[29] Dehydration Flashcards
What is dehydration?
When the body loses more fluid than it takes in
Is dehydration serious?
It can be if it is untreated
What % of an infants body weight is made up of water?
As much as 80%
What happens to the proportion of body water by 3 years?
It falls to about 65%
How is body water distributed?
Between the cells (intra-cellular) and the extracellular compartments
What can the extracellular compartment be further divided into?
- Intravascular space
- Extravascular (interstitial) space
What separates the intravascular and extravascular space?
Capillary endothelium
Depletion of what compartment can lead to dehydration?
Any
What may acute loss of fluid from the intravascular compartment be associated with?
Shock
What do the clinical signs of dehydration depend on?
The concentration of electrolytes in the intracellular and extracellular compartments
What are the major ions within the extracellular compartment?
- Sodium
- Bicarbonate
What is the major ion within the intracellular compartment?
- Potassium
What is balanced in normal body fluids?
Intake and output
What does normal fluid balance depend on?
- Fluid intake
- Urine volume
- Stool volume
- Sweating
- Insensible loss
When does dehydration occur, with regard to fluid balance?
When losses exceed input
Why do infants have a higher risk of dehydration?
- Higher SA to weight ratio than older children, leading to greater insensible water losses
- Higher basal fluid requirements
- Immature renal tubular reabsorption
- Inability to obtain fluids for themselves when thirsty
What are the causes of dehydration in children?
- Diabetes
- Vomiting and diarrhoea, e.g. gastroenteritis
- Heatstroke
- Fever
- Conditions that make it hard to swallow fluids, e.g. sore throat
What are the risk factors for dehydration?
- Infants
- Children that have passed 6 or more diarrhoeal stools in the previous 24 hours
- Children that have had vomiting 3 or more times in the previous 24 hours
- Children that have been unable to tolerate, or not offered, oral fluids
- Children with malnutrition
What infants in particular are at risk of dehydration?
- Under 6 months of age
- Low birthweight
What are the symptoms of dehydration?
- Feeling thirsty
- Dark yellow and strong-smelling urine
- Feeling dizzy or lightheaded
- Feeling tired
- Reduced urine output
- Few or no tears when crying
What needs to be determined in the history in dehydration?
- Cause of dehydration
- Severity of dehydration
What are the signs of dehydration?
- Sunken eyes
- Soft spot on head sinks inwards
- Cold and blotchy-looking hands and feet
- Dry mouth, lips, and eyes
What do you need to assess/obtain on physical examination in dehydration?
- Weight
- Severity of dehydration
- Signs of cause of dehydration
What is the importance of measuring the weight in dehydration?
Acute water loss can be estimated from the difference between actual weight and a recent weight made before dehydration occurred, and so regular weighing will allow accurate measurement of fluid replacement
How can the cause of dehydration be assessed on examination?
Should perform a thorough examination to identify the foci of infection
What should be included on thorough examination to identify the cause of dehydration?
- Ears
- Throat
- Chest
- Abdomen
What physical things etc signs should be assessed when determining the severity of dehydration?
- Mental state
- Skin turgor
- Dryness of mucous membranes
- Fontanelle
- Eye turgor
- Skin perfusion
- Pulse rate and character
What are the signs of mild dehydration?
Only physical sign may be dry mouth
What are the physical signs of moderate dehydration?
- Lethargy
- Inelastic skin
- Sunken fontanelle
- Sunken eyes
- Pulse may be fast, but of normal volume
- Slow refilling of skin when blanched
What are the signs of severe dehydration?
- Very confused, only semi-conscious
- Mottled skin
- No refilling of skin when blanched
- Fontanelle and eyes deeply sunken
- Poor eye turgor
- Thready and fast pulse
Why is it important to assess how severe dehydration is?
So you can calculate how much fluid replacement is required
What investigations should be done in dehydration?
- U&s
- Urine assessment
What findings may be present on U&Es in dehydration?
- Hyper or hyponatraemia
- Low bicarbonate
Why can hyper or hyponatraemia occur in dehydration?
Due to differential loss of sodium
What is the importance of identifying hyper or hyponatraemia in dehydration?
It will change your management
When might you get low bicarbonate in dehydration?
