Respiratory Failure 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
- Insufficient oxygen in the atmosphere
What is the cause of type 1 respiratory failure?
Decreased oxygenation
What is the cause of type 2 respiratory failure?
Decreased ventilation
What are the effects of type 1 respiratory failure?
- Decreased alveolar partial pressure of O2
- Normal arterial partial pressure of O2
- Normal PaCO2
- Normal pH
What are the effects of type 2 respiratory failure?
- Decreased alveolar partial pressure of O2
- Decreased arterial partial pressure of O2
- Increased PaCO2
- Decreased pH
What are the two types of hypoventilation?
Airway obstruction due to physical blockage or problems with initiation or mechanics of breathing
Give examples of airway obstruction hypoventilation
- Asphyxia
- Smooth muscle constriction
- Obstructive sleep apnoea
- Bronchial obstruction (asthma, chronic bronchitis, cystic fibrosis)
What causes the other type of hypoventilation (initiation)?
- 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 therefore 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)
Give some examples of oxygen transport disorders
- Anaemia
- Iron deficiency
- Haemorrhage
- Carbon monoxide poisoning
What are the 6 clinical signs of respiratory distress?
Tachypnoea
Tachycardia
Laboured breathing
Loss of consciousness
Fatigue
Cyanosis
What are the clinical effects of insufficient O2 supply?
Dyspnoea, cyanosis, fatigue, coma
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 leading to 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 and cardiac arrhythmia
- Death
State the equation used to find the alveolar oxygen pressure and some common values that can be inputed
Alveolar oxygen pressure (PAO2) = fraction of oxygen in inspired gas x (barometric pressure - H2O vapour pressure) - (arterial carbon dioxide pressure / respiratory exchange ratio)
Or (simplified) alveolar oxygen pressure = oxygen inspired - oxygen consumed
Fraction of oxygen in inspired gas - 0.21 in ambient air
Barometric pressure - 100 kPa at sea level
H20 vapour pressure - 6 kPa in humidified air
Pa CO2 - measured in patient
RER - assume 0.8 unless told otherwise
PAO2 - calculated
How to calculate respiratory exchange ratio?
Respiratory exchange ratio = VCO2 produced / VO2 consumed
