Chapter 8: Nutrition and fluid balance
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Source: Data from Arends et al. ([5]) and Todorovic and Mafrici ([181]). Reproduced with permission of PENG – Parenteral and Enteral Nutrition Group (www.peng.uk.com) of the British Dietetic Association (www.bda.uk.com).
Evidence‐based approaches
Rationale
Nutritional support, to maintain or replete body composition, should be considered for anybody unable to maintain their nutritional status by taking their usual diet (NCCAC [108]). Supports include the following:
- Patients unable to eat their usual diet (e.g. because of anorexia, mucositis, taste changes or dysphagia) should be given advice on modifying their diet.
- Patients unable to meet their nutritional requirements, despite dietary modifications, should be offered oral nutritional supplements.
- Patients unable to take sufficient food and dietary supplements to meet their nutritional requirements should be considered for an enteral tube feed.
- Patients unable to eat at all should have an enteral tube feed. Reasons for complete inability to eat are outlined in Box 8.1.
- Parenteral nutrition may be indicated in patients with a non‐functioning or inaccessible gastrointestinal tract who are likely to be ‘nil by mouth’ for 5 days or longer. Reasons for a non‐functioning or inaccessible gastrointestinal tract include the conditions outlined in Box 8.2.
Enteral nutrition should always be the first option when considering nutritional support.
Box 8.1
Reasons for complete inability to eat
- Carcinoma of the head and neck area or oesophagus
- Surgery to the head or oesophagus
- Radiotherapy treatment to the head or neck
- Fistulae of the oral cavity or oesophagus
- Dysphagia due to cerebrovascular accident (CVA)
- Head injury
- Persistent vegetative state (PVS)
Box 8.2
Reasons for a non‐functioning or inaccessible gastrointestinal tract
- Bowel obstruction
- Short bowel syndrome
- Gut toxicity following bone marrow transplantation or chemotherapy
- Uncontrolled vomiting and enterocutaneous fistulae
Patients in any group may have an increased requirement for nutrients due to an increased metabolic rate, as found in those with burns, major sepsis, trauma or cancer cachexia (Arends et al. [5], Gandy [58], Todorovic and Mafrici [181]). Patients should have their nutritional requirements estimated prior to the start of nutritional support and should be monitored regularly.
Methods of assessing nutritional status
Before the initiation of nutritional support, the patient must be assessed. The purpose of assessment is to identify whether a patient is undernourished, determine why this may have occurred, and provide baseline data for planning and evaluating nutritional support (NCCAC [108], Robertson [153]). It is helpful to use more than one method of assessing nutritional status. For example, a dietary history may be used to assess the adequacy of a person's diet but does not reflect actual nutritional status, whereas percentage weight loss does give an indication of nutritional status. However, percentage weight loss taken in isolation gives no idea of either dietary intake or the likelihood of improvement or deterioration in nutritional status (NCCAC [108]).
A holistic assessment of a patient can be carried out with the use of the appropriate performance status or frailty questionnaire. These include the ECOG (Eastern Cooperative Oncology Group) scale (ECOG‐ACRIN Cancer Research Group [48]), the Karnofsky Performance Scale (Mor et al. [105]) and the PRISMA‐7 Questionnaire (Guidelines and Protocols Advisory Committee [64]). More differentiated tools may be used to monitor daily activities or to quantify physical performance, such as the Five‐Times Sit‐to‐Stand Test and the Timed ‘Up & Go’ Test, and hand dynamometers can be used to assess muscle function (Makizako et al. [95]).
Bodyweight and weight loss
Body mass index (BMI), or comparison of a patient's weight with a chart of ideal bodyweight, gives a measure of whether the patient has a normal weight, is overweight or is underweight. It may be calculated from weight and height using the following equation:
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Tables are available to allow the rapid and easy calculation of BMI (BAPEN [14]). These comparisons, however, are not good indicators of whether the patient is at risk nutritionally, as an apparently normal weight can mask severe muscle wasting.
Of greater use is the comparison of current weight with the patient's usual weight. Percentage weight loss is a useful measure of the risk of malnutrition:
 |
A patient would be identified as malnourished if they had any of the following:
- BMI less than 18.5 kg/m2
- Unintentional weight loss greater than 10% within the past 3–6 months
- BMI less than 20 kg/m2 and unintentional weight loss greater than 5% within the past 3–6 months (NCCAC [108]).
