Chapter 21 Nutrition and blood, fluid and electrolytes

CHAPTER CONTENTS

Nutrition 415

Introduction 415

Nutritional support 415

Protein 415

Energy 416

Electrolytes and trace elements 416

Vitamins 416

Nutritional assessment 416

Identifying those requiring nutritional supplementation 416

Treatment of malnutrition 416

First-line advice that should be given at surgery or ward level 417

Patients who may benefit from nutritional support through supplementation 417

Monitoring the patient 417

Oral nutritional supplements (sip feeds) 417

Types of supplements available 417

When to refer to a dietitian 418

Enteral tube feeding 418

Nasogastric tube feeding 419

Tube feed regimen 419

Administration of medicines via enteral feeding tube 420

Administration of continuous nasogastric feeding using a fine-bore tube 420

Gastrostomy or jejunostomy tube feeding 421

Parenteral nutrition 421

Indications 421

Intravenous nutrition solutions 422

Preparation of intravenous nutrition solutions 422

Incompatibilities 422

Administration of intravenous nutrition 423

Complications of intravenous nutrition 423

Care of the patient receiving intravenous nutrition 423

Changing the infusion pack 423

Intravenous nutrition at home 424

Summary 424

Vitamins 424

Blood 427

Introduction 427

The anaemias 427

Iron deficiency anaemia 427

Clinical features 427

Oral iron 427

Parenteral iron therapy 428

Megaloblastic anaemia 429

Pernicious anaemia 429

Treatment of other causes of vitamin B₁₂ deficiency 430

Folate deficiency 430

Anaemia associated with chronic renal failure 430

Erythropoietin 430

Iron overload 430

Aplastic and haemolytic anaemias 431

Anaemia in pregnancy 431

Drugs used in neutropenia 432

Fluid and electrolytes 432

General 432

Compartments or spaces 432

Osmolality 432

What is osmolality? 432

Plasma osmolality 433

Body’s defence against hyperosmolality 433

When can hypo-osmolality result? 434

Oral preparations for fluid and electrolyte imbalance 434

Oral potassium 434

Potassium removal 434

Oral sodium 435

Oral rehydration therapy 435

Oral bicarbonate 435

Parenteral preparations for fluid and electrolyte imbalance 435

Mole 435

Intravenous sodium 436

Intravenous glucose 436

Intravenous potassium 437

Bicarbonate 437

Minerals 437

Calcium supplements 437

Phosphate 437

Fluoride 437

Self-assessment questions 437

KEY OBJECTIVES

After reading this chapter, you should be able to do the following.

Nutrition:

• identify the type of patients who may benefit from nutritional supplementation

• explain how the basal metabolic index is calculated

• list the foods that may be encouraged before resorting to prescribable supplements

• explain what is meant by enteral tube feeding

• list the indications for parenteral nutrition

• detail the monitoring required during intravenous nutrition

• distinguish between water-soluble and fat-soluble vitamins.

Fluid and electrolytes:

• distinguish between an intracellular compartment, an extracellular space and an intravascular compartment

• identify the main sources of water intake and water loss

• identify how the body is protected from hyperosmolality

• recognise the signs and symptoms of hypokalaemia

• name the main indication for oral rehydration therapy.

Blood:

• name the main constituents of the blood

• state where the blood cells are derived

• state the main functions of the blood cells

• name the clinical features of iron deficiency anaemia

• name the additional features of megaloblastic anaemia

• state the name, dose, frequency of administration and side effects of oral iron

• explain what is meant by pernicious anaemia

• describe the treatment of pernicious anaemia

• describe the role of folic acid in pregnancy.

NUTRITION

INTRODUCTION

People who are ill can greatly benefit from well-managed nutritional support. Team working is the key to the success of this aspect of patient care. Within the nutritional support team, medical, surgical, nursing, dietetic and pharmaceutical skills must be available if patients are to receive high-standard, cost-effective therapy.

Malnutrition occurs in both the community and hospital settings. It occurs when an individual’s nutrient intake falls below the metabolic requirements. The early detection of malnutrition is important as, if left untreated, it can severely compromise patient recovery.

The body has only limited reserves of immediately available energy and nitrogen sources. In the absence of adequate food ingestion, energy is derived from stores of glycogen in the liver, from muscle protein, and from fat in adipose tissue. However, glycogen stores are limited and are exhausted within the first 24 h of starvation. Over the next few days, muscle protein is broken down to provide glucose. In more prolonged starvation, fat is used to provide the energy source, and the brain adapts to utilise ketone bodies. When the fat stores have been utilised, accelerated protein breakdown resumes and leads eventually to death.

