Enteral feeding

The child with AKI may initially take oral fluids readily, driven by thirst. However, vomiting is common. Most children fail to achieve nutritional targets through diet alone. As the duration of the acute illness can be prolonged, the passing of a fine bore nasogastric tube is recommended. The tube can be passed at the time of sedation or when anaesthetised for procedures including the insertion of a peritoneal dialysis catheter or arterial line [5]. This allows the provision of early nutritional support because anorexia, vomiting or food refusal can impair management and may increase parental anxiety.

A continuous 24 hour feeding regimen using an enteral feeding pump at a slow rate (10–20 mL/hour) is advantageous in the initial stages of treatment when vomiting is present. As oral intake improves, the transition from continuous to overnight feeding provides the outstanding nutritional prescription until appetite improves sufficiently to allow tube feeding to be discontinued. Those children with persistent diarrhoea may tolerate a hydrolysed protein feed (see Tables 7.6, 7.11) before considering parenteral nutrition.

Parenteral nutrition

The parenteral route is only considered when enteral nutrition is not tolerated. Standard hospital parenteral nutrition (PN) regimens are often unsuitable for the child with AKI because of their electrolyte composition and the amount of fluid they provide. An appropriate daily nutritional prescription to meet individual requirements should be agreed by the dietitian, pharmacist and medical staff. When formulating PN, nitrogen and electrolyte modified solutions, together with increased energy from carbohydrate and fat solutions where fluid allowance is limited, need to be considered. On CRRT the loss of nutrients through filtration and dialysis needs to be compensated for in the replacement fluids (see Fluid); levels need to be greater than those found in standard PN regimens. For many children PN is temporary and the enteral route is re-established as soon as gut function returns.

Energy

Little is known about the energy requirements of infants and children with AKI [7]. A minimum of the estimated average requirement (EAR) for energy [8] for healthy children of the same chronological age provides a guide (Table 12.4). These recommendations can be difficult to achieve during acute treatment; it is important to provide the maximum energy intake tolerated within the prescribed fluid allowance. The early addition of glucose polymers to water (flavoured with squash or cordial if desired) or to drinks of choice is recommended. It is prudent to start at a concentration of 0.5 kcal (2 kJ)/mL, building up to a concentration of 1 kcal (4 kJ)/mL, or 25% carbohydrate (CHO) concentration, depending on individual tolerance. Liquid glucose polymer preparations can also be used, but require dilution with water to be tolerated by children. It is recommended to start with a 1:5 dilution of liquid glucose polymer, building up to a final 1:3 dilution. The neutral preparations can be flavoured with squash or cordial. When fluid is severely restricted, ice cubes and lollies can be prepared with these energy dense solutions and offered at frequent intervals. Energy rich CHO drinks including original bottled Lucozade Energy (17.2% CHO concentration) and Mountain Dew (13% CHO concentration) can be useful alternatives for those children who refuse to drink prescribed energy supplements.

EAR, estimated average requirement [8, 9]; CRRT, continuous renal replacement therapy.

^* These guidelines are rarely achieved in the acute stage when fluid is restricted.

^† If dialysis is prolonged, increased protein may be required.

A list of energy supplements that can be considered is given in Table 12.5. These can be successfully added to infant formulas to increase energy density:

• in infants up to 6 months of age, 0.85–1.0 kcal/mL (3.6–4 kJ/mL) is usually tolerated
  
• in infants from 6 to 12 months of age, 1.0–1.5 kcal/mL (4–6 kJ/mL) should be tolerated

CKD, chronic kidney disease; AKI, acute kidney injury.

In children over 12 months of age, or whose weight is >8 kg, a nutritionally complete paediatric feed can be considered and modified as necessary to meet individual requirements (Table 12.5). The energy density can be built up to 1.5–2.0 kcal/mL (6–8 kJ/mL). Fat emulsions can be given as a prescribed medicine during the day.

A few children develop insulin resistance and hyperglycaemia can occur. If managed on PD, this can be exacerbated by the absorption of glucose from the PD fluid together with the intake of high CHO supplements. Insulin infusions need to be considered to control blood glucose levels before the reduction of dietary CHO.

