ChemPath - Paediatric Clinical chemistry Flashcards
What are the common problems in LBW babies
Respiratory distress syndrome (lack of surfactant in the lungs, common <34w)
Retinopathy of prematurity (An abnormal growth of blood vessels in the eye → vision loss )
Intraventricular haemorrhage
Patent ductus arteriosus
Necrotising enterocolitis
What is necrotising enterocolitis and how does it present
Inflammation of the bowel wall → necrosis and perforation
Symptoms = bloody stools, abdominal distension, intramural air
Describe the development of the kidney in infants and when is GFR maturity reached
Nephrons start to develop from week 6 → produce urine from week 10 → full complement from week 36
Functional maturity of GFR is not reached until 2 years of age
Describe the glomerulus in infants
Large surface area: volume ratio (relatively low GFR for their surface area) which leads to:
- Slow excretion of solute load
- Limited amount of Na+ available for H+ exchange - susceptible to acidosis
Describe the proximal convoluted tubule in infants
Short PCT: lower resorptive capability (but usually adequate due to a small load)
Reabsorption of bicarbonate is also not as effective (propensity to acidosis)
Renal threshold for glycosuria is much lower in neonates i.e. glycosuria appears at a lower plasma glucose level in neonates
Describe the loop of Henle and distal convoluted tubule in infants
The LoH/DCT are short - reduced concentration ability
Their DCT is relatively unresponsive to aldosterone (despite fully developed RAAS) → persistent loss of sodium + increased potassium retention
Describe fluid balance in infants
In utero = more ECF
After birth → pulmonary resistance decreases → ANP release → re-distribution
All babies can lose up to 10% in the first week of life due to fluid shifts
What is the difference in electrolyte requirements in infants vs adults
5x more fluid
3.5x more sodium (higher if <30 weeks)
2x more potassium
What are the causes of insensible (uncontrollable) water loss in infants
High surface area
High skin blood flow
High metabolic/respiratory rate
High transepidermal fluid loss (skin is not keratinised in premature infants)
Which drugs used in infants may lead to electrolyte disturbance
Bicarbonate - contains high sodium
Antibiotics - contains high sodium
Caffeine/theophylline - increases renal sodium loss
Indomethacin - oliguria
What are the causes of hypernatraemia in infants
More common in the first 2 weeks, if >2 weeks may be due to dehydration
Salt poisoning
Osmoregulatory dysfunction
What are the causes of hyponatraemia in infants
4-5 days: Excess total body water due to excessive intake, SIADH secondary to infection (pneumonia, meningitis) or IVH
After 4-5 days: Sodium loss due to immature tubular function in patients on diuresis
Factitious: Na is normal but appears low
Congenital adrenal hyperplasia
What is congenital adrenal hyperplasia
Most common cause is 21-hydroxylase (21-OH) deficiency → reduced cortisol / aldosterone → salt loss
+ accumulation of 17-OH progesterone and 17-OH pregnenolone → produce high levels of androgens
Identified on Gurthrie spot
What are the clinical features of congenital adrenal hyperplasia
Hyponatraemia/hyperkalaemia with volume depletion (lack of aldosterone) → salt-losing crisis
Hypoglycaemia (lack of cortisol)
Ambiguous genitalia in female neonates (not obvious in male neonates – present with salt-losing crisis)
Growth acceleration
What are the reasons for neonatal hyperbilirubinaemia in the first 10 days of life
High level of bilirubin synthesis (due to reduction in HbF)
Low rate of transport into the liver
Enhanced enterohepatic circulation
