Complications of weight loss (bariatric) surgery: what can go wrong and when to get help

Weight loss surgery, also called bariatric surgery, makes the stomach smaller so that you feel full sooner and eat less. The NHS lists the main types as gastric bypass, gastric band, gastric balloon and sleeve gastrectomy, with endoscopic sleeve gastroplasty and some less common bypass-type operations also described. Each is done under general anaesthetic or, in the case of the balloon, with local anaesthetic or sedation.

The NHS calls weight loss surgery a common and safe procedure, but adds that every operation carries risk. Complications fall into two broad groups: those linked to the operation itself and the days after it, and those linked to living with a smaller stomach and, in some operations, a rerouted gut. Knowing which group a symptom belongs to helps you judge how quickly to act.

Complications are a reason to be informed and to attend follow-up, not a reason to avoid asking for help. Most people who have a problem and report it early can have it treated, and your surgical team will usually have given you written advice on who to contact.

The NHS lists several problems that can happen in the days or weeks after surgery. These are the ones most likely to need urgent attention.

• Blood clots. The NHS explains that clots are possible because of how the blood flows and clots after surgery. They often start in the lower leg (deep vein thrombosis) and may sometimes travel to the lungs (pulmonary embolism). A clot that causes pain or swelling can be treated with anticoagulant medicines.

• Stomach leak. In the days or weeks after a gastric bypass or sleeve gastrectomy there is a small chance that food could leak out of the stomach. The NHS says this can cause a serious infection inside the tummy that needs antibiotic treatment.

• Wound infection. Wounds can become infected after any surgery. The NHS advises that keeping a wound clean reduces the risk and helps healing.

• Blocked gut. The stomach or small intestine can sometimes become narrower or blocked, and food can get stuck. The NHS says scarring and reduced blood flow can cause this.

Some complications emerge weeks, months or years after surgery. The NHS describes the following.

The NHS explains that weight loss surgery can make it harder for your gut to absorb vitamins and minerals from food, so there is a risk of becoming malnourished. There are not always symptoms. When they do occur they can include feeling tired or lacking energy all the time, shortness of breath, noticeable heartbeats (palpitations), paler than usual skin, pins and needles, and feeling weak.

Because deficiency can build quietly, the NHS says follow-up appointments will usually involve blood tests to check your vitamin and mineral levels, a physical health check, advice and support about diet and exercise, and emotional or psychological support. These are held in a weight loss surgery clinic for at least the first 2 years and may then change to a yearly check-up with a GP for the rest of your life.

To reduce the risk, the NHS advises eating a balanced diet, taking any extra nutritional supplements you have been told to take, and attending your blood tests and appointments. If you develop tiredness, breathlessness or pins and needles, mention it to your GP or surgical team rather than assuming it is simply part of recovery.

Having a smaller stomach means you must change how you eat and drink. The NHS says you need to eat slowly, chew carefully, eat only small amounts at a time, be careful with foods that could block the stomach, such as soft white bread, and take vitamin and mineral supplements. To reduce the risk of a blocked gut it also suggests cutting food into small chunks, chewing thoroughly and not drinking during meals.

A typical NHS diet plan after surgery moves from water and fluids such as thin soup in the first 2 weeks, to runny or puréed food in weeks 3 and 4, to soft food such as mashed potato in weeks 5 to 8, and a gradual return to a healthy, balanced diet from week 8 onwards. Your own plan may differ and you should follow the one your team gives you.

If you have a gastric band, you will be given a follow-up appointment at which the band is adjusted according to your food intake and weight loss, which is another reason follow-up attendance matters.

The NHS gives clear thresholds for people who have had weight loss surgery. They apply whenever symptoms appear, including long after the operation.

• Call 999 or go to A&E if you have difficulty breathing with pain and swelling in a leg, chest pain with pain and swelling in a leg, severe tummy pain, non-stop bleeding from the bottom, a lot of blood in the toilet or large clots, or you are vomiting blood or poo, or your sick looks like coffee grounds or soil.

• Ask for an urgent GP appointment or call NHS 111 if you have redness, tenderness, swelling or pain in a leg that is not getting better or is getting worse, a high temperature or feeling hot, cold or shivery, a fast heartbeat, tummy pain, fast breathing, difficulty swallowing or regular vomiting. The NHS says these could be a sign of a blood clot or a problem with the stomach.

• See a GP if you have pain in or around a wound, red, hot and swollen skin, or pus coming from a wound.

The NHS advises avoiding pregnancy for 12 to 18 months after surgery, until weight has stabilised, because the effects of rapid weight loss on a developing baby are not yet understood. It also notes that fertility may increase because of weight loss.

You will usually be offered an exercise plan to help prevent weight loss leading to muscle loss, with activity increased gradually as you recover. Excess skin and the emotional adjustment to a changing body can be difficult in their own right, and the support offered at follow-up includes emotional and psychological help.

The NHS says weight loss surgery may be available if you have a body mass index (BMI) of 40 or more, or a BMI between 35 and 40 with a condition that might improve with weight loss, and you agree to lifestyle changes and regular check-ups. It adds that availability varies across areas of the UK and that surgery can be paid for privately but can be expensive. Some people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds may be considered at a BMI below 40.

Whichever route you take, complications are managed by a surgical team and, in an emergency, by your nearest A&E. If you had surgery privately or abroad and have a problem, NHS emergency care will still assess you. It helps to keep a copy of your operation notes and know which procedure you had.