Abnormal pulmonary gas exchange

Question 1

respiratory failure in type 1

Answer 1

PaO2 is less than 8kPa and paCO2 is normal or low

Question 2

respiratory failure in type 2

Answer 2

PaCO2 is greater than 6.5kPa and PaO2 is usually low

Question 3

4 abnormal states associated with hypoxaemia

Answer 3

V/Q imbalance, diffusion impairment, alveolar hypoventilation, shunt

Question 4

V/Q mismatch

Answer 4

localised poor ventilation of alveoli due to some focal disease. Hypoxaemia due to low V/Q responds well to increased oxygen concentration in poorly ventilated alveoli

Question 5

shunt

Answer 5

blood that passes from right side of heart venouss blood to the left side of the heart arterial blood without contacting any ventilated alveoli. happens as a result of pulmonary disease. cannot oxygenate because blood is going through area of lung that is not being ventilated.

Question 6

why hypoxaemic in pneumonia

Answer 6

usually V/Q mismatch because of bronchitis and focal bronchopneumonia which respond to elevations in the conc of oxygen in any inhaled air but sometimes there is shunt when there are very large areas of consolidation

Question 7

alveolar hypoventilation

Answer 7

reduction in amount of air moved in and out of chest. carbon dioxide still being delivered back to the lungs via venous blood so due to gas physics, the carbon dioxide levels rise and oxygen levels Falkland so oxygen available for gas exchange will be in short supply so arterial cons of co2 will rise and this gives you type 2 response failure. can be corrected by raising inspired air conc of oxygen

Question 8

diffusion impairment

Answer 8

no change in CO2 levels (CO2 diffuses faster), makes it take longer for blood and alveolar air to equilibrate particularly for oxygen as it is less efficient. equilibration usually takes 0.25 seconds and capillary transit time is around 0.75 but in disease equilibration takes above 0.75 seconds so there is less time for haemoglobin to be oxygenated. worse on exercise. Rarely clinically the sole cause of hypoxaemia. corrected by increasing oxygen. bad when alveolar wall is thickened

Question 9

why alveolar hypoventilation

Answer 9

tracheal obstruction, neurological problems, mechanical problems (chest wall damage), functional problems (muscle paralysis)

Question 10

COPD why hypoxaemia

Answer 10

V/Q mismatch due to airway obstruction or bronchopneumonia, diffusion impairment due to loss of alveolar surface area in emphysema, alveolar hyperventilation due to reduced respiratory drive, shunt but only due to pneumonia in acute exacerbation if really bad