Case 3: Rana Osmen - Obstruction/Croup

LRT: Trachea

Anterior to esophagus

Held open by C cartilage rings

Trachealis muscle at back (against esophagus)

LRT: Bronchi

Trachea divide at carina into right and left main bronchi

• Enter hilum

Right bronchus shorter, wider, more vertical

• Easy aspiration

Bronchi Divisions

Main bronchi → Lobar (secondary) bronchi → Tertiary bronchi → Divide until terminal bronchioles → Respiratory bronchioles

Cartilage to smooth muscles moving down

LRT: Alveoli

Alveolar ducts and sacs budding from respiratory bronchioles

Respiratory zone (gas exchange)

LRT: Lungs

Right: Bigger, 3 lobes

Left: Smaller, 2 lobes

Extend to 6th costal cartilage (rib)

Lung Surfaces

Apex: Top of superior lobes, above clavicles

Hilum: Middle, attach to mediastinal structures

Costal: Outer, convex part

Diaphragmatic: Bottom, contact with diaphragm

Lung Fissures

Right:

• Oblique: Between superior, middle, and inferior lobes

• Horizontal: Between superior and middle lobes

Left:

• Oblique: Between superior and inferior lobes

Lung Innervation

ANS

• Sympathetic bronchodilator fibres

• Parasympathetic bronchoconstrictor fibres

Pleura

Visceral

Parietal

Visceral Pleura

Around lungs (touching)

• Left + right

Few/no pain fibres

Parietal Pleura

Line outer cavity (not touching lungs)

Afferent fibre innervation

Extend to 9th costal cartilage (ribs)

Pleural Spaces/Cavities

Contain lungs + lubricating serous fluid

Mediastinum

Middle space between pleural spaces

Pleural Pressure

Negative pressure (< -4 mmHg)

Fluid suction into lymphatic channels decrease pressure in pleural space

• Hydrostatic force hold lungs open to thoracic wall

Pleural Pressure: Inspiration

Chest expansion pulls lungs outwards = Increase negative pressure

Air enters lungs

Pleural Pressure: Clinical Importance

Trauma (lung punctures) = Air entering intrathoracic space = Increase pressure = Prevent breathing

Pleural Fluid

Mucoid/serous fluid in pleural cavity produced by parietal pleural capillaries

Lubricate pleural cavity for lung movement

• Decrease friction with chest wall

Transpulmonary Pressure

Alveolar P - Pleural P = Elastic force in lungs (recoil pressure)

Respiratory Cycle

Negative-pressure breathing

1. Inspiration: Diaphragm, external intercostal, scalene muscles contract to pull lungs down/out = Increase alveolar volume

   • Alveolar P decreases (< atmospheric P)

   • Air enters lungs (P gradient)

2. Expiration: Diaphragm, external intercostal, scalene muscles relax to compress lungs (elastic recoil) = Decrease alveolar volume

   • Alveolar P increases (> atmospheric P)

   • Air leaves lungs (P gradient)

Pulmonary Resistance

Airway resistance + pulmonary tissue resistance (overcome with pleural fluid)

R = 1/r^4

• Diameter decrease = resistance increase

Flow

Flow = Pressure difference/Resistance

Decrease airway diameter/radius from obstruction = Increase resistance = Decrease airflow

Extrathoracic Obstruction

Obstruction in URT

Extrathoracic Obstruction: Inspiration

Difficult

1. Obstruction = Narrow airway = Increase flow = Decrease pressure on airway wall

2. Atmospheric P > Alveolar P = Airway collapse inward = Worsen obstructive lesion

Hear: Stridor

Extrathoracic Obstruction: Expiration

Alveolar P > Atmospheric P = Pressure opens airway

Intrathoracic Obstruction

Obstruction in LRT

Intrathoracic Obstruction: Inspiration

Muscle contraction expands lungs = Open obstructed airway

Intrathoracic Obstruction: Expiration

Difficult

Alveolar P > Atmospheric P = Collapse airway

Hear: Wheezing

Flow-Volume Loop

From pulmonary function test

Read clockwise

Flow-Volume Loop: Extrathoracic Obstruction

Difficult inspiration = Depressed inspiration loop

Flow-Volume Loop: Intrathoracic Obstruction

Difficult expiration = Depressed expiration loop

Croup: Description

Respiratory illness affecting URT (larynx, trachea)

Croup: Epidemiology

Common in children <6 years (small airways)

Usually in fall and winter

Croup: Etiology

Viral infections (most common)

• Mostly: Parainfluenza virus

• Others: Adenovirus, resp syncytial virus, enterovirus, rhinovirus, coronavirus, echovirus

Bacterial infection (less common)

Airway abnormalities

Resp pathologies (allergies, asthma)

Croup: Pathogenesis

1. Inflammation and edema narrow upper airway

• Subglottic larynx region and trachea

2. Decrease airflow

3. Cause:

   • Stridor

   • Increased resp rate, inspiratory volume, resp effort

   • Hypoxia, hypercapnia, resp failure

Croup: Investigations

No lab tests or imaging

Take history, physical, and response to treatment

Croup: Clinical Presentation

Stridor

Barky cough

Croup: Treatment

Usually self-contained

Steroids: Anti-inflammatory reduce edema + obstruction

• Dexamethasone

• Nebulized budesonide

• Severe: Nebulized epinephrine

Epiglottitis: Description

Upper airway inflammation and obstruction

Life-threatening

Epiglottitis: Epidemiology

All ages

• Vulnerable: < 12 months, > 85 years

Epiglottitis: Etiology

Bacterial infection

• Staphylococcus and streptococcus

Viral and fungal infections

Epiglottitis: Pathogenesis

1. Edema in supraglottic structures (epiglottis surface and aryepiglottis folds)

   • Epiglottis shifts posteriorly

   • Obstruct airway

2. Inflammation narrow airway lumen = Decrease airflow

Epiglottitis: Investigation

Imaging after physical for confirmation

• X-ray

• Laryngoscopy

• Ultrasound

Epiglottitis: Clinical Presentation

Fever

Sore throat

Painful swallowing (odynophagia) + drooling

Epiglottitis: Treatment

Antibiotics: Bacterial infection

• 3rd gen cephalosporin

Corticosteroids: Anti-inflammatory + reduce swelling

• Dexamethasone

• Budesonide

Children: Immediate intubation