ABGs

Question 1

Mnemonic for ABGs

Answer 1

ROME

Respiratory = pH and CO2/HCO3 are Opposite
(All increase/decrease together)

Metabolic = pH and CO2/HCO3 are Equal
(pH increases as CO2/HCO3 decreases and vice versa)

Question 2

Causes for Respiratory Alkalosis

Answer 2

anxiety leading to hyperventilation
pulmonary embolism
salicylate poisoning*
CNS disorders: stroke, subarachnoid haemorrhage, encephalitis
altitude
pregnancy

Question 3

Causes for Respiratory Acidosis

Answer 3

COPD
decompensation in other respiratory conditions e.g. life-threatening asthma / pulmonary oedema
sedative drugs: benzodiazepines, opiate overdose

Question 4

Causes for Metabolic Alkalosis

Answer 4

vomiting / aspiration (e.g. peptic ulcer leading to pyloric stenos, nasogastric suction)
diuretics
liquorice, carbenoxolone
hypokalaemia
primary hyperaldosteronism
Cushing's syndrome
Bartter's syndrome
congenital adrenal hyperplasia

Question 5

Causes for Metabolic Acidosis

Answer 5

Chloride <10-18>

Normal anion gap ( = hyperchloraemic metabolic acidosis)

• gastrointestinal bicarbonate loss: diarrhoea, -
• ureterosigmoidostomy, fistula
• renal tubular acidosis
• drugs: e.g. acetazolamide
• ammonium chloride injection
• Addison’s disease

Raised anion gap

• lactate: shock, hypoxia
• ketones: diabetic ketoacidosis, alcohol
• urate: renal failure
• acid poisoning: salicylates, methanol