Loading...
Please wait while the page loadsChildren's Nursing · Respiratory
How breathing works, where oxygen exchange happens, what to check at the bedside, and which signs mean a child needs help sooner rather than later.
Save for later
Airway order
Never Phone Liam To Buy Brownies Always — Nose, Pharynx, Larynx, Trachea, Bronchi, Bronchioles, Alveoli.
Golden rule
Better numbers but worse child = worse child. Always trust what the child looks like over what the monitor says.
Efficiency: TSB
Gas exchange works because the barrier is Thin, the Surface area is huge, and the Blood supply is dense.
Cell types
1 is Thin (Type I for gas exchange). 2 is Goo (Type II makes surfactant).
Where does air travel and where does oxygen actually swap into the blood?
Conducting zone
Respiratory zone
Alveolar detail
Cell types
Red flags
Fick's Law of Diffusion
Rate ∝ Surface area × Pressure gradient ÷ Membrane thickness
Gas exchange is faster when the surface area is large, the pressure difference is steep, and the membrane is thin. Disease processes that reduce surface area (e.g. collapse), thicken the membrane (e.g. pneumonia), or lower the gradient all impair gas exchange.
Exam Tip
“Gas exchange occurs by passive diffusion down a partial pressure gradient across the respiratory membrane.”
Clinical pearl
This is why tiny swollen airways matter so much in children. If a 4 mm airway swells by 1 mm, you lose about 75% of the space inside it. In practice, that means a small amount of oedema in an infant can cause a very big breathing problem very quickly.
What structures protect the lungs and how does the body keep the airways clean?
Right vs left lung
Pleura
Defence mechanisms
Immune defences
Clinical pearl
As children get older, they gradually develop more tiny side routes for air movement. These connections can help air bypass a blocked area a little, which is one reason very young children can struggle faster when small airways are full of mucus or swelling.
What drives air in and out, and what do the lung volume terms mean?
Inspiration
Expiration
Breathing control
Lining changes
Boyle's Law
P₁V₁ = P₂V₂ — Pressure and volume are inversely related
When the thoracic cavity expands during inspiration, pressure inside the chest drops below atmospheric pressure, and air rushes in. During expiration, the cavity shrinks, pressure rises, and air is pushed out.
Poiseuille's Law
Resistance ∝ 1 ÷ radius⁴
Airway resistance is inversely proportional to the fourth power of the radius. This is why a small reduction in airway diameter (e.g. 1mm of mucosal swelling in an infant) causes a massive increase in resistance and work of breathing.
Inspiration
Expiration
Clinical pearl
Boyle’s law in plain terms: bigger chest space means lower pressure, so air gets pulled in. Smaller chest space means higher pressure, so air moves back out. That is the basic pressure rule behind normal breathing.
How does oxygen travel in the blood and what goes wrong when it cannot?
O₂ transport
CO₂ transport
V/Q matching
Gas exchange efficiency: TSB
Red flags
Low V/Q (Shunt)
High V/Q (Dead Space)
Exam Tip
“In bronchiolitis, inflammation, oedema, and mucus narrow the bronchioles, reducing ventilation and causing a low V/Q mismatch.”
Clinical pearl
O₂-Hb curve in plain English: a right shift means haemoglobin lets go of oxygen more easily, which helps tissues pick it up. A left shift means oxygen is held more tightly, as happens in the lungs and in foetal haemoglobin.
Why can respiratory illness turn faster in children?
Airway structure
Chest and breathing
Reserve and demand
Muscle and immunity
Why This Matters
Infants are more vulnerable to respiratory compromise because they have narrower airways, higher oxygen demand per kilogram, and less physiological reserve. A 4 mm airway with 1 mm of swelling loses roughly 75% of its cross-sectional area.
Exam Tip
“Infants are more vulnerable to respiratory compromise because they have narrower airways, higher oxygen demand, and less physiological reserve.”
Clinical pearl
The airway’s normal cleaning system works less well with smoking exposure, dehydration, general anaesthesia, and cold dry air. When that clearance slows down, mucus sits around more easily and infection risk goes up.
