Differentiate between hypoxia and hypoxaemia
Give examples of when a patient might be hypoxic but not hypoxaemic
- Severe anaemia
- Poor perfusion
What is respiratory failure? Differentiate between Type 1 an Type 2 respiratory failure.
Respiratory failure= pO2< 8kPa when breathing air at sea level
What systemic effects does hypoxia have?
What systemic effects does hypercapnia have?
What are the causes of hypoxaemia? (5)
What effects does chronic hypoxaemia have?
Explain why someone who is acutely exposed to high altitudes (atmospheric pressue <101kPa) will have a low pO2 and low pCO2.
Low inspired pO2 level
Peripheral chemoreceptors stimulated
--> Hyperventilation-- causes low pCO2
What adaptations does someone who lives at high altitudes have?
- Increased 2-3 DPG
- Increased capillary density
Is hypoventilation a type 1 or type 2 respiratory failure? Why?
(Artificial ventilation required)
Give some causes of hypoventilation.
Explain why a patient with with COPD will not require ventilatory support until the later stages of the condition.
Time allowed for some compensatory mechanisms to develop
(May need ventilation during acute complications eg lung infection)
Outline how the body responds to chronic hypercapnia. (Kidney and Central chemoreceptors)
Kidney: renal compensation of respiratory acidosis
Central chemoreceptors: Choroid complex imports HCO3- into CSF. Restores CSF pH to normal. Central chemoreceptors 'reset'
How would you treat hypoxia in a patient with chronic type 2 respiratory failure?
Check bicarb- may be only sign of CO2 retention
Controlled oxygen therapy- avoid risk of worsening hypercapnia
Explain how a V/Q mismatch (due to poor ventilation of alveoli/pulmonary embolism) leads to Type 1 respiratory failure.
(eg COPD-early stages, asthma, RDS, pneumonia, pulmonary embolism)
- Drop in pO2
- Hyperventiation stimulated- increased CO2 removal
- Hyperventilation insufficient to correct fall in pO2
Explain why a diffusion impairment within the alveoli causes type 1 respiratory failure and not type 2.
O2 diffuses less readily than CO2 - always affected more by any change in diffusion barrier
Give an example of a condition which can initally cause Type 1 respiratory failure that can progress to Type 2 respiratory failure and explain how this happens
More and more airways- narrowed, exhaustion sets in
Ventilatory support required
Explain why treating a hypoxic patient with uncontrolled oxygen can only worsen hypercapnia. (2 mechanisms)
How should it be controlled instead?
Controlled oxygen therapy- continuously monitor oxygen and CO2 levels
What is a patient going to require if controlled oxygen therapy still causes hypercapnia?