Fluid, Electrolytes, Feeding, and Nutrition ✅ Flashcards
What is the total body fluid in neonates distributed among?
3 major fluid spaces - plasma, interstitial, and cellular space
Is the proportion of fluid in each of the compartments the same in infants and adults?
No, very different
How does the extra cellular fluid expressed as a percentage of body weight differ at 26 weeks, term, and in the adult?
In 26 weeks, 50% of fluid is extracellular fluid. In term, around 35%, and in adults, around 20%.
Therefore, relatively less dry weight in younger.
Volume of intracellular fluid is the same.
What is the result of the differing proportion of fluids in each compartment in the neonate compared to an adult?
A different approach to fluid management is required
What % of the total body weight is water in the early fetal period?
95%
What % of the total body weight is water at term?
75%
What happens to the distribution of fluid throughout the compartments as the foetus grows?
The amount of fluid in the extracellular spaces decreases gradually, and there is a slow increase in intracellular fluid
Why is it important to consider the change in fluid distribution throughout the neonatal period?
It affects decision-making about fluid changes, especially in the sick preterm infant
What factors affect the neonatal fluid balance?
- GFR
- RDS
- Transepidermal water loss (TEWL)
- Complications of prematurity
How does the GFR in an extremely preterm infant compare to that of a term infant?
It is only around 1/4 of that of a term infant
What is the result of the GFR being lower in an extremely preterm infant compared to a term infant?
It makes them vulnerable for fluid overload and hyponatraemia, as well as dehydration and hypernatraemia
What else can increase the risk of hypernatraemia in an extremely preterm infant?
Their immature renin-angiotensin mechanism increases the risk following rapid correction of sodium
What happens to all babies in the immediate post-natal period, regarding their renal function?
They undergo a diuretic phase
What regulates the diuretic phase in the immediate post-natal period?
An increase in atrial natriuretic peptide
What does the diuretic phase in the immediate post-natal period lead to?
A physiological contraction of the extracellular volume
Describe the sodium balance in a neonate?
There is a negative sodium balance early on, followed by sodium retention in the kidney
What is a negative sodium balance early on followed by sodium retention in the kidney important for?
Growth
At what gestational age are premature infants able to maintain an adequate water balance over a wide range of fluid intake?
> 30 weeks
What can affect fluid homeostasis in extremely preterm infants (<30 weeks)?
- Administration of fluid blouses
- Infection
- Hypotension
- Mechanical ventilation
How does RDS affect fluid balance?
Infants with RDS have a delayed diuretic phase, and their extracellular volume is not decreased
What is the result of the extracellular volume of infants with RDS not being decreased due to the delayed diuretic phase?
It is important not to give extra fluids and sodium before the diuretic phase
Why is there a high transepidermal water loss (TEWL) in babies?
Due to their large surface area and thin, permeable, non-keratinised skin
How does the TEWL in infants of 25 weeks gestation compare to that of term infants?
It can be up to 15 times higher
What can reduce the TEWL in preterm infants?
- Nursing inside an incubator with high humidity
- Humidification of respiratory gases
- Good skin care
How high is the humidity in an incubator?
Up to 80%
What neonatal complications can lead to hyponatraemia?
- Pneumothorax
- Intraventricular haemorrhage
- Conditions requiring surgery
What might complications of prematurity lead to, regarding sodium?
Hyponatraemia
How can complications of prematurity lead to hyponatraemia?
- Diminished capacity to excrete a free water load
- Increased sodium loss in the urine
- Iatrogenic fluid administration of hypotonic, low sodium solutions
Is true SIADH common in neonates?
No, probably rare
What are the fluid requirements of a term neonate at day 1?
Around 50ml/kg/day
What are the fluid requirements for a term neonate at day 7?
Around 150ml/kg/day
What are the fluid requirements of a preterm neonate at day 1?
60-70ml/kg/day
What are the fluid requirements of a preterm neonate at day 7?
Up to 175ml/kg/day
What are the energy requirements of a term infant?
