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Preparing the Malnourished Patient for Parenteral Nutrition (PN)
Published in Michael M. Rothkopf, Jennifer C. Johnson, Optimizing Metabolic Status for the Hospitalized Patient, 2023
Michael M. Rothkopf, Jennifer C. Johnson
Similarly, hyperammonemia can occur if the patient’s liver is unable to properly process the protein intake provided in the parenteral nutrition. Patients who have underlying liver disease, whether diagnosed or not, may develop elevations in their ammonia levels on PN therapy. On rare occasions, this phenomenon has provided an opportunity to diagnose a urea cycle disorder was not previously identified.
Inborn Errors of Metabolism
Published in Praveen S. Goday, Cassandra L. S. Walia, Pediatric Nutrition for Dietitians, 2022
Surekha Pendyal, Areeg Hassan El-Gharbawy
The purpose of the urea cycle is to convert the ammonia arising from ingested protein and endogenous protein turnover to urea in the liver. Six different enzymes and two transport proteins are required for the completion of the urea cycle (Figure 23.4). Deficiency in any of the six enzymes can result in the buildup of ammonia to toxic levels causing neurologic damage. Deficiencies in transport proteins, citrin, and ornithine translocase cause metabolic disorders that are clinically different from the classic UCD. Except for OTC deficiency, all enzyme defects in the urea cycle are inherited in an autosomal-recessive manner. OTC deficiency is inherited as an X-linked dominant trait and is usually lethal in males. Hyperammonemia is a common biochemical feature of all UCDs with the proximal enzyme defects (e.g., Carbamoylphosphate synthetase I [CPS I], argininosuccinate synthetase [ASS]) generally having a more severe presentation than distal defects (e.g., argininosuccinic acid lyase [ASL], arginase [ARG]).
Cellular and Immunobiology
Published in Karl H. Pang, Nadir I. Osman, James W.F. Catto, Christopher R. Chapple, Basic Urological Sciences, 2021
Masood Moghul, Sarah McClelland, Prabhakar Rajan
At times of cellular stressProteins are broken down into amino acids for energy source and enter the TCA cycle.Ammonia, a highly toxic byproduct of amino acid breakdown, must be excreted.The conversion of ammonia into urea (urea cycle) takes place in the liver (and to a lesser extent, in the kidneys).
Current understanding of the etiology of cyclic vomiting syndrome and therapeutic strategies in its management
Published in Expert Review of Clinical Pharmacology, 2022
Rosita Frazier, Thangam Venkatesan
Testing for CVS should generally be limited to upper endoscopy and abdominal imaging to rule out organic pathology such as gastric volvulus or intermittent small bowel obstruction. Biochemical testing including CBC, basic chemistry panel, amylase, lipase, and liver tests may be performed. Gastric emptying can be normal, delayed, and often rapid in CVS and is not recommended. Extensive testing should be avoided and only pursued in the appropriate clinical setting [56,57]. For example, brain imaging might be considered in patients with localized neurological symptoms. In the appropriate setting, other conditions such as acute hepatic porphyria which can have a similar clinical presentation might be considered. In this scenario, testing with a spot urine porphobilinogen and aminolevulinic acid should be done. If hypoglycemia or hyponatremia is noted, testing for adrenal insufficiency is recommended. In children, investigations to rule out urea cycle defects are recommended when episodes are triggered by fasting, intercurrent illness, or high protein meals.
Hyperammonemia in the setting of Roux-en-Y gastric bypass presenting with osmotic demyelination syndrome
Published in Journal of Community Hospital Internal Medicine Perspectives, 2021
Carly Rosenberg, Michael Rhodes
With the increasing rate of obesity in the USA, bariatric surgery continues to be offered as a weight loss treatment. However, over time, there have been multiple case reports on the correlation between RYGB and hyperammonemia in the absence of cirrhosis or liver disease [1–4]. The onset of hyperammonemic encephalopathy after RYGB has been shown to present at various intervals, ranging from months to years [1]. In this case, the patient had a RYGB approximately 20 years prior to presentation. RYGB hyperammonemia has been observed more so in women, and in some cases, women with X-linked heterozygous ornithine transcarbamylase deficiency who had previously been asymptomatic [1]. Multiple nutritional deficiencies have been associated with this syndrome as well including hypoalbuminemia, multiple amino acid deficiencies, hypoglycemia and low zinc levels, many of which were seen in this patient [2]. Nutritional deficiencies are thought to play a role in the urea cycle, interfering with the elimination of ammonia. In addition, RYGB alters the anatomy of the gastrointestinal system, which can cause intestinal overgrowth, leading to the production of ammonia from urease-producing bacteria (Figure 2) [1,2].
Hyperammonemic encephalopathy associated with 5-fluorouracil in a patient with previous orthotopic liver transplantation
Published in Baylor University Medical Center Proceedings, 2020
Hemnishil K. Marella, Rahul Peravali, Amit L. Jain, Satheesh Nair, Benedict Maliakkal, Uchenna Agbim, Rajanshu Verma
The biological basis for 5-FU–induced encephalopathy is not completely understood, but multiple pathways have been proposed. The mechanism that most likely contributed to this patient’s encephalopathy is accumulation of toxic byproducts of 5-FU catabolism. For example, fluorocitrate, the final metabolite of 5-FU, has been shown to inhibit aconitase, a Krebs cycle enzyme.16 The Krebs cycle shares several intermediates with the urea cycle, the pathway responsible for converting highly toxic ammonia to urea.17 Therefore, inhibition of the Krebs cycle by 5-FU metabolites can impair the urea cycle, resulting in accumulation of ammonia and lactic acidosis. It is important for physicians to closely monitor the neurological status of their patients after initiation of treatment and be aware of hyperammonemic encephalopathy as a possible adverse effect of 5-FU therapy.