1- Diamox, a diuretic which causes bicarbonate wastage
(bicarbonaturia).
2- Renal tubular acidosis (RTA); resulting from either:
a. Type I, classic (Distal) RTA: In this condition, there is
inability to secrete H+ load.
b. Type II, proximal RTA: In this condition, the PCT is unable
to reabsorb HCo 3 - as there is a set up of HCo 3 - Tm at low
level e.g. HCo 3 - Tm of 16 mmol/l, so any HCo 3 - above this
concentration will be lost in urine.
c. Type III RTA: There is both inability to secrete H+ load
and proximal HCo 3 - wastage.
d. Type IV RTA: There is hyperkalaemic hyperchloraemic
metabolic acidosis with hyporeninaemic
hypoaldosteronism. This is usually seen in diabetics with
mild renal impairment.B- Gastrointestinal causes of metabolic acidosis with normal anion
gap:
1- Diarrhoea; There is loss of K+ and HCo 3 - , every litre of
diarrhoea fluid contains 30-50 mmol of HCo 3 -.
2- Fistula or tube drainage: Each litre of the small intestinal fluid
contains 60 mmol HCo 3 - while pancreatic fluid contains 120
mmol/litre.
3- Ureterosigmoid or ileal loop urine diversion: In these
conditions there is loss of mucosal HCo 3 - (normally present in
high concentration in intestinal mucous) in exchange with the
urinary CL- (hyperchloraemia).