Surgical nutrition

Defining malnutrition

A definition of malnutrition for the surgical patient is: ‘a nutritional state in which nutrient intake does not match nutrient needs—due to underlying disease(s), the surgical stress response, chronic or acute inflammation, intestinal malabsorption (e.g. diarrhoea) and/or patient‐related factors (e.g. socioeconomic status)—leading to losses in lean tissue and diminished function’.

The key nutrition goals before elective surgery are to evaluate the patient for pre‐existing malnutrition, treat any malnutrition to optimise readiness for surgery, prevent predictable postoperative malnutrition and support anabolism for rehabilitation.

The Global Leadership Initiative on Malnutrition (GLIM) was convened in January 2016 to standardise clinical practice in malnutrition diagnosis and management. A two-step approach for malnutrition diagnosis was developed: first, screening to identify ‘at-risk’ status by the use of a validated screening tool; and second, assessment to diagnose and grade the severity of malnutrition. Criteria for malnutrition were retrieved from existing approaches and ranked by consensus expert opinion. The top five ranked criteria comprised three phenotypic criteria (non-volitional weight loss, low body mass index [BMI], and reduced muscle mass) and two aetiologic criteria (reduced food intake or assimilation, and inflammation or disease burden). Diagnosis of malnutrition required at least one phenotypic criterion and one aetiologic criterion. Phenotypic metrics for grading severity as stage 1 (moderate) and stage 2 (severe) malnutrition were proposed. It was recommended that the aetiologic criteria be used to guide intervention and anticipated outcomes.

Nutrition screening

Validated screening tools and surgical nutrition guidelines are produced by the European Society for Clinical Nutrition and Metabolism, the American Society of Parenteral Enteral Nutrition and the American Society for Enhanced Recovery with Perioperative Quality Initiative. All provide details on selecting nutrition screening tools, malnutrition assessment tools, and treatment for malnourished and at‐risk patients. All recommend routine screening for malnutrition and subsequent nutrition assessment with a validated malnutrition assessment tool or a comprehensive nutrition assessment by a registered dietician if the nutrition screen is positive.

In 2006, the BAPEN developed the Malnutrition Universal Screening Tool (‘MUST’) and this has gained widespread acceptance in UK practice.

If a patient scores 2 or above, they are classified at high risk of developing malnutrition or have pre-existing malnutrition. Many UK hospitals have treatment plans or community dietetic referral criteria based on ‘MUST’ scores.

The Mini Nutritional Assessment (MNA) includes more information than ‘MUST’ and is often used in older adults. In addition to percentage weight loss and BMI, the short form MNA includes food intake, mobility, neuropsychological status and a measurement of calf circumference.

Duke University preoperative nutrition score (PONS) utilises questions from the validated MUST to assess for malnutrition risk in perioperative patients. A score ≥ 1 signifies malnutrition risk, and the authors recommend that such patients should be considered for preoperative nutrition therapy. ^,

Whichever tool is used, the next step is to intervene for patients identified as being at risk.

Trauma

A major advance in understanding occurred more than 80 years ago when Sir David Cuthbertson described the loss of nitrogen from skeletal muscle that occurred following trauma. Cuthbertson concluded that the response to injury could be considered as occurring in two phases:

• 1.

  The ‘ebb’ phase, which is a short-lived response associated with hypovolaemic shock, increased sympathetic nervous system activity and reduced metabolic rate.

• 2.

  The ‘flow’ phase, which is associated with a loss of body nitrogen and resultant negative nitrogen balance.

These changes result in the following:

• Ebb phase

  • Decreased resting energy expenditure

  • Increased glycogen breakdown

  • Increased gluconeogenesis

• Flow phase

  • Increased resting energy expenditure

  • Increased heat production, pyrexia

  • Increased muscle catabolism and wasting, and loss of body nitrogen

  • Increased breakdown of fat and reduced fat synthesis

  • Increased gluconeogenesis and impairment of glucose tolerance

If the changes of the ‘ebb phase’ are not replaced by the ‘flow phase’, then despite any advances in surgery, anaesthesia and intensive care support, death of the patient is the inevitable outcome.

