Session 7: Hypoxia & Respiratory Failure Flashcards
Steps of the oxygen supply chain.
Air -> Airways -> Alveolar gas -> Alveolar membrane -> Arterial blood -> Regional arteries -> Capillaries -> Tissues
Define hypoxia.
Reduced oxygen at tissue level. This can be abnormalities of any point of the oxygen supply chain which can lead to hypoxia.
Define hypoxaemia.
Decrease in pO2 in the blood.
Is it possible to be hypoxic without hypoxaemia?
Yes.
Explain how it is possible to be hypoxic without being hypoxaemic.
E.g. severe anaemia where there is reduced oxygen carrying capacity due to low Hb levels. This leads to hypoxia but not reduced pO2 in arteries.
Also poor perfusion which can lead to hypoxia of the affected tissue like in an MI despite having normal gas exchange in lungs and normal pO2 in arteries.
What is respiratory failure defined as?
When arterial pO2 falls below 8kPa or 60 mmHg when breathing air at sea level.
Define Type 1 Respiratory failure
A pO2 below 8kPa
Normal or low pCO2
Define type 2 respiratory failure.
A pO2 below 8kPa
High pCO2 of above 6.7 kPa
Effects of hypoxia.
Impaired CNS function
Central cyanosis
Cardiac arrhythmias
Hypoxic vasoconstriction of the pulmonary vessels
Effects of hypercapnia.
Respiratory acidosis
Impaired CNS functions like drowsiness, confusion, coma and tremors.
Peripheral vasodilation leading to warm hands and bounding pulse.
Cerebral vasodilation leading to headache.
What is needed to maintain arterial pO2 at a normal level?
Normal inspired pO2
Normal alveolar ventilation
Matching V/Q
Normal alveolar capillary membrane (no thickening)
No right to left shunts.
Why is it important to not have a right to left shunt to maintain arterial pO2?
CO from right heart needs to pass through gas exchanging alveoli
Considering the factors needed to maintain normal arterial pO2.
Why might hypoxaemia arise?
Low inspired pO2 at e.g. high altitude.
Hypoventilation
V/Q mismatch
Diffusion impairment
Right to left shunts.
Intra-lung shunt like ARDS
What type of respiratory failure is hypoventilation?
Type 2 resp
What type of respiratory failure is V/Q mismatch?
Type 1 resp failure