Introduction

The World Health Organization (WHO, 2016) revealed that 5.9 million children under the age of 5 died in 2015; children living in sub‐Saharan Africa are more than 14 times more likely to die before they reach their 5th birthday. Leading causes are preterm birth, pneumonia, birth asphyxia, diarrhoea and malaria. WHO noted that of the deaths recorded, more than half could have been prevented or treated with simple interventions.

As described in Brady (2015), the cells of the human body function within a narrow range of parameters and there are various mechanisms that operate to enable this balance to be maintained. Much of this book will address the imbalance due to illness and this chapter will focus on the pathophysiology that disrupts normal homeostatic control.

Children’s nurses will often care for children and young people whose ability to maintain homeostasis will be severely impaired and in such situations, it becomes imperative that the nurse can detect subtle changes indicating altered homeostasis, initiate appropriate emergency care, and escalate his/her concerns appropriately to other members of the multidisciplinary team, to instigate the best evidence‐based care. Integral to this is the ability to clearly communicate the changes in the child/young person to their family or carers and to be able to explain any treatments provided.

This chapter will use the term ‘child’ to refer to those in the 0–18‐year age range, except where specific information is provided for neonates and premature infants.

Dehydration

Children are more prone to dehydration due to their large surface area to volume ratio and higher percentage of water volume ranging between 60% and 80% (Kanneh, 2010) depending on their age. Fluid loss due to acute gastroenteritis accounts for about 1.7 million cases globally of which 760 000 deaths per year occurred in children under 5 years old (WHO, 2013).

Dehydration due to gastrointestinal fluid loss

Please revisit Chapter 12, Outerridge (2015).

Babies under 1 year are particularly susceptible to dehydration because of their large surface area and immature kidneys that are unable to concentrate urine (Gormley‐Fleming, 2015).

Babies are also more susceptible to gastrointestinal infections that cause diarrhoea and vomiting because of reduced hydrochloric acid in their stomach and an immature immune system, especially if the baby was born prematurely. At birth, the stomach contents are less acidic with a neutral pH of 7 due to the amniotic fluid that has been swallowed while in utero (Chamley et al., 2005). Gradually with the introduction of feeding, especially breast feeding, Lactobacillus bifidus proliferates and this helps to increase the acidity within the stomach. Furthermore, Westerbeek et al.’s (2006) review of the literature clearly identified the beneficial effects of breast feeding in preterm babies due to the presence of bifidobacteria and lactobacilli, which suppress the growth of potentially pathogenic bacteria. By about 10 years of age, gastric secretions have reached adult levels; thus, children are vulnerable to gastrointestinal infections during the early part of their life and this is a relatively common problem seen in both the developed and developing world.

When a child loses fluid through vomiting and diarrhoea, s/he can quickly become dehydrated and experience medical ‘shock’, where the volume of circulating fluids is insufficient to perfuse the organs. Normally, with the onset of dehydration, receptors in the anterior hypothalamus detect changes in the osmolality and volume of the extracellular fluid (in the interstitial spaces and plasma) triggering messages of thirst in the individual, who can address this need; however, very young children are unable to verbalise this except through crying to alert their parent or carer who in turn provides the necessary fluids.

An unwell child has a reduced blood volume that leads to a decrease in blood pressure, although it is important to note that hypotension is a late sign in children due to their ability to compensate for fluid loss. The reduced circulating blood volume stimulates the kidneys to release the enzyme renin, which acts on angiotensin converting it to angiotensin I, which is converted into angiotensin II by the angiotensin‐converting enzyme (ACE) produced by the lungs and nephrons. Angiotensin II causes aldosterone to be produced by the adrenal cortex, which leads to vasoconstriction of the arterioles, which subsequently helps to increase the blood pressure (Fig. 4.1).

A child who has lost fluid will also have lost weight, so it is important that the child is accurately weighed, enabling an estimation of their weight loss to be calculated and fluid rehydration commenced appropriately. Therefore, all children under 2 years of age should be weighed naked. As a nurse you will also record observations of temperature, pulse, respiratory rate, blood pressure, oxygen saturation, capillary refill time, as well as noting the appearance of their skin and eye turgor, fontanelle depression and urine output (Rudolph, Lee & Levene, 2011).

The fontanelle in infants under 18 months is a useful indicator of their state of hydration, with a depressed fontanelle indicating dehydration. Early signs of shock include restlessness and tachycardia with a weak pulse, pallor and a widening core‐peripheral temperature gap. These observations become even more crucial as the child’s condition worsens and they become quiet and lethargic. The amount of urine produced will reduce as the body strives to conserve fluid, and kidney perfusion reduces due to hypotension.

To gain a more accurate clinical picture, blood samples are taken promptly, such as blood gas analysis, urea and electrolytes, and blood glucose (Table 4.1) to identify the cause and initiate treatment.

