Movement of body fluid and electrolytes

Body fluids and associated electrolytes are in constant motion around the body by diffusion, osmosis and active transport in order to achieve a state of homeostasis. Thus, the body works continuously to achieve optimal fluid and electrolyte balance. Electrolytes are substances that develop an electrical charge when dissolved in water and play an important part in controlling the osmosis of water between body compartments and its movement in and out of the cells. Sodium of one of the most important electrolytes in the ill child.

Sodium

Most sodium is kept outside the cells and potassium inside via the sodium–potassium pump mechanism. The movement of sodium and water are closely related; generally where one goes, the other follows. Thus, under normal circumstances, the sodium–potassium pump prevents too much water entering the cells. In hyponatraemia, a low serum sodium level means that the extracellular fluid is very dilute and water is drawn into the cells (Figure 85.1). This can result in cerebral oedema and brain herniation. A high serum sodium or hypernatraemia has the opposite effect but can also have serious neurological consequences (Figure 85.1), although further discussion of this is beyond the remit of this chapter.

What is hyponatraemia?

Normal sodium levels are 135–145 mmol/L. Hyponatraemia occurs when levels fall below these limits and is not uncommon in the child with fluid and electrolyte imbalance. Severe hyponatraemia occurs when plasma sodium levels fall below 130 mmol/L and severe acute hyponatraemia occurs when a normal plasma sodium falls below 130 mmol/L in less than 48 hours (Playfor 2013). This is a potentially life-threatening event that needs careful monitoring, care and treatment by the multidisciplinary team. Children are more at risk of detrimental effects of hyponatraemia because they cannot tolerate over-hydration, they have a higher brain : skull size ratio (meaning that there is little space for expansion as the brain cells fill with water) and hormonal changes render female adolescents, in particular, more prone to its development. Other children particularly at risk include those with central nervous system conditions, sepsis, gastroenteritis or those in the perioperative period. Stress, pain, nausea, certain anaesthetics or types of ventilation can cause what is known as the syndrome of inappropriate antidiuretic hormone (SIADH). This hormone normally conserves water in the body in times of dehydration; however, in SIADH it is produced unnecessarily and this can cause hyponatraemia resulting from the retention of water.

Management of the child with hyponatraemia

As with any aspect of children’s nursing, a family centred approach is essential. Careful and appropriate information giving, involving the child and family and open communication will help to reduce anxiety. Good communication within the multidisciplinary team, and adherence to local policies are key aspects of the children’s nurse’s role in ensuring safe and effective care for the hyponatraemic child. Ongoing monitoring and assessment of the child for signs and symptoms of hyponatraemia and fluid imbalance (see Chapter 77) are key. Accurate recording and reporting of all intake and output in the fluid balance chart (including the child’s daily weight) and documentation in the nursing notes are also of vital importance. In particular, the type, amount and rate of intravenous (IV) fluids should be recorded accurately together with any losses (e.g. gastric losses) that may need to be replaced. The child receiving IV fluids should be closely observed and their blood, urea and electrolytes (including BM) obtained on a regular basis and results evaluated by the multidisciplinary team. IV requirements should be adjusted accordingly if the child is also taking oral fluids. Hourly observation of the IV site, for the presence of inflammation and/or phlebitis (using an appropriate tool), is also an important part of the role of the nurse.

Treatment of hyponatraemia may involve the administration of sodium chloride solution (according to local policy) to raise serum sodium levels and/or fluid restriction. In general, correction of sodium levels should not be too rapid as this can result in neurological damage. Regular blood tests (urea and electrolytes) and urine collection for osmolality and electrolytes will be required as directed by the individual child’s situation. The children’s nurse has key role in supporting the family and ensuring that these tests are carried out and results reported back to appropriate medical staff in a timely manner.

Preventing hyponatraemia

Children’s nurses, as members of the multidisciplinary team, may help prevent hyponatraemia by having a thorough working knowledge of suitable types and amounts of fluids for children in their care along with normal serum electrolyte levels. All professionals working with sick children should be familiar with local policies. They also need to be aware of the causes of hyponatraemia, the factors that put some children particularly at risk and an understanding of SIADH. Specific clinical guidelines have been developed throughout the United Kingdom for local use in response to the National Patient Safety Alert 22 ‘Reducing the risk of hyponatraemia when administering intravenous infusions to children’. It is imperative that children’s nurses adhere to such guidance along with other members of the multidisciplinary team. Regular training, supervision and adequate reporting of incidents or near misses will help to ensure the safety of children at risk of hyponatraemia.