Ammonia and nutritional therapy in the critically ill: when to worry, when to test and how to treat?

Abstract

Purpose of reviewHyperammonaemia is almost always develops in patients with severe liver failure and this remains the commonest cause of elevated ammonia concentrations in the ICU. Nonhepatic hyperammonaemia in ICU presents diagnostic and management challenges for treating clinicians. Nutritional and metabolic factors play an important role in the cause and management of these complex disorders.Recent findingsNonhepatic hyperammonaemia causes such as drugs, infection and inborn errors of metabolism may be unfamiliar to clinicians and risk being overlooked. Although cirrhotic patients may tolerate marked elevations in ammonia, other causes of acute severe hyperammonaemia may result in fatal cerebral oedema. Any coma of unclear cause should prompt urgent measurement of ammonia and severe elevations warrant immediate protective measures as well as treatments such as renal replacement therapy to avoid life-threatening neurological injury.SummaryThe current review explores important clinical considerations, the approach to testing and key treatment principles that may prevent progressive neurological damage and improve outcomes for patients with hyperammonaemia, especially from nonhepatic causes.

An Important, Potentially Life-Threatening Cause of Acute Adult Disorders of Consciousness Is Missing From the Evaluation Done by Chang et al

“…We recently read a comprehensive review by Chang et al (1) on acute adult disorders of consciousness (DoC) for intensivists, but we noticed that a crucial cause of DoC was not mentioned. Severe liver failure is a common cause of hyperammonemia in ICU patients and requires urgent treatment to avoid neurologic complications and even death (2). However, nonhepatic hyperammonemia in ICU patients can pose diagnostic and management challenges for clinicians (2–4).…”

“…Although diffusive therapies may have some theoretical advantages, there is no clear evidence that any particular modality is superior. Peritoneal dialysis and exchange transfusion have both been DoC as inferior treatment strategies and the role of more complex blood purification methods is still unclear (2–4). Conventional hemodialysis can rapidly reduce ammonia concentrations.…”

“…The correlation between plasma ammonia and the severity of encephalopathy and cerebral edema is somewhat variable (5). Levels of more than 100 μmol/L are highly predictive of encephalopathy in hepatic hyperammonemia, while ammonia concentrations over 150 μmol/L in adults are associated with intracranial hypertension that may lead to neurologic injury and death from brainstem herniation (2–4).…”

“…Severe liver failure is a common cause of hyperammonemia in ICU patients and requires urgent treatment to avoid neurologic complications and even death (2). However, nonhepatic hyperammonemia in ICU patients can pose diagnostic and management challenges for clinicians (2)(3)(4). Nutritional and metabolic factors can also contribute to these complex disorders and need to be considered in management (2)(3)(4).…”

“…However, nonhepatic hyperammonemia in ICU patients can pose diagnostic and management challenges for clinicians (2)(3)(4). Nutritional and metabolic factors can also contribute to these complex disorders and need to be considered in management (2)(3)(4). Causes of nonhepatic hyperammonemia, such as drugs, infection, and inborn errors of metabolism may be unfamiliar to clinicians and may be overlooked.…”