What should you check, which signs matter most, and what are the key conditions?
Start from the end of the bed
Work of breathing signs
Distress vs failure
Upper vs lower airway
Red flags
Common Mistake
Do not rely on SpO₂ alone. A child can maintain saturations while their work of breathing steadily increases. By the time saturations drop, the child may be close to exhaustion. Always assess the whole picture: effort, colour, behaviour, feeding, and trend.
Clinical pearl
A full respiratory assessment is not just "count the rate and check the sats". It is how the child looks, how hard they are working, how well they are feeding or talking, what their colour is doing, what their circulation looks like, and whether the trend is improving or drifting the wrong way.
| Structure | Key features | Main job |
|---|---|---|
| Nose | Tiny hairs, mucus lining, ridges (turbinates), rich blood supply | Warms, moistens, and filters breathed-in air |
| Pharynx | Back of the throat split into three sections | Shared passage for food and air; the epiglottis helps stop food going into the airway |
| Larynx | Voice box with vocal cords, epiglottis, and supporting cartilage | Makes sound and helps protect the lower airway during swallowing |
| Trachea | Cartilage rings and a moving-hair lining | Keeps the airway open and helps move mucus and debris upward |
| Bronchi | Main branches to each lung; the right side is wider, shorter, and straighter | Carries air into each lung; the right side is easier to accidentally aspirate into |
| Bronchioles | Small airways with no cartilage and smooth muscle walls | Narrow or open to change airflow |
| Alveoli | Tiny air sacs with very thin walls and lots of capillaries | Where oxygen moves into the blood and carbon dioxide moves out |
Clinical Pearl
Remember: thin membrane, large surface area, and rich blood supply are the three structural reasons gas exchange is so efficient at the alveolar level.
| Feature | Infant | Adult |
|---|---|---|
| Position | Higher: C3-C4 | Lower: C4-C6 |
| Shape | Cone-shaped at top | More cylindrical |
| Narrowest point | Subglottis (cricoid ring) | Glottic aperture |
| Epiglottis | Narrower, omega-shaped, floppier | Flatter, more stable |
| Subglottic diameter | ~4 mm full-term, ~3.5 mm premature | Much wider |
| Vocal cords | 6-8 mm and shorter | ~20 mm |
| Trachea | 4-5 cm, narrow and soft | ~11 cm, more rigid |
| Occiput/neck | Large occiput, short neck | More proportional |
| Function | Can breathe and swallow simultaneously | Cannot |
| Term | Definition | Approximate value |
|---|---|---|
| Tidal Volume (TV) | Volume of air in or out with a normal breath | ~500 ml |
| Inspiratory Reserve Volume (IRV) | Extra air you can inhale after a normal breath | ~3000 ml |
| Expiratory Reserve Volume (ERV) | Extra air you can exhale after a normal breath | ~1100 ml |
| Residual Volume (RV) | Air always left in the lungs | ~1200 ml |
| Vital Capacity (VC) | TV + IRV + ERV | ~4600 ml |
| Total Lung Capacity | VC + RV | ~5800 ml |
| Functional Residual Capacity (FRC) | ERV + RV; air left after normal expiration | ~2300 ml |
Clinical pearl
Residual volume is the air that always stays behind after the biggest breath out you can do. That leftover air helps stop the lungs collapsing completely. You cannot measure it with standard spirometry alone.