NUTRITIONAL SUPPORT

The aim of nutritional support is to arrest catabolism due to these losses, to reverse weight loss and to restore the patient to a positive nitrogen balance. This can be accomplished by administering calories, nitrogen (protein), fluid, electrolytes, vitamins and trace elements. The place of nutritional support is well recognised. Advances in the management of severe illness and trauma have meant that more patients survive the initial phase of their illness and require continuing supportive treatment. This involves the administration of appropriate fluids, electrolytes and nutritional requirements.

PROTEIN

If nutrition is deficient, not only does the patient lose weight by the loss of skeletal muscle but also tissue repair and immune mechanisms are significantly inhibited, as these processes require active cell turnover and therefore new protein formation. Amino acids are the building blocks of protein. They can be divided into two groups: essential amino acids and non-essential amino acids. It is necessary that nutrition solutions contain a balanced content of essential amino acids and a broad spectrum of non-essential amino acids.

ENERGY

Energy is provided as carbohydrate or fat.

ELECTROLYTES AND TRACE ELEMENTS

Sufficient quantities of electrolytes and trace elements must be given, not only for maintenance, but also to replace any significant losses. The action of each is summarised below:

• sodium

— predominant cation in extracellular fluid

— maintains integrity of cell membrane along with potassium

• potassium

— major intracellular cation

— required for transport of glucose across cell membrane

• calcium

— continuous supply necessary to form and maintain skeleton and to maintain homeostasis in nerve and muscle tissue

• magnesium

— important factor in many enzyme reactions

• iron

— required for haemoglobin synthesis

• copper

— involved in release of iron from liver

• zinc

— essential for many enzyme reactions

• cobalt

— essential constituent of vitamin B₁₂

• manganese

— involved in calcium and phosphorus metabolism

• iodine

— required in synthesis of thyroid hormones

• fluoride

— required for maintenance of skeleton

• chromium

— deficiency leads to glucose intolerance.

VITAMINS

All vitamins can be supplied by parenteral and enteral feeding regimens.

NUTRITIONAL ASSESSMENT

Nutritional support must be designed to suit the particular metabolic and nutritional needs of each individual. Careful assessment of the patient’s nutritional state is required before deciding on a treatment plan. This is normally carried out by the dietitian, who will obtain information from a variety of sources, including the patient, relatives, doctor and nursing staff. Close liaison between dietetic, medical and nursing staff is important.

IDENTIFYING THOSE REQUIRING NUTRITIONAL SUPPLEMENTATION

There are many screening tools available to help identify those patients who are at risk of malnutrition. Most of these require the patient’s current body mass index (BMI) to be measured and also request that an estimation of the rate of weight loss is determined.

The BMI is calculated as the weight in kilograms over the height in metres squared, i.e.:

Weight categories may be classified in terms of BMI as follows.

• Underweight: < 18 kg/m²

• Normal: 18–24.9 kg/m²

• Overweight: 25–29.9 kg/m²

• Obesity: 30–39.9 kg/m²

• Extreme obesity: > 40 kg/m²

Not all patients with a BMI < 18 kg/m² are necessarily malnourished. For some healthy individuals, this may be normal. Consideration must also be given to the person’s medical condition and evidence of weight loss. Weight loss ≥ 10% of usual body weight is considered significant and requires action. Food and fluid intake are also important and action is required if, over the course of 3 days, patients are:

• leaving more than half of their meals

• unable to eat solid food or having physical feeding problems

• unable to retain or absorb food.

TREATMENT OF MALNUTRITION

It is important to determine the cause of malnutrition because, in many cases, treating the cause can result in improvement in food intake without any major intervention (e.g. poor appetite can be associated with fever, depression and recurrent infection). Treatment of these conditions usually results in improvement in appetite. Patients who have physical disabilities and/or swallowing problems may have their nutritional intake significantly improved by providing modified cutlery and crockery and/or altering the consistency of their food. In cases of acute malabsorption lasting 4 or more days, the cause should be identified and the dehydration corrected by advising adequate fluid intake.

