Unsolicited show notes for Core EM, ep. 24.0 on hepatic encephalopathy.
- Liver failure can result in the buildup of ammonia in the blood.
- High levels of ammonia interfere with cognitive function.
- Ammonia level is not particularly helpful, especially in the ED. More useful for trending relative to a known baseline. Hepatic encephalopathy is a clinical diagnosis.
- Don’t anchor on HE; patients with liver failure are at risk for a slew of other problems too.
Ong, et al. evaluated whether or not there was a correlation between the severity of HE and ammonia level. Although levels of “ammonia increased with the severity of hepatic encephalopathy, “there remains substantial overlap in ammonia levels by grade of hepatic encephalopathy, which may be explained by variability in ammonia levels throughout the day, a possible lag between elevation in ammonia level and hepatic encephalopathy in some patients, or the possibility that compounds other than ammonia are also involved in the pathogenesis of hepatic encephalopathy.”
As the severity of HE increases, the distribution becomes more and more shotgunny. Ong et al. agree with Swami:
Because of the substantial overlap in total ammonia levels and partial pressures between cirrhotic patients with and without hepatic encephalopathy, a single level has little clinical utility in the diagnosis of hepatic encephalopathy. A careful clinical evaluation in patients with cirrhosis presenting with altered mental status remains the “gold standard” for diagnosis.
Ong JP, Aggarwal A, Krieger D, et al. Correlation between ammonia levels and the severity of hepatic encephalopathy. Am J Med. 2003;114(3):188-93.