Gastric Bypass

Gastric Bypass: Surgery, Risks, Side Effects & Results

Risks and complications

General risks which apply to all abdominal surgery include but are not limited to:

  • The anaesthetic (greater in the morbidly obese)
  • Deep venous thrombosis (DVT)
  • Pulmonary embolism
  • Death
  • Infection
  • Bleeding
  • Pneumonia
  • Heart attack
  • Stroke
  • Bowel obstruction
  • Intra-abdominal abscess
  • Damage to intra-abdominal organs
  • Adhesions
  • Wound infections
  • Incisional hernias.


It is unusual that you will need a blood transfusion as the risk of significant bleeding is less than 1%.


Any surgery carries a risk of infection. The most common types are wound infections, urinary infections and chest infections. More serious types are blood infections, abscess and peritonitis.

Although fortunately rare, some of these infections can progress to death, even if the source of infection is corrected and appropriately treated.


Blood clots in the veins in the legs or pelvis (DVT) can migrate to the lung (pulmonary embolism or PE) which can be fatal.

These can occur after any type of surgery, and the risk persists after surgery for up to three weeks.

The risk of this type of complication after bariatric surgery is less than 1%. However as it is such a serious complication and can result in sudden death, the surgical team take a number of steps to try and minimise the risks.

You will be given injections to thin the blood, stockings to compress your legs and when you are asleep in the operating theatre, machines will be used to squeeze the blood from your legs.

These machines are continued to be used on the ward when you are in bed and you will be encouraged to get up and walk about the ward as soon as possible.

The risk of DVT is about 1:200 and the risk of pulmonary embolism about 1:1000. If you are identified as being a high risk candidate, you may be discharged home on blood thinning injections for up to three weeks in an effort to minimise your risk.

Chest problems

Pulmonary complications such as pneumonia, aspiration and atelectasis (partial collapse of the base of the lungs) can occur after any type of surgery under general anaesthetic.

The risk of this complication can be reduced by stopping smoking, early mobilisation after surgery and working with physiotherapists with chest exercises and incentive spirometry.

Incisional hernias

Incisional hernias are common after open bariatric surgery but thankfully rarer after laparoscopic bariatric surgery.

The risk is approximately 1% and if they do occur they tend to be small and easily repaired at a later date.

Small bowel obstruction

The small intestine can get blocked by twists around scar tissue (adhesion) inside the abdomen that can occur after surgery. The other less common cause of bowel obstruction is an internal hernia.

These types of obstructions can occur at any time and can occur many years after surgery. The rate of bowel obstruction after a laparoscopic gastric bypass is around 5%.

If not treated appropriately and quickly, there is the risk of compromise to the bowels blood supply and if the bowel dies this can lead to perforation and serious complications or even death.

Most obstructions after laparoscopic surgery can be successfully repaired laparoscopically.

Wound infection

These can occur with any type of surgery and even in clean surgery they occur in up to 5% of cases. They may require antibiotics, opening and drainage of the wound with packing.

These wounds are then allowed to heal over a longer period of time with dressings as an outpatient.

Patients who smoke are at increased risk of wound infection.

Damage to spleen or other organs

The spleen lies close to the upper portion of the stomach and can be injured during surgery. Fortunately it is very rare to injure the spleen during laparoscopic surgery and the rate is under 1%.

If this was to happen you may require conversion to an open procedure and removal of the spleen. This will be avoided wherever possible.

Pancreatitis is a rare but reported complication as is liver injury. These rarely require any surgical intervention.

Bowel Injury

Rarely the intestines or stomach can be injured at the time of surgery. If this occurs and is recognised, it will be repaired laparoscopically but the operation may be aborted at that point and rescheduled for a later date.

If bowel injury was not recognised at the time then there is a risk of developing life-threatening peritonitis requiring further surgery and probable admission to Intensive Care.


The mortality rate in gastric bypass is 1:200. You should recognise that although your healthcare team do everything possible to minimise the risk, it cannot be reduced to zero.

By undertaking bariatric surgery you are exchanging your risk of decreased life expectancy from weight related illnesses, i.e. approximately four years for an Australia woman, for a short term increase in your risk of death during and immediately after the operation.

Although the procedure is carried out with keyhole surgery it is still major surgery and you and your family should realise that any complications of this procedure could result in death.

Specific risks related to gastric bypass surgery

Risks which apply particularly to laparoscopic gastric bypass include all of the above, but there are additional specific risks related to the procedure.


The risk of a leak is about 1% and usually occurs in the first few days after surgery. This can lead to peritonitis, intra-abdominal abscess or even death.

At the time of surgery a leak test is performed in the operating theatre to confirm that you do not have a leak before you are transferred to recovery.

Drains are inserted around the anastomosis and a further x-ray leak test is performed the day after surgery, before the drains are removed.

The key to successful management of a leak is early recognition and appropriate intervention.

However it is not always possible to demonstrate a leak with x-ray techniques and it may be necessary to take you back to theatre for further laparoscopic surgery because a leak is suspected but cannot be demonstrated. This is performed on the better-than-sorry basis.

A leak at the anastomosis (where the stomach pouch is attached to the small bowel) is the most common cause for serious complications after laparoscopic gastric bypass surgery. Treatment usually requires a return to the operating theatre, closure of the leak and insertion of drains.

A feeding tube is also usually inserted directly into the bowel. These procedures are usually performed laparoscopically but it may be necessary for a more traditional open approach to be used.

Typically in this situation, the patient requires admission to Intensive Care and may or may not require a period on a ventilator.

Other complications can result from these leaks such as kidney failure requiring dialysis. It may be necessary to transfer you to a large teaching hospital for further care.

If your surgeon is unhappy with your post operative recovery, they may take you back to theatre for a laparoscopy.

This may mean that you have a 2nd procedure which shows no abnormality. However studies have shown that early intervention for complications produces the best outcomes.

For uninsured patients this may result in additional theatre and anaesthetic fees.

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