Abstract

Ammonia is a compound that is thought to be central to the pathogenesis of hepatic encephalopathy. It is an important biomarker and may also serve as a prognostic indicator in acute liver disease where ammonia levels may be predictive of cerebral edema and herniation. In this chapter, we aim to review and discuss its role in hepatic encephalopathy to include: the cycle within the human body, appropriate measurement and collection, confounding factors and differential diagnosis, the correlation between levels and development of encephalopathy, the physiopathology and increased morbiditymortality with the incremental rise, clinical utility of sequential measurement, and lastly, an overview of novel treatments and the tight interconnections with ammonia.

Keywords: ammonia, hepatic encephalopathy, role, pathogenesis, novel treatment

### 1. Introduction

Ammonia, a colorless gas with a unique odor is thought to be central to the pathogenesis of hepatic encephalopathy (HE). It is an important biomarker and may also serve as a prognostic indicator in acute liver disease where ammonia levels may be predictive of cerebral edema and herniation. In this chapter, we aim to review and discuss its role in HE understanding its rise and fall as part of the urea cycle, appropriate measurement and collection, and examine the paradigms differentiating acute liver failure with chronic liver disease. We want to recognize other diseases that may elevate ammonia levels and discuss how different treatments target its reduction.
