Paediatric Intensive Care: Developmental Physiology and Age-Specific Pitfalls
Core concepts
Paediatric intensive care rests on developmental physiology. Infants have higher metabolic and oxygen consumption rates, limited physiological reserve, and a compliant chest wall with horizontal ribs, predisposing to early fatigue and apnoea. Cardiac output is rate-dependent because stroke volume is relatively fixed; bradycardia is therefore a pre-arrest rhythm. Weight-based calculations must be second nature: 4-2-1 rule for maintenance fluids, 10 mL/kg fluid boluses, and drug doses per kilogram with maximum adult caps.
Understand the paediatric airway: large occiput, relatively large tongue, anterior and cephalad larynx, short trachea, and narrowest point historically described at the cricoid. Recognise the different aetiology of shock in children, where compensated shock with tachycardia and prolonged capillary refill may precede hypotension, which is a late and ominous sign.
Be familiar with bronchiolitis, croup, asthma, diabetic ketoacidosis and its cerebral oedema risk, status epilepticus, sepsis, and congenital heart disease with duct-dependent circulation. Understand the difference between cyanotic and acyanotic lesions and the principles of prostaglandin therapy.
Traps in questions
- Accepting a normal blood pressure as excluding shock in a child; hypotension is a late finding.
- Using adult fluid bolus volumes or adult drug doses without weight adjustment.
- Forgetting that children compensate respiratory acidosis well until sudden decompensation occurs.
- Missing hypoglycaemia or hypocalcaemia in the collapsed neonate.
- Overlooking non-accidental injury patterns in inconsistent histories.
Worked example
A 12 kg child needs maintenance fluid. Using 4-2-1: 4 mL/kg for the first 10 kg (40), plus 2 mL/kg for the next 2 kg (4), giving 44 mL/hour. Rule of thumb: in paediatric resuscitation, reassess after each 10 mL/kg bolus and look for hepatomegaly, new crackles or worsening work of breathing before giving more.