100kcal/kg/day
What are the energy requirements of a preterm infant?
120kcal/kg/day
What are the energy requirements of an IUGR infant?
Up to 140kcal/day/kg
What fluids are given to infants in the first 2-3 days of life if IV fluids are required?
Solute-free dextrose solution
Why is a solute free dextrose solution used in the first 2-3 days of life?
- Na/K-ATPase mechanism is affected during intensive care for sick babies
- Infants have a limited ability to handle solute load in administered fluid
What is the Na/K-ATPase mechanism responsive for?
Maintaining sodium and potassium balance
Why do infants have a limited ability to handle solute load in administered fluid?
Due to renal impairment
What does serum sodium levels reflect?
Sodium and water balance
What is considered to be hypernatraemia?
> 145mmol/L
What is happening with regard to sodium and fluid in hypernatraemia?
There is an absolute or relative deficit of body water in relation to body sodium
What is considered to be hyponatraemia?
<135mmol/L
What is happening with regard to sodium and water in hyponatraemia?
There is a relative or absolute excess of body water
What needs to be clinically assessed when determining the cause of hypo or hypernatraemia?
Change in weight and clinical context
What does weight gain in the first few postnatal days with normal serum sodium indicate?
Isotonic expansion of extracellular space and a positive sodium and water balance (at a time when it should be negative)
What does hyponatraemia with weight loss or inadequate weight gain indicate?
Sodium depletion
What is required when sodium depletion is suspected to be the cause of hyponatraemia?
Supplemental sodium
How is hyponatraemia caused by fluid excess treated?
- Fluid restriction
- Treatment of underlying cause
What does hypernatraemia with weight loss suggest?
Dehydration
What does hypernatraemia with weight gain suggest?
Sodium and water overload
Where does most of the potassium in the body exist?
In the intracellular compartment
Do blood levels of potassium reflect total body potassium?
No, not usually
What maintains the high intracellular potassium concentration?
The Na/K-ATPase
How does the Na/K-ATPase maintain the high intracellular potassium concentration?
By pumping sodium out and potassium into the cell
What is potassium necessary for?
The electrical responsiveness of muscle cells, and the contractile to of cardiac, skeletal, and smooth muscles
When must potassium rich fluids be avoided?
If there is oliguria or anuria due to renal compromise
What is the daily sodium requirement of a term infant?
2.5-3.5mmol/kg
What is the daily potassium requirement of a term infant?
2.5-3.5mmol/kg
What is the daily chloride requirement of a term infant?
5mmol/kg
What is the daily phosphorus requirement of a term infant?
1.0-1.5mmol/kg
What is the daily calcium requirement of a term infant?
1.2-1.5mmol/kg
What is the daily magnesium requirement of a term infant?
0.6mmol/kg
What is the daily sodium requirement of a preterm infant?
3-4mmol/kg
What is the daily potassium requirement of a preterm infant?
2-3mmol/kg
What is the daily chloride requirement of a preterm infant?
1.5-4.5
What is the daily phosphorus requirement of a preterm infant?
1.9-4.5mmol/kg
What is the daily calcium requirement of a preterm infant?
3-5.5mmol/kg
What is the daily magnesium requirement of a preterm infant?
0.3-0.6mmol/kg
What is the normal weight loss in the first week in a healthy term infant?
About 5-7%
Why do term infants normally loose 5-7% of their birth weight?
- Physiologic contraction of extracellular water volume
- Catabolism secondary to low caloric intake
When is the weight loss of a term infant most marked?
On day 2-3
When should an infant regain their birth weight?
Within 2 weeks
When might the initial weight loss in infants be more marked?
In breastfed infants
What can weight loss in excess to 10% lead to?
Hypernatraemic dehydration
How much weight does a baby gain in the first 6 months?
Average of around 30g/day
When should an infant double their birth weight?
Around 4-5 months
When should an infant treble their birth wight?
1 year of age
What are the benefits of breast feeding to the baby?
