What are the features of the paediatric cardiovascular system that differ from adults and what implications do these have?
Features
Implications
- Myocardium less contractile
- Ventricle is less compliant and less able to generate tension during contraction
- Limits size of and changes in stroke volume
- Cardiac output becomes rate dependent
- Bradycardia associated with reduced cardiac output and in the neonate external compression should be started if the rate is <60 bpm
- Myocardium less contractile
- Ventricle is less compliant and less able to generate tension during contraction
- Limits size of and changes in stroke volume
- More prone to developing low cardiac output ('cold') shock during sepsis
- Vagal parasympathetic tone is most dominant
- Sinus arrhythmia is common
- Prone to bradycardia with hypoxia, which should should be treated with oxygen and ventilation initially
- Vagal parasympathetic tone is most dominant
- Sinus arrhythmia is common
- Prone to bradycardia with hypoxia, which should should be treated with oxygen and ventilation initially
- Resting and maximal heart rate values decrease spontaneously with age
- Age dependent parameters should be targeted during resuscitation
- Cardiac output is 300-400 ml/kg/min at birth and decreases to 200 ml/kg/min within a few months
- Age dependent parameters should be targeted during resuscitation
- Ductus arteriosus contracts in the first few days of life and fibroses within 2-4 weeks
- Closure is pressure dependent with neonatal pulmonary vasculature reacting to the rise in PaO2 and pH and the fall in PaCO2 at birth
- Alterations in pressure and in response to hypoxia and acidosis can lead to reversion to the transitional circulation in the first few weeks after birthv
What are the features of the pediatric haematologcial system that differ from adults and what implications do these have?
Features
Implications
- Foetal haemoglobin (HbF) forms, 70-90% of the haemoglobin molecules at birthDrops to around 5% HbF by 3 months with HbA predominating
- Foetal haemoglobin contains less 2,3-DPG and combines more readily with oxygen
- Allows the foetus is able to retrieve oxygen from maternal blood
- Haemoglobin levels change rapidly with age:
- Newborn born with levels 180-200 g/L
- Levels drop over 3-6 months to 90-120 g/L
- Stabilises thereafter to at approximately 130 g/L
- Haemoglobin levels should be interpreted in an age dependent manner
- Development of the coagulation system not complete until about 6 months of age
- Vitamin K dependent factors are 70% of adult values at birth
- Vitamin K is given at birth to prevent haemorrhagic disease of the newborn
- Coagulation screening tests are prolonged in normal infants up to the age of 6 months, which is reflected in values for the normal ranges
- Total blood volume smaller in children than infants
- Relative blood volume per unit mass larger in the newborn and decreases with age
- Lower total blood volume leads to reduced tolerance for blood loss during surgery or trauma
- Transfusion is generally recommended when 15% of the circulating blood volume has been lost
- Higher relative blood volume required to support higher basal metabolic rate
- Affects pharmacokinetics of certain drugs