ABG

Question 1

pH normal range

Answer 1

7.35 - 7.45

Question 2

PaO2 normal range

Answer 2

11-13 kpa

Question 3

PaCo2 normal range

Answer 3

4.7 - 6 kPa

Question 4

HCO3- normal range

Answer 4

24-30 mmol/l

Question 5

base excess normal range

Answer 5

-2 to 2+ mmol/l

Question 6

anion gap normal range

Answer 6

12-16 mmol/l

Question 7

Rule of thumb for expected PaO2?

Answer 7

expected PaO2 (kPa) is roughly 10 less than the FiO2

Question 8

If a PaO2 is lower than expected, what does this imply & what could be causing it?

Answer 8

that a disease process in the lungs is interfering with gas exchange

e.g. pulm fibrosis, PE, pneumonia, pulmonary oedema

Question 9

What PaO2 to count as resp failure?

& T1 and T2?

Answer 9

<8

T1: <6.5 PaCO2 (kPa)
T2: >6.5 PaCO2 (kPa)

memory aid:
in type ONE resp failure, ONE gas is abnormal
in type TWO resp failure, TWO gases are abnormal

Question 10

Common causes of T1 RF

Answer 10

pneumonia
pulmonary oedema
pulmonary embolism
pulmonary fibrosis

Question 11

Common causes of T2 RF

Answer 11

COPD
resp centre depression
resp muscle weakness
abnormal chest wall architecture

Question 12

Causes of resp acidosis

Answer 12

any of the causes of Resp failure

Question 13

Causes of resp alkalosis

Answer 13

always due to hyperventilation

• anxiety
• underlying severe disease process, such as sepsis or stroke

Question 14

Causes of metabolic acidosis

Answer 14

ALWAYS CALCULATE ANION GAP

Normal:
- HCO3- loss from gut e.g. diarrhoea

Raised (>16):

• ketoacidosis
• renal failure
• lactic acidosis
• salicyclate toxicity
• methanol ingestion
• ethylene glycol (antifreeze) ingestion

Question 15

Causes metabolic alkalosis

Answer 15

excessive vom (classically pyloric stenosis)
other GI losses
primary or secondary hyperaldosteronism
hypercalcaemia
use of diuretics
bicarbonate ingestion

Question 16

is low HCO3- alkalosis or acidosis?

Answer 16

acidosis

Remember: bicarbonate is an alkaline substance ((some people take sodium bicarb to combat stomach acid), so an excess of it is seen in alkalosis and a shortage in acidosis)