| Type | Mechanism | Examples |
|---|---|---|
| Hypoxic | Not enough oxygen is getting from the lungs into the blood | Altitude, obstruction, pneumonia, bronchiolitis |
| Anaemic | The blood cannot carry oxygen properly even if the lungs are working | Anaemia, haemorrhage, carbon monoxide poisoning |
| Ischaemic | Blood flow to tissues is too poor to deliver enough oxygen | Heart failure, pulmonary embolism, shock |
| Histotoxic | Cells cannot use the oxygen that reaches them | Cyanide poisoning |
| Problem | Mechanism | Examples |
|---|---|---|
| Low V/Q (shunt) | Air is not reaching part of the lung well, but blood still flows past it | Pneumonia, bronchiolitis, oedema |
| High V/Q (dead space) | Air reaches the alveoli, but not enough blood gets past to pick up oxygen | Pulmonary embolism |
| Problem | What it means | Examples |
|---|---|---|
| Poor ventilation | Not enough fresh air reaches the alveoli | Mucus plugging, bronchospasm, bronchiolitis, severe fatigue |
| Thicker barrier | Gas has further to cross before it gets into the blood | Pneumonia, pulmonary oedema, inflammation |
| Less surface area | There is less working lung available for exchange | Collapse, severe infection, widespread alveolar disease |
| Poor perfusion | Blood is not matching the air-filled alveoli properly | Shock, severe circulatory compromise, dead-space problems |
| Condition | What's going on | Key signs |
|---|---|---|
| Bronchiolitis | Usually caused by RSV. The smallest airways swell and fill with mucus, so air gets trapped and oxygen levels can fall. | Tachypnoea, recession, wheeze, low saturations, poor feeding |
| Asthma | The airways tighten, swell, and make extra mucus. | Expiratory wheeze, cough, dyspnoea, accessory muscle use |
| Croup | The area just below the vocal cords swells, narrowing the upper airway. | Barking cough, inspiratory stridor, hoarse voice, worse at night |
| Pneumonia | Fluid or infection in the air sacs makes gas exchange harder. | Fever, crackles, tachypnoea, productive cough, low saturations |
| Respiratory Distress Syndrome | Premature babies may not have enough surfactant, so the air sacs are harder to keep open. | Grunting, nasal flaring, tachypnoea, cyanosis, intercostal recession |
| Epiglottitis | Swelling of the epiglottis causes life-threatening upper-airway obstruction. | Drooling, tripod position, stridor, toxic appearance, no barking cough |
| Pertussis | Whooping cough causes intense coughing fits and lots of mucus. | Inspiratory 'whoop', post-tussive vomiting, apnoea in young infants |
Clinical pearl
Do not examine the throat in suspected epiglottitis. It can trigger complete airway obstruction. Treat it as an emergency and get senior help immediately.
Red Flag
Apnoea can be the presenting sign of bronchiolitis in infants under 6 weeks. A baby who pauses breathing, even briefly, in the context of coryzal symptoms needs urgent assessment.
| Severity | Features | SpO₂ |
|---|---|---|
| Mild–moderate | SpO₂ ≥92%, able to talk in sentences, RR and HR mildly raised, no cyanosis | ≥92% |
| Severe | SpO₂ <92%, too breathless to complete sentences, RR >30 (>5 yr), HR >120, accessory muscle use | <92% |
| Life-threatening | Silent chest, cyanosis, poor respiratory effort, exhaustion, altered consciousness, SpO₂ <92% despite O₂ | <92% on O₂ |
Exam Tip
A silent chest in a known asthmatic is a life-threatening emergency — it means air movement is so poor that wheeze has disappeared. Escalate immediately.
PEWS is a structured scoring system used to detect early deterioration in children. It scores behaviour, cardiovascular, and respiratory components, then triggers a defined escalation response.
| Score | Meaning | Action |
|---|---|---|
| 0–2 | Normal range | Continue observation per ward policy |
| 3–4 | Caution — increased concern | Inform nurse in charge; increase frequency of observations |
| 5–6 | Urgent — significant deterioration risk | Urgent medical review required |
| ≥7 | Emergency — immediate risk | Immediate emergency response; call for senior help now |
Clinical Pearl
Always document PEWS alongside observations. A rising trend — even within the “normal” range — is clinically significant and should be communicated to the team.
