List 4 causes of an elevated serum ammonia concentration in critically ill patients
College Answer
Hepatic failure
Inherited disorders of urea cycle
Drugs: Valproate, glycine, carbamezapine
Porta-systemic shunts
Increased protein load: GI bleed, TPN,
Infection with urease splitting organisms – proteus Gastric bypass, urinary diversion procedures Cancers – myeloma
Chemotherapy.
Discussion
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
Infections
Neoplasms
Drugs
|
Congenital causes
Autoimmune 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
|
References
Conway, Edward Joseph, and Robert Cooke. "Blood ammonia." Biochemical Journal 33.4 (1939): 457.
Shambaugh, G. E. "Urea biosynthesis I. The urea cycle and relationships to the citric acid cycle." The American journal of clinical nutrition 30.12 (1977): 2083-2087.
McDermott Jr, William V., Raymond D. Adams, and Athol G. Riddell. "Ammonia metabolism in man." Annals of surgery 140.4 (1954): 539.
Vince, Angela, et al. "Ammonia production by intestinal bacteria." Gut 14.3 (1973): 171-177.
Vince, Angela J., and Sigrid M. Burridge. "Ammonia production by intestinal bacteria: the effects of lactose, lactulose and glucose." Journal of medical microbiology 13.2 (1980): 177-191.
Dohrenwend, Paul, and Richard D. Shih. "Glycine Induced Hyperammonemia After Bladder Rupture During Transurethral Resection of a Bladder Tumor." Journal of Medical Cases 4.4 (2013): 250-253.
Felipo, Vicente, and Roger F. Butterworth. "Neurobiology of ammonia." Progress in neurobiology 67.4 (2002): 259-279.
Hashim, Ibrahim A., and Jennifer A. Cuthbert. "Elevated ammonia concentrations: Potential for pre-analytical and analytical contributing factors." Clinical biochemistry 47.16 (2014): 233-236.
Clay, Alison S., and Bryan E. Hainline. "Hyperammonemia in the ICU." CHEST Journal 132.4 (2007): 1368-1378.
Weng, Te-I., Frank Fuh-Yuan Shih, and Wen-Jone Chen. "Unusual causes of hyperammonemia in the ED." The American journal of emergency medicine 22.2 (2004): 105-107.
Hawkes, N. D., et al. "Non-hepatic hyperammonaemia: an important, potentially reversible cause of encephalopathy." Postgraduate medical journal 77.913 (2001): 717-722.