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Please wait while the page loadsChildren's Nursing · Free Resource
One page for the respiratory anatomy, physiology, bedside assessment, and red flags you keep getting asked about.
Quick framework
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.
Conducting zone
Respiratory zone
| Structure | Key features | Main job |
|---|---|---|
| Nose | Ciliated epithelium, goblet cells, turbinates, rich blood supply | Warms, humidifies, filters inspired air |
| Pharynx | Three sections: naso-, oro-, and laryngopharynx | Passageway for air and food; epiglottis helps prevent aspiration |
| Larynx | Vocal cords, epiglottis, thyroid, cricoid, and arytenoid cartilages | Voice production and lower-airway protection during swallowing |
| Trachea | C-shaped cartilage rings and ciliated pseudostratified columnar epithelium | Keeps the airway open and clears debris via the mucociliary escalator |
| Bronchi | Right bronchus is wider, shorter, and more vertical than the left | Conducts air to each lung; the right side is more prone to aspiration |
| Bronchioles | No cartilage; smooth muscle walls; terminal to respiratory transition | Regulates airflow via bronchoconstriction and bronchodilation |
| Alveoli | Around 300 million sacs with ~0.5 μm thin walls and a dense capillary network | Site of gas exchange by simple diffusion |
Exam tip
A 4 mm airway with 1 mm swelling causes about 75% loss of area. By Poiseuille's law, halving the radius creates a huge rise in resistance, so minor oedema in an infant can become life-threatening.
Gas exchange at the alveolus
Type I and Type II cells
Right versus left lung
Pleura
Bypass routes
As children grow, collateral channels increase. Canals of Lambert connect bronchioles to alveoli, and pores of Kohn connect neighbouring alveoli, allowing air to bypass blocked areas.
Why the lining changes
Upper airways
Ciliated pseudostratified columnar epithelium supports mucus trapping and mucociliary clearance.
Bronchioles
Epithelium becomes thinner from simple columnar to cuboidal as the airway narrows.
Alveoli
Simple squamous Type I cells minimise diffusion distance so the priority shifts from defence to gas exchange.
| 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 |
Boyle's law
Volume up, pressure down, air rushes in. As thoracic volume increases, intrapulmonary pressure falls below atmospheric pressure and air moves into the lungs. As the thorax recoils, pressure rises and air moves out.
Inspiration
Expiration
| 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 |
Residual volume
Residual volume helps prevent lung collapse. It cannot be measured with standard spirometry and instead needs methods such as helium dilution or body plethysmography.
Why gas exchange is efficient: TSB
Thin
Around 0.5 μm membrane means a very short diffusion distance.
Surface area
Around 300 million alveoli create a huge surface area for diffusion.
Blood supply
A dense capillary network maintains the diffusion gradient.
O₂ transport
CO₂ transport
| Type of hypoxia | Mechanism | Examples |
|---|---|---|
| Hypoxic | Low PaO₂ in blood; problem at the lung level | Altitude, obstruction, pneumonia, bronchiolitis |
| Anaemic | Too little functioning Hb; lungs are fine but blood cannot carry O₂ well | Anaemia, haemorrhage, carbon monoxide poisoning |
| Ischaemic | Reduced blood flow to tissue; oxygen is present but cannot reach cells well | Heart failure, pulmonary embolism, shock |
| Histotoxic | Cells cannot use delivered oxygen because metabolism is blocked | Cyanide poisoning |
O₂-Hb dissociation curve
A right shift means oxygen is released more easily to tissues, as seen with increased temperature, increased CO₂, lower pH, and increased 2,3-DPG. A left shift means oxygen is held more tightly, as seen in the lungs and in foetal haemoglobin.
Central chemoreceptors
Located in the medulla. They detect rising CO₂ through H⁺ concentration in cerebrospinal fluid and act as the primary driver of breathing.
Peripheral chemoreceptors
Located in the carotid bodies and aortic arch. They detect low O₂ and also respond to rising CO₂ and falling pH.
Ventilation and perfusion
V means air moving in and out of alveoli. Q means blood flowing past alveoli. These should be matched at roughly 0.8. Hypoxic pulmonary vasoconstriction helps by diverting blood away from poorly ventilated areas.
| Problem | Mechanism | Examples |
|---|---|---|
| Low V/Q (shunt) | Blood flows past unventilated alveoli | Pneumonia, bronchiolitis, oedema |
| High V/Q (dead space) | Alveoli are ventilated but not perfused | Pulmonary embolism |
Nasal hairs and turbinates (Nose)
Filter larger particles and increase surface area for warming and humidifying inspired air.
Mucus and goblet cells (Airway lining)
Sticky mucus traps dust, bacteria, and pathogens before they reach the lower airway.
Mucociliary escalator (Trachea and bronchi)
Cilia beat upward to move mucus and debris toward the pharynx for swallowing or coughing.
