Resp Investigations

Question 1

List some common lung function tests

Answer 1

PEFR
Spirometry
Lung volumes + diffusion capacity
Muscle function tests
Exercise tests

Question 2

Give 2 contraindications of spirometry

Answer 2

MI within the last 12 weeks

Unresolved pneumothorax

Question 3

Explain why someone with IPF may not be able to breathe out for the full 6 seconds during spirometry

Answer 3

IPF = restrictive lung disease. Increased lung elastic recoil, but decreased compliance, so as soon as they exhale, the airways collapse down. Therefore air expelled quickly, long before 6 seconds.

Question 4

Give 2 uses of flow volume loops

Answer 4

Picks up early small airway disease

Can distinguish between intra and extra thoracic obstruction

Question 5

List 4 causes of increased diffusion capacity

Answer 5

Pulmonary haemorrhage
Polycythaemia
Athlete - very fit
Alveolar inflammation

Question 6

What are the normal ranges on an ABG?

Answer 6

pH: 7.35 - 7.45
PaO2: >10kPa
PaCO2: 4.7 - 6kPa
Base excess: -2 to +2mmol/L

Question 7

What does a high base excess suggest?

Answer 7

Lots of HCO3- in blood - usually metabolic alkalosis (but could be comp resp acidosis)

Question 8

What does a low base excess suggest?

Answer 8

Little HCO3- in blood - usually metabolic acidosis (but could be comp resp alkalosis)

Question 9

A patient has a low pH, high pCO2, and low HCO3-

What is going on?

Answer 9

Mixed acidosis - resp and met

Question 10

If you’re not sure if an ABG is deranged due to something like anxiety or an actual lung pathology, what could you do?

Answer 10

An alveolar-arterial gradient

Question 11

Why do you get tingly lips when you hyperventilate?

Answer 11

As blood becomes more alkalotic, H+ ions dissociate from albumin to lower pH. This leaves more albumin to bind to free calcium ions, reducing free calcium ion concentration, resulting in parasthesia.

Question 12

Why does sepsis cause metabolic acidosis?

Answer 12

Reduced end-organ perfusion results in anaerobic respiration, producing lactate - cause metabolic acidosis

Question 13

Why does cardiac arrest tend to cause a mixed acidosis?

Answer 13

During arrest, there is a period of both decreased ventilation and decreased end organ perfusion. This results in both increased CO2, and increased lactate - both contribute to acidosis.