Nutrition

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4 Nutrition

Chapter Contents

Dietary requirements 119
Protein–energy malnutrition 121
Nutritional support in the hospital patient 124
Nutritional support in the home patient 130
Refeeding syndrome 130

Dietary requirements

Energy

Food is necessary to provide the body with energy. The SI unit of energy is the joule (J), and 1 kJ = 0.239 kcal. The conversion factor of 4.2 kJ, equivalent to 1 kcal, is used in clinical nutrition.

Energy expenditure gives a reasonably accurate estimate of dietary requirements. Daily energy expenditure is the sum of:

• the basal metabolic rate (BMR)
• the thermic effect of food eaten
• occupational activities
• non-occupational activities.
• BMR. This is usually taken from standardized tables that require knowledge of the subject’s age, weight and sex.
• Physical activity.The physical activity ratio (PAR) is expressed as multiples of the BMR for both occupational and non-occupational activities of varying intensities.
• Total daily energy expenditure:

image

The estimated ‘average’ daily requirement is:

• for a 55-year-old female: 8100 kJ (1940 kcal)
• for a 55-year-old male: 10 600 kJ (2550 kcal).

This figure is at present made up of 50% carbohydrate, 35% fat and 15% protein plus or minus 5% alcohol. In developing countries, however, carbohydrate may constitute more than 75% of the total energy input, and fat less than 15% of the total energy input.

Energy requirements increase during the growing period, with pregnancy and lactation, and sometimes following infection or trauma. In general, the increased BMR associated with inflammatory or traumatic conditions is counteracted or more than counteracted by a decrease in physical activity, so that total energy requirements are not increased.

In the basal state, energy demands for resting muscle are 20% of the total energy required, abdominal viscera 35–40%, brain 20% and heart 10%. There can be more than a 50-fold increase in muscle energy demands during exercise.

Protein

In the UK the adult daily reference nutrient intake (RNI) for protein is 0.75 g/kg, with protein representing at least 10% of the total energy intake. Most affluent people eat more than this, consuming 80–100 g of protein per day. The total amount of nitrogen excreted in the urine represents the balance between protein breakdown and synthesis. In order to maintain nitrogen balance, at least 40–50 g of protein are needed. The amount of protein oxidized can be calculated from the amount of nitrogen excreted in the urine over 24 hours using the following equation (most proteins contain about 16% of nitrogen):

image

In practice, urinary urea is more easily measured and forms 80–90% of the total urinary nitrogen (N). In healthy individuals urinary N excretion reflects protein intake. However, urinary N excretion does not match intake either in catabolic conditions (negative N balance), or during growth or repletion following an illness (positive N balance).

Protein contains many amino acids.

• Indispensable (essential) amino acids. These are tryptophan, histidine, methionine, threonine, isoleucine, valine, phenylalanine, lysine and leucine. They cannot be synthesized and must be provided in the diet.
• Dispensable (non-essential) amino acids. These can be synthesized in the body, but some may still be needed if there are insufficient precursors in the diet.

Animal proteins, such as those in milk, meat and eggs, are of high nutritional value, as they contain all indispensable amino acids. Conversely, many proteins from vegetables are deficient in at least one indispensable amino acid.

In developing countries, adequate protein intake is achieved mainly from vegetable proteins. By combining foodstuffs with different low concentrations of indispensable amino acids (e.g. maize with legumes), protein intake can be adequate, provided enough vegetables are available.

Amino acids may be utilized to synthesize products other than protein or urea. For example, haem requires glycine.

Fat

Dietary fat is chiefly in the form of triglycerides, which are esters of glycerol and free fatty acids. Fatty acids vary in chain length and in saturation. Unsaturated fatty acids are monounsaturated or polyunsaturated. The hydrogen molecules related to these double bonds can be in the cis or the trans position; in most natural fatty acids in food, they are in the cis position.

