occur after gastric bypass surgery.

Kidney Failure

A rare complication of gastric bypass surgery is kidney failure. Risk factors include prolonged operations (longer than 5 hours) and BMI >55.

Kidney Stones

Kidney stones may develop after gastric bypass surgery. Rarely, this can result in kidney failure.

Complications from Anesthesia

Complications can occur with any anesthesia, although they are especially likely in morbidly obese individuals who also have sleep apnea.

The anesthesiologist will discuss possible anesthesia complications with each patient, based on his or her health history and health status.

Other Complications

There is a possibility that other complications, unknown at this time, may occur. Although gastric bypass surgery has been performed since 1967, “new” complications may arise that may not have been reported before. To help identify any new complications, it is important for all patients to continue to follow up with us after surgery.

Specialist weight loss surgeon

Dr Govind Krishna


Dr Govind Krishna is an expert is weight loss surgery with 20+ years of experience performing gastric surgery. He has performed over 2,000+ weight loss and gastric operations and offers affordable surgical solutions for those wishing to consider weight loss surgery.

He offers an empathetic, non-judgemental approach to weight loss management and his mission is to help his patients restore their health and move on with their lives.

He holds a Master of Surgery (MS) degree specialising in gastric surgery and is a Fellow of the Australasian College of Surgeons (FRACS). Dr Krishna consults across South-Western Sydney at Campbelltown, Fairfield, Liverpool and Hurstville.

Learn more about Dr Krishna’s significant weight loss surgical experience below.

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