Metabolism
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An unconscious child with hyperammonaemia and keto-acidosis
At the
age of 28 weeks Angela was admitted to the Emergency Department at her local
hospital in a coma, having suffered a convulsion after feeding. She had a mild
infection and slight fever at the time.
Since birth she had been a sickly child, and she frequently vomited and became drowsy after feeding. She was bottle fed and at one time cows’ milk allergy was suspected, although the problems persisted when she was fed on a soya-milk substitute. She had always shown poor muscle tone, and indeed at times was described as a "floppy baby", unable to hold her head up unsupported.
On admission she was moderately hypoglycaemic (plasma glucose 2.8 mmol /), ketotic and her plasma pH was 7.29. Analysis of a blood sample showed normal levels of insulin, but considerable hyperammonaemia (plasma ammonium ion concentration 500 µmol/L; reference range 40 - 80 µmol/L).
She was ketotic and acidotic. What treatment would be appropriate for this?
The standard treatment for acidosis is intravenous bicarbonate to permit respiratory compensation for the acidosis by shifting the bicarbonate / carbon dioxide equilibrium to the left
She was hypoglycaemic. What treatment would be appropriate for this?
Intravenous glucose.
What would be the appropriate treatment for her hyperammonaemia?
A rectal infusion of lactulose.
See the exercise on Hyperammonaemic coma due to liver failure for discussion of how intestinal bacterial fermentation of lactulose acidifies the intestinal contents and permits lowering of plasma ammonia.
Click here for a summary of the ammonia-lowering action of the products of lactulose fermentation. Press the space bar to advance the animation
A glucose tolerance test gave normal results, and she showed a normal increase in insulin secretion in response to the glucose load.