When PN is initiated, a high concentration of dextrose solution up to 25% is indicated, with lipids providing 10%–20% of non-protein energy.

Protein

In children with AKI who are being managed conservatively, protein should be limited to the reference nutrient intake (RNI) [9] level to minimise uraemic symptoms. This needs to be gradually increased as tolerated if RRT is started, with its associated increased solute removal and possible protein losses. The RNI for protein [9] is not appropriate for the child with AKI on RRT and requirements should be individually determined. The age and weight of the child, the serum biochemistry and RRT modality, when implemented, all need to be considered. Nutritional guidelines are shown in Table 12.4.

Once RRT is established, the following increments can be used as a guide to increase protein intake to the levels given in Table 12.4:

• exclude protein if the serum urea is ≥40 mmol/L
  
• introduce 0.5 g protein/kg if the serum urea is ≥30 mmol/L and < 40 mmol/L
  
• give 1 g protein/kg if the serum urea is ≥20 mmol/L and <30 mmol/L
  
• give the RNI for height age (infants) or chronological age (children) if the serum urea is <20 mmol/L

CRRT allows the nutritional support of highly catabolic states but contributes to nitrogen loss through the filtration of free amino acids and small peptides across haemofilters. Maxvold et al. [10] demonstrated that at similar blood and dialysate/prefiltered replacement fluid flow rates, there is an equivalent urea clearance with haemofiltration and haemofiltration with dialysis. A negative nitrogen balance occurred in children with AKI on PN containing 1.5 g/kg/day of protein and an energy intake 20%–30% above resting energy expenditure. An 11%–12% loss of dietary amino acids was found on both modalities. A significant daily accumulative glutamine loss may potentiate nitrogen imbalance. A dose adjustment of amino acid formulation may be needed to overcome negative nitrogen balance in children with AKI on CRRT. An adult study by Scheinkestel et al. [11] showed that a protein intake of 2.5 g/kg/day and meeting energy requirements increased the likelihood of achieving a positive nitrogen balance and improving survival. Nutrition therapy in AKI remains an area of many unanswered questions, especially for those managed on CRRT, and Li et al. illustrate this in their review of adult AKI studies [12]. There are few paediatric studies.

Nutritional supplements, using a nasogastric tube, are frequently used to meet protein requirements in the initial stages of treatment. For infants standard whey based formulas (which are already low in electrolytes and phosphate) are recommended. These can be modified as required. Kindergen and Renastart, renal specific low phosphate, low potassium infant formulas (Table 12.5), can be beneficial for infants not receiving RTT or receiving intermittent haemodialysis when serum biochemistry levels are unstable. Nutritionally complete, energy dense infant formulas (Infatrini, Similac High Energy, SMA High Energy) can be useful if blood biochemistry allows when on RTT. The phosphate content of these feeds is higher than in standard infant whey based formulas so serum phosphate levels should be regularly reviewed. For the older child a number of nutritionally complete supplements are available. These can be used solely or in combinations with their protein, phosphate and potassium contents being assessed prior to use (Table 12.5). If protein hydrolysate formulas are indicated (in particular when the diarrhoeal phase is prolonged in HUS) they should be modified with respect to biochemical parameters as well as to meet individual nutritional requirements. Introduction should be gradual and delivery is usually by the nasogastric route. Once the child’s appetite improves and protein intake is met through eating, energy supplemented drinks can replace nutritionally complete formulas or protein supplements.

Fluid

The volume of fluid prescribed during conservative treatment is based on insensible fluid requirements of 400 mL/m² body surface area/day or approximately 20 mL/kg body weight/day, with a 12% increase for each degree Celsius above normal body temperature and a reduction if the child is ventilated. Insensible losses should be added to the previous day’s urine output to give the total daily fluid allowance. On RRT, the fluid prescription is determined by monitoring the volume of fluid removed by ultrafiltration plus insensible losses. Ideally fluid removal on RRT should be flexibly managed to allow the maximum space for increased nutritional fluids. Maximal nutrient intakes using supplements should be provided within the fluid allowance and divided as evenly as possible throughout the day. A written prescription plan should be provided for the ward nurses and families.

