ChemPath: Paediatric Clinical Chemistry Flashcards
What is the average birthweight of male babies born at term?
3.3 kg
List some common problems in LBW babies (5).
- Respiratory distress syndrome
- Retinopathy of prematurity
- Intraventricular haemorrhage
- Patent ductus arteriosus
- Necrotising enterocolitis
What is necrotising enterocolitis?
- Inflammation of the bowel wall progressing to necrosis and perforation
- Characterised by bloody stools, abdominal distension and intramural air (pneumatosis intestinalis)
In the developing fetus, when do:
- Nephrons develop
- Start producing urine
- Have fully competent nephrons
- Achieve functional maturity of glomerular function
- Nephrons develop = week 6
- Start producing urine = week 10
- Have fully competent nephrons = week 36
- Achieve functional maturity of glomerular function = 2 years
What are the implications of the large SA:V ratio (kidney) of babies?
- Low GFR for surface area
- Results in slow excretion of solute load
- Limited Na+ available for H+ exchange -> hence susceptible to acidosis
List some key differences of the neonatal kidneys compared to adult kidneys and their implications (5).
- Glomerulus: large sa:v -> so low GFR meaning
slow excretion of solute load + less Na to exchange for H+ -> propensity for acidosis - PCT: is short so lower reabsorptive capability -> renal threshold for glycosuria is much lower in neonates, and reduce reabsorption of bicarbonate leading to a propensity to acidosis
- Loop of Henle & DCT: short -> to reduced concentrating ability (maximum urine osmolality of 700 mmol/kg) -> more dilute urine produced -> so meaning high water requirement + inc risk of dehydration
- DCT: relatively unresponsive to aldosterone -> persistent 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)
Why does glycosuria occur at a lower plasma glucose level in neonates?
Short proximal tubule means that they have a lower ability to reabsorb glucose
Describe how body water content is different in neonates compared to adults.
Term neonates are 75% water compared to 60% in adults (and 85% in preterm infants)
What happens to the body water content in the first week of life?
- 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 which is not a problem
- Roughly 40 mL/kg loss in preterm infants
How are the daily fluid and electrolyte requirements different in neonates compared to adults?
- 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
Why do babies have higher insensible water loss?
- High surface area
- Increased skin blood flow
- High respiratory rate and metabolic rate
- Increased transdermal fluid loss (since skin is not keratinised in premature infants hence is less good of a barrier)
Drugs can cause electrolyte disturbances in neonates. Give examples of drugs that an do this and briefly describe the mechanism.
- 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
What is hypernatraemia usually caused by in neonates?
- Dehydration
NOTE: usually uncommon after 2 weeks
NOTE: food poisoning and osmoregulatory dysfunction are differentials
Also consider drugs - bicarbonates, antibiotics
What is hyponatraemia usually caused by in neonates?
Congenital adrenal hyperplasia
Outline the pathophysiology of congenital adrenal hyperplasia.
- Most commonly caused by 21-hydroxylase deficiency
- Leads to reduced cortisol and aldosterone production
- Build up of 17-OH progesterone and 17-OH pregnenolone which goes towards androgen synthesis
Outline the clinical features of congenital adrenal hyperplasia.
- Hyponatraemia/hyperkalaemia
- Hypoglycaemia
- Ambiguous genitalia in female neonates
- Growth acceleration
Explain pathophysiology of neonatal unconjugated hyperbilirubinaemia & 3 three reasons for this
After birth, there is a switch from making fetal Hb (HbF) to adult Hb (HbA)
Hence excess RBC needs to be broken down, causing
1. increased synthesis of unconjugated bilirubin
- Low rate of transport of br into liver meaning Br builds up in circulation
- Enhanced enterohepatic circulation
Causes neonatal jaundice which is common in 1st 10 days of life
How much bilirubin can 1 g/L of albumin bind?
10 mM/L
How much albumin does the average term neonate have? How much bilirubin can this albumin bind?
34 g/L of albumin
340 mM/L of bilirubin
What is the issue with too much free bilirubin in neonates?
It can cross the blood-brain barrier leading to kernicterus (bilirubin encephalopathy)
What are the three management options for hyperbilirubinaemia in neonates and at what br threshold would they be indicated?
- No treatment
- Phototherapy (350 term, 120 premie)
- Exchange transfusion (450 terrm, 230 premie)
List some causes of neonatal jaundice.
- G6PD deficiency
- haemolytic anaemia (ABO, rhesus)
- Crigler-Najjar syndrome
What is prolonged jaundice?
Jaundice that lasts >14 days in term babies or >21 days in preterm babies
List some causes of prolonged jaundice.
- Prenatal infection/sepsis
- Hypothyroidism
- Breast milk jaundice
What level of conjugated hyperbilirubinaemia is considered pathological?
More than 20 µmol/L
List some causes of conjugated hyperbilirubinaemia (4).
- 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
At what point during pregnancy is most calcium and phosphate laid down?
3rd trimester
How are calcium and phosphate levels different in babies?
- After birth, calcium levels will fall
- Phosphate is higher in babies (they are good at reabsorbing it)
List the main biochemical features of osteopaenia of prematurity.
- Calcium is usually normal
- Phosphate < 1 mmol/L
- ALP > 1200 U/L (10 x adult ULN)
How is osteopaenia of prematurity treated?
- Phosphate/calcium supplements
- Alfacalcidol (vitamin D analogue)
List some presenting features of rickets.
- Frontal bossing
- Bowed legs
- Muscular hypotonia
Or present acutely with
* Tetany/hypocalcaemic seizure
* Hypocalcaemic cardiomyopathy
List some genetic causes of rickets.
- 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 conditions are treated with 1,25-OH vitamin D
What happens to bone structure in osteopenia of prematurity?
Fraying, splaying and cupping of bones
How should sodium/potassium balance be managed in pre-term infants (<30 weeks)?
Monitor plasma Na+ daily
Give K+ supplements once urine output 1ml/kg/hr has been achieved [this is the normal adult output]
