Paediatric Biochemistry Flashcards
Why is paediatric biochemistry important?
Especially in premature babies, their biochemistry is significantly different to adults and must be mitigated for.
Why is low birth weight important?
It is the leading cause of infant mortality, with over 2/3rd of deaths caused by a low birth weight.
What is the average birth weight of a male infant at 40 weeks?
3.3 kg
What are the common problems in infants at a low birth weight?
Respiratory distress syndrome - Associated retinopathy of prematurity (a low oxygen) Intraventricular haemorrhage Patent ductus arteriosus Necrotising enterocolitis
What is necrotising enterocolitis
An inflammation of the bowel wall, more common in premature babies. It causes necrosis and perforation of the bowel wall, presenting with abdominal distension, bloody stool and intramural air on AXR
Describe the renal function of infants.
The kidneys begin to develop at 6 weeks gestation, begin to produce urine at 10 weeks, and have a full complement of nephrons at 36 weeks.
Full glomerular filtration rates are not reached until 2 years of age.
They have a short proximal tubule, causing a lower reabsorption rate, but this is usually adequate for the small filtered load (low GFR). They have a lower threshold for glycosuria, beginning at a BG of 7, the adult threshold is a BG of 10)
They have short, shallow loops of Henle, causing a reduced concentrating ability. Infants have a maximum urine osmolality of 700mmol/kg, adults can go up to 1500)
They have less aldosterone-sensitive distal tubules so have a persistent sodium loss.
What is the persistent sodium loss in infants?
1.8mmol/kg/day, caused by the distal tubules being less sensitive to aldosterone
Why is there high water loss in infants?
They have a higher surface area to boy weight ratio
Their skin blood flow is increased
They have a higher metabolic/respiratory rate than adults
They have increased trans epidermal fluid loss
What weight loss is normal in the first week of life? Why does this happen?
Up to a 10% loss of weight is normal. This is due to ANP redistributing fluid in the child.
How should electrolyte supplementation be controlled in infants?
Beware of giving potassium before a urine output is established; this is to avoid hyperkalaemia.
Sodium poising can also occur to drugs (bicarbonate (to control acidosis), antibiotics)
How do you check for sodium poisoning in infants?
Take a urea, creatinine and electrolytes in paired urine and plasma. Do this regularly.
What can cause a hyponatraemia in infants?
This is rare, and can be caused by congenital adrenal hyperplasia, causing a reduced aldosterone and a reduced cortisol.
This may also cause an increase in androgens, causing ambiguous genitalia in female babies.
It can also be caused by administering caffeine/theophylline for premature babies to assist with apnoea.
Is hypernatraemia in infants common?
Yes, especially in infants in the first two weeks of life. But beware of alternative causes such as dehydration, drugs and milk formula.
It can also be caused by intraventricular haemorrhage, or administering sodium bicarbonate when treating acidosis.
Why is hyperbilirubinaemia common in infants?
They instantly reduce their levels of foetal haemoglobin and begin to produce adult haemoglobin. There is an increased hepatic circulation, and this causes an unconjugated hyperbilirubinaemia.
What are the normal levels of albumin and bilirubin in infants?
The infant is born with 34g/L of albumin, each gram being able to carry 10 micrograms of bilirubin, giving a normal bilirubin of 340 micrograms/L.
