Respiratory failure

Question 1

What is cytotoxic hypoxia

Answer 1

• reduced ability to utilise O₂

Question 2

Intrapleural pressure

Answer 2

• slightly more negative at the bottom of the lungs

Question 3

Why and how does ventilation vary where you are in the lungs?

Answer 3

• at the apex of the lung, the perfusion (Q) is lowest
• moving up the lung ventilation progressively increases
• ventilation highest at the base

Question 4

How and does perfusion vary at the lungs?

Answer 4

• perfusion at the apex of the lungs is really low: PA >Pa>Pv
• in the middle of the lung, perfusion is sporadic: Pa>PA>Pv
• at the base of the lungs, perfusion is constant: Pa>Pv>PA

Question 5

What is the V/Q ratio at the apex of the lungs?

Answer 5

• greater than 1
• ventilation > perfusion

Question 6

the watershed effect in zone 2 of the lungs

Answer 6

• Alveolus pressure is similar to arterial pressure which allows perfusion to occur
• when they reach the venule end the alveolar pressure is greater than venule pressure
• occludes the blood way until arterial pressure builds enough to overcome it

Question 7

Explain Hypoxemia due to reduced PiO₂ (partial pressure of inspired oxygen)

Answer 7

• decreased atmospheric pressure results in decreased PiO₂ even though the concentration of oxygen in the air is the same
• therefore…

Question 8

Explain Hypoxemia due to Hypoventilation

Answer 8

• inadequate alveolar ventilation
• leads to low alveolar PO₂
• Hypoxaemia accompanying a reduced PIO2 or hypoventilation is characterised by normal A-a gradient (DA‐aO2).

Question 9

Explain Hypoxemia due to diffusion limitation

Answer 9

• pressure of oxygen in the blood increases
• due to a thicker membrane
• higher risk of not equilibrating
• increasing the pressure gradient between the alveoli and the arterial pressures

Question 10

Explain Hypoxemia from V/Q mismatch

Answer 10

• blood from areas with a high VA/Q mixes with blood from low Va/Q areas
• this leads to low pulmonary venous PO2

Question 11

What is the V/Q ratio in the middle of the lungs?

Answer 11

• 1
• ventilation is the same as perfusion

Question 12

What is the V/Q ratio at the base of the lungs?

Answer 12

• less than 1
• ventilation < perfusion

Question 13

Explain Hypoxaemia due to right-to-left shunt

Answer 13

• shunted blood fails to undergo gas exchange
• intrapulmonary shunt: arteriovenous malformations, lung consolidation (pneumonia)
• Intracardiac shunt: congenital or acquired heart defects
• it mixes with pulmonary capillary blood→ low pulmonary venous/left ventricular PO2
• therefore decreased oxygenated blood goes around the body
• giving oxygen does not fix the issue

Question 14

What is hypercarbic respiratory failure? also what is the cause

Answer 14

• increased PCO₂

- due to weakness or increased dead space

• increasing VE (ventilation) can compensate however patients are at risk of respiratory failure due to fatigue or developing pneumonia