The sick child: recognising deterioration before it arrives
A child holds their blood pressure until the very end. That is what makes them dangerous.
Children are not small adults, and the difference that matters most in an emergency is physiological reserve. A child with significant fluid loss or sepsis maintains a normal blood pressure through vigorous tachycardia and peripheral vasoconstriction — often for hours, and often while looking deceptively stable. When that reserve is exhausted, deterioration is not gradual. Hypotension in a child is a pre-terminal sign.
The whole of paediatric emergency recognition follows from that. You do not look for a falling blood pressure; you look for the compensation — the heart rate, the peripheries, the capillary refill, the level of alertness — and you act while the numbers still look acceptable.
🩺 Where this lives: Diarrhoeal illness remains among the leading causes of death in children under five worldwide, and the treatment that prevents most of those deaths is a sachet of oral rehydration salts costing very little. ORS works because glucose-coupled sodium co-transport in the small bowel continues to function even when secretory diarrhoea is pouring fluid out — so giving glucose and salt together drags water back in. It is one of the highest-impact interventions in medicine, and it is frequently under-used in favour of intravenous fluid that a child who can drink does not need.
💡 A note on doses and volumes. This chapter gives none. Paediatric dosing is weight-based, fluid volumes are calculated per kilogram, and applying a remembered figure to the wrong child is precisely how these errors become fatal. Learn the principles and the recognition here; calculate every number from the child's weight and your local protocol.
Why children deteriorate the way they do
The second half of that figure inverts adult practice and is worth stating plainly: paediatric cardiac arrest is usually the end point of respiratory or circulatory failure, not a primary cardiac event. Hypoxia and hypovolaemia produce bradycardia, and bradycardia precedes arrest. So a bradycardic child is not a cardiology problem — it is an airway and breathing problem, and the response is oxygenation and ventilation, urgently.
The rapid assessment
LOOK BEFORE YOU TOUCH — the first impression
APPEARANCE Alert? Interacting? Consolable? Making
eye contact? A child who does not respond
normally to their parent is seriously ill.
BREATHING Work of breathing — recession, nasal
flaring, grunting, head bobbing, tracheal
tug. Noisy breathing tells you where the
obstruction is.
CIRCULATION Colour — pale, mottled, cyanosed.
Then the structured assessment:
AIRWAY patent, maintainable, or obstructed
BREATHING rate, effort, air entry, saturations.
A SILENT chest or a FALLING respiratory
rate in a tiring child is exhaustion, not
improvement — the same trap as the asthma
chapter.
CIRCULATION heart rate, capillary refill, peripheral
temperature, pulse volume, urine output.
Blood pressure last, and interpreted with
suspicion.
DISABILITY alertness, pupils, posture, and CHECK THE
GLUCOSE.
EXPOSURE temperature, rash — and look everywhere,
including the nappy area.
Fever and the febrile child
🔍 Sorting the well child from the sick one
Most fever is viraland self-limiting. The clinical task is not to identify every virus but to identify the small number of children who are seriously unwell, and to recognise those whose risk is higher.
Higher risk groupsInfants, particularly under three months, in whom signs are non-specific and deterioration is fast; the unimmunised; the immunosuppressed; and children with a prolonged or recurrent fever.
Red flagsA non-blanching rash, neck stiffness or a bulging fontanelle, a rapidly rising respiratory rate or grunting, prolonged capillary refill, reduced urine output, and any of the general danger signs above.
Meningococcal diseaseCan progress from mild illness to death within hours. A non-blanching rash in a febrile child is treated as meningococcal sepsis until proven otherwise — antibiotics immediately, before transfer and before investigations.
Common serious causesPneumonia, urinary tract infection (frequently missed because it has no localising signs in infants), meningitis, and — in endemic areas — malaria, dengue and enteric fever from the tropical infections chapter.
Safety-nettingMost children go home. What makes that safe is telling the parent specifically what would mean returning, and when.