The essential fatty acids (EFAs) are linoleic and α-linolenic acids, both of which are precursors of prostaglandins. Eicosapentaenoic and docosahexaenoic acids are also necessary, but can be made to a limited extent in the tissues from linoleic and linolenic; thus a dietary supply is not essential.

Synthesis of triglycerides, sterols and phospholipids is very efficient, and even with low-fat diets, subcutaneous fat stores can be normal.

Dietary fat provides 37 kJ (9 kcal) of energy per gram. A high fat intake has been implicated in the causation of cardiovascular disease, cancer (e.g. breast, colon and prostate), obesity and type 2 diabetes. It is suggested that the consumption of saturated fatty acids should be reduced, accompanied by an increase in monounsaturated fatty acids, e.g. oleic acids (the ‘Mediterranean diet’), or polyunsaturated fatty acids, e.g. linoleic acid. Any increase in polyunsaturated fats should not, however, exceed 10% of the total food energy, particularly as this requires a big dietary change.

Increased consumption of partially hydrogenated vegetable and fish oils in margarines has led to a higher trans fatty acid consumption, and their intake should not be above more than the current estimated average of 5 g per day or 2% of the dietary energy. This is because trans fatty acids (also called trans fats) behave as if they were saturated fatty acids, with an increase in the risk of cardiovascular disease. A total ban of trans fats is in place in many countries.

The current recommendations for fat intake for the UK are as follows:

• Total fat intake should be no more than 35% of the total dietary energy, and restriction to 30% is desirable.
• Saturated fatty acids should provide ~10% of the dietary energy.
• cis-Monounsaturated acids (mainly oleic acid) should continue to provide approximately 12% of the dietary energy.
• cis-Polyunsaturated acids should provide 6% of dietary energy, and are derived from n-6 and n-3 polyunsaturated fatty acids, which should provide approximately 0.5% of total energy intake.

Cholesterol is found in all animal products. Eggs are particularly rich in cholesterol, which is virtually absent from plants. The average daily intake in the UK is 300–500 mg. Cholesterol is also synthesized, and only very high or low dietary intakes will significantly affect blood levels.

Essential fatty acid deficiency may accompany protein–energy malnutrition (PEM), but it has been clearly defined as a clinical entity only in patients on long-term parenteral nutrition who are given glucose, protein and no fat. Alopecia, thrombocytopenia, anaemia and a dermatitis occur within weeks, with an increased ratio of triene (n-9) to tetraene (n-6) in plasma fatty acids.

Carbohydrate

Carbohydrates are readily available in the diet, providing 17 kJ (4 kcal) per gram of energy (15.7 kJ (3.75 kcal) per gram monosaccharide equivalent).

Carbohydrate intake comprises the polysaccharide (starch), the disaccharides (mainly sucrose) and the monosaccharides (glucose and fructose). Carbohydrate is cheap compared with other foodstuffs; a great deal is therefore eaten, usually more than required.

Protein–energy malnutrition

Starvation uncomplicated by disease is relatively uncommon in developed countries, although some degree of undernourishment is seen in very poor areas. Most nutritional problems occurring in the population at large are due to eating wrong combinations of foodstuffs, such as an excess of refined carbohydrate or a diet low in fresh vegetables. Undernourishment associated with disease is common in hospitals and nursing homes. Surgical complications, with sepsis, are a common cause.

The majority of the weight loss, leading to malnutrition, is due to poor intake secondary to the anorexia associated with the underlying condition. Disease may also contribute by causing malabsorption and increased catabolism, which is mediated by complex changes in cytokines, hormones, side-effects of drugs and immobility. The elderly are particularly at risk of malnutrition because they often suffer from diseases and psychosocial problems such as social isolation or bereavement.

