title: "Week 2: Respiratory"
Week 2: Respiratory
Why Children Are Prone to Respiratory Failure
Infants have smaller diameter airways (increased resistance), compliant chest walls (less support), fewer alveoli (VQ mismatch risk), and fetal Hb until 6 months (less O2 offload).
Infant airway is narrowest at the cricoid cartilage (vs glottic opening in adults), has a longer floppy epiglottis, and a large tongue and occiput.
Acute Upper Airway Obstruction
Allow children with acute upper airway obstruction to adopt a position of their choice. Don't force them to lie down.
Differential Diagnosis
| Condition | Key Features |
|---|---|
| Croup | Young child, barking cough, hoarse voice, stridor, systemically well |
| Epiglottitis | Toxic, high fever, drooling, no cough, sits leaning forward |
| Bacterial tracheitis | URTI prodrome, S. aureus, prefers lying flat, tender trachea |
| Foreign body | Abrupt onset, choking episode, unilateral findings |
| Peritonsillar abscess | Severe unilateral sore throat, trismus, "hot potato" voice |
| Retropharyngeal abscess | Sore throat, neck stiffness, torticollis, dysphagia |
Croup (Laryngotracheobronchitis)
Croup is caused by parainfluenza virus (types 1, 2, 3). Peak age ~2 years. Classic triad: barking "seal" cough, hoarse voice, stridor.
- D - Dexamethasone (0.15-0.6 mg/kg PO)
- N - Nebulised adrenaline if severe (0.5 mL/kg of 1:1000)
- O - Oxygen only if life-threatening
Croup symptoms worsen at night due to increased oedema. Stridor at rest = severe croup.
Croup is a clinical diagnosis. Alarm features: agitation, drowsiness, persistent stridor at rest, hypoxia (only if life-threatening).
Epiglottitis
Epiglottitis is caused by Haemophilus influenzae type b (Hib). Rare now due to vaccination. Child is toxic, drooling, sitting forward with neck extended.
Do NOT examine the throat in suspected epiglottitis - can trigger laryngospasm. "Cherry red epiglottis" on laryngoscopy.
Epiglottitis has NO COUGH - this differentiates it from croup.
Pertussis (Whooping Cough)
Bordetella pertussis - gram-negative intracellular coccobacillus. 1 in 125 babies under 6 months with pertussis will die.
- Incubation (7-10 days)
- Catarrhal/Prodromal (1-2 weeks) - rhinorrhoea, dry cough, MOST CONTAGIOUS
- Paroxysmal (1-6 weeks) - severe coughing fits, inspiratory "whoop", post-tussive vomiting
- Convalescent - gradual recovery, cough may persist for months
Treat pertussis with azithromycin (intracellular penetrating antibiotic). Vaccinated individuals won't develop disease but remain contagious.
Pneumonia
Streptococcus pneumoniae is the most common bacterial cause of pneumonia in children. Mycoplasma causes "walking pneumonia" in older children.
Suspect empyema if fever persists after 48 hours of appropriate pneumonia treatment.
| Effusion Type | Features |
|---|---|
| Simple | Non-loculated, sterile transudate |
| Complicated/Empyema | Loculated, bacterial invasion |
Common empyema organisms: S. pneumoniae, S. aureus, Group A Strep.
Bronchiolitis vs Croup
| Feature | Bronchiolitis | Croup |
|---|---|---|
| Peak age | 3-6 months | 2 years |
| Pathogen | RSV | Parainfluenza |
| Season | Winter | Autumn |
| Sound | Wheeze + crackles | Barking cough + stridor |
| Sex | M > F (3:2) | M > F (3:2) |
| Treatment | Supportive only | Steroids ± neb adrenaline |
RSV (Respiratory Syncytial Virus) is the most common cause of bronchiolitis. Peak age 3-6 months.
Parainfluenza (types 1, 2, 3) is the most common cause of croup. Peak age ~2 years.
Bronchiolitis
Bronchiolitis = first episode of viral-induced wheeze with crackles in infants under 12 months. Caused by inflammation and mucus plugging of terminal bronchioles.
No benefit from antibiotics, bronchodilators, or corticosteroids in bronchiolitis. Treatment is purely supportive.
Severity Assessment
| Feature | Mild | Moderate | Severe |
|---|---|---|---|
| SpO2 | ≥90% | Persistently <90% | Persistently <90% despite low-flow O₂ / requiring HFNP |
| Feeding | >75% normal | >50% normal | <50% normal |
| HR | Normal | Mild tachy | >180 |
| Cyanosis | No | No | Yes |
Bronchiolitis management is supportive: oxygen to maintain SpO2 ≥90% (don’t chase mid-high 90s), plus hydration (NG or IV at 2/3 maintenance if severe).
Source: local paediatric bronchiolitis guideline.
Viral-Induced Wheeze
Viral-induced wheeze is very common in first 2 years. Rhinovirus is the most common cause in school-aged children.
May trial salbutamol in viral wheeze if child is over 1 year old. No role in bronchiolitis under 12 months.
Asthma
Asthma = recurrent, reversible airway hyperresponsiveness. Triggers: allergens, viral URTIs, exercise, stress. Associated with atopy.
Diagnosis by Age
| Age | Approach |
|---|---|
| 0-12 months | Do NOT diagnose asthma. Usually bronchiolitis or floppy airways. |
| 1-5 years | Recurrent symptoms + response to salbutamol. Trial therapy. |
| 6-11 years | Spirometry with bronchodilator response (FEV1 ↑ >10%) OR FeNO ≥25 ppb |
| Adolescents | Spirometry (FEV1 ↑ >12% AND ≥200 mL) OR FeNO ≥40 ppb |
Spirometry Pattern (Obstructive)
Viral-induced wheeze = only triggered by URTI. Asthma = chronic disease, multiple triggers, atopic history, interval symptoms.
- Asthma: Atopy, Always (interval symptoms), All triggers
- Viral wheeze: URTI-triggered only, no interval symptoms
Practice Questions
What is the most likely causative organism?
What is the first-line treatment?
What should you NOT do?
What is the appropriate fluid management?