FIRST-LINE ADVICE THAT SHOULD BE GIVEN AT SURGERY OR WARD LEVEL

First-line dietery advice should be tried before any other interventions, unless otherwise directed. Patients should initially be encouraged to:

• eat frequent small meals

• have nourishing between-meal snacks

• use full-fat milk enriched with 4 tablespoons of skimmed milk powder/pint

• add extra cream, sugar and butter to desserts, sauces and breakfast cereals

• use Build Up or Complan as nourishing drinks between meals.

Increasing the energy and protein density of the diet through foods is much more acceptable from the patient’s point of view.

PATIENTS WHO MAY BENEFIT FROM NUTRITIONAL SUPPORT THROUGH SUPPLEMENTATION

Dietary supplementation is most appropriately used in patients:

• with malignancy

• before or after major surgery

• with malabsorptive conditions

• with degenerative conditions (e.g. multiple sclerosis, motor neurone disease, Huntington’s disease).

It is worth considering nutritional support for those people with:

• pressure sores or leg ulcers

• swallowing difficulties

• dementia

• chronic medical or physical problems.

MONITORING THE PATIENT

Once a patient has been identified as being ‘nutritionally compromised’, the above first-line advice should be given. It is important that an individual’s progress is reviewed to establish the success of first-line treatment. For some patients, modification of their normal diet and possibly the introduction of a non-prescribable product such as Build Up will be sufficient to reverse the nutritional decline. This conservative management of nutritional needs is likely to be supervised by nursing staff either at ward level or in the patient’s home. The frequency of review and monitoring will be different in acute and primary care, but it is important to highlight the need for further intervention.

ORAL NUTRITIONAL SUPPLEMENTS (SIP FEEDS)

If the nutritional problem persists, it may be necessary to commence the patient on an appropriate sip feed, the choice depending on patient preference. Referral to the community or hospital dietitian should be considered at this point depending on local protocol.

All patients should be reviewed after being com-menced on a sip feed. In primary care, this will usually be after 4 weeks, or sooner if clinically thought necessary. In patients in whom there has been no improvement, referral to the local dietitian should be considered. Most patients usually manage to drink one or two supplements per day in addition to ordinary foods.

In secondary care, this first review may be within 24–48 h. Patients should be reviewed prior to dis-charge and only be discharged from hospital on a sip feed if it is clinically indicated. At this point, the patient’s condition may have resolved, and sip feeding can be stopped or continued for 7 days post discharge.

Once the nutritional problem appears to have resolved, sip feeds and fortified diet should be dis-continued and the patient should be encouraged to monitor their weight for 3 months. If problems recur, then the supplements and fortified diet should recommence, and this will become a new episode of care.

TYPES OF SUPPLEMENTS AVAILABLE

Prescribable supplements fall into three main groups.

Sip feeds.

This group can be subdivided into complete supplements that contain all the essential nutrients (vitamins, minerals, energy and protein) and incomplete supplements that do not contain a full range of the essential nutrients. The energy content of the supplement varies. Some provide 1 kcal/mL, while others contain 1.5 kcal/mL. Some nutritional supplements have higher fibre content. These products are often based on milk, fruit juice or yoghurt and are available in several flavours. The majority of these products are lactose- and gluten-free and are suitable for patients with malabsorption, diarrhoea and known coeliac disease.

Single-nutrient supplements.

These are energy-, protein- or fat-only, depending on the type of sup-plement, and are available in liquid or powder form. The energy-only supplements are intended for patients with protein and fluid restrictions.

Other specialised products.

A variety of specialised supplements are available, such as semielemental feeds for use with patients who have malabsorption, products such as supplemented puddings for patients with swallowing difficulties, and the less frequently used products specifically for patients with renal disease or liver failure or who are HIV-positive. Dietetic advice is required before patients are commenced on these products.

Examples of prescribable supplements currently on the market are shown in Box 21.1.

Box 21.1 Examples of prescribable supplements

Sip feeds

1 kcal/mL

• Enrich

• Clinutren ISO

• Ensure

• Fresubin 1000 Complete

1.25 kcal/mL

• Provide Xtra

1.5 kcal/mL

• Clinutren 1.5

• Enlive Plus

• Enrich Plus

• Ensure Plus

• Fortijuce

• Fortisip

Single-nutrient supplements

• Calogen

• Maxijul

• Maxipro

• Polycal

• Polycose

• Protifar

• Vitapro

Other specialised products

• Calshake

• Elemental 028

• Peptamen

• Scandishake

Deciding which product to prescribe should be based on patient requirements, taste preference and local policy. Although it is possible to survive on some of the complete supplements in the absence of food, it is generally recommended that supplements are taken in addition to food and should not replace meals or snacks. Supplements used inappropriately can inhibit the patient’s ability to resume meeting their nutritional requirements from ordinary food.