Electrolytes and minerals

The intake of electrolytes, especially potassium, is likely to be restricted in conservative management. Serum levels and the use of RRT will dictate requirements thereafter. Any dietary restrictions should be minimised to avoid compromising nutritional intake.

Potassium rich foods including citrus fruits, fruit juices, bananas, potato crisps and chocolate are commonly brought into hospital by relatives. All carers should be advised about choosing foods with a low potassium content when serum potassium levels are elevated so that rich food sources are withdrawn (Table 12.6).

^* Allowance will depend on individual assessment.

Once serum phosphate levels are above the reference ranges, the intake of phosphate rich foods should be moderated. A lower phosphate intake can partly be achieved when protein intake, particularly that of dairy products, is modified (Table 12.7). Cow’s milk is generally restricted or eliminated from the diet during the acute phase because of its high protein, phosphate and potassium content. Avoidance of cow’s milk also reduces the potential cow’s milk protein or lactose intolerance which can follow the diarrhoeal prodrome in patients with HUS. If the milk restriction proves difficult a low protein milk substitute, such as Sno-Pro or Renamil (Table 12.5), can be advised.

^* Allowance will depend on individual assessment.

^† Caution: vitamin A content (p. 266).

Reduction in sodium intake can aid compliance when fluid intake is restricted by reducing thirst. This can be achieved by the avoidance of salted snacks and a no added salt diet (Table 12.8).

^* Many processed/manufactured foods contain high amounts of salt and even lower salt varieties can have a high salt content.

The level of the above restrictions depends on each individual child and their clinical condition. They should be frequently monitored to avoid unnecessary restrictions when their appetite is typically poor and their nutrition is easily compromised.

Micronutrients

Vitamin supplementation should be considered if dialysis treatment is prolonged. A general paediatric vitamin supplement of water soluble vitamins should be adequate for the majority of children as appetite improves. Iron supplementation may be indicated in some children during the recovery phase, particularly in those who had a poor diet history prior to the onset of AKI.

When on CRRT water soluble vitamins, especially folic acid, thiamin and vitamin C are lost. Requirements when on this treatment are unknown and a minimum of the RNI [9] should be given. Patients receiving CRRT also lose magnesium and calcium; this often leads to negative balances requiring additional supplementation. Zinc is also abnormally lost but serum levels do not generally fall [13, 14].

High energy, low protein foods

These include sugar, glucose, jam, marmalade, honey, syrup and should be encouraged where possible. The liberal use of polyunsaturated or mono-unsaturated oils in cooking or margarine spread on bread, toast or added to meals and vegetables can contribute significantly to the child’s energy intake. Special low protein dietary products such as bread and biscuits are rarely needed.

Energy supplements

Anorexia, nausea and vomiting are features of CKD and can be exacerbated by uraemia. These symptoms, together with an abnormal sense of taste, contribute to a reduced energy intake. Energy supplements are helpful in meeting this deficit. A number of supplements are available and enable a flexible approach (Table 12.5). Combined fat and CHO supplements or glucose polymer alone, if additional fat is not tolerated, can be successfully added to infant formulas, tube feeds and oral nutritional supplements. The concentrations of CHO and fat should be increased gradually to establish tolerance. Assuming normal gut function, the following upper limits for CHO and fat can be worked towards:

• infants <6 months: 12% CHO and 5% fat
  
• infants >6 months to 1 year: 15% CHO and 6% fat
  
• toddlers aged 1–2 years: 20% CHO and 7% fat
  
• older children: 32% CHO and 9% fat

Liquid glucose polymers are useful when diluted with a fizzy drink or diluted squash and the volume used will depend on the fluid allowance. Powdered glucose polymers are useful in children who drink plenty of water or squash. Each day a target amount to use should be negotiated and a personalised record chart can aid compliance.