Respiratory Failure

Question 1

Definition of respiratory failure

Answer 1

• inadequate gas exchange due to dysfunction of one or more essential components of the resp system
• common end point of all severe diseases of the respiratory system
• acute, chronic, acute-on-chronic

Question 2

Consequences of respiratory failure

Answer 2

Inability to maintain O2/CO2 at normal levels - hypoxia/hypercapnia

Question 3

Symptoms of respiratory failure (2)

Answer 3

• Breathlessness (air hunger)
• Consequences of hypoxia - long standing hypoxia results in pulm htn, secondary right heart strain, polycythemia (stimulation of erythropoietin release from kidney)

Question 4

Features of type 1 respiratory failure

Answer 4

• Hypoxemia without hypercapnia
• failure of alveolar-capillary units (gas exchange affected more than ventilation)
• eg flooding of alveolar spaces (fluid/pus), PE, collapse of lung, loss of normal alveolar structures due to irreversible damage
• initially correctable by hyperventilation/high O2 conc, but not when severe

Question 5

Features of type 2 respiratory failure

Answer 5

• Hypoxemia with hypercapnia
• added component of poor ventilation - CO2 retention
• eg failure of neuromuscular system/chest wall mechanics, airway obstruction
• initial acidosis caused by CO2 retention - tachycardia - reduced level of consciousness & increasingly poor respiratory effort - respiratory arrest & death

Question 6

Progression of respiratory failure

Answer 6

• type 1 often progresses to type 2
• progression of disease or exhaustion of the patient - compensatory measures fail - insufficient O2 delivered to tissues + ventilation falls w CO2 retention
• CO2 retention - hypoxia + acidosis - death