- Most suitable source of nutrition
- Reduced risk of infection
- May be protective in eczema
- Beneficial effect on later ‘cardiovascular’ health
- May improve later cognitive function
- May protect against SIDS
What infections does breastfeeding reduce the risk of?
- Gastroenteritis
- Otitis media
- Probably severe lower respiratory tract infection requiring hospitalisation
When might breastfeeding be protective in eczema?
In infants with a positive family history
In what ways does breastfeeding have a beneficial effect on later cardiovascular health?
Improves plasma lipid profile, blood pressure, and risk of obesity
What confounds the evidence that breastfeeding reduces the risk of SIDS?
May be through maternal education, socio-economic status, and birth weight
What are the advantages of breastfeeding in a preterm infant?
- Better gastrointestinal tolerance
- Reduced incidence of necrotising enterocolitis (NEC) and systemic infection
- Improved cognitive outcome
- Lower BP, more favourable plasma lipid profile, and higher bone mass during childhood and adolescence
What are the benefits of breastfeeding for the mother?
- Better mother-infant bonding
- Sense of personal achievement
- More rapid weight loss
- Readily available without any preparation
- Easy to express and store
- Delayed return to menses
- Uterine involution through oxytocin
- No cost
- Some protection against osteoporosis, ovarian and breast cancer
Why might a delayed return to menses be beneficial?
Increased time-interval to next child is important when alternative birth control is not available
What happens to the breast in pregnancy?
There is a marked increase in the number of breast ducts
What causes the increase in the number of breast ducts in pregnancy?
Response to progesterone, oestrogen, and placental lactometer
When does secretion of prolactin start?
In the last trimester
What triggers the secretion of colostrum?
Prolactin from the anterior pituitary causes glandular tissue to secrete small amounts of colostrum
What controls milk flow after birth?
The let down reflex
What mediates the let down reflex?
- Afferent impulse from the baby rooting at the nipple
- Oxytocin secretion from the posterior pituitary
How does oxytocin stimulate cause milk to be released?
Oxytocin squeezes milk into large ducts through smooth muscle fibre stimulation around alveoli
What maintains milk production?
- Prolactin secretion
- Effective suckling and emptying of breast milk
What is the energy content of breast milk?
67kcal/100ml
What are the main constituents of breast milk?
- Fat (54%)
- Carbohydrate (40%)
- Protein (6%)
Describe the protein content of breast milk, and how it differs from cows milk?
- It has a relatively low amount of protein, but with a high whey:casein ratio of 0.7
- It has twice as much lactalbumin as cows milk, but no lactoglobin
- There are high levels of amino acids such as taurine, aspartic acid, glutamic acid, and asparagine
What is a large amount of the nitrogen in breast milk derived from?
Non-protein sources
How does the absorption of fat in breast milk compare to cows milk?
It is better
Why is the absorption of fat better in breast milk compared to cows milk?
Due to smaller size of fat globules and lipase content
How does the fat content of breast milk compare to cows milk?
- Higher amount of unsaturated fatty acids
- Higher amount of vitamins A, C, E, and nicotinic acid
- Less of vitamins B and K
Is the renal solute load high or low in cows milk?
Low
How do the calcium and phosphate levels in breast milk compare to cows milk?
They are lower, but better absorbed
What are the maternal contraindications to breastfeeding?
- Severe acute illness, e.g. sepsis
- Breast abscess
- Chemotherapy
- Some mental health drugs, e.g. lithium
- Active TB
- HIV
What are the neonatal contraindications to breastfeeding?
- Metabolic conditions such as galactosaemia, phenylketonuria
- Lactose intolerance
In what condition might breastfeeding be difficult to establish?
Severe cleft lip/palate
What is the alternative option to breastfeeding?
Artificial, or formula feeding
What are the key differences between breastfeeding and formula feeding?
- High casein protein content and relatively low whey:casein ratio
- Low lactose content
- No immunological benefits
- Higher calcium, phosphate, and iron content, but less absorption and bioavailability