As a result of diarrhoea
What does low bicarbonate due to diarrhoea cause?
Metabolic acidosis
What metabolic abnormality may occur if there has been excessive vomiting?
Excessive loss of hydrogen ions, which may cause an initial metabolic alkalosis
What urine assessments should be done in dehydration?
Assess urine for specific gravity or osmolality, and consider measuring urine electrolytes
Should an assessment of urinary volume over a known period be done in dehydration?
It is helpful, but difficult to collect, and treatment should not be delayed to measure urine output
What are the different types of dehydration?
- Isotonic
- Hyponatraemic
- Hypernatraemia
What is the most common type of dehydration?
Isotonic
What is isotonic dehydration?
When there are equal losses of sodium and water
Will the seurm sodium be high, normal, or low in isotonic dehydration?
Normal
How do the physical signs of dehydration correlate to the fluid loss in isotonic dehydration?
The physical signs will be proportional to the degree of fluid loss
Define clinically hyponatraemic dehydration?
Dehydration with serum sodium <130mmol/L
Physiologically, when does hyponatraemic dehydration occur?
Generally, when fluid losses have been replaced with hypotonic solutions such as water
How does hyponatraemic dehydration present?
The child will be lethargic, and skin dry and inelastic
What is hypernatraemic dehydration clinically defined as?
Dehydration when serum sodium is >150mmol/L
When is hyponatraemic dehydration more likely?
- Acute and severe water loss
- Common in breast-fed baby in first 2 weeks of life
- Concentrated formula feeds
Why might hyponatraemic dehydration occur in a breastfed baby in the first two weeks of life?
If there is difficulty establishing feeds
What might lead to a parent giving a baby concentrated formula feeds?
The parent incorrectly measuring scoops of powdered milk
How does hypernatraemic dehydration present?
Infant appears very hungry, but has fewer clinical signs of dehydration. The skin feels doughy.
Metabolic acidosis is a common feature
What % dehydration is considered to be mild?
5%
How can a child with mild dehydration be treated?
May be treated at home using oral hydration therapy
When is oral rehydration likely to be successful in dehydration?
When vomiting is not a major feature
What should be used in oral rehydration therapy?
Oral rehydration solutions such as Dioralyte
In what forms can oral rehydration solutions such as Dioralyte be dispensed?
- Oral solution
- Effervescent tablets or powders
Should breast feeding be maintained when using oral rehydration solutions?
Yes
When can normal milk feed be resumed in dehydration if the baby is bottle fed?
Once diarrhoea has settled
When do you need to pay closer attention to the fluid balance in dehydration?
In a child with more significant dehydration, particularly if there is vomiting
What do you do in assessment of the fluid balance in a significantly dehydrated child involve?
- Maintaining an accurate input-output chart
- Weighing the child twice daily
- Frequent measurement of serum electrolytes
What principles do the calculations of rehydration require?
- Estimate or acute fluid loss
- Estimate of maintenance fluid requirements
- Estimate of on-going losses
How is an estimate of acute fluid loss made?
Difference between actual weight and recent normal weight
What should be done if recent normal weight is unknown when estimating acute fluid loss?
Rely on clinical assessment of dehydration
What is the estimated maintenance fluid requirement for a 0-6 month old?
150mL/kg/24 hours
What is the estimated maintenance fluid requirement for a 6-12 month old?
120mL/kg/24 hours
What is the estimated maintenance fluid requirement for a 12-24 month old?
100mL/kg/24 hours
What is the estimated maintenance fluid requirement for a >24 month old?
80mL/kg/24 hours
How are on-going losses estimated in dehydration?
If possible, they should be measured carefully on an hourly basis, and added to the fluid regimen every 4 hours
What does the rate of rehydration depend on?
The type of dehydration
How should rehydration be given if the patient is shocked?
Circulation must be restored by boluses of colloid
How should rehydration be given if hypernatraemia dehydration?
Must correct more slowly over 48 hours
Why is it important to correct hypernatraemic dehydration slowly?
To avoid rapid shifts of water within the brain resulting in cerebral oedema
What are the complications of dehydration?
- Shock
- Severe metabolic acidosis
- Death