• In the fed state, insulin/glucagon ratios are high. Insulin promotes synthesis of glycogen, protein and fat, and inhibits lipolysis and gluconeogenesis.
• In the fasted state, insulin/glucagon ratios are low. Glucagon acts mainly on the liver and has no action on muscle. It increases glycogenolysis and gluconeogenesis, as well as increasing ketone body production from fatty acids. It also stimulates lipolysis in adipose tissue. Catecholamines have a similar action to glucagon but also affect muscle metabolism. These agents both act via cyclic adenosine monophosphate (cAMP) to stimulate lipolysis, producing free fatty acids that can then act as a major source of energy.
• During weight loss, uncomplicated by disease, the proportion of lean to fat tissue loss (or proportion of energy derived from protein metabolism) is greater in thin than in overweight/obese individuals.

Clinical features

Patients are sometimes seen who have loss of weight or malnutrition as the primary symptom (failure to thrive in children). Mostly, however, malnourishment is only seen as an accompaniment of some other disease process, such as malignancy. Severe malnutrition is seen mainly with advanced organic disease or after surgical procedures followed by complications. Three key features that help in the detection of chronic PEM in adults are described below. These features are also used in the Malnutrition Universal Screening Tool (see Fig. 4.1):

image

Fig. 4.1 Malnutrition Universal Screening Tool (MUST).

Reproduced with permission from the British Association for Parenteral and Enteral Nutrition (BAPEN): http://www.bapen.org.uk.

• The body mass index (BMI): calculated as weight/height2 (kg/m2):

• probable risk of chronic PEM: < 18.5 kg/m2
• possible risk of chronic PEM: 18.5–20 kg/m2
• little or no risk of chronic PEM: > 20 kg/m2.

In patients with oedema or dehydration the BMI may be somewhat misleading.

• Weight loss in the previous 3–6 months

• > 10%, high risk
• 5–10%, possible risk
• < 5%, low/no risk of developing PEM.
• Acute disease effect: Diseases that have resulted or are likely to result in no dietary intake for more than 5 days are associated with a high risk of malnutrition (e.g. prolonged unconsciousness, persistent swallowing problems after a stroke, or prolonged ileus after abdominal surgery).

• Other factors

• History of decreased food intake/loss of appetite.
• Clothes becoming loose-fitting (weight loss) and a general appearance indicating obvious wasting.
• Physical and psychosocial disturbances likely to have contributed to the weight loss.

PEM leads to a depression of the immunological defence mechanism, resulting in a decreased resistance to infection. It also detrimentally affects muscle strength, and produces fatigue, poor wound healing and decreased psychological function (e.g. depression, anxiety, hypochondriasis, loss of libido).

Treatment

When malnutrition is obvious and the underlying disease cannot be corrected at once, some form of nutritional support is necessary. Nutrition should be given enterally if the gastrointestinal tract is functioning adequately. This can most easily be done by encouraging the patient to eat more often and by giving a high-calorie supplement. If this is not possible, a liquefied diet may be given intragastrically via a fine-bore tube or by a percutaneous endoscopic gastrostomy (PEG). If both of these measures fail, parenteral nutrition is given.

Nutritional support in the hospital patient

Some form of nutritional supplementation is required in those patients who cannot eat, should not eat, will not eat or cannot eat enough. All patients should be screened on admission for their nutritional requirements and a care plan drawn up by a trained multidisciplinary team. Plans are discussed with patients and consent is taken for any invasive procedure (e.g. naso-gastric tube, parenteral nutrition). If the patient is unable to give consent, the healthcare team should act in the patient’s best interest, taking into account previously expressed wishes of the patient and views of the family. It is usually necessary to provide nutritional support for:

• all severely malnourished patients on admission to hospital
• moderately malnourished patients who, because of their physical illness, are not expected to eat for more than 3–5 days
• normally nourished patients expected not to eat for more than 5 days or to eat less than half their intake for more than 8–10 days.