Observation	Finding
Temperature	Depends on the underlying cause, may be raised due to infection
Heart rate	Tachycardic
Respiratory rate	Tachypnoea
Colour	Pallor with peripheral mottling or cyanosis
Blood pressure	May be normal or low
Level of consciousness	Restless, confused,
Oxygen saturations	May be normal or low depending on the cause
Capillary refill	More than 2 seconds

Kanneh (2010) explained that blood tests help to clarify the type of dehydration present (Table 4.2); stating that since normal plasma sodium in a child is greater than 145 mmol/l, symptoms would be apparent when the sodium level was less than 120 mmol/l or above 150 mmol/l. NICE (2015b) guidance exists to guide appropriate fluid rehydration.

Test	Finding
Blood gas	Anaerobic tissue metabolism
Haemoglobin (Hb)	Reduced due to haemorrhage
Packed cell volume (PCV)	Decreased due to haemorrhage Raised if less than 55% plasma due to hypovolaemia
Urea	Raised urea indicating reduced GFR and kidney excretory capacity due to hypovolaemia
Sodium	Raised if the fluid volume in the blood vessels and cells is reduced giving a higher concentration of solute
Plasma osmolality	Raised if there is less fluid in the blood vessels giving a concentrated plasma
Blood glucose	Hypoglycaemia
Electrocardiogram	Cardiac arrhythmia due to abnormal potassium levels
Central venous pressure (CVP)	Low in severe dehydration. A CVP line will monitor fluid replacement

About 70% of dehydrated children have isonatraemic dehydration with plasma sodium levels between 135–145 mmol/l and normal plasma osmolality of 275–295 mOsm/kg H₂O. This is usually due to diarrhoea and vomiting and in this situation the amount of sodium and water loss is equal and the kidneys facilitate equilibrium by compensating; however, the extracellular fluid in the blood vessels and interstitial space is reduced with the ensuing hypotension.

About 10% of dehydration is hyponatraemic where more sodium is lost via micturition and usually arises due to severe burns or vomiting and diarrhoea. Intravenous fluids may be given or the child could be encouraged, if well enough, to drink large quantities of sugary drinks, thereby counteracting the fluid loss as the cells take in the glucose and leave the water in the extracellular spaces. Careful monitoring is required to ensure the correct diagnosis, since the imbalance could be due to water intoxication where too much water has been consumed or where the cause is due to inappropriate ADH syndrome.

Twenty percent of children will have hypernatraemic dehydration with plasma sodium levels greater than 145 mmol/l and plasma osmolality greater than 295 mOsm/kg H₂O. In this situation, more water is lost than sodium and it is a manifestation of conditions such as diabetes insipidus, hyperpyrexia and hyperventilation with loss of fluids due to increased insensible loss. Another reason could be the accidental administration of hypertonic intravenous fluids. In an effort to dilute the plasma, fluid in the cells passes into the circulatory system. A similar situation arises with diabetes mellitus, where there is hyperglycaemia instead of hypernatraemia. The end result is a reduced volume in the circulatory system and in the interstitial spaces.

Dehydration due to blood loss

Children may suffer haemorrhage following surgery or trauma; the cause needs to be ascertained promptly and investigations commenced as per Table 4.1, plus obtaining a full blood count (FBC) where the haemoglobin (Hb) and packed cell volume levels (PCV) will be decreased due to haemorrhage. As well as administering intravenous fluids (0.9% saline), a blood transfusion may also be given depending on the severity of the blood loss. Drugs to strengthen cardiac function (inotropes) may also be required.

The child requiring surgery

In the past, concern has been raised regarding the possibility of regurgitation and aspiration of acidic gastric contents for all patients undergoing surgery, and to reduce this incidence all patients requiring surgery were fasted overnight prior to undergoing surgery. However, with children this is recognised as dangerous because of the risk of dehydration; it is also unnecessary due to their different physiology, for instance, babies have faster stomach emptying times, especially if fed breast milk (Neill & Knowles, 2004).

The RCN (2005) has provided clear guidance regarding pre‐operative fasting for children, which has been further endorsed by Brady et al.’s (2009) systematic review. Brady et al. (2009) observed that children who were allowed to drink up to 2 hours before surgery were less thirsty and more comfortable than those who were fasted for longer. Current guidance advises that 6 hours prior to surgery, all patients should be advised to stop taking solid food, milk and milk‐containing drinks, and should only drink clear fluids until 2 hours prior to their operation, after which they fast. Breast milk can be given up to 4 hours prior to surgery; however, for children who are at a higher risk of regurgitation, individual decisions will be made by the clinical staff in the best interest of the child and this may include commencing intravenous fluids to prevent dehydration (Aker & O’Sullivan, 1998).