💡 Exam angle: a febrile infant under three months is treated far more cautiously than an older child, because the signs of serious bacterial infection are non-specific — poor feeding, irritability or lethargy may be all there is — and progression is rapid. Questions frequently offer "reassure and review" for a young infant with fever; the safe answer involves investigation and a low threshold for admission and antibiotics.
Diarrhoea and dehydration
WHY ORS WORKS, AND WHY ZINC IS GIVEN
In secretory diarrhoea the gut is pouring out fluid, but
the GLUCOSE-COUPLED SODIUM co-transporter in the small
intestine keeps working. Giving glucose and sodium
together drives sodium absorption, and water follows.
That is why ORS must contain BOTH — plain water does not
work, and sugary drinks alone can worsen the diarrhoea
osmotically.
ZINC reduces the duration and severity of the episode and
the likelihood of further episodes over the following
months. It is given alongside ORS.
CONTINUE FEEDING throughout, including breastfeeding.
Withholding food prolongs recovery and worsens nutrition.
ANTIBIOTICS are NOT routine — most acute diarrhoea is
viral. They are reserved for specific indications such as
dysentery or cholera per local guidance.
ANTIMOTILITY drugs are NOT given to young children.
The commonest error in childhood diarrhoea is reaching for a drip when the child can still drink. Intravenous fluid is for the child who is severely dehydrated, shocked, or unable to take oral fluid — everyone else does better with ORS, and a cannula carries its own risks. The judgement is made from the four signs in the figure, not from a laboratory result.
Fluids, glucose and prescribing
💡 Exam angle: hypotonic maintenance fluid causing hyponatraemia has caused deaths in children and appears in safety-oriented questions. Sick children have high antidiuretic hormone activity, so free water is retained; giving hypotonic fluid then drops the sodium, and rapid hyponatraemia causes cerebral oedema. Isotonic maintenance fluid with sodium monitoring is the safe practice. This is a genuine "the routine prescription was the harm" scenario.
Clinical reasoning: four presentations
🔍 Case 1 — the normal blood pressure
PresentationA 3-year-old with two days of diarrhoea is brought in. Heart rate 168, capillary refill 4 seconds, cool hands, lethargic and not interested in drinking. Blood pressure is recorded as normal for age.
TrapThe normal blood pressure reading as stability.
ReasoningMarked tachycardia, delayed capillary refill, cool peripheries and lethargy are compensated shock. A child maintains blood pressure until compensation fails — so a normal reading here means the crash has not happened yet, not that it will not.
AnswerTreat as severe dehydration with shock: urgent intravenous access, weight-based fluid resuscitation per protocol, check the glucose, and reassess frequently. Do not wait for hypotension.
🔍 Case 2 — the rash
PresentationA 4-year-old has had fever for eight hours and now has a few small purple spots on the legs that do not blanch under a glass. He is irritable but talking. Observations show tachycardia.
Key clueA non-blanching rash with fever.
ReasoningMeningococcal disease can progress from this appearance to death within hours. Waiting for the child to look sicker, or for a lumbar puncture, wastes the time in which treatment works.
AnswerImmediate parenteral antibiotics without waiting for investigations or transfer, alongside resuscitation and urgent senior involvement. A non-blanching rash in a febrile child is meningococcal sepsis until proven otherwise.
🔍 Case 3 — the cannula that was not needed
PresentationA 2-year-old with diarrhoea for one day is alert and irritable, has slightly sunken eyes, is drinking eagerly, and has a skin pinch that returns slowly. The team proposes admission for intravenous fluids.
Key cluesAlert, thirsty and drinking — this is some dehydration, not severe.
ReasoningA child who can and will drink should receive oral rehydration. It is at least as effective for this level of dehydration, avoids the risks of cannulation, and can be supervised without a bed.
AnswerSupervised oral rehydration with ORS, plus zinc, continued feeding, and reassessment. Reserve intravenous fluid for severe dehydration, shock, or an inability to drink.
🔍 Case 4 — the slowing heart
PresentationAn 18-month-old with bronchiolitis has been working hard to breathe for hours. He is now quieter, with less recession, and his heart rate has fallen from 180 to 90. The nurse reports he "seems to have settled".