Nutritional requirements for adults

• Water. Typical requirements are ~2–3 L/day. Increased requirements occur in patients with large-output fistulae, naso-gastric aspirates and diarrhoea. Reduced requirements are often necessary in patients with oedema, hepatic failure, renal failure (oliguric and not dialysed) and brain oedema.
• Energy. Typical requirements are ~7.5–10.0 MJ/day (1800–2400 kcal/day). Disease increases resting energy expenditure but decreases physical activity. Extra energy is given for repletion and reduced energy for obesity.
• Protein. Typically 10–15 g N/day (62–95 g protein/day) or 0.15–0.25 g N/kg/day (0.94–1.56 g protein/kg/day). Extra protein may be needed in severely catabolic conditions, such as extensive burns.
• Major minerals. Typical requirements for sodium and potassium are 70–100 mmol/day. Increased requirements occur in patients with gastrointestinal effluents (see Table 11.2). The excretion of these minerals in various effluents can provide an indication of the additional requirements. Low requirements may be necessary in those with fluid overload (or patients with hypernatraemia and hyperkalaemia). The requirements of calcium and magnesium are higher for enteral than for parenteral nutrition because only a proportion of these minerals is absorbed by the gut.
• Trace elements. The requirements for enteral and parenteral nutrition are similar for trace elements such as iodide, fluoride and selenium that are well absorbed. For other trace elements, such as iron, zinc, manganese and chromium, the requirements for parenteral nutrition are substantially lower than for enteral nutrition. Daily requirements are shown in Table 4.1.
• Vitamins. Many vitamins are given in greater quantities in patients receiving parenteral nutrition than in those receiving enteral nutrition. This is because patients on parenteral nutrition may have increased requirements, partly because of severe disease, partly because they may already have depleted pools of vitamins, and partly because some vitamins degrade during storage. Vitamin K is usually absent from parenteral nutrition regimens and therefore it may need to be administered separately. Daily vitamin requirements are shown in Table 4.2.

Table 4.1 Daily dietary electrolyte and trace element requirements

Electrolyte/trace element Daily requirement
Na+ 70–220 mmol
K+ 60–120 mmol
Mg2+ 5–20 mmol
Ca2+ 15–20 mmol
Zn2+ 50–100 µmol
Mn2+ 120 µmol
Fe2+ 70 µmol
Cu2+ 20 µmol
Cl− 70–220 µmol
PO−3 15–25 µmol
F− 50 µmol
I− 1 µmol

Table 4.2 Daily requirements of fat-soluble and water-soluble vitamins

Vitamin Daily requirement
Fat-soluble  
A (retinol) 700 mcg
D (cholecalciferol) No dietary intake required (if fully ambulant)
K 1 mcg/kg body weight
E (α-tocopherol) 10 mg
Water-soluble  
B1 (thiamin) 0.4 mg per 1000 kcal
B2 (riboflavin) 1.3 mg
Niacin 6.6 mg per 1000 kcal
B6 (pyridoxine) 15 mcg per g of dietary protein
B12 (cobalamin) 1.5 mcg
Folate 200 mcg
C (ascorbic acid) 40 mg

Enteral nutrition (EN)

Feeds can be given by various routes:

• By mouth. Food can be supplemented with solid or liquid supplements. These can be given by using blenderized food or milk-based drinks. Various formulae are available. Advice should be obtained from a dietitian.
• By fine-bore nasogastric tube (Box 4.1).
• By PEG. PEG is useful for patients who need enteral nutrition for a prolonged period (e.g. more than 30 days), such as those with swallowing problems following a head injury, or elderly people after a stroke. A catheter is placed percutaneously into the stomach under endoscopic control.
• By needle catheter jejunostomy. A fine catheter is inserted into the jejunum at laparotomy and brought out through the abdominal wall.

Box 4.1 Enteral feeding via nasogastric tube

The procedure should be explained to the patient and consent taken.

