Causes of Hypoxemia Flashcards
What are the causes of hypoxemia?
- Lowered inspired PO2
- Alveolar hypoventilation
- Diffusion limitation
- Right to Left shunt
- Ventilation to perfusion mismatch
What causes a lowered inspired O2?
i. Lower barometric pressure
ii. Decrease FiO2
What is the consequence of lowered inspired O2?
Low PaO2, PAO2, PaCO2, and PACO2
Carotid body stimulation
Hyperventilation
Increase respiratory rate
What are some diagnostics for hypoxemia from lowered inspired O2?
Arterial blood gas test
What causes alveolar hypoventilation?
i. Obstruction of airway
ii. Paralysis of weakened respiratory muscles (diaphragm)
iii. CNS suppression with drugs
What are the consequences of alveolar hypoventilation?
-Lower PaO2 and PAO2
-Higher PaCO2 and PACO2
Lower ventilation to alveoli, the PCO2 goes up because the VCO2 that the tissues are making is still the same
How could you diagnose Alveolar hypoventilation?
Arterial blood gas
What is the cause of diffusion limitation in the lungs?
Thickening of the blood gas barrier
What are the consequences of diffusion limitations?
Can be severe only at exercise
Low PaO2
High PaCO2
How do you diagnose diffusion limitation?
Measure DL
What are some causes of a L-R shunt?
i. Bronchial circulation emptying into pulmonary veins
ii. Coronary venous blood enters LV via Thebesian veins
iii. Congenital effect venous blood enters arterial circulation- PDA, septal defect
iv. Atelectasis of the lung
What are the consequences of a R-L shunt?
Lowered PaO2
Higher PaCO2
How can you diagnose a RL shunt?
Iso-shunt graph and shunt equations
What are the causes of ventilation perfusion mismatch?
i. Some normal variation of this (not severe)
ii. Lung disease
Get a larger difference in alveolar O2 vs arterial O2
What are the consequences of Va/Q mismatch?
Lowered PaO2
Higher PaCO2
