aka Metabolic Muddle 010
You’ve just been handed over a patient who has an altered mental status when the phone rings. It’s the lab – you’re told that your patient has a serum ammonia level of 250 umol/L (reference range, 11-35 umol/L).
Q1. What are the possible causes of hyperammonaemia?
Answer and interpretation
Except for obvious liver failure, hyperammonaemia is easily forgotten as a potential cause of metabolic encephalopathy. Ammonia is produced by the hepatic metabolism of amino acids and is primarily degraded via the urea cycle.
The causes of hyperammonemia include:
Overproduction of ammonia
- Protein load
- gastrointestinal hemorrhage
- gastric bypass
- multiple myeloma
- allogeneic stem cell transplantation
- parenteral nutrition
- Increased catabolism
- vigorous exercise
- urease-producing infection (e.g. Proteus and Klebsiella spp.)
- congenital ureteric obstruction associated with infection
- Liver failure (acute or chronic)
- Drugs and toxins
- hepatotoxic drugs (e.g. paracetamol, halothane) and toxins (e.g. mushrooms)
- Metabolic errors
- urea cycle disorders
- organic acidaemias
- fatty acid oxidation disorders
In the absence of obvious liver dysfunction or a drug cause, metabolic errors should be considered. Some metabolic errors can go undiagnosed until adulthood.
- Crosbie DC et al. Late-onset ornithine transcarbamylase deficiency: a potentially fatal yet treatable cause of coma. Crit Care Resusc. 2009 Sep;11(3):222-7. [PMID 19737127]
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.