Acid-base abnormality

Question 1

Causes of normal anion gap metabolic acidosis

Answer 1

GI bicarbonate loss: diarrhoea, uterosignoidostomy, fistula

Renal tubular acidosis

Drugs e.g. acetozolamide

Ammonium chloride injection

Addison’s disease

Question 2

Causes of raised anion gap metabolic acidosis

Answer 2

Lactate: shock, hypoxia

Ketones: DKA, alcohol

Urate: renal failure

Acid poisoning: salycylates, methanol

Question 3

Causes of metabolic alkalosis

Answer 3

Vomiting/ aspiration

Liquorice, carbenoxolone

Hypokalaemia

Primary hyperaldosteronism

Cushing’s syndrome

Bartter’s syndrome

Congenital adrenal hyperplasia

Question 4

Causes of respiratory acidosis

Answer 4

COPD

Decompensation in other respiratory conditions e.g. life-threatening asthma/ pulmonary oedema

Sedative drugs: benzodiazepines, opiate overdose

Question 5

Causes of respiratory alkalosis

Answer 5

Anxiety leading to hyperventilation

Pulmonary embolism

Salicylate poisoning

CNS disorders: stroke, SAH, encephalitis

Altitude

Pregnancy

Question 6

Anion gap calculation

Answer 6

(Na+ + K+) - (Cl- + HCO3-)

Normal range is 10-18mmol/L

Question 7

Salicylate poisoning

Answer 7

Early stimulation of respiratory centre leads to a respiratory alkalosis

Later the direct acid effects of salicylates (combined with acute renal failure) may lead to an acidosis