Cough and sneeze reflexes (Airway and nose)
Forceful expiration helps expel irritants and protect the airway from obstruction.
Alveolar macrophages (Alveoli)
Provide the final line of defence by phagocytosing bacteria and particles.
IgA antibodies (Mucosal surfaces)
Neutralise pathogens within airway secretions.
| Feature | Paediatric difference | Clinical significance |
|---|---|---|
| Airways | Narrower, shorter, softer cartilage | Small swelling causes major obstruction via Poiseuille's law |
| Nose | Obligate nose breathers until roughly 3-6 months | Congestion alone can trigger respiratory distress |
| Chest wall | Ribs are more horizontal and compliant | Children rely on the diaphragm and recession becomes visible early |
| Respiratory rate | Higher: neonate 30-60, infant 25-50 | Higher metabolic demand and smaller FRC mean less oxygen reserve |
| O₂ consumption | ~6-8 ml/kg/min versus ~3-4 in adults | Children desaturate faster and tolerate hypoxia for less time |
| FRC | Lower relative to body size | Smaller oxygen reserve causes quicker desaturation |
| Diaphragm | More type II fast-twitch fibres | Fatigues more easily and decompensation can come earlier |
| Immune system | More immature with fewer IgA antibodies | Greater susceptibility to infections such as RSV and pertussis |
Important note
Mucociliary clearance is impaired by smoking, dehydration, general anaesthesia, and cold dry air, increasing the risk of chest infection.
| Condition | Pathophysiology | Key signs |
|---|---|---|
| Bronchiolitis | RSV causes inflammation and mucus plugging in bronchioles, leading to air trapping, V/Q mismatch, and hypoxia. | Tachypnoea, recession, wheeze, low saturations, poor feeding |
| Asthma | Chronic inflammation causes bronchoconstriction, mucus hypersecretion, and airway oedema. | Expiratory wheeze, cough, dyspnoea, accessory muscle use |
| Croup | Parainfluenza causes subglottic oedema and upper-airway narrowing. | Barking cough, inspiratory stridor, hoarse voice, worse at night |
| Pneumonia | Alveolar consolidation from fluid or pus reduces surface area for gas exchange and worsens V/Q mismatch. | Fever, crackles, tachypnoea, productive cough, low saturations |
| Respiratory Distress Syndrome | Premature Type II cells produce insufficient surfactant, increasing surface tension and causing atelectasis. | 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 | Paroxysmal coughing fits follow Bordetella pertussis infection with mucus hypersecretion. | Inspiratory 'whoop', post-tussive vomiting, apnoea in young infants |
Respiratory distress — compensating
Respiratory failure — decompensating
How to start your assessment
Start from the end of the bed
Before you touch them, look at colour, position, alertness, and whether they can cry, feed, or talk properly.
Count properly
Respiratory rate means a full 60 seconds when you can. Fast counting on a squirmy child is how people miss tachypnoea.
Document the effort
Write the work of breathing, SpO₂, oxygen device, and how the child looked, not just one number on the obs chart.
| 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
Trying to pull in more air with each breath
Tracheal tug
Increased upper-airway effort
Subcostal recession
The diaphragm is working hard and the child is drawing in below the ribs
Intercostal recession
Visible increased work between the ribs
Sternal recession
More marked distress with the chest pulling in centrally
Head bobbing
Infant compensation and fatigue risk
Grunting
The child is trying to keep alveoli open at end-expiration
Red flags — escalate immediately
Epiglottitis
Do not examine the throat in suspected epiglottitis. It can trigger complete airway obstruction. Treat it as an emergency and get senior help immediately.
| Method | Description | When used |
|---|---|---|
| Nasal prongs / cannulae | Low-flow oxygen; can be sutured for stability | Mild to moderate hypoxia in stable patients |
| HFNC | Heated humidified high-flow oxygen with some PEEP effect | Bronchiolitis and moderate distress |
| CPAP | Continuous positive pressure via prongs or mask to splint the airway and prevent alveolar collapse | 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 | % of haemoglobin saturated with oxygen | Normal range in children is 94-98%; inaccurate in carbon monoxide poisoning or poor perfusion |
| Auscultation | Breath sounds and air entry | Listen for wheeze, crackles, stridor, or a silent chest |
| Respiratory rate | How fast the child is breathing | Tachypnoea is often early distress; a falling rate in a worsening child suggests decompensation |
| Work of breathing | How hard breathing looks | Look for recession, flaring, head bobbing, tracheal tug, grunting, and abdominal breathing |
| Oxygen requirement | FiO₂ and delivery method needed | Escalating need suggests worsening disease; always document FiO₂, rate, and device |
| General appearance | Overall clinical picture | Alertness, tone, colour, feeding, and cry often matter more than a single monitor number |
Quick mnemonic recap