Distribution of body fluids

Fluids are contained within a number of compartments in the body. Intracellular fluid is contained within the cells. Extracellular fluid, contained outside the cells, is further subdivided into three types: interstitial fluid that surrounds the cell (e.g. that found in cartilage or connective tissue); intravascular fluid, found within the blood vessels; and transcellular fluid found in body cavities (e.g. cerebrospinal or intestinal fluid). 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 balance.

Mechanisms of fluid balance

The kidneys have a vital role in fluid balance by filtering plasma fluid during the formation of urine. There are three additional key mechanisms that control fluid balance in the body: thirst, antidiuretic hormone and the renin-angiotensin-aldosterone system.

Management of the child with fluid imbalance

As with any aspect of children’s nursing, a family centred approach is essential. Careful and appropriate information sharing, involving the child and family, open communication and thorough preparation, including play and distraction techniques, will help to reduce anxiety. Ongoing monitoring and assessment of the child, together with the multidisciplinary team, and adherence to local policies are key aspects of ensuring safe and effective care. Appropriate measuring, recording and reporting of all intake and output in the fluid balance chart and documentation in the nursing notes are also vital. Some children (e.g. those with meningitis or electrolyte disturbance) may need fluid restriction, while those in specialist areas may have very individual requirements. Communication with the medical team is paramount.

Oral fluid requirements

Oral fluids are the preferred option for maintaining fluid balance in children where possible. If the child has a history of vomiting, an oral rehydration solution (ORS), such as Dioralyte, given orally or via a nasogastric tube, may be recommended. Parents have a key role in encouraging ORS intake (as opposed to water or other oral fluids) in small but frequent amounts. However, many children who are ill require intravenous therapy. Oral requirements for neonates vary according to hospital policies. However, as a general rule, by 5 days old onwards, 150 mL/kg/day body weight are required.

Intravenous fluid requirements

The choice of the intravenous fluid will be governed by local policy and the individual assessment of the child. If shock is present, a rapid bolus of 0.9% sodium chloride may initially be given. The fluid deficit, based on the estimated percentage of dehydration, may also be calculated and is normally replaced by sodium chloride 0.9% over the next 48 hours if the child is hypo- or hypernatraemic. This should take account of any boluses given. Large volumes of IV medication and ongoing losses should also be taken into consideration when calculating IV fluid requirements. Maintenance fluids are calculated by the formula below. For example;

• 6-kg infant would require 6 × 100 mL = 600 mL/day or 6 × 4 = 24 mL/hr.
  
• 25-kg child would need 1000 + 500 + 100 = 1600 mL/day or 40 + 20 + 5 = 65 mL/hr.
  
• Maximum daily amounts should be specified in local policies.

Ongoing monitoring and assessment of the child, accurate recording, reporting and evaluation are key aspects of the children’s nurse’s role as a member of the multidisciplinary team.