Xiii / PTX: Physiological consequences of a tension pneumothorax + Describe the anatomy relevant to insertion of intercostal catheter

Definition PTX: progressive build-up of air in the pleural space

Pathophysiology of Tension PTX

  • Normally, in a spontaneously breathing patient, intrapleural pressure (P) is sub-atmospheric during resp cycle
    • Due to opposing forces of chest wall & lung recoil
  • PTX develops secondary to breach in visceral, parietal, or mediastinal pleura
  • Defects create a 1-way valve
  • Air enters pleural cavity on inspiration but cannot exit on expiration
  • Consenquently, ↑intrapleural P results in:
    • Ipsilateral lung collapse
    • Chest wall expansion
    • Diaphragmatic depression
    • Mediastinal & contralateral compression
  • Life threatening CV collapse due to impeding venous return (VR) & mediastinal compression

Mechanism of Effects


  • ↓ lung vol, ↓VC, ↓FRC, ↓TLC, ↓RV → restrictive defect
    • Expansion of pleural space
    • Deflation of ipsilateral lung & expansion of chest wall
  • ↓PαO2
    • Lung collapse → creates areas w ↓V/Q
    • ↑PA – α difference
  • ↑ PVR
    • Persistent hypoxaemia → hypoxic VC of pulmonary vessels
  • ↑WoB
    • Maximal resp efforts required to overcome the ↑ intrapleural P


  • ↓CO
    • ↑ intrapleural P → ↓VR → ↓preload & mechanical obstruction due to ↑intrapleural P → ↓CO
  • ↑HR
    • ↑sympathetic activity 2° to baroreceptor activation from ↓BP
    • Compensatory due to ↓CO

Anatomy for ICC Insertion

  • ICC: tube inserted into pleural space to allow drainage of contents
  • Location → “Safe triangle”
Safe Triangle
  • Incision into 4th/5th IC space
  • Layers from skin to pleura:
    1. Skin
    2. Fascia
    3. External IC m.
    4. Internal IC m.
    5. Innermost IC m.
    6. Parietal fascia of thorax
    7. Parietal pleura
  • Muscle of IC space innervated by neurovascular bundle → sits in groove of rib above
    • VAN from sup. → inf.
    • Bundle lies b/w innermost and internal IC m.