Causes Of Hypoxaemia And Hypercapnia Flashcards
What causes insufficient ventilation?
Obstruction of airways or failure to breathe adequately
What causes insufficient gas exchange?
Exchange surface dysfunction or VQ mismatch
What are the four causes of hypoxaemia?
Insufficient ventilation, insufficient gas exchange, insufficient oxygen carrying capacity and insufficient oxygen in the atmosphere
What defines respiratory failure?
When PaO2 < 8kPa when breathing air at sea level
What is the cause of type 1 respiratory failure?
Decreased oxygenation
What is the cause of type 2 respiratory failure?
Decreased ventilation
What is the PaO2 in type 1 respiratory failure?
Decreased
What is the PaO2 in type 2 respiratory failure?
Decreased
What is the PAO2 in type 1 respiratory failure?
Normal
What is the PAO2 in type 2 respiratory failure?
Decreased
What is the PaCO2 in type 1 respiratory failure?
Normal
What is the PaCO2 in type 2 respiratory failure?
Increased
What is the pH in type 1 respiratory failure?
Normal
What is the pH in type 2 respiratory failure?
Decreased
What is PAO2?
Oxygen pressure in the alveoli
What is PaO2?
Arterial oxygen concentration
What does it mean if there’s insufficient oxygen in the atmosphere?
Less O2 in atmosphere -> less O2 in alveoli so less arterial O2
What are the two types of hypoventilation?
Airway obstruction due to physical blockade or problems with initiation or mechanics of breathing
Give examples of airway obstruction hypoventilation
- Asphyxia, choking
- smooth muscle constriction
- excess mucus secretions
- obstructive sleep apnoea
- bronchial obstruction (asthma, chronic bronchitis, cystic fibrosis)
What causes the other type of hypoventilation (not airway obstruction)?
- Drug (opioid) overdose
- stroke
- neuromuscular disease (muscular dystrophy, motor neurone disease)
- issues with lung mechanics (COPD, pulmonary fibrosis, NRDS, pneumothorax)
What causes oxygenation problems?
V/Q mismatch
What is the dead space effect?
Reduced perfusion of lung regions increases V/Q ratio
What are the effects of the dead space effect?
Heart failure, blocked vessels and loss /damage of capillaries
What is the shunt effect?
Reduced ventilation or limited diffusion, causing a decrease in V/Q ratio
Give some diseases where the shunt effect happens
Pneumonia
atelectasis (Collapsed lung)
Respiratory distress syndrome
Give some examples of oxygen transport disorders
Anaemia (blood loss or Hb)
Iron deficiency (decreased production)
Haemorrhage (increased loss)
Carbon monoxide poisoning (CO prevents O2-Hb binding
What are the 6 clinical signs of respiratory distress?
Tachypnoea, dyspnoea Tachycardia Laboured breathing, audible lung sounds Tiredness, loss of consciousness Fatigue Cyanosis
What are the clinical effects of insufficient O2 supply?
Dyspnoea, cyanosis, fatigue, coma, seizure
What is dyspnoea?
Shortness of breath
What are the effects of acute insufficient O2 supply?
Hypoxaemia -> tissue hypoxia -> organ failure -> death
What are the effects of chronic insufficient O2 supply?
Polycythaemia, hypoxic pulmonary vasoconstriction -> pulmonary heart failure
What is Polycythaemia?
Increased Hb concentration in blood
What are the clinical signs of insufficient carbon dioxide removal?
Dyspnoea, confusion, seizure, unconsciousness
What is the pathway of insufficient CO2 removal?
Hypercapnia ->acidosis ->organ failure + cardiac arrhythmia -> death