The central nervous system and the neurohypophyseal axis play key roles in regulating these metabolic changes via a range of hormones and cytokines. Afferent nerve impulses stimulate the hypothalamus to secrete hypothalamic releasing factors that, in turn, stimulate the pituitary gland to release prolactin, arginine vasopressin (antidiuretic hormone [ADH]), growth hormone and adrenocorticotrophic hormone.

Sepsis

The metabolic response to sepsis is also characterised by alterations in protein, carbohydrate and fat metabolism, with the following key differences:

• The breakdown of skeletal muscle and nitrogen losses can be substantial (more than 15–20 g/day).

• There is increased production of glucose by the liver (both gluconeogenesis and glycogenolysis), resulting in an elevated plasma glucose.

• In contrast to the situation following trauma, there is an increased rate of glucose uptake and oxidation by peripheral tissues.

• Decrease in the peripheral uptake of triglyceride and defective ketogenesis in the presence of sepsis leads to hypertriglyceridaemia.

A significant abnormality in the patient with sepsis is the disruption of the microstructure of the hepatocyte mitochondria, particularly of the inner membrane. There is a block in energy transduction pathways, with consequent reduction in the aerobic metabolism of both glucose and fatty acids. The body therefore depends on anaerobic metabolism of glucose, which results in lactate production. An adequate supply of glucose is therefore essential. If gluconeogenesis is impaired or inadequate, then hypoglycaemia may ensue. Hypoglycaemia during sepsis indicates an extremely poor prognosis and is frequently associated with mortality.

Nutrition after surgery

In addition to the response to trauma and/or sepsis, general surgery patients may face multiple barriers to adequate food intake including gut obstruction or paralysis and organisational barriers in hospital (e.g. missed meals or tube feeds withheld due to scheduled clinical investigations). Nutritional monitoring and review should continue postoperatively. Patients identified as malnourished, or at risk, require individualised treatment plans that may include therapeutic diets (e.g. high protein), fortified foods, high-protein oral nutrition supplements, enteral nutrition and/or PN.

Evidence for micronutrients in surgery

Additional nutrients may complement the protein anabolic response. Corn oil supplementation for 8 weeks had no effect on muscle protein synthesis rate, whereas omega‐3 fatty acid supplementation was found to augment muscle protein synthesis. A meta‐analysis of 13 RCTs of supplemental vitamin D in adults aged > 60 years compared with placebo or standard treatment on muscle function found that supplementation with at least 800 IU of vitamin D decreased postural sway, reduced time to complete the ‘Timed Up and Go Test’, and marginally increased lower extremity strength. However, these findings have no implications for surgical care currently.

Nasogastric tubes

Nasogastric (NG) feeding via fine-bore tubes (polyvinyl chloride or polyurethane) may be used in patients with a functioning gut who require nutritional support for a short period of time. The fine-bore tube may be manipulated through the pylorus into the duodenum to reduce the risk of gastric aspiration. In patients with delayed gastric emptying, double-lumen tubes may be useful: one lumen resides in the stomach and is used to aspirate gastric contents while the more distal lumen is placed in the jejunum for feeding. Regardless of initial position, it is common for NG tubes to become misplaced, with a potential for pulmonary aspiration. In the UK, the National Patient Safety Agency produces reports on incidents (including a number of fatalities) related to NG feeding tubes and issues advice on reducing potential harm. Radiographic confirmation should be obtained if NG feeding tube placement cannot be confirmed by pH monitoring (pH < 5.5 indicates gastric placement); individual hospitals often have their own governance protocols.

Other complications associated with the use of nasoenteric tubes include:

• Pulmonary atelectasis

• Oesophageal necrosis, stricture formation

• Tracheo-oesophageal fistulas

• Sinusitis, post-cricoid ulceration