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
