Respiratory failure

• What are the 2 types of respiratory failure?


  Type 1

  • hypoxaemia
  • PaO2 < 8 kPa
  • Normal or low PaCO2

  Type 2

  • hypercapnia & hypoxaemia
  • PaO2 < 8 kPa
  • PaCO2 > 6 kPa
• What is the primary cause of Type 1 respiratory failure?


  Ventilation perfusion mismatch

  -> lungs are perfused but not adequately ventilated -> hypoxaemia without hypercapnia
• Other than ventilation-perfusion mismatch, what are the other causes of Type 1 respiratory failure?


  Shunt

  O2 diffusion limitation
• What is O2 diffusion limitation? How can it cause Type 1 resp failure?

  When transit time for RBCs in pulmonary capillaries is too short for O2 to equilibrate fully between alveolar air & Hb

  Typically occurs during strenuous exercise or at high altitudes, can also occur in interstitial lung diseases
• What is shunt? How can it cause type 1 resp failure?


  More severe form of V/Q mismatch

  Blood bypassing ventilated areas of the lung - entirely due to anatomical or functional reasons

  • E.g. Atelectasis or vascular anomalies
• What causes type 2 resp failure?


  Inadequate alveolar ventilation → hypercapnia with or without hypoxaemia

  • Decreased minute ventilation
  • Limits ability of resp system to response to increased CO2 production
  • Increased physiological dead space (e.g. PE or COPD)
  • Increased ares in the lung that are ventilated but not perfused → wasted ventilation → contributes to hypercapnia
  • Inadequate compensation
• What are the Inx for resp failure?


  Obs

  Full Hx & examination

  ECG

  Bloods (ABG (diagnosis of resp failure), FBC, U&Es, LFTs, CRP, D-dimer, Troponin, NT-proBNP)

  CXR

  CT thorax

  Echo

  Pulmonary function tests

  Apart from ABG, everything else is to find underlying cause
• What is the DDx of resp failure?


  Acute Respiratory Distress Syndrome (ARDS)

  COPD

  Pneumonia
• ARDS 


  Acute Respiratory Distress Syndrome
• What are the RFs for resp failure?

  COPD

  Pneumonia

  ARDS

  Neuromuscular disorders

  Chest wall abnormalities

  Pulmonary vascular diseases
• What are the signs & symptoms of resp failure?

  SOB

  Confusion/altered consciousness (brain hypoxia)

  Cough

  Cyanosis

  Use of accessory muscles

  Tachypnoea (compensatory)

  Pursed-lip breathing (to prevent airway collapse)

  Peripheral oedema

  Polycythaemia (compensatory)

  Specific features of underlying cause
• What is the treatment for resp failure?


  Immediate

  • O2 therapy (1st line)
  • Non-invasive ventilation
  • Invasive ventilation
  • Extracorporeal membrane oxygenation

  Determine underlying cause & treat

  Lung transplantation (severe cases)