Arterial blood gas interpretation

Question 1

1) When analysing a patient’s ABG, what is checked first?
2) What indicates this?

Answer 1

1) Is the patient hypoxaemic?
2) PaO2 on air is <10 kPa

Question 2

What is done next when analysing a patients ABG?

Answer 2

Check acid-base balance

Question 3

If there’s an acid/base imbalance, what is done next?

Answer 3

See if the cause is respiratory or metabolic

Question 4

1) What does a bicarbonate < 22 mmol/l suggest?
2) What does a PaCO2 < 4.7 kPa suggest?
3) What does a PaCO2 > 6.0 kPa suggest?
4) What does a bicarbonate > 26 mmol/l suggest?

Answer 4

1) Metabolic acidosis
2) Respiratory alkalosis
3) Respiratory acidosis
4) Metabolic alkalosis

Question 5

1) Name a cause of metabolic acidosis with a normal anion gap (hyperchloremic MA)
2) Name a cause of metabolic acidosis with a raised anion gap
3) Name a cause of metabolic alkalosis
4) Name a cause of respiratory acidosis
5) Name a cause of respiratory alkalosis

Answer 5

1) GI bicarbonate loss (prolonged diarrhoea, fistula, ureterosigmoidostomy), addison’s disease, renal tubular acidosis, ammonium chloride injection
2) High urate (renal failure), ketones (DKA, alcohol), lactate (sepsis, shock,hypoxia), acid poisoning (salicylate, methanol)
3) Vomiting, increased aldosterone release (causes include Conn’s syndrome - primary hyperaldosteronism - liver cirrhosis, HF, loop + thiazide diuretics)
4) COPD, decompensation in other pulmonary disorders i.e. asthma, neuromuscular disease
5) PE, hyperventilation syndromes i.e. anxiety

Question 6

Name 3 symptoms of metabolic acidosis

Answer 6

• Tachycardia
• Confusion or dizziness
• Fatigue
• Loss of appetite
• Headache
• Rapid breathing or long, deep breathing
• Nausea and vomiting
• Feeling weak
• Breath that smells sweet or fruity

Question 7

Name 3 symptoms of metabolic alkalosis

Answer 7

• Irritability.
• Muscle twitching, cramps, spasms
• Fatigue
• Confusion
• Tremor
• Tingling and numbness.
• arrhythmia
• Seizures
• Coma