Metabolic Mayhem a Headache

1. There is a metabolic acidosis with a high anion gap (HAGMA).
2. The bicarbonate has decreased by more than the anion gap has increased which is due to a coexistent normal anion gap acidosis (NAGMA).
3. There is a respiratory alkalosis. The pCO2 of 12mmHg is much lower than the respiratory compensation you would expect with this degree of metabolic acidosis (expected pCO2 = 1.5 * HCO3 +8 = 25 ).

The combination of these three abnormalities has led to relatively normal pH despite severe acid-base disturbance.

There are two ways of remembering this.

The easy way is to remember ‘left total knee replacement’:

Lactate
Toxins
Ketones
Renal Failure

The more complicated way is CATMUDPILES:

Cyanide, Carbon monoxide
Alcoholic ketoacidosis
Toluene
Methanol, metformin
Uraemia
Diabetic Ketoacidosis
Phenformin, pyroglutamic acidosis, propylene glycol, paracetamol
Isoniazid, Iron
Lactic acidosis (many causes)
Ethanol, Ethylene glycol
Starvation, salicylates

The history suggests starvation ketoacidosis. There were ketones in the urine confirming this diagnosis.

The easy way to remember is OGRe:

Others (eg chloride)
GI loss of bicarb
Renal loss of bicarb

The more difficult way is to remember is USED CARP (the A and the R can be reversed – this is optional):

Ureteroenterostomy
Small bowel fistula
Extra Chloride
Diarrhoea
Carbonic anhydase inhibitors
Addisons disease
Renal tubular acidosis
Pancreatic fistula

Neurosurgeons like to give everyone lots of normal saline. The chloride is high.

The likely diagnosis is hyperchloraemic metabolic acidosis secondary to normal saline.