Unwell children should have their weight and height measured frequently. It may be useful to measure them on a daily basis (Shaw and McCarthy [167]). These measurements must be plotted onto centile charts. A single weight or height cannot be interpreted as there is much variation of growth within each age group. It is a matter of concern if a child's weight begins to fall across the centiles or if the weight plateaus.
Obesity and oedema may make interpretation of bodyweight difficult; both may mask loss of lean body mass and potential malnutrition (Cederholm et al. [32]).
Accurate weighing scales are necessary for measurement of bodyweight. Patients who are unable to stand may require sitting scales or hoist scales.
It is often not appropriate to weigh palliative care patients, who may experience inevitable weight loss as disease progresses. Psychologically, it may be difficult for patients to see that they are continuing to lose weight (Shaw [164]). Measures of nutritional status, such as clinical examination and current food intake, may still be used in addition to measures of bodyweight.
Skinfold thickness and bioelectrical impedance
Skinfold thickness measurements can be used to assess stores of body fat. They are rarely used in routine nutritional assessment due to the insensitivity of the technique and the variation between measurements made by different observers. They are more appropriate for long‐term assessments or research purposes and the technique should only be used by practitioners who are practised in using skinfold thickness callipers because of the potential for intra‐investigator variation in results (Durnin and Womersley [47]).
Bioelectrical impedance analysis (BIA) is a convenient body composition assessment tool that is non‐invasive, provides rapid results and requires minimal operator training (Cederholm et al. [32]). BIA estimates body composition indirectly. A low‐voltage current is passed through the body, and tissue resistance and reactance is measured. Empirical equations are then used to estimate body composition (Raeder et al. [148]). This technique works well in healthy individuals, as the validation equations in the individual devices are based on the body composition of healthy individuals. It may be of limited use in some hospital patients with abnormal hydration status (e.g. severe dehydration or ascites) and it is also less reliable at the extremes of the BMI ranges (Gonzalez and Heymsfield [61], Leahy et al. [82]).
Clinical examination
Observation of the patient may reveal signs and symptoms indicative of nutritional depletion:
- Physical appearance: emaciated or wasted appearance; loose dentures, teeth, clothing or jewellery.
- Oedema: will affect weight and may mask the appearance of muscle wastage. It may also indicate plasma protein deficiency and is often a reflection of the patient's overall condition rather than a measure of nutritional status.
- Mobility: weakness and impaired movement may result from loss of muscle mass.
- Mood: apathy, lethargy and poor concentration can be features of undernutrition.
- Pressure sores and poor wound healing: may reflect impaired immune function as a consequence of undernutrition and vitamin deficiencies (Gandy [58]).
Specific nutritional deficiencies may be identifiable in some patients. For example, thiamine deficiency characterized by dementia is associated with high alcohol consumption. Rickets is seen in children with vitamin D deficiency.
A more structured approach can be taken by using an assessment tool such as Subjective Global Assessment (SGA) or patient‐generated SGA (PG‐SGA) (Bauer et al. [19]). This involves a systematic evaluation of muscle and fat sites around the body and assessment for oedema in the ankles or sacral area in immobile patients. Such an assessment can be used to determine whether the patient is malnourished and can be repeated to assess changes in nutritional status.
Dietary intake
Nutrient intake can be assessed via a diet history (Gandy [58]). A 24‐hour recall may be used to assess recent nutrient intake and a food chart may be used to monitor current dietary intake. A diet history may also be used to provide information on food frequency, food habits, preferences, meal pattern, portion sizes, the presence of any eating difficulties and changes in food intake (Robertson [153]). A food chart on which all food and fluid taken is recorded is a useful method of monitoring nutritional intake, especially in the hospital setting or when dietary recall is not reliable (Gandy [58]).
Biochemical investigations
Biochemical tests carried out on blood may give information on the patient's nutritional status. The most commonly used are as follows:
- Plasma proteins: changes in plasma albumin may arise due to physical stress, changes in circulating volume, changes in hepatic and renal function, shock conditions or septicaemia. Plasma albumin and changes in plasma albumin are not direct reflections of nutritional intake and nutritional status as it has been shown that they may remain unchanged despite changes in body composition (NCCAC [108]). In addition, albumin has a long half‐life of 21 days, so it cannot reflect recent changes in nutritional intake. It may be useful to review serum albumin concentrations in conjunction with C‐reactive protein (CRP), which is an acute‐phase protein produced by the body in response to injury or trauma. CRP greater than 10 mg/L and serum albumin less than 30 g/L suggest ‘illness’ (Arends et al. [5]). Prealbumin and retinol binding protein levels are more sensitive measures of nutrition support, reflecting recent changes in dietary intake rather than nutritional status. However, they may be expensive to measure and are not measured routinely in hospital.
