Paediatric critical illness is uncommon enough in most UK Emergency Departments that it can catch trainees off-guard, yet it is tested reliably in the FRCEM SBA exam precisely because its consequences of mismanagement are catastrophic and preventable. Unlike adult cardiac arrest, which is predominantly of primary cardiac aetiology, paediatric arrest is almost always the endpoint of a period of respiratory or circulatory deterioration that a competent clinician should identify and interrupt. Understanding this distinction, and mastering the structured approach that follows from it, is both sound clinical practice and essential preparation for FRCEM SBA paediatric revision.
Key Points: Seriously Ill Child in the ED
- The vast majority of paediatric cardiac arrests are secondary to respiratory failure or shock, not primary cardiac events. Early recognition and intervention saves lives.
- Use the Paediatric Assessment Triangle (PAT) for rapid across-the-room assessment: appearance, work of breathing, and circulation to skin.
- NICE NG51 (Sepsis) and the RCPCH Sepsis Toolkit define high-risk features in children; fever with any high-risk feature mandates immediate action.
- Fluid resuscitation in paediatric septic shock uses 10 ml/kg IV/IO 0.9% sodium chloride boluses, reassessing after each, with a ceiling of 40 ml/kg before escalating to vasopressors.
- APLS weight estimation: use a length-based tool (Broselow tape) or the formula (age + 4) x 2 for children aged 1 to 10 years.
- Escalate early: PICU referral, paediatric surgical input, and activation of the paediatric major haemorrhage protocol should never be delayed by a desire to manage without help.
Epidemiology and Clinical Context
Paediatric critical illness in the UK Emergency Department spans neonates through to adolescents, and the differential diagnosis shifts substantially with age. In neonates, duct-dependent congenital heart disease, early-onset sepsis from Group B Streptococcus or E. coli, and inborn errors of metabolism are the dominant concerns. In infants aged one to twelve months, bronchiolitis, meningitis, intussusception, and non-accidental injury (NAI) rise to prominence. Toddlers and pre-school children present with croup, febrile convulsions, meningococcal disease and foreign body aspiration. School-age children develop acute asthma, diabetic ketoacidosis (DKA), anaphylaxis and appendicitis. In adolescents, DKA, asthma, deliberate self-harm, and trauma dominate.
Approximately one in five children attending a UK ED with fever has a serious bacterial infection, and paediatric sepsis carries significant mortality when treatment is delayed beyond the first hour. The CEMACH and NCEPOD reports have repeatedly identified failure to recognise and respond to signs of deterioration as a preventable cause of paediatric death. The Royal College of Paediatrics and Child Health and NICE (NG51) have codified high-risk features to support earlier recognition.
Pathophysiology: Why Children Deteriorate Differently
Children are not small adults, and nowhere is this more consequential than in critical illness. Several physiological characteristics define how they respond to respiratory and circulatory stress.
Respiratory reserve is limited. The chest wall is highly compliant, the airways are proportionally narrower (resistance rises with the fourth power of radius reduction), and the diaphragm is the primary muscle of respiration. Increased work of breathing fatigues the diaphragm rapidly. A child with moderate croup or bronchiolitis can maintain adequate gas exchange for a period through compensatory tachypnoea and accessory muscle use, but fatigue precipitates sudden decompensation with little warning. Clinicians must recognise the signs of impending respiratory failure before the child tires.
Cardiovascular compensation is initially vigorous but brittle. Children maintain cardiac output primarily through heart rate rather than stroke volume. In early shock, sympathetically mediated tachycardia and peripheral vasoconstriction maintain blood pressure remarkably well, so hypotension is a very late sign of haemodynamic compromise in children. By the time a child is hypotensive, they may have lost 25 to 40 percent of their circulating blood volume. A persistently tachycardic child with poor perfusion and an altered mental state is in shock regardless of the systolic blood pressure reading.
Metabolic vulnerability is high. The brain-to-body mass ratio is larger in children, glucose stores are smaller, and the metabolic rate per kilogram is higher. Hypoglycaemia complicates a wide range of paediatric illnesses including sepsis, adrenal insufficiency, and prolonged seizures, and must be excluded actively in every seriously ill child.
Structured ED Assessment: ABCDE and the Paediatric Assessment Triangle
The Paediatric Assessment Triangle
The Paediatric Assessment Triangle (PAT), endorsed by APLS and widely incorporated into UK paediatric emergency curricula, allows a structured across-the-room first impression within thirty seconds. It comprises three domains:
- Appearance: tone, interactivity, consolability, gaze, and speech or cry. An abnormal appearance (floppiness, poor eye contact, inconsolable crying, or silence) is a red flag.
- Work of breathing: abnormal sounds (stridor, wheeze, grunting), abnormal positioning (tripoding, sniffing position), retractions, and nasal flaring.
- Circulation to skin: pallor, mottling, cyanosis, and prolonged capillary refill time (greater than two seconds centrally).
