Protein-energy malnutrition is a common problem in surgical patients admitted to hospital. More than one in three of all adults admitted to hospital are at risk of malnutrition, according to the most recent results from the British Association of Parenteral and Enteral Nutrition (BAPEN) Nutrition Screening Week 2010 in the UK and Ireland, where all patients admitted to hospital in a three-day period are screened according to the Malnutrition Universal Screening Tool (MUST) criteria.¹ Nutritional status is known to deteriorate over the course of the hospital stay, which has more profound effects on those patients already depleted at the time of their admission.² In St James’s Hospital, among surgical patients who underwent a nutrition assessment on admission and prior to discharge, 70% lost an average of 4% of their admission weight during a hospital stay of 16 days.³ The deleterious effects of impaired nutritional status on clinical outcome and hospital costs are widely acknowledged. If malnutrition is adequately documented in hospital admission and appropriate nutrition therapy is initiated, then an improvement in clinical outcome should be expected. 

Identification of malnutrition 

All patients admitted to hospital should be screened for malnutrition and this can be undertaken using a simple, safe, inexpensive and reliable tool that can be completed quickly by any healthcare professional. Although screening for malnutrition in healthcare has expanded enormously, a gold standard for the optimal definition is still lacking. 

A number of methods have been used to identify malnutrition, eg. the nutrition risk index (NRI),⁴ the nutrition risk score (NRS),⁵ the subjective global assessment (SGA)⁶ and the MUST,⁷ all of which use a variety of criteria to assess nutrition risk. Table 1 details specific considerations when assessing surgical patients. 

Obesity rates are increasing and an emerging nutritional problem is the malnutrition of obesity, and surgeons are now seeing an alarming increase in the prevalence of overweight and obese hospitalised patients, estimated at 35-40%.⁸ BMI below 20kg/m² may not detect all patients who require nutritional intervention since obese patients can still be at risk if a considerable amount of weight has been lost over a short period to time. Contrary to the general belief that the abundant supply of adipose tissues will be the primary fuel, the injured obese patient experiences a relative block in both lipid metabolism and utilisation, resulting in significantly increased rates of protein mobilisation to provide substrates for the synthesis of glucose, resulting in increased nitrogen loss compared to equally injured non-obese patients.⁹ Starvation, or ‘letting them live off their excess fat’, is an inappropriate strategy, which places patients at risk for increased loss of lean body mass. 

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Consequences of malnutrition  

The consequences of malnutrition can be profound and affect every organ system. Patients who undergo gastrointestinal surgery are at risk of nutritional depletion from inadequate nutritional intake, both preoperatively and post-operatively, the stress of surgery and the subsequent increase in metabolic rate. Nutritional depletion is associated with changes in body composition, tissue wasting and impaired organ function, which leads to impaired immune and muscle function.  

Malnutrition is associated with increased postoperative complications: increased post-operative infection, impaired wound healing, adverse effects on the functioning of the GI tract and pressure sores. Poor nutritional status is also associated with increased mortality, independent of factors such as age, impaired cardiorespiratory function and type of surgery.^10,11 Malnourished patients spend 30-75% longer in hospital, require longer post-operative convalescence time and require more frequent readmissions, outpatient appointments and GP visits, which impacts greatly on quality of life, at a greater economic cost.¹² In 2010, the cost of malnutrition in Ireland was estimated to exceed E1.5 billion per annum, representing more than 10% of the healthcare budget.¹³ The clinical and financial benefits of nutritional intervention are well documented in undernourished surgical patients.¹⁴

Metabolic changes in surgical patients 

Surgery evokes a series of hormonal and metabolic changes commonly referred to as the stress response. The stress response to surgery is characterised by sympathetic nervous system activation which encompasses a wide range of endocrinological (hyperglycaemia, insulin resistance), immunological (cytokine production, acute phase response) and haematological (neutrophil leucocytosis, lymphocyte proliferation) effects.¹⁵

This results in increased resting energy expenditure, typically increased by about 10% post-operatively, extensive protein and fat catabolism, negative nitrogen balance, hyperglycaemia, and increased hepatic glucose production, associated with a progressive loss of body cell mass. The amount of protein degradation is influenced by the type of surgery and also by the nutritional status of the patient. A more prolonged hypermetabolic state is associated with a pronounced negative nitrogen balance. For example, after major abdominal surgery, up to 0.5 kg day of lean body mass may be lost, which can cause significant muscle wasting and weight loss.¹⁶

Cytokines play an important role in mediating immunity and inflammation and have an important role in determining longer-term metabolic changes. IL-6 is an important cytokine associated with surgery and peak circulating values are found 12-24 hours after surgery.¹⁷ The size of IL-6 response reflects the degree of tissue damage, and also promotes the acute phase reaction as well as other cytokines.¹⁸

Perioperative nutritional support benefits surgical patients 

Nutritional support leads to improved nutritional status and clinical outcome, with the greatest benefit for severely depleted patients.¹⁹ The use of preoperative enteral nutrition has been compared with an ad libitum oral diet, mostly in patients who had cancer. Evidence suggests that if malnourished individuals are adequately fed for at least seven to 10 days preoperatively then surgical outcome can be improved.²⁰ The obvious disadvantage of this is the increased length of hospital stay resulting from admission for nutritional support and the delay in surgical intervention. 

