RESP: Respiratory Failure - Causes & Complications

Question 1

What are the causes of hypoxaemia and how do these relate to the clinical signs of hypoxaemia?

Answer 1

• Insufficient ventilation - ⬆️PaCO2, ⬇️PaO2, cyanosis, dyspnoea
• Insufficient gas exchange rate - ⬇️PaO2, cyanosis, ⬆️ventilation
• Insufficient capacity/distribution of O2 in/by the blood - variable, could be decreased Hb, CO poisoning etc.
• Insufficient oxygen in atmosphere - (⬇️PaO2, cyanosis, ⬆️ventilation)

Question 2

What pathologies explain the causes of hypoxaemia? Explain them

Answer 2

• Insufficient ventilation
  
  • Obstruction of airways (Gross blockage, airway narrowing)
    
    • Aphyxia, choking
    • Obstructive sleep apnoea
    • Bronchial obstruction (asthma, chronic bronchitis, cystic fibrosis)
  • Failure to effectively inflate/compress lungs (disruption of efferent neural signalling/conduction; abnormal lung mechanics e.g. decreased compliance
    
    • Drug overdose (typically opioids)
    • Stroke
    • MND, muscular dystrophy
    • COPD
    • Fibrosis
    • Pneumothorax
    • NRDS
• Insufficient gas exchange rate
  
  • Exchange surface dysfunction (oedema; hyaline membrane; fibrosis)
  • VQ inequality (dead-space effect; pulmonary shunt)
    
    • Reduced perfusion of lung regions causes an increase in V/Q ration (dead-space effect)
      
      • Heart failure
      • Blocked vessels
      • Loss/damage to capillaries
    • Reduced ventilation or limited diffusion causes decrease in V/Q ratio (shunt effect)
      
      • Pneumonia
      • Atelectasis
      • RDS
• Insufficient capacity/distribution of O2 in/by blood
  
  • Reduction in available Hb-O2 binding sites (fewer RBCs, more competition for Hb binding site)
    
    • Anaemia (Iron deficiency, haemorrhage)
    • CO poisoning
  • CVS dysfunction (⬇️Cardiac output, blood vessel obstruction)
• Insufficient oxygen in atmosphere
  
  • Altitude
  • Environmental suffocation (enclosed spaces, liquid N2 exposure)

Question 3

What are the causes of type 1 respiratory failure, and how would readings differ from normal for PAO2, PaO2, PaCO2, and pH?

Answer 3

Caused by ⬇️ oxygenation.
PAO2 - Normal
PaO2 - ⬇️
PaCO2 - Normal
pH - Normal

A-a gradient is increased

Question 4

What are the causes of type 2 respiratory failure, and how would readings differ from normal for PAO2, PaO2, PaCO2, and pH?

Answer 4

Caused by ⬇️ventilation (asthma, COPD, NMD, drug overdoes, apnoea)

PAO2 - ⬇️
PaO2 - ⬇️
PaCO2 - ⬆️ - Results in hypercapnia
pH - ⬇️

Question 5

How do PaO2, pH, PaCO2, CaO2, deO2Hb, SaO2 and A-a gradient differ for the causes of respiratory failure?

Answer 5

Insufficient ventilation:
- PaO2 - ⬇️
- pH - ⬇️
- PaCO2 - ⬆️
- CaO2 - ⬇️
- deO2Hb - ⬆️
- SaO2 - ⬇️
- A-a gradient - Normal

Insufficient oxygenation:
- PaO2 - ⬇️
- pH - Normal
- PaCO2 - Normal
- CaO2 - ⬇️
- deO2Hb - ⬆️
- SaO2 - ⬇️
- A-a gradient - ⬆️

Insufficient O2 carrying capacity:
- PaO2 - Normal
- pH - Normal
- PaCO2 - Normal
- CaO2 - ⬇️
- deO2Hb - Anaemia = ⬇️, CO = normal
- SaO2 - Normal
- A-a gradient - Normal

Insufficient O2 in atmosphere:
- PaO2 - ⬇️
- pH - ⬆️
- PaCO2 - ⬇️
- CaO2 - ⬇️
- deO2Hb - ⬆️
- SaO2 - ⬇️
- A-a gradient - Normal

Question 6

What are the clinical signs/symptoms of respiratory distress?

Answer 6

• Shortness of breath, tachypnoea, dyspnoea
• Tachycardia
• Laboured breathing, audible lung sounds
• Tiredness, drowsiness, loss of consciousness
• Fatigue (generally or upon exercise)
• Cyanosis

Question 7

What are the clinical consequences of hypoxaemia?

Answer 7

• Dyspnoea (shortness of breath)
• Cyanosis
• Fatigue
• Coma
• Seizure

Acute hypoxaemia → Tissue hypoxia (e.g. cerebral hypoxia) → organ failure → death

Chronic hypoxaemia -< Polycythaemia, hypoxic pulmonary vasoconstriction → Pulmonary heart failure

Question 8

What are the clinical consequences of hypercapnia?

Answer 8

• Dyspnoea
• Confusion
• Seizure
• Unconsciousness

Hypercapnia → acidosis → organ failure → cardiac arrhythmia → death