ABG's

Question 1

What are the indications for ABG?

Answer 1

exacerbations of COPD - titrating inspired oxygen concentration.
severe asthma
diabetic Ketoacidosis
severe sepsis
acute LVF and pulmonary oedema.
post-resuscitation
tricyclic antidepressant & opiate overdose

Question 2

Where is ABG sampling carried out?

Answer 2

• radial artery at wrist

- femoral artery at groin

Question 3

What test is done before ABG sampling is carried out?

Answer 3

Allan’s test - occlude both radial/ulnar arteries until hand turns pale, release ulnar artery and if colour returns patency of ulnar artery is confirmed

Question 4

What are the normal ranges for:

• pH
• H+
• PO2
• PCO2
• Bicarb
• Base excess

Answer 4

pH: 7.35-7.45
H+: 35-45
PO2: 10.0-13.3kPa
PCO2: 4.7-6.0 kPa
Bicarb: 24-30mmol/l
Base Excess: -2 to +2

Question 5

What is important to record when doing an ABG

Answer 5

Inspired oxygen - as if pt is on oxygen ‘normal ranges’ for ABG’s grossly abnormal

Question 6

what is base excess?

Answer 6

this is the amount of acid that would needed to be added to bring the pH back to normal.

• if this is negative: acid needs taken away = acidotic
• if this is positive: acid needs added = alkalotic

Question 7

what is an acidosis with elevated PaCO2?

Answer 7

respiratory acidosis

Question 8

What is an acidosis with low PaCO2?

Answer 8

Metabolic acidosis

Question 9

What is an alkalosis with low PACO2?

Answer 9

Respiratory alkalosis

Question 10

What is an alkalosis with high PaCO2?

Answer 10

Metabolic alkalosis

Question 11

What is anion gap used for?

Answer 11

provides useful information in assessing intoxications and the cause of a metabolic acidosis
-may get an abnormal anion gap with acidoses and can class the acidosis by presence or absence of an anion gap

Question 12

Are anions +ve or -ve?

Answer 12

-ve

Question 13

Are cations +ve or -ve?

Answer 13

+ve

Question 14

How to work out anion gap?

Answer 14

(Na + K) - (Cl + HCO)

Question 15

What is the normal range for the anion gap?

Answer 15

-4 to +12

Question 16

if the anion gap is elevated what does this indicate?

Answer 16

-excess or exogenous acid

Question 17

if the anion gap is decreased what does this indicate?

Answer 17

• this is less common

- lab error, myeloma or hypoalbuminaemia

Question 18

List some causes of elevated anion gap associated with metabolic acidosis

Answer 18

M - methanol
U - uraemia
D- DKA/alcohol ketoacidosis
P- Paraldehyde
I - isoniazid
L - lactic acidosis
E - Ethylene glycol
S - Salicylate

Question 19

If the bicarbonate is raised in a COPD patient what does this suggest?

Answer 19

-chronic CO2 retainer