Procedure

• Insert a fine-bore tube intranasally with a wire stylet
• Confirm the position of the tube in the stomach by aspiration of gastric contents and auscultation of the epigastrium
• Check by X-ray if aspiration or auscultation is unsuccessful

Problems

• No satisfactory way of keeping nasogastric tubes in place (up to 60% come out)

Main complications

• Regurgitation and aspiration into bronchus
• Erosive tissue damage in the nose or pharynx
• Blockage of the naso-gastric tube. Regular flushing of the tube is necessary
• Gastrointestinal side-effects, the most common being diarrhoea (worse with antibiotic therapy)
• Metabolic complications, including hyperglycaemia and hypokalaemia, as well as low levels of magnesium, calcium and phosphate

Diet formulation

A polymeric diet with whole protein and fat can be used (Box 4.2), except in patients with severely impaired gastrointestinal function who may require a predigested (i.e. elemental) diet. In these patients, the nitrogen source is purified low-molecular-weight peptides or amino acid mixtures, with the fat sometimes being given partly as medium-chain triglycerides. Appropriate diets can be used for patients with, for example, chronic kidney disease (low protein) or anorexia (e.g. high-nitrogen or high-calorie diets).

Box 4.2 Standard enteric diet, providing 8.4 MJ per day (= 2000 kcal)

Energy

• Carbohydrate as glucose polymers (49–53% of total energy)
• Fat as triglycerides (30–35% of total energy)

Nitrogen

• Whole protein (10–14 g of nitrogen/day)

Additional

• Electrolytes, vitamins and trace elements

Features

• Ratio of energy to nitrogen kJ : g = 620 : 1 (kcal : g = 150 : 1)
• Osmolality = 285–300 mOsm/kg

Management

Daily amounts of enteral diet vary between 2 and 2.5 L, and the full amount can be started immediately.

Hypercatabolic patients require a high supply of nitrogen (15 g daily) and often will not achieve positive N balance until the primary injury is resolved.

The success of enteral feeding depends on careful supervision of the patient, as there are frequent mechanical complications (e.g. tube occlusion) and often the full daily amount given is less than prescribed. Monitoring of weight, biochemistry and diet charts should be performed daily, as hypokalaemia, hyponatraemia, hypophosphataemia and hyperglycaemia (requiring insulin therapy) often occur.

Parenteral nutrition

Peripheral parenteral nutrition

Specially formulated mixtures for peripheral use are available, with a low osmolality and containing lipid emulsions. Heparin and corticosteroids can be added to the infusion and local application of glyceryl trinitrate patches reduces the occurrence of thrombophlebitis and prolongs catheter life. Peripheral cannulae can be inserted into a mid-arm vein (20 cm) and can last up to 5 days. A longer (60 cm) peripherally inserted central catheter (PICC) inserted into an antecubital fossa vein has its distal end lying in a central vein; here there is less risk of thrombophlebitis and hyperosmolar solutions can be given. With careful management, these catheters can last for up to a month. Peripheral parenteral nutrition is often preferred initially, allowing time to consider the necessity for inserting a central venous catheter.

Total parenteral nutrition via a central venous catheter (TPN)

A silicone catheter is placed into a central vein, usually using the infraclavicular approach to the subclavian vein (Box 4.3). The skin-entry site should be dressed carefully and not disturbed unless there is a suggestion of catheter-related sepsis.

• Complications following catheter placement include central vein thrombosis, pneumothorax and embolism, but the major problem is catheter-related sepsis. Organisms, mainly staphylococci, enter along the side of the catheter, leading to septicaemia. Sepsis can be prevented by careful and sterile placement of the catheter, by not removing the dressing over the catheter entry site, and by not giving other substances (e.g. blood products, antibiotics) via the central vein catheter. Sepsis should be suspected if the patient develops fever and leucocytosis. In two-thirds of cases, organisms can be grown from the catheter tip after removal. Treatment involves removal of the catheter and appropriate systemic antibiotics.

Box 4.3 Central catheter placement for parenteral nutrition

This should be performed only by experienced clinicians under aseptic conditions in an operating theatre.

Give an explanation and obtain consent from the patient.

