7s: Paediatric Clinical Chemistry Flashcards
birthweight average and normal range
<1000g when are they usually born
2.5 - 4kg
average 3.3kg at 40 GA
<1000g babies likely to be born before 30 GA
Common problems in LBW babies
RDS
- common before 34 GA
- lack of surfactant in lungs
Retinopathy of prematurity (ROP)
- abnormal growth of blood vessels in the eye → vision loss
Intraventricular haemorrhage (IVH)
Patent ductus arteriosus (PDA)
Necrotising Enterocolitis (NEC)
- inflammation of bowel wall → necrosis and perforation
- sx = bloody stools, abdominal distension, intramural air
Why being born early is bad
The last trimester of pregnancy is very important for laying down stores (e.g. fat and glycogen) for birth
- When you are born too early, it is a huge shock to the system because you are not ready for it
Renal development in neonates
Nephrons start to develop week 6
Produce urine week 10
full complement from week 36
functional maturity of GFR not until 2 years old
Baby kidney anatomy: glomerulus, PCT, Loop of Henle/DCT
Glomerulus
Baby large SA:V (low GFR compared to surface area)
- slow excretion of solute load
- limited amount of Na+ available for H+ exchange (water into cell, acid out of cell)
PCT
Short PCT → lower resorptive capacity (usually adequate for small filtered load)
Reduced reabsorption → renal threshold for glycosuria much lower
- glycosuria appears at a lower plasma glucose level in neonate
- reabsorption of bicarbonate is also not as effective (→ neonates’ propensity to acidosis)
Loop of Henle/DCT
short → reduced concentration ability
- relatively unresponsive to aldosterone → persistent loss of Na
- reduced K excretion (upper limit 6 mmol/L)
summary of differences in neonatal kidneys (explains all of the sodium balance findings in neonates)
- low GFR for surface area → slow excretion
- short PCT → lower resorptive ability + reduced reabsorption of bicarbonate
- LoH and DCT short → reduced concentrating ability
- DCT unresponsive to aldosterone → persistent Na loss (and K retention)
ECF changes in utero vs birth
In utero babies have more ECF than adults
After birth, pulmonary resistance goes down → release of ANP (atrial natriuretic peptide potent vasodilator) → redistribution of the fluid
- All babies lose weight in the 1st week of life
- Roughly 40 ml/kg lost is normal in a term baby (higher (100 ml/kg) in a preterm baby)
- Babies can lose up to 10% of their birth weight in the first week of life and this is not a problem
Daily sodium and K requirements for healthy neonates
Na requirements higher in neonates born <30 weeks
- Plasma Na+ should be measured daily in neonates born <30 weeks
K+ should be given once UO of >1ml/kg/hr has been achieved
- aldosterone = increase K+ excretion, increase Na+ reabsorption
- _Alodserone insensitivity is normal in neonat_e → increased K+ (mild hyperkalaemia) and persistent Na losses
Babies have much higher requirements that adults, which is why they need to feed constantly
Causes of electrolyte disturbances
High insensible water loss
- High surface area
- High skin blood flow
- High metabolic/respiratory rate
- High transepidermal fluid loss (skin is not keratinised in premature infants)
Drugs:
- Bicarbonate (for acidosis) = Contains high sodium content
- Antibiotics = Contains high sodium content (sodium salts)
- Caffeine/theophylline (for apnoea) = Increases renal sodium loss
- Indomethacin (for PDA) = Causes oliguria
- Growth
Hypernatraemia
uncommon after 2 weeks of age → dehydration
if repeated hypernatraemia, consider rarer causes:
- salt poisoning
- osmoregulatory dysfunction
routine measurement of urea, creatinine and electrolytes and paired urine and plasma on a admission may differentiate the rare causes
Give an endocrine cause of hyponatraemia and explain what this is and it’s clinical features
Congenital Adrenal Hyperplasia
Most common cause is 21-OH deficiency → reduced cortisol/aldosterone → salt loss
lack of 21-OH → accumulation of 17-OH progesterone/pregnenolone → produces high levels of androgens
CLINICAL FEATURES:
- 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)
- growth acceleration
Give an endocrine cause of hyponatraemia and explain what this is and it’s clinical features
Congenital Adrenal Hyperplasia
Most common cause is 21-OH deficiency → reduced cortisol/aldosterone → salt loss
lack of 21-OH → accumulation of 17-OH progesterone/pregnenolone → produces high levels of androgens
CLINICAL FEATURES:
- 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)
- growth acceleration
Hb and BR
Hb decreases after birth as HbA is made
BR is lower in neonates
Reasons for neonatal hyperbilirbuinaemia (unconjugated)
- high levels of BR synthesis
- low rate of transport into the liver
- enhanced enterohepatic circulation
BR and the brain
- Free bilirubin crosses the BBB and can cause kernicterus (bilirubin encephalopathy)
Tx and BR thresholds
Causes of cBR
Biliary atresia (MOST COMMON; 1: 17,000)
- 20% are associated cardiac malformations, polysplenia, situs inversus
- Early surgery is essential (<6 months)
Choledochal cyst
Ascending cholangitis in TPN (Total Parenteral Nutrition)
- The lipids in the TPN seem to cause an ascending cholangitis
Inherited metabolic diseases:
- galactosaemia
- a1-anti-tryptase deficiency
- tyrosinaemia 1
- peroxisomal disease
Ca and PO
Ca falls after birth
PO higher in babies as good at reabsorbing PO
Ca and PO
Ca falls after birth
PO higher in babies as good at reabsorbing PO
Osteopenia of prematurity (fraying, splaying and cupping go long bones)
BIOCHEMISTRY:
- Ca NORMAL
- Phosphate <1 mmol/L
- ALP >1200 U/L (10 x adult ULN)
- Vit D (rarely measured)
Tx:
- PO/Ca supplements
- 1a-calcidiol
Rickets = osteopenia due to deficient activity of vit D
Presentation
- frontal bossing
- bowlegs/knock knees
- muscular hypotonia
- tetany/hypocalcaemic seizure
- hypocalcaemia cardiomyopathy
Genetic causes of rickets
- Pseudo-vitamin D deficiency I (defective renal hydroxylation)
- Pseudo-vitamin D deficiency II (receptor defect)
- Familial hypophosphataemia
- Low tubular maximum reabsorption of phosphate
- Raised urine phosphoethanolamine
- NOTE: top two conditions may be treated with 1,25-OH vitamin D