The combination of PAT findings directs the clinician toward a physiological category (respiratory distress, respiratory failure, compensated shock, decompensated shock, ALTE/BRUE-type presentation, or combined cardiopulmonary failure) before the hands-on ABCDE assessment begins.
ABCDE Resuscitation Approach
Airway: In a child with reduced consciousness (AVPU score of P or U), positioning (neutral in infants, sniffing in older children), a chin-lift or jaw-thrust, and suction are first-line. Oropharyngeal airways are sized from the centre of the mouth to the angle of the jaw. Nasopharyngeal airways are better tolerated in the semi-conscious child. Definitive airway management with rapid sequence intubation should be performed by the most experienced clinician available, using APLS weight-based drug doses.
Breathing: High-flow oxygen via a non-rebreathe mask in all seriously ill children. For bronchospasm, salbutamol (2.5 mg if under 5 years, 5 mg if 5 years or older) via nebuliser and ipratropium bromide should be given together in the first hour of acute severe asthma, following British Thoracic Society guidance. Capnography and pulse oximetry are continuous monitoring standards. Blood gas sampling (capillary, venous, or arterial depending on clinical urgency) provides pH, pCO2, pO2, lactate, glucose and electrolytes.
Circulation: Obtain IV access rapidly; if two peripheral attempts fail, proceed immediately to intraosseous (IO) access. In the UK, the EZ-IO device is the standard IO tool. Fluid boluses of 10 ml/kg 0.9% sodium chloride are given over 10 to 15 minutes and reassessed after each. Current APLS and NICE guidance recommends not exceeding 40 ml/kg in septic shock without vasopressor initiation and PICU involvement. Blood glucose must be checked immediately; hypoglycaemia (below 3 mmol/L) is treated with 2 ml/kg of 10% dextrose IV. Packed red cells at 10 to 15 ml/kg are used in haemorrhagic shock, with early activation of the paediatric major haemorrhage protocol for massive haemorrhage.
Disability: Use the AVPU scale and pupillary responses. Calculate GCS in children old enough to cooperate with the verbal component (modified paediatric GCS for younger children). Hypoglycaemia, hyponatraemia, and non-convulsive status epilepticus must be excluded in any child with altered consciousness.
Exposure: Full exposure to identify rashes (petechiae or purpura raise urgent concern for meningococcal disease), signs of NAI (bruising in non-mobile infants, unusual distribution of injuries), and temperature. Core temperature measurement is mandatory.
Key Investigations
Bedside investigations in the seriously ill child should not delay resuscitation but should run in parallel. Essential investigations include blood gas (venous or arterial), glucose (point-of-care), lactate, full blood count, blood cultures before antibiotics, CRP, urea and electrolytes, coagulation screen, and a 12-lead ECG in any child with haemodynamic instability or arrhythmia. Urine should be collected for urinalysis and microscopy. Lumbar puncture is deferred until haemodynamic stability is established and coagulopathy excluded; do not withhold antibiotics while awaiting LP.
Specific High-Yield Scenarios for FRCEM SBA Paediatric Revision
Paediatric Sepsis
NICE NG51 defines high-risk features in children with suspected sepsis including temperature above 38.5 degrees, heart rate more than two standard deviations above the normal for age, altered mental state, non-blanching rash, and signs of poor perfusion. Any high-risk feature triggers immediate action: IV/IO access, blood cultures, IV antibiotics within one hour, and senior review. Cefotaxime or ceftriaxone are first-line for suspected bacterial meningitis or meningococcal disease; piperacillin-tazobactam or co-amoxiclav plus gentamicin for undifferentiated sepsis, according to local protocol.
Duct-Dependent Congenital Heart Disease
The neonate who collapses at home in the first two weeks of life and arrives profoundly shocked must raise the suspicion of a duct-dependent lesion (coarctation of the aorta, critical aortic stenosis, hypoplastic left heart). Prostaglandin E1 (alprostadil) infusion, started at 5 to 10 nanograms/kg/minute, maintains ductal patency and can be dramatically life-saving. This diagnosis should be on every ED clinician’s mental model for the collapsed neonate.
Anaphylaxis
Paediatric anaphylaxis is managed according to Resuscitation Council UK guidelines. Intramuscular adrenaline is the cornerstone: 0.15 mg (0.15 ml of 1:1000) for children aged 6 to 12 years and 0.3 mg for those over 12 years, given into the anterolateral thigh. For children under 6 years, 0.15 mg is appropriate. Candidates preparing for FRCEM SBA paediatric revision should note that adrenaline dosing and the route of administration are high-frequency SBA topics. Related content on anaphylaxis, anaphylactoid reactions, urticaria, acute allergy, angioedema, and hereditary angioedema is covered in dedicated lessons within the MRCEM Single Best Answer revision course at EM Learning Centre.
