ABGs

Question 1

What are the normal values for ABGs?

Answer 1

H+ = 36-43 mmol/L
PH = 7.35-7.45
PaCO2 = 4.6-6.0 kPa
PaO2 = 10.5 - 13.5 kPa
HCO3 = 23-30 mmol/L

Question 2

What defines resp failure?

Answer 2

PaO2 <8 kPa on room air (21% O2)
* if they are on O2 therapy it should be around 10kPa less than inspired O2 level

Question 3

Results for metabolic acidosis

Answer 3

H+ = raised
HCO3 = decreased
PCO2 = decreased (if compensation present)

Question 4

Results for metabolic alkalosis

Answer 4

H+ = decreased
HCO3 = raised
PCO2 = raised (if compensation present)

Question 5

Results for respiratory acidosis

Answer 5

H+ = raised
PCO2 = raised
HCO3 = raised (if compensation present)

Question 6

Results for respiratory alkalosis

Answer 6

H+ = decreased
PCO2 = decreased
HCO3 = decreased (if compensation present)

Question 7

Define type 1 respiratory failure and possible causes

Answer 7

= normal/low PaCO2 (with low PaO2)
- aim for SpO2 94-98%

• pneumonia
• PE
• pulmonary oedema
• pulmonary fibrosis

Question 8

Define type 2 respiratory failure and possible causes

Answer 8

= raised PaCO2 (with low PaO2)
- aim for SpO2 88-92%

• COPD
• neuromuscular disease/ severe kyphoscoliosis
• obesity hypoventilation

Question 9

How do you calculate the anion gap and what is the normal value for this?

Answer 9

Anion gap = [Na+] - ([Cl-] + [HCO3-])
Normal = 8-16 mmol/L
(Used in differential diagnosis of metabolic acidosis)

Question 10

Reasons for raised anion gap

Answer 10

• making too much H+/can’t excrete H+
• renal failure
• diabetic or other ketoacidosis
• lactic acidosis
• toxins eg. Salicylate

Question 11

Reasons for normal anion gap in metabolic acidosis

Answer 11

• losing too much HCO3
• renal tubular acidosis
• diarrhoea
• carbonic anhydrase inhibitors
• ureteric diversion