| Age | Usual respiratory rate | What to keep in mind |
|---|---|---|
| Newborn | 30-60 breaths/min | Can be irregular, but pauses and colour change are not something to brush off |
| Infant (1-12 months) | 25-50 breaths/min | Count for a full minute if they are wriggly or upset |
| Toddler (1-3 years) | 20-40 breaths/min | A fever or crying child may sit at the higher end |
| Preschool (3-5 years) | 20-30 breaths/min | Look at the trend as well as the number |
| School age (6-12 years) | 15-25 breaths/min | If they look tired, a "normal" rate can still be worrying |
| Adolescent | 12-20 breaths/min | Closer to adult values, but still assess alongside effort and colour |
Nasal flaring
Tracheal tug
Subcostal recession
Intercostal recession
Sternal recession
Head bobbing
Grunting
| Method | Description | When used |
|---|---|---|
| Nasal prongs / cannulae | Low-flow oxygen; can be sutured for stability | Mild to moderate hypoxia in stable patients |
| HFNC | Warm high-flow oxygen that also gives a small pressure effect | Bronchiolitis and moderate distress |
| CPAP | Continuous pressure through prongs or a mask to help keep the airway and air sacs open | Significant distress |
| Face mask | Simple mask or non-rebreather with variable FiO₂ | Moderate to severe hypoxia and emergencies |
| Head box | Perspex box over a neonate's head delivering controlled oxygen | Neonates and small infants who cannot tolerate nasal devices |
| Blow-by ('waft') | Oxygen tubing held near the face | Very distressed child refusing a device |
| Assessment | What it tells you | Key points |
|---|---|---|
| Pulse oximetry | The oxygen number from the probe | In children aim for 94-98%; the reading can mislead if the child is cold, moving, or poorly perfused |
| Listening with a stethoscope | What the breath sounds are like and how much air is moving | Listen for wheeze, crackles, stridor, or a silent chest |
| Respiratory rate | How fast the child is breathing | Fast breathing can be an early warning sign; a slower rate in a worsening child can mean they are tiring |
| Work of breathing | How hard they seem to be working for each breath | Look for recession, flaring, head bobbing, tracheal tug, grunting, and tummy breathing |
| Oxygen requirement | How much oxygen and which device they need | Needing more oxygen usually means the illness is worsening; document the device, flow, and FiO₂ if given |
| General appearance | The overall picture | How awake they are, their colour, tone, feeding, and cry can matter more than one isolated monitor number |
Clinical pearl
Infants have to suck, swallow, and breathe in a tight rhythm. If breathing gets harder, feeds often become stop-start. Coughing, pausing, short feeds, sweating, or tiring with feeds should make you reassess the breathing picture, not just the feeding chart.
Airway order
Never Phone Liam To Buy Brownies Always
Inspiration
I EAT — External intercostals + diAphragm, acTive
Boyle’s law
Volume up, pressure down, air rushes in
Alveolar cells
1 is Thin, 2 is Goo
Oxygen transport
~98.5% bound to haemoglobin (4 O₂ per Hb molecule), ~1.5% dissolved in plasma.
CO₂ transport
~70% as bicarbonate, ~23% bound to Hb, ~7% dissolved in plasma.
Normal V/Q ratio
~0.8 overall. Ideally matched ventilation to perfusion for efficient gas exchange.
Why infants deteriorate faster
Narrower airways, higher O₂ consumption per kg, lower FRC, more compliant chest, and a diaphragm that tires quickly.
Signs of increased WOB
Nasal flaring, tracheal tug, subcostal/intercostal/sternal recession, head bobbing, grunting.
Target SpO₂ in children
94–98% on room air. Aim ≥92% in bronchiolitis per NICE. Always assess alongside clinical picture.
Say this in your exam
Ready to apply what you have learned? Try a full exam-style mock with clinical scenarios, guided questions, and first-class answer support.
Sources & References
NICE (2021) — Bronchiolitis in children: diagnosis and management (NG9)BTS/SIGN (2022) — British Guideline on the Management of AsthmaResuscitation Council UK (2021) — 2021 Resuscitation GuidelinesWaugh A & Grant A (2018) — Ross and Wilson Anatomy and Physiology in Health and Illness (13th edn)RCPCH (2020) — Paediatric Early Warning SystemsAlso practice with