• The patient is placed supine with 5° of head-down tilt to avoid air embolism
• The skin below the midpoint of the right clavicle is infiltrated with 1–2% lidocaine and a 1 cm skin incision is made
• A 20-gauge needle on a syringe is inserted beneath the clavicle and first rib, and angled towards the tip of a finger held in the suprasternal notch
• When blood is aspirated freely, the needle is used as a guide to insert the cannula through the skin incision and into the subclavian vein
• The catheter is advanced so that its tip lies in the distal part of the superior vena cava
• A skin tunnel is created under local anaesthetic using an introducer inserted through a point about 10 cm below and medial to the incision and passed upwards to the incision
• The proximal end of the catheter (with hub removed) is passed backwards through the introducer to emerge 10 cm below the clavicle, where it is sutured to the chest wall
• The original infraclavicular entry incision is now sutured
• Complications during insertion include arterial puncture, pneumothorax and brachial plexus injury

Nutrients

With TPN it is possible to provide sufficient nitrogen for protein synthesis and calories to meet energy requirements. Electrolytes, vitamins and trace elements are also necessary. All of these substances are infused simultaneously.

Nitrogen source

Most patients receive at least 11–15g N per day, in the form of synthetic L-amino acids.

Energy source

This is provided by glucose, with additional calories provided by a fat emulsion. Fat infusions provide a greater number of calories in a smaller volume than can be provided by carbohydrate. Fat infusions are not hypertonic and they also prevent EFA deficiency.

EFA deficiency has been reported in long-term parenteral nutritional regimens without fat emulsions. It causes a scaly skin, hair loss and delay in healing.

Electrolytes, vitamins and trace elements

Initially, the electrolyte status should be monitored on a daily basis and electrolyte solutions given as appropriate (see Tables 4.1 and 4.2).

Water-soluble vitamins can be given daily but fat-soluble vitamins should be given weekly, as overdose can occur. A trace-metal solution is available for patients on long-term parenteral nutrition, but if the patient requires blood transfusions trace-metal supplements are not needed.

Administration and monitoring

• Peripheral parenteral nutrition is administered via 3 L bags over 24 hours, with the constituents being premixed under sterile conditions. Table 4.3 shows the composition, which provides 9 g of nitrogen and 1700 calories in 24 hours.
• Central venous TPN regimens are based on premixed 3 L bags in most hospitals. A standard parenteral nutrition regimen, which provides 14 g of nitrogen and 2250 calories over 24 hours, is also given in Table 4.3.

Table 4.3 Examples of parenteral nutrition regimens

  Constituent Amount
Peripheral: all mixed in 3 L bags and infused over 24 hours
Nitrogen L-amino acids 9 g/L 1 L
Energy Glucose 20% 1 L
Lipid 20% 0.5 L
  + Trace elements, electrolytes, water-soluble and fat-soluble vitamins, heparin 1000 U/L and hydrocortisone 100 mg; insulin is added if required. Nitrogen 9 g, non-protein calories 7206 kJ (1700 kcal)
Central: all mixed in 3 L bags and infused over 24 hours
Nitrogen L-amino acids 14 g/L 1 L
Energy Glucose 50% 0.5 L
Glucose 20% 0.5 L
+ Lipid 10% 0.5 L
Fractionated soya oil 100 g/L, soya oil 50 g, medium-chain triglycerides 50 g/L
  + Electrolytes, water-soluble and fat-soluble vitamins, trace elements, heparin and insulin may be added if required. Nitrogen 14 g, non-protein calories 9305 kJ (2250 kcal)

Monitoring includes:

• Blood tests. Daily plasma electrolytes and glucose. Twice-weekly FBC, liver biochemistry and function, calcium, phosphate. Magnesium and zinc weekly.
• Nutritional status. Weekly weight and skin-fold thickness.
• Nitrogen balance (p. 120) assessment. This requires complete collections of urine.

