Bariatric surgery is now firmly established in the UK with several thousand procedures being performed every year (Welbourn et al, 2014). One anastomosis gastric bypass (OAGB) is a recognised bariatric procedure (De Luca et al, 2018; Mahawar et al, 2018a) accounting for the third highest number of bariatric procedures worldwide (Angrisani et al, 2018) and being performed by an increasing number of British surgeons (Parmar et al, 2016). Nurses working in a variety of clinical settings might come in contact with patients who have undergone this bariatric procedure and be called on to care for them. This makes it important for nurses to be aware of the anatomical and physiological changes associated with this procedure, routine care of these patients, and the identification and management of complications.
The name
The International Federation for the Surgery of Obesity and Metabolic Disorders has now concluded that the official identifier of this procedure should be ‘one anastomosis gastric bypass’ (De Luca et al, 2018), but several surgeons continue to use the name ‘mini gastric bypass’, which was given to this procedure by the surgeon who first conceived it (Rutledge, 2001). Others believe the term ‘mini’ does not convey the full clinical implications of this major bariatric procedure that carries a mortality of approximately 0.1 % (Parmar and Mahawar, 2018). ‘Omega loop gastric bypass’ and ‘single anastomosis gastric bypass’ are other names sometimes used for this procedure.
Anatomical and physiological changes
The procedure involves the creation of a long and narrow gastric pouch based on the lesser curvature of the stomach, followed by an anastomosis between the lower end of the gastric pouch and small bowel approximately 150-200 cm distal to the duodeno-jejunal flexure (Figure 1). The physiological effects of this anatomical configuration are probably similar to those seen with the much more common bariatric procedure, the Roux-en-Y gastric bypass (RYGB) (Figure 2) (Mahawar, 2016; Dardzińska et al, 2017).
Although in the past it was assumed that physical restriction of food intake and malabsorption of consumed calories are the main mechanisms through which an RYGB works, it is now emerging that the effects on hunger and satiety mediated through previously incompletely understood neuro-hormonal pathways and other signals probably play a much bigger role (Chakravartty et al, 2015). The same is probably true of the OAGB.
Preoperative care
Preparing patients for bariatric surgery needs input from a variety of professionals: bariatric physicians, endocrinologists, dieticians, psychologists, specialist nurses, anaesthetists, and chest physicians as needed. When it comes to OAGB specifically, most surgeons would also perform a preoperative oesophago-gastro-duodenoscopy and an ultrasound scan of the abdomen (Mahawar et al, 2018b). Some surgeons believe severe gastro-oesophageal reflux disease or large hiatus hernia to be a contraindication for this procedure (Mahawar et al, 2018a).
Early postoperative care
Almost all OAGB procedures are currently carried out laparoscopically. The early postoperative care of these patients is not much different from that of any other major bariatric procedure (such as RYGB or sleeve gastrectomy) and the focus is on early mobilisation, analgesia, anti-emetics, and a combination of mechanical (compression stockings and/or intermittent compression devices) and pharmacological prophylaxis (with low molecular weight heparin) for deep vein thrombosis. The only specific precaution with this procedure, which is also true of RYGB, is that the patient should avoid non-steroidal anti-inflammatory drugs (NSAIDs) because these drugs are associated with a higher incidence of ulceration at the gastro-intestinal anastomosis (Coblijn et al, 2014).
With the widespread adoption of enhanced recovery protocols, most patients return to the surgical ward without a nasogastric tube, drain or catheter. This should facilitate early mobilisation. Furthermore, most of them can have sips of water as early as a few hours after surgery and commence liquid/pureed diet on the first or second postoperative day depending on the local preference and protocols. Patients can introduce soft solid food after a month and gradually build up to 3-4 very small meals daily of normal texture food over the next few months (Thorell et al, 2016). Nurses should, however, check local protocol with their bariatric surgical teams.
Preoperative screening, diagnosis and treatment of obstructive sleep apnoea and the minimally invasive nature of surgery have meant that it is now rare for patients to need high-dependency care or critical care in the postoperative period. Patients with diagnosed obstructive sleep apnoea who use a continuous positive airway pressure pump at home should, however, be advised to bring it with them to the hospital so that they can use it during their hospital stay. There is no evidence to suggest that this treatment would compromise the integrity of staple lines following the surgery (de Raaff et al, 2018).
Long-term care
Long-term routine care of these patients is very similar to that of RYGB patients. Most surgeons recommend routine proton pump inhibitors for approximately 6 months for prophylaxis of marginal ulcers and ursodeoxycholic acid for the same duration for prophylaxis of gallstones during the period of rapid weight loss (Mahawar et al, 2018b).
Patients are also recommended lifelong supplementation with multivitamins, iron, calcium, vitamin D, and vitamin B12. The exact dosages of supplementation for each micronutrient for this procedure (as with other bariatric procedures), are yet to be scientifically determined, but it has been suggested that OAGB patients should be advised lifelong supplementation with two multivitamin/mineral tablets, each containing at least 1 mg of copper and 15 mg of zinc; parenteral supplementation with vitamin B12 1 mg every 3 months or oral supplementation with vitamin B12 1.5 mg daily; iron supplementation with at least 120 mg of elemental iron daily; calcium supplementation with 1500 mg of elemental calcium, and vitamin D 3000 international units daily (Mahawar et al, 2018c).
Management of associated diseases
Patients suffering from obesity often have a range of comorbidities. Most obesity-associated comorbidities, such as type 2 diabetes, hypertension or dyslipidaemia, improve as patients lose weight after OAGB and a large number come off all their medications for these conditions (Parmar and Mahawar, 2018). It usually takes around 12-24 months for patients' weight to reach a steady state after most bariatric procedures, and the same is true of OAGB patients. During this period, the requirement of medications for obesity-associated comorbidities will decrease and appropriate adjustments need to made for each individual patient (O'Kane et al, 2016). In the long term, most patients will regain some of the lost weight and very few will regain all of their lost weight, at which point the need for these medications may again increase.
Absorption of pharmacological drugs
Drug absorption is variably altered by bariatric procedures (Bland et al, 2016) and even though studies examining absorption of specific drugs after OAGB are currently lacking, the basic principles of management remain the same. Through its effect on gastric emptying, gastric pH and intestinal absorption, OAGB can either lead to increased or decreased serum drug levels. Drugs being used for obesity-associated comorbidities can generally be managed as detailed above and drugs used for other conditions need to be titrated according to the clinical response. This might mean altering the dose, as necessary. For drugs that have a narrow therapeutic index or are prone to toxicity, such as lithium, immunosuppressive agents, antiepileptics etc, it is advised that the drug levels should be closely monitored in the postoperative period along with clinical response in a specialist setting.
Procedure-specific complications
Although these patients are at risk of a number of early and late complications associated with major abdominal surgery, specific major early complications that nurses need to be aware of are bleeding, gastrointestinal leaks, chest infection, and pulmonary embolisms (with or without deep vein thrombosis). Persistent tachypnoea and tachycardia of > 120 beats per minute should prompt an urgent medical review after any bariatric procedure (Hamilton et al, 2003). As with other patient groups, hypotension is a late sign and health professionals should not wait for it before raising an alarm bell.
In the long term, specific procedure-related complications that patients can experience are anastomotic ulcerations, gastro-oesophageal reflux, anaemia, secondary hyperparathyroidism and, rarely, protein–calorie malnutrition (Mahawar et al, 2018c). Internal herniation of the small bowel through the so-called Petersen's space between the colon and the small bowel is rare with this procedure, but not impossible (Mahawar, 2018).
Anastomotic ulcers are more common in patients who smoke and those who use NSAIDs (Carr et al, 2014). Patients typically present with epigastric pain with or without nausea/vomiting. Most ulcers heal on conservative management with proton pump inhibitors and sucralfate. Patients presenting with heartburn, retrosternal discomfort and other features of acid/bile gastrooesophageal reflux also generally respond well to treatment with proton pump inhibitors. Approximately 1-3% of patients need conversion to a Roux-en-Y configuration for persistent symptoms of reflux in the long term (Parmer and Mahawar, 2018).
Protein–calorie malnutrition is rare with the use of a 150 cm bilio-pancreatic limb (Mahawar et al, 2018d). Too rapid or excessive weight loss, hypoalbuminaemia and other features of protein-calorie malnutrition such as oedema, liver dysfunction, etc should prompt an urgent involvement of the bariatric teams, as the patient may well need enteral/parenteral feeding support and/or revision or reversal of the procedure. One of the key advantages of this procedure is that it can be almost completely reversed.
Summary
Nurses working in a range of clinical environments might come across patients who have undergone OABG. It is therefore important that nurses understand the anatomical and physiological alterations associated with this procedure. This short review will enable nurses to offer better care to these patients.