There is substantially more evidence to support early post-operative nutritional intervention by an appropriate route. The rationale for early enteral nutritional support is to limit the hyper-metabolic response to major surgery, to preserve nutritional status, to modulate the immuno-inflammatory response, to decrease the risk of infection and gut-origin sepsis, and to enhance recovery of quality of life. There is also evidence that artificial nutritional support in malnourished patients is cost-effective by reducing the costs associated with length of stay and morbidity.²¹ Artificial nutritional support is provided using either enteral tube feeding or parenteral (IV) nutrition; generally when patients have adequate accessible gastrointestinal absorptive capacity, enteral tube feeding is preferred as it is both more physiological, cheaper and may also help to maintain gut barrier function.²²

Early enteral nutrition 

Early post-operative enteral feeding in patients undergoing GI resection is safe and well tolerated, even when started within 12 hours of surgery.²³ Although gastric and colonic function may be impaired for several days after surgery, small bowel function/motility recovers four to eight hours after surgical trauma and moderate absorptive capacity exists even in the absence of normal peristalsis.²⁴ The Enhanced Recovery after Surgery (ERAS) programme rests on evidence-based perioperative care to modify or help minimise surgical stress and recommends the practice of carbohydrate loading preoperatively and early feeding post-operatively, and has demonstrated significant improvements in patient outcomes after colorectal surgery.²⁵

An appropriate delivery method should be selected (nasogastric [NG], nasojejunal [NJ], percutaneous endoscopic gastrostomy-jejunostomy [PEG-J]) depending on the anticipated duration of enteral feeding, aspiration risk and GI anatomy. Jejunostomy feeding is particularly useful after oesophagogastric surgery. A systematic review and meta-analysis of randomised controlled trials which compared any type of enteral feeding started < 24 hours after elective GI surgery versus nil by mouth management concluded that early feeding reduced infective risks by approximately 30% and mean length of hospital stay by nearly one day.²⁶

The choice of feed to be given via enteral tube feeding is influenced by a patient’s nutritional requirements, any abnormality of gastrointestinal absorption, motility, or diarrhoeal loss, and the presence of other system abnormality, such as renal or liver failure. Most commercial feeds contain 1.0kcal/ml, with higher energy versions containing 1.5kcal/ml. They are generally available in fibre-free and fibre-enriched forms. As both inadequate or excessive feeding can be harmful, expert dietetic advice should be sought regarding feed prescription. Also very undernourished patients can be at risk of refeeding syndrome and nutrition support should be initiated and monitored closely in consultation with the dietitian. 

Immunonutrition

More recent research has also focused on the composition of nutritional regimens, in particular the potential for specific nutrients to influence the metabolic response to disease. Immunonutrition refers to enteral diets supplemented with immune modulators such as L-arginine, omega-3 fatty acids, glutamine and ribonucleic acids, alone or in combination. A large meta-analysis of 11 prospective randomised controlled trials (n = 1,009) with enteral immunonutrition showed a significant reduction in infectious complications and reduced overall length of stay in patients with critical illness and GI cancer.²⁷ Omega-3 polyunsaturated fatty acids (PUFAs) have been shown to attenuate the hyper-inflammatory response and immunosuppression in critical illness.²⁸ Feeding with π-3 PUFA from fish oil can alter eicosanoid and cytokine production, yielding an improved immunocompetence and a reduced inflammatory response to injury.²⁹ A double-blinded randomised controlled trial in St James’s Hospital also demonstrated that perioperative π-3-supplemented enteral nutrition (2.2g EPA/day) was associated with preservation of lean body mass post-oesophagectomy.³⁰ While these and other studies hold some promise, further studies are awaited before widespread use of this therapy can be recommended. 

Conclusion  

Early identification of patients who will benefit from nutritional support should be a priority and this can be achieved by implementation of routine nutritional screening in all patients. Obesity and malnutrition are not mutually exclusive. 

Nutritional support leads to improved nutritional status and has been associated with improved clinical outcomes, reduction in morbidity and length of stay, with the greatest benefit for severely depleted patients. In the future we may see a move away from standard nutritional products to ‘immunonutrition’ in an attempt to modulate metabolic pathways in surgery.