WHEN TO REFER TO A DIETITIAN

This will depend on local policy and the nutritional screening tool used. Referral for dietary advice should be considered when:

• the BMI is under 18 kg/m² and there is significant weight loss, i.e. > 10% of usual body weight, and dietary supplements have been prescribed but there is no improvement

• the patient has another medical condition requiring dietary intervention (e.g. diabetes, renal disease, malabsorption)

• the patient’s weight and/or intake continue to deteriorate.

The dietitian will complete a full nutritional assess-ment and recommend specific further treatment for the patient. The dietitian is able to assess the appro-priateness of introducing an alternative supplement if there has been an intolerance or palatability problem.

ENTERAL TUBE FEEDING

People who cannot meet their nutritional or fluid requirements and who have a functioning small intestine (e.g. patients with neurological conditions or stroke, who have had head and neck surgery, who have had gut resection or who have other gastrointestinal disease) need to be fed using an alternative method. The most commonly used alternative methods are via a nasogastric, gastrostomy or jejunostomy tube. The decision as to the most suitable method for each individual patient is based on:

• the length of time the patient is expected to require feeding by an alternative route; for short-term feeding (e.g. up to 4 weeks), the nasogastric route will be used

• the functioning of the gastrointestinal tract; the majority of patients will have a gastrointestinal tract that is fully functional, and long-term feeding will be required – the feeding route used will therefore be gastrostomy.

If the patient’s stomach and duodenum need to be temporarily or permanently bypassed, jejunostomy is the required route.

NASOGASTRIC TUBE FEEDING

A fine-bore nasogastric tube is used to facilitate this form of feeding. Because there is a wide range of systems available, it is advisable to seek the advice of the dietitian and nutrition nurse specialist.

The importance of ensuring correct positioning of a nasogastric tube cannot be overemphasised. Confirmation that the tube is not kinked and is in the stomach rather than in the oesophagus or lung must be made before starting a feed, by aspirating the stomach contents and testing with pH-indicating paper.

X-ray confirmation is time-consuming and costly, and so it is now used only for certain categories of patient (e.g. the unconscious) or when neither gastric position nor misplacement has been confirmed by the above test.

In the acutely ill or unconscious patient, it is important to establish that the stomach is emptying. This is an important precaution to take and can prevent potential hazards such as vomiting or gastric reflux, which may lead to aspiration pneumonia. It is also important that the volume of feed given is increased gradually, particularly in patients who have received nothing via their gut for several days, in order to prevent gastrointestinal side-effects.

Regular aspiration of gastric contents is especially important for patients receiving intensive care, for the unconscious and for those on drug therapy that may interfere with absorption. Absorption can be assumed if there is little or no aspirate, abdominal distension or nausea and when bowel sounds are normal. Gastric emptying can be enhanced and gastric reflux minimised by raising the head of the bed while feeding.

A wide range of commercially made preparations are available. For those totally unable to feed in the normal way, it is essential to use nutritionally complete foods, of which there are a number. Nutritional supplements and nutritionally complete foods are classed as borderline substances approved for use in specific clinical conditions such as dysphagia, inflammatory bowel disease, malabsorption states and bowel fistulae. Despite the name given to them, nutritionally complete foods may still not meet the patient’s entire needs, and additional vitamins and minerals may be required.

The availability of nutritional preparations, diverse in composition and nutrient ratios, permits the selection of a feed to meet the specific requirements of the patient. Manufactured polymeric feeds generally suit most tube-fed patients. Compared with hospital-made feeds, they are sterile until opened, their composition is known and constant, and they are more convenient. The dietitian will be able to advise on the most appropriate feed to use.

To reduce the risk of bacterial contamination, correct preparation and storage of feeds are necessary. All individually prepared feeds can be stored at room temperature if unopened. The feeds must be clearly labelled to indicate the date and time by which they must be used. To minimise the risk of growth of micro-organisms, hospital-made feeds should be administered within 4–6 h of hanging, and aseptically administered sterile feeds within 12–24 h. Reservoirs and administration sets should be renewed once every 24 h. Bacteriological testing of the feeds should also be carried out as per the local control of infection policy.

