The measurement of serum osmolality and its application to clinical practice and laboratory: literature review / A medida da osmolalidade sérica e sua aplicação na prática clínica e laboratorial: revisão da literatura

ABSTRACT Introduction: Serum osmolality is an essential laboratory parameter to understand several clinical disorders such as electrolyte disturbances, exogenous intoxication and hydration status. Objective: This study aims to update knowledge about the osmolality examination through research papers published to date. Materials and methods: The survey was conducted on PubMed database. It highlights main concepts, both historical and physiological aspects, and the clinical applications of the serum osmolality test. In addition, an extensive survey of formulas for the serum osmolality calculation was conducted. Discussion: The measurement of serum osmolality is relevant in changes in intracellular and extracellular balance, as a trusted and valuable indicator of solute concentration in the blood. The mathematