Acid/Base disorders

Question 1

Causes of metabolic acidosis

Answer 1

Metabolic acidosis is commonly classified according to the anion gap.

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

Question 2

Causes of metabolic alkalosis?

Answer 2

Metabolic alkalosis may be caused by a loss of hydrogen ions or a gain of bicarbonate. It is due mainly to problems of the kidney or gastrointestinal tract

Causes
-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 3

Causes of 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 of respiratory alkalosis?

Answer 4

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