Arterial Blood Gas Interpretation

Question 1

1) Assess Oxygenation

Answer 1

Hypoxaemia
PaO2 should be 10kpa less than the Fi02 percentage

Question 2

2) Determime pH

Answer 2

Acidosis or alkalosis

Question 3

3) Determine Respiratory Component

Answer 3

Respiratory acidosis or respiratory alkalosis- if it doesn’t fit these pictures, move onto look at the metabolic component

Question 4

4) Determine the metabolic component

Answer 4

Metabolic acidosis or metabolic alkalosis (looking at the HCO3)

Question 5

5) Combine

Answer 5

Look at primary disturbance- what is causing the insult. May be a mixed picture as well.

Is there compensation;

Acidosis can be compensated by;
Respiratory- increasing resp rate. Decreases CO2
Metabolic- increase bicarbonate reabsoprtion by the kidneys. Increases HCO3

Alkalosis can be compensated by;
Respiratory- decreases resp rate. Increases CO2
Metabolic- decreases bicarbonate reabsorption by the kidney. Decreases HCO3

Partial compensation- pH not normal yet
Full- pH normal (bear this in mind in step 2- may be fully compensated)

Metabolic by the kidneys takes a few days, respiratory is fast.

Question 6

Respiratory acidosis

Answer 6

Hypoventilation

COOD, severe asthma attack, myasthenia gravis, guilloan barre syndrome

Question 7

Respiratory alkalosis

Answer 7

Hyperventilation

Anxiety
Pain
PE
pneumonia
Pulmonary oedema
Asthma attack (can also hypoventilate)

Question 8

Metabolic acidosis

Answer 8

Increased anion gap- MUDPILES (new acid added to body)

Methanol, uraemia, DKA, propylene glycol, iron (or isoniazid), lactate (SEPSIS), ethylene glycol, salicylate (aspirin) (and paracetamol)

Normal anion gap- retaining H+

Renal failure, renal tubular acidosis, Addison’s

Or losing HCO3 in diarrhoea

NB- normal value is between 10-18 (positive ions - negative ions)

Question 9

Metabolic alkalosis

Answer 9

Acid loss

Vomiting, diuretics, hyperaldosteronism (Coshing’s, Conn), hypokalaemia

NB- vomiting: due to loss of H+ from stomach (bicarb normal/raised), diarrhoea: due to loss of bicarb from intestines (will be reduced)

Question 10

Hyperventilation

Answer 10

Can cause increased or normal oxygen

Causes decreased CO2

Question 11

Type 1 Respiratory failure

Answer 11

NB- hypoxia without hypercapnia

Impaired diffusion- pneumonia, ARDS, pulmonary fibrosis

V/Q Mismatch;

Low VQ- mucus plug in asthma or COPD, airway collapse in emphysema (no ventilation as airway is blocked (V), but perfusion is fine (Q)

High V/Q- PE (ventilation is fine as airway isn’t collapsed (V), but perfusion is reduced due to embolus (Q)

Question 12

Type 2 respiratory failure

Answer 12

NB- hypoxia with hypercapnia

Alveolar hypoventilation ( CO2 can’t get out)COPD, guillian barre, central nervous system depression