- Haemoglobin: this is often below haematological reference values in malnourished patients (men 135–175 g/L; women: 115–155 g/L). This can be due to a number of reasons, such as loss of blood from circulation, increased destruction of red blood cells, or reduced production of erythrocytes and haemoglobin, for example due to dietary deficiency of iron or folate.
- Serum vitamin and mineral levels: clinical examination of the patient may suggest a vitamin or mineral deficiency. For example, gingivitis may be due to a deficiency of vitamin C. Goitre is associated with iodine deficiency, and muscle weakness and cramps may be caused by magnesium deficiency (Gandy [58]). Serum vitamin and mineral levels are rarely measured routinely; however, they should be monitored in people receiving long‐term artificial nutritional support or where there is concern about vitamin and mineral status, for example in cases of malabsorption. Long‐term vitamin and mineral monitoring should be carried out in accordance with NICE guidelines (NCCAC [108]).
- Immunological competence: total lymphocyte count may reflect nutritional status although levels may also be depleted with malignancy, chemotherapy, zinc deficiency, age and non‐specific stress (Gandy [58]).
If a patient is considered to be malnourished by one or more of the above methods of assessment then referral to a dietician should be made immediately (NCCAC [108]).
Methods of calculating nutritional requirements
The body requires protein, energy, fluid and micronutrients (such as vitamins, minerals and trace elements) to function optimally. Nutritional requirements should be estimated for patients requiring any form of nutritional support to ensure that these needs are met.
Resting energy requirements may be estimated using figures per kilogram of bodyweight or fat‐free mass, depending on body mass index and disease state. Total energy requirements can be estimated by taking into account activity level (Todorovic and Mafrici [181]) (Table 8.7). Careful adjustments may be necessary in cases of low bodyweight, oedema or obesity, in order to avoid overfeeding.
Table 8.7 Guidelines for estimation of a patient's daily energy and protein requirements
| Factor | Amount per kilogram of bodyweight |
|---|---|
| Energy (kcal) | 25–30 |
| Energy (kJ) | 105–126 |
| Protein (g) | 1–1.5 |
| Fluid (mL) | 35 (18–60 years) |
| 30 (>60 years) | |
| Plus consider an additional 2–2.5 mL per °C in temperatures above 37°C |
| Note: these guidelines will not always be appropriate for patients who are severely ill or who are outside the body mass index range of 18.5–30 kg/m2 (Gandy [58]). |
Fluid and nitrogen (i.e. protein) requirements can be calculated in a similar way. If additional nitrogen is being given in situations where losses have increased (e.g. due to trauma, gastrointestinal losses or major sepsis), then it is important to ensure that energy balance is met to assist in promoting a nitrogen balance.
Vitamin and mineral requirements can be calculated as detailed in Dietary Reference Values for Food Energy and Nutrients for the United Kingdom (COMA and DH [39]). However, these requirements apply to groups of healthy people and are not necessarily appropriate for those who are ill. A patient deficient in a vitamin or mineral may benefit from additional supplements to improve their condition. Macronutrient and micronutrient requirements for children are also listed in the COMA and DH ([39]). Calculations are usually done using the reference nutrient intake (RNI). For children, the actual bodyweight, not the expected bodyweight, is used when calculating requirements. This is to avoid excessive feeding.
Methods of measuring the height and weight of an adult patient
Accurately measuring the height and weight of a patient is an essential part of nutrition screening. Accurate measurements of bodyweight may also be required for estimating body surface area and calculating drug dosages, such as for anaesthesia and chemotherapy. All patients should have their height and weight measured on admission to hospital, and weight should be measured at regular intervals during their hospital stay according to local policy and individual clinical need.
When height cannot be measured, it may be estimated using ulna length, which has been shown to have a moderate correlation with height (Madden et al. [93]). See also the section on pre‐procedural considerations below.