How the FRCEM SBA Exam Tests This Topic
FRCEM SBA paediatric revision questions are mapped to the RCEM Curriculum, which requires competency in the recognition and initial management of life-threatening conditions across all age groups. Questions in this domain typically present with a clinical vignette describing a child with a combination of physiological parameters and ask the candidate to identify the correct immediate management step, the most likely diagnosis, or the appropriate investigation or escalation threshold.
Common question stems include: identification of the correct fluid bolus volume and rate; the appropriate next step when two peripheral IV attempts have failed; recognition of duct-dependent cardiac disease in a collapsed neonate; the correct adrenaline dose for anaphylaxis by weight; and identification of NICE high-risk sepsis features. The exam rewards candidates who apply a structured framework rather than those who rely on pattern recognition alone. Notably, the exam frequently tests the distinction between compensated and decompensated shock, which requires understanding that hypotension is a late sign in children.
Pitfalls in this topic account for a disproportionate loss of marks: candidates who select a fluid bolus of 20 ml/kg (acceptable in adults, not current APLS paediatric guidance), who delay IO access excessively, or who fail to recognise that a normotensive but tachycardic child with prolonged capillary refill time is in shock, all lose marks. The RCEM curriculum also expects candidates to understand escalation pathways including PICU referral criteria and the paediatric major haemorrhage protocol.
Revision Pearls: High-Yield Facts
- Cardiac arrest in children is almost always preceded by respiratory failure or circulatory shock; the arrest itself is largely preventable with timely intervention.
- Normal blood pressure does not exclude shock in a child. Tachycardia, prolonged capillary refill time, cool peripheries and altered mental state together constitute shock.
- Weight estimation: use a length-based tape (Broselow) or the APLS formula (age + 4) x 2 for children aged 1 to 10 years.
- IO access is not a last resort; it is the standard second-line access when peripheral cannulation fails after two attempts, and drugs given IO reach the central circulation in comparable time to IV.
- In the collapsed neonate, always consider prostaglandin E1 infusion for duct-dependent congenital heart disease until proven otherwise.
- Glucose must be checked actively in every seriously ill child; hypoglycaemia is common across diverse aetiologies and is rapidly correctable.
- Antibiotics in suspected sepsis must not be delayed by the need to perform lumbar puncture; treat first, investigate when stable.
- Petechiae in a febrile child with haemodynamic compromise is meningococcal disease until proven otherwise; do not wait for laboratory confirmation before giving parenteral benzylpenicillin or cefotaxime.
Common Pitfalls: Where Candidates Lose Marks
- Selecting 20 ml/kg as the initial fluid bolus: current APLS guidance uses 10 ml/kg aliquots with reassessment after each.
- Delaying IO access beyond two failed peripheral attempts.
- Reassured by normal blood pressure in a tachycardic, poorly perfused child.
- Omitting glucose measurement as an early bedside investigation.
- Delaying antibiotics while awaiting lumbar puncture in a child with suspected bacterial meningitis.
- Failing to consider duct-dependent congenital heart disease in a collapsed neonate presenting in the first two weeks of life.
- Incorrect adrenaline dose or route in paediatric anaphylaxis (IV instead of IM as first-line).
How EM Learning Centre Supports Your MRCEM Single Best Answer Revision
Paediatric emergency medicine is a high-stakes component of FRCEM SBA paediatric revision, and it rewards structured, systematic preparation. The EM Learning Centre provides a comprehensive suite of resources designed specifically for trainees preparing for the MRCEM and FRCEM SBA exams. Our question bank includes clinically realistic, examiner-quality SBA questions mapped to the RCEM curriculum, with detailed explanations that go beyond simply identifying the correct answer, explaining the underlying clinical reasoning and the evidence base.
Lessons covering acute allergy, anaphylactoid reactions, angioedema, hereditary angioedema, and urticaria sit within the platform and complement the paediatric critical illness content, ensuring that candidates are prepared for the full range of acute paediatric presentations they will encounter in the exam and in clinical practice. Visit the EM Learning Centre homepage to explore the full course library and begin your structured FRCEM SBA exam preparation today.
References
- National Institute for Health and Care Excellence. Sepsis: recognition, diagnosis and early management (NG51). NICE (nice.org.uk).
- Resuscitation Council UK. Paediatric Advanced Life Support Guidelines. Resuscitation Council UK (resus.org.uk).
- Royal College of Paediatrics and Child Health. Sepsis Toolkit and Paediatric Early Warning Systems. RCPCH (rcpch.ac.uk).
- British Thoracic Society. BTS/SIGN British Guideline on the Management of Asthma. British Thoracic Society (brit-thoracic.org.uk).
- Royal College of Emergency Medicine. RCEM Curriculum and Paediatric Emergency Medicine Standards. RCEM (rcem.ac.uk).
- National Institute for Health and Care Excellence. Fever in under 5s: assessment and initial management (NG143). NICE (nice.org.uk).