TUBE FEED REGIMEN

Nausea and abdominal distension may be induced if the feed is administered too quickly. Continuous administration can minimise this problem, using either gravity drip or pump-assisted feeding. Continuous drip administration also minimises the risk of diarrhoea, which may result from administering bolus feeds, particularly if the feed is hyperosmolar. Pump-assisted feeding will help patients who have some impairment of gastrointestinal function, as the flow rate can be controlled to meet their absorptive capacity, and this is the administration method of choice.

Whatever method of feeding is used, accurate entries should be made on the patient’s fluid balance chart and a record kept of the patient’s tolerance of the feed. ‘Today’s feed tolerance will influence tomorrow’s feeding regimen’. Doctors and nurses require access to details of the daily regimen, which has been worked out for each patient, including:

• a breakdown of energy, protein, electrolyte values, vitamins and minerals

• the total volume

• instructions regarding the volume of feed to be given per hour and how many hours in a 24-h period the feed is to be administered.

Nurses have a considerable contribution to make to the care of the patient fed by tube. They are involved in:

• assisting in the assessment of the patient’s nutritional state

• communicating with dietetic and medical staff

• storing feeds appropriately

• initiating and supervising the feed

• observing the patient (e.g. for respiratory difficulty, tolerance of the feed)

• providing the patient with encouragement

• keeping accurate records.

Diarrhoea in enterally fed patients is not usually caused by the feed. Causes including recent or current drug therapy (e.g. antibiotics) or infection should be ruled out. There are some feeds on the market that are supplemented with soluble fibre, which has been advocated for the treatment of diarrhoea. The soluble fibre provides a substrate for colonic microflora to produce short-chain fatty acids. These fatty acids act in the ascending colon to promote absorption of water and sodium and therefore have a possible role in preventing diarrhoea.

Feeds with fructo-oligosaccharides or prebiotics that are undigested in the small intestine but pass to the colon, where they are fermented, also assist in preventing diarrhoea. Moreover, they selectively promote the growth of bifidobacteria and therefore reduce colonisation by Escherichia coli and Clostridium difficile. Examples of these feeds are Jevity Plus and Fresubin Isofibre.

ADMINISTRATION OF MEDICINES VIA ENTERAL FEEDING TUBE

Enteral feeding tubes may be used as an alternative route for the administration of medicines. When prescribed by this route, medicines are administered in the form of a solution, suspension or emulsion. If the drug is not normally available in a liquid form, the pharmacist should be consulted for advice and assistance. It may be possible for a liquid form of the drug to be prepared in the pharmacy using a suitable formulation that takes account of the properties of the drug, such as stability in an aqueous form.

Crushing of tablets into the necessary fine powder cannot be achieved satisfactorily on the ward. If tablets are insufficiently powdered, there is a risk of the tube being blocked, with consequent risk of underdosage. It should be borne in mind that some solid dose forms cannot be crushed, even to give a coarse powder. In some cases, the crushing of a tablet may destroy the essential properties of the product.

Apart from using an oral liquid, it may be acceptable to administer the injectable form of the drug via the enteral feeding tube. If this procedure is adopted, clear instruction must be given by the prescriber on the patient’s drug prescription sheet. The pharmacist must first be consulted to ensure that the procedure is satisfactory and that there is no suitable alternative. Adding a medicine to a feed is not recommended, as chemical or physical interaction may adversely affect the drug, the feed, or both. An unknown quantity of the drug may be lost if the food is altered or some is lost due to spillage or leakage from the delivery system.

The standard procedure for checking the position of the tube must be followed before administering medicines via the tube. To administer the medication, the tube is first clamped. The barrel of a suitably sized syringe is then attached. The medicine is poured into it and the clamp released. The medication is allowed to flow in by gravity. The tube is clamped again. Prior to and following the administration of each medication, a volume of water (20–30 mL) should be instilled. This will minimise the risk of tube blockage and ensure that the medicine has passed through the tube and out into the stomach.

ADMINISTRATION OF CONTINUOUS NASOGASTRIC FEEDING USING A FINE-BORE TUBE

For short-term feeding (e.g. up to 4 weeks), a fine-bore nasogastric tube is generally used. This procedure is outlined in Box 21.2.

Box 21.2 Administration of continuous nasogastric feeding using a fine-bore tube

Documentation

• Feed prescription sheet

The medicine

• Feed in feed container

The environment

• Patient seated or in bed; warmth, comfort, privacy (if preferred)

The nurse and the patient

• Patient identified; explanation given to patient

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