ABGS

Question 1

What is the normal range of paco2?

Answer 1

4.7-6

Question 2

What is the normal range for PaO2?

Answer 2

11-13

Question 3

What is the normal range for HCO3-?

Answer 3

22-26

Question 4

What is FiO2?

Answer 4

Fraction of inhaled O2

Question 5

What is type 1 and type 2 Resp failure?

Answer 5

Type 1 = hypoxia
Type 2 = hypoxia and hypercapnia

Question 6

What is the mechanism behind type 1 Resp failure?

Answer 6

Ventilation perfusion mismatch
The volume of air flowing is not matched to flow of blood in lung tissue

Question 7

What are some examples of type 1 Resp failure? (3)

Answer 7

Pulmonary oedema
Bronchoconstriction
Both reduced ventilation and normal perfusion

PE
Reduced perfusion with normal ventilation

Question 8

What is the mechanism for type 2 Resp failure?

Answer 8

Alveolar hypoventilation
Prevents adequate oxygenation and can’t eliminate CO2 form blood

Question 9

What are 4 examples of type 2 Resp failure and how they work?

Answer 9

• Increased resistance due to airway obstruction
• e.g. COPD
• Reduced compliance of lung tissue/chest wall
• e.g. pneumonia, rib fractures, obesity
• Reduced strength of respiratory muscles
• e.g. Guillain-Barre, MND
• Drugs acting to reduce ventilation
• e.g. opiates

Question 10

How does blood become acidic in resp acidosis?

Answer 10

CO2 binds to H2O and forms H2CO3 (carbonic acid)

Question 11

What is respiratory compensation?

Answer 11

Occurs quickly
Increasing or decreasing alveolar ventilation to blow off or retain co2

Question 12

What is metabolic compensation?

Answer 12

Takes a few days to occur
Kidneys either reduce or increase HCO3-

Question 13

What is the main mechanism that causes Resp acidosis?
Give 5 examples of how this occurs

Answer 13

Inadequate ventilation leads to CO2 retention

Resp depression from opiates
COPD
Asthma
Msk e.g. guillaim barre
Iatrogenic e.g. incorrect ventilation settings

Question 14

What is the main mechanisms of Resp alkalosis?
Give 6 examples of how this occurs.

Answer 14

Excessive alveolar ventilation (hyperventilation) blows co2 off

Anxiety
Pain increases Resp rate
Hypoxia leads to increased ventilation in order to compensate
PE
Pneumothorax
Iatrogenic (excessive ventilation)

Question 15

Both anxiety and PE cause Resp alkalosis how would you tell the difference?

Answer 15

Anxiety = raised PaO2
PE = reduced PaO2

Question 16

What are the 2 main causes of metabolic acidosis?
Give examples that fit into each mechanism

Answer 16

Increased acid production = high anion gap
- DKA
- lactic acidosis
- aspirin overdose
- renal failure

Decreased acid excretion/increased rate of HCO3- loss = normal anion gap
- GI loss of HCO3- e.g. diarrhoea
- renal tubular disease
- Addisons disease

Question 17

What is the mechanism that causes metabolic acidosis?
Give 3 examples

Answer 17

Decreased H+ concentration causes increase in bicarbonate

• GI loss of H+ = vomiting
• renal loss of H+ e.g.loop and thiazide diuretics, HF, nephrotic syndrome, cirrhosis,conns (these all increase aldosterone activity .: increasing h+ loss)
• iatrogenic

Question 18

What can cause mixed acidosis? (3)

Answer 18

Cardiac arrest
Multi organ failure
Severe COPD with sepsis

Question 19

What can cause mixed alkalosis? (3)

Answer 19

Liver cirrhosis in addition to diuretic use
Hyperemesis gravidaeam
Excessive ventilation in COPD

Question 20

What is the equation of the anion gap?

Answer 20

Cations - anions

(Na+ + K+) - (Cl- + HCO3-)

Question 21

What is the normal range for anion gap?

Answer 21

4-12