TrapReduced effort and a falling heart rate read as improvement.
ReasoningA tiring child stops working. Reduced respiratory effort with a falling heart rate in a previously distressed infant is exhaustion progressing toward respiratory arrest — and in children, bradycardia is driven by hypoxia.
AnswerTreat as impending respiratory arrest: oxygen, airway support and ventilation as needed, with immediate senior and critical care involvement. The apparent settling is the emergency.
Commonly confused
Confusion
The distinction
Why it matters
Normal BP vs stable child
Children hold pressure until compensation fails
Hypotension is pre-terminal, not an early warning.
Bradycardia in a child vs an adult
In children it usually means hypoxia
Treat the airway and breathing, not the rhythm.
Quieter child vs improving child
Reduced effort may be exhaustion
The apparent settling can precede arrest.
Some vs severe dehydration
Alert and drinking versus lethargic and unable
Decides oral versus intravenous rehydration.
ORS vs plain water or sugary drinks
ORS needs glucose AND sodium together
Water alone does not drive absorption.
Fever in an infant vs an older child
Under three months, signs are non-specific
Far lower threshold for investigation and admission.
Hypotonic vs isotonic maintenance fluid
Hypotonic fluid causes hyponatraemia
A routine prescription that has killed children.
Rapid revision
MUST-KNOW FACTS
1. Children compensate well and decompensate abruptly.
2. TACHYCARDIA is early; HYPOTENSION is PRE-TERMINAL.
3. Paediatric arrest is usually respiratory or circulatory in origin.
4. BRADYCARDIA in a sick child means hypoxia — treat airway and breathing.
5. Assess appearance, work of breathing and circulation before touching.
6. General danger signs: unable to drink or feed, vomits everything,
convulsions, lethargic or unconscious.
7. A parent saying the child is "not themselves" is reporting data.
8. Check the GLUCOSE in every sick child — stores are small.
9. Everything is weight-based; a dose without a weight is a guess.
10. Hypotonic maintenance fluid causes HYPONATRAEMIA — use isotonic.
11. Dehydration is graded on condition, eyes, drinking and skin pinch.
12. Alert and thirsty = some dehydration → ORS.
13. Lethargic and unable to drink = severe → intravenous fluid.
14. ORS works via glucose-coupled sodium co-transport.
15. Plain water and sugary drinks do not substitute for ORS.
16. ZINC reduces duration and recurrence of diarrhoea.
17. CONTINUE FEEDING, including breastfeeding, throughout.
18. Antibiotics are not routine in acute childhood diarrhoea.
19. Antimotility drugs are not given to young children.
20. Most fever is viral — the task is finding the seriously ill minority.
21. Fever under 3 months warrants a much lower threshold for investigation.
22. NON-BLANCHING RASH with fever = meningococcal sepsis until proven otherwise.
23. Give antibiotics immediately in suspected meningococcal disease.
24. Urinary infection in infants has no localising signs — test the urine.
25. A silent chest or falling respiratory rate in a tiring child is exhaustion.
26. Safety-net explicitly: tell the parent what would mean coming back.
💡 Exam angle: the reliable threads are (a) the normal blood pressure in a shocked child, (b) bradycardia meaning hypoxia, (c) the quieter child who is actually tiring, (d) oral rehydration where the child can drink, and (e) immediate antibiotics for a non-blanching rash. Paediatrics runs the same pattern as the rest of this stream, only faster: the reassuring sign is the dangerous one, and the margin for delay is narrower.
Syllabus points
Why children compensate then decompensate abruptly
Bradycardia as a sign of hypoxia
The rapid assessment: appearance, breathing, circulation
General danger signs
The febrile child and higher-risk groups
Non-blanching rash and meningococcal disease
Assessing dehydration from four signs
Oral rehydration salts and how they work
Zinc, continued feeding and what not to give
Weight-based prescribing and checking glucose
Maintenance fluid and the hyponatraemia risk
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