ChemPath: Paediatric Clinical Chemistry Flashcards

1
Q

What is the average birthweight of male babies born at term?

A

3.3 kg

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2
Q

List some common problems in LBW babies.

A
  • Respiratory distress syndrome
  • Retinopathy of prematurity
  • Intraventricular haemorrhage
  • Patent ductus arteriosus
  • Necrotising enterocolitis
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3
Q

What is necrotising enterocolitis?

A
  • Inflammation of the bowel wall progressing to necrosis and perforation
  • Characterised by bloody stools, abdominal distension and intramural air (pneumatosis intestinalis)
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4
Q

In the developing fetus, when do:

  1. Nephrons develop
  2. Start producing urine
  3. Have fully competent nephrons
  4. Achieve functional maturity of glomerular function
A
  1. Nephrons develop = week 6
  2. Start producing urine = week 10
  3. Have fully competent nephrons = week 36
  4. Achieve functional maturity of glomerular function = 2 years
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5
Q

What are the implications of the large SA:V ratio of babies?

A
  • Low GFR for surface area
  • Results in slow excretion of solute load
  • Limited Na+ available for H+ exchange
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6
Q

List some key differences of the neonatal kdineys compared to adult kidneys and their implications.

A
  • Short proximal tubule so lower reabsorptive capability
  • Reduce reabsorption of bicarbonate leading to a propensity to acidosis
  • Loop of Henle and distal collecting ducts are short and juxtaglomerular leading to reduced concentrating ability (maximum urine osmolality of 700 mmol/kg)
  • Distal tubule is relatively unresponsive to aldosterone leading to persisten sodium loss and reduced potassium excretion (sodium loss of 1.8 mmol/kg/day, and upper limit of K+ of 6 mmol/L in neonates)
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7
Q

Why does glycosuria occur at a lower plasma glucose level in neonates?

A

Short proximal tubule means that they have a lower ability to reabsorb

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8
Q

Describe how body water content is different in neonates compared to adults.

A

Term neonates are 75% water compared to 60% in adults (and 85% in preterm infants)

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9
Q

What happens to the body water content in the first week of life?

A
  • Pulmonary resistance drops and you get release of ANP leading to redistribution of fluid
  • This can lead to up to 10% weight loss within the first week of life
  • Roughly 40 mL/kg loss in preterm infants
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10
Q

How are the daily fluid and electrolyte requirements different in neonates compared to adults?

A
  • Sodium, potassium and water requirements are higher

NOTE: sodium requirements are particularly high in preterm neonates (<30 weeks), so plasma Na+ should be measured daily in these patients. K+ supplements should be given once urine output > 1mL/kg/hr has been achieved

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11
Q

Why do babies have higher insensible water loss?

A
  • High surface area
  • Increased skin blood flow
  • High respiratory rate and metabolic rate
  • Increased transdermal fluid loss

NOTE: skin is not keratinised in premature infants

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12
Q

Drugs can cause electrolyte disturbances in neonates. Give examples of drugs that an do this and briefly describe the mechanism.

A
  • Bicarbonate for acidosis (contains high Na+)
  • Antibiotics (usually sodium salts)
  • Caffeine/theophylline (for apnoea) - increases renal Na+ loss
  • Indomethacin (for PDA) - causes oliguria

NOTE: growth can also cause electrolyte disturbance

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13
Q

What is hypernatraemia usually caused by in neonates?

A
  • Dehydration

NOTE: usually uncommon after 2 weeks

NOTE: food poisoning and osmoregulatory dysfunction are differentials

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14
Q

What is hyponatraemia usually caused by in neonates?

A

Congenital adrenal hyperplasia

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15
Q

Outline the pathophysiology of congenital adrenal hyperplasia.

A
  • Most commonly caused by 21-hydroxylase deficiency
  • Leads to reduced cortisol and aldosterone production and shunting of 17-OH progesterone and 17-OH pregnenelone which goes towards androgen synthesis
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16
Q

Outline the clinical features of congenital adrenal hyperplasia.

A
  • Hyponatraemia/hyperkalaemia
  • Hypoglycaemia
  • Ambiguous genitalia in female neonates
  • Growth acceleration
17
Q

List three reasons for neonatal hyperbilirubinaemia.

A
  • High level of bilirubin synthesis
  • Low rate of transport into the liver
  • Enhanced enterohepatic circulation
18
Q

How much bilirubin can 1 g/L of albumin bind?

A

10 µM/L

19
Q

How much albumin does the average term neonate have? How much bilirubin can this albumin bind?

A

34 g/L of albumin

340 µM/L of bilirubin

20
Q

What is the issue with free bilirubin?

A

It can cross the blood-brain barrier leading to kernicterus

21
Q

What are the three bilirubin thresholds in neonates?

A
  • No treatment
  • Phototherapy
  • Exchange transfusion
22
Q

List some causes of neonatal jaundice.

A
  • G6PD deficiency
  • haemolytic anaemia (ABO, rhesus)
  • Crigler-Najjar syndrome
23
Q

What is prolonged jaundice?

A

Jaundice that lasts >14 days in term babies or >21 days in preterm babies

24
Q

List some causes of prolonged jaundice.

A
  • Prenatal infection/sepsis
  • Hypothyroidism
  • Breast milk jaundice
25
Q

What level of conjugated hyperbilirubinaemia is considered pathological?

A

More than 20 µmol/L

26
Q

List some causes of conjugated hyperbilirubinaemia.

A
  • Biliary atresia (MOST COMMON)
  • Choledochal cyst
  • Ascending cholangitis in TPN
  • Inherited metabolic diseases (e.g. galactosaemia, alpha-1 antitrypsin deficiency, tyrosinaemia, peroxisomal disorders)

NOTE: 20% of biliary atresia is associated with cardiac malformations, polysplenia, situs inversus

27
Q

At what point during pregnancy is most calcium and phosphate laid down?

A

3rd trimester

28
Q

How are calcium and phosphate levels different in babies?

A
  • After birth, calcium levels will fall
  • Phosphate is higher in babies (they are good at reabsorbing it)
29
Q

List the main biochemical features of osteopaenia of prematurity.

A
  • Calcium is usually normal
  • Phosphate < 1 mmol/L
  • ALP > 1200 U/L (10 x adult ULN)
30
Q

How is osteopaenia of prematurity treated?

A
  • Phosphate/calcium supplements
  • 1-alpha calcidol
31
Q

List some presenting features of rickets.

A
  • Frontal bossing
  • Bowed legs
  • Muscular hypotonia
  • Tetany/hypocalcaemic seizure
  • Hypocalcaemic cardiomyopathy
32
Q

List some genetic causes of rickets.

A
  • Pseudo-vitamin D deficiency I (defective renal hydroxylation)
  • Pseudo-vitamin D deficiency II (receptor defect)
  • Familial hypophosphataemias (low tubular maximum reabsorption of phosphate, raised urine phosphoethanolamine)

NOTE: top two conditionsare treated with 1,25-OH vitamin D