BNF for Children (BNFC) 2018-2019

replace losses in children with cysticfibrosis particularly in

warm weather.

Oral rehydration therapy (ORT)

Diarrhoea in children is usually self-limiting, however, in

children under 6 months of age, and more particularly in

those under 3 months, symptoms of dehydration may be less

obvious and there is a risk of rapid and severe deterioration.

Intestinal absorption of sodium and water is enhanced by

glucose (and other carbohydrates). Replacement offluid and

electrolytes lost through diarrhoea can therefore be achieved

by giving solutions containing sodium, potassium, and

glucose or another carbohydrate such as rice starch.

Oral rehydration solutions should:

.enhance the absorption of water and electrolytes;

.replace the electrolyte deficit adequately and safely;

.contain an alkalinising agent to counter acidosis;

.be slightly hypo-osmolar (about 250 mmol/litre) to prevent

the possible induction of osmotic diarrhoea;

.be simple to use in hospital and at home;

.be palatable and acceptable, especially to children;

.be readily available.

It is the policy of the World Health Organization (WHO) to

promote a single oral rehydration solution but to use it

flexibly (e.g. by giving extra water between drinks of oral

rehydration solution to moderately dehydrated infants).

The WHO oral rehydration salts formulation contains

sodium chloride 2. 6 g, potassium chloride 1. 5 g, sodium

citrate 2. 9 g, anhydrous glucose 13. 5 g. It is dissolved in

sufficient water to produce 1 litre (providing Na+ 75 mmol,

K+ 20 mmol, Cl– 65 mmol, citrate 10 mmol, glucose

75 mmol/litre). This formulation is recommended by the

WHO and the United Nations Children’s fund, but it is not

commonly used in the UK.

Oral rehydration solutions used in the UK are lower in

sodium ( 50 – 60 mmol/litre) than the WHO formulation since,

in general, patients suffer less severe sodium loss.

Rehydration should be rapid over 3 to 4 hours (except in

hypernatraemic dehydration in which case rehydration

should occur more slowly over 12 hours). The patient should

be reassessed after initial rehydration and if still dehydrated

rapidfluid replacement should continue.

Once rehydration is complete further dehydration is

prevented by encouraging the patient to drink normal

volumes of an appropriatefluid and by replacing continuing

losses with an oral rehydration solution; in infants, breast-

feeding or formula feeds should be offered between oral

rehydration drinks.

Oral bicarbonate

Sodium bicarbonate p. 586 is given by mouth forchronic

acidotic statessuch as uraemic acidosis or renal tubular

acidosis. The dose for correction of metabolic acidosis is not

predictable and the response must be assessed. For severe

metabolic acidosis, sodium bicarbonate can be given

intravenously.

Sodium supplements may increase blood pressure or cause

fluid retention and pulmonary oedema in those at risk;

hypokalaemia may be exacerbated.

Sodium bicarbonate may affect the stability or absorption

of other drugs if administered at the same time. If possible,

allow 1 – 2 hours before administering other drugs orally.

Wherehyperchloraemic acidosisis associated with

potassium deficiency, as in some renal tubular and

gastrointestinal disorders it may be appropriate to give oral

potassium bicarbonate, although acute or severe deficiency

should be managed by intravenous therapy.

Parenteral preparations for fluid and electrolyte

imbalance

Electrolytes and water

Solutions of electrolytes are given intravenously, to meet

normalfluid and electrolyte requirements or to replenish

substantial deficits or continuing losses when it is not

possible or desirable to use the oral route. When intravenous

administration is not possible,fluid (as sodium chloride 0. 9 %

p.^589 or glucose^5 %p.^590 ) can also be given

subcutaneously by hypodermoclysis.

In an individual patient the nature and severity of the

electrolyte imbalance must be assessed from the history and

clinical and biochemical examination. Sodium, potassium,

chloride, magnesium, phosphate, and water depletion can

occur singly and in combination with or without

disturbances of acid-base balance.

Isotonic solutions may be infused safely into a peripheral

vein. Solutions more concentrated than plasma, for example

15 % glucose, are best given through an indwelling catheter

positioned in a large vein.

Maintenancefluid requirementsin children are usually

derived from the relationship that exists between body-

weight and metabolic rate; thefigures in the table below may

be used as a guide outside the neonatal period. The glucose

requirement is that needed to minimise gluconeogenesis

from amino acids obtained as substrate from muscle

breakdown. Maintenancefluids are intended only to provide

hydration for a short period until enteral or parenteral

nutrition can be established.

It is usual to meet these requirements by using a standard

solution of sodium chloride with glucose p. 590. Solutions

containing 20 mmol/litre of potassium chloride p. 601 meet

usual potassium requirements when given in the suggested

volumes; adjustments may be needed if there is an inability

to excretefluids or electrolytes, excessive renal loss or

continuing extra-renal losses. The exact requirements

depend upon the nature of the clinical situation and types of

losses incurred.

Fluid requirements for children over 1 month:

Body-weight 24 -hour fluid requirement

Under 10 kg 100 mL/kg

10 – 20 kg 100 mL/kg for the first 10 kg

+ 50 mL/kg for each 1 kg body-weight over

10 kg

Over 20 kg 100 mL/kg for the first 10 kg

+ 50 mL/kg for each 1 kg body-weight

between 10 – 20 kg + 20 mL/kg for each 1 kg

body-weight over 20 kg

(max. 2 litres in females, 2. 5 litres in males)

ImportantThe baselinefluid requirements shown in the

table should be adjusted to take account of factors that

reduce water loss (e.g. increased antidiuretic hormone, renal

failure, hypothermia, and high ambient humidity) or

increase water loss (e.g. pyrexia or burns).

Replacement therapy: initial intravenous replacement

fluid is generally required if the child is over 10 % dehydrated,

or if 5 – 10 % dehydrated and oral or enteral rehydration is not

tolerated or possible. Oral rehydration is adequate, if

tolerated, in the majority of those less than 10 % dehydrated.

Subsequentfluid and electrolyte requirements are

determined by clinical assessment offluid balance.

Intravenous sodium

Intravenoussodium chloride in isotonic ( 0. 9 %) solution

provides the most important extracellular ions in near

physiological concentrations and is indicated insodium

depletion. It may be given for initial treatment of acutefluid

loss and to replace ongoing gastro-intestinal losses from the

upper gastro-intestinal tract. Intravenous sodium chloride is

commonly given as a component of maintenance and

replacement therapy, usually in combination with other

electrolytes and glucose.

Chronic hyponatraemiashould ideally be corrected byfluid

restriction. However, if sodium chloride is required, the

584 Fluid and electrolyte imbalances BNFC 2018 – 2019

Blood and nutrition

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