List 4 causes of an elevated serum ammonia concentration in critically ill patients
Inherited disorders of urea cycle
Drugs: Valproate, glycine, carbamezapine
Increased protein load: GI bleed, TPN,
Infection with urease splitting organisms – proteus Gastric bypass, urinary diversion procedures Cancers – myeloma
This question closely resembles, though is not identical to, Question 14 from the second paper of 2012. There, one may find a discussion of the usefulness of the serum ammonia levels in critical illness.
Here, one is merely expected to regurgitate a series of differentials.
Using a familiar template, an easily remembered list would look like this:
- Hepatic vascular insufficiency, eg. hepatic necrosis due to ischaemia
- Hepatic failure
- Portosystemic shunts
- Infection with urea splitting organisms eg. Proteus mirabilis, H.pylori
- Multiple myeloma
- Drugs - eg. valproate, carbamazepine
- Congential disorders of urea cycle
- Increased protein catabolism, eg. chemotherapy, starvation, GI bleeding, or TPN
More detail, you beg? Impossibly large tables, useless for the purpose of rapid revision?
Vascular and cardiac causes
Urinary and renal causes
Endocrine and Metabolic causes
Another method of arranging the differentials, according to the physiological mechanism:
Increased substrate for ammoniagenesis
Bypass of normal metabolism
Acquired urea cycle defects
Congenital urea cycle defects
Excess of exogenous ammonia
Reabsorption of excreted ammonia
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