Complications

• Catheter-related: (see above).
• Metabolic (e.g. hyperglycaemia — insulin therapy is usually necessary).
• Fluid and electrolyte disturbances.
• Hypercalcaemia.
• Liver dysfunction: steatosis, cholestasis, fibrosis and cirrhosis, usually after 3–4 months of TPN. Transient abnormal liver biochemistry is common in the early stages of TPN and usually resolves spontaneously.
• Metabolic bone disease: after 3 months of TPN, osteopenia and osteomalacia occur.

Nutritional support in the home patient

In both high- and low-income countries there is considerably more undernutrition in the community than in hospital. However, the principles are very similar: detection of malnutrition and the underlying risk factors; treatment of underlying disease processes and disabilities; correction of specific nutrient deficiencies and provision of appropriate nutritional support. A systematic review of the use of nutritional supplements in the community came to the following conclusions:

• Acceptability and compliance are likely to be better when a choice of supplements (differing in type, flavour and consistency) and the schedule are decided in conjunction with the patient and/or carer.
• Supplements are generally of value in patients with a BMI < 20 kg/m2.

Enteral tube feeding

This is often given at home. The commonest reason for starting home tube feeding is for swallowing difficulties in patients with stroke, motor neurone disease, multiple sclerosis and Parkinson’s disease.

• A PEG is used rather than a nasogastric tube in most patients, as long-term feeding is necessary.
• The swallowing capabilities of patients should be assessed regularly in order to avoid unnecessary tube feeding.

Home parenteral nutrition

This is practised much less frequently, usually for patients with intestinal resection and the short bowel syndrome. The potential value of intestinal transplantation in patients with long-term intestinal failure is still being assessed.

Refeeding syndrome

The refeeding syndrome can occur within hours of refeeding by the oral, enteral or parenteral route. It is under-recognised and can be fatal. It involves a shift from the use of body fat as an energy source during starvation to the use of carbohydrate as an energy source during refeeding. This augments insulin release and there is rapid intracellular transport of phosphate, magnesium and potassium, resulting in hypophosphataemia, hypomagnesaemia and hypokalaemia.

• Phosphate concentration. Phosphate concentration in the serum can fall within hours to < 0.4 mm/L (1 mg/dL), which results in widespread organ dysfunction (muscle weakness, parathesiae, cardiac failure, immune suppression, coma, hallucinations and fits).
• Fluid overload. Fluid overload leading to cardiac failure and pulmonary oedema occurs due to poor cardiac function from malnutrition.
• Glucose intolerance. Refeeding with carbohydrate can lead to severe hyperglycaemia, as insulin levels are low and there is increased insulin resistance. Thiamin deficiency can be precipitated, leading to the Wernicke–Korsakoff syndrome. Intravenous thiamine should be given before refeeding in those at risk.
• Cardiac arrhythmias. Prolonged QT with ventricular tachyarrhythmias occurs, leading to sudden death.

Management

All malnourished patients must be monitored frequently, both clinically (with physical examination and daily weighing) and biochemically, and starting before initial feeding.

Initially, refeeding over the first 3–7 days is limited to 800 mL/day plus insensible losses of fluid. Changes in body weight are a general indication of fluid requirements. Daily calorie intake should be 15–20 kcal/kg with approximately 100 g carbohydrates and 1.5 g protein per kg body weight. Sodium should be to 60 mmol/day (1.5 g).

Adjustments to the initial regimen depends on clinical response but should always be increased slowly.

Further reading

National Institute for Health and Clinical Excellence. Guidelines for nutrition support in adults. Clinical guidelines 32. London: NICE; 2008.

Ziegler TR. Parenteral nutrition in the critically ill patient. New Engl J Med. 2009;361:1088-1097.

Further information

http://www.who.int/nutgrowthdb/

World Health Organisation site provides information on worldwide nutrition issues, resources and research

http://www.bapen.org.uk.

British Association for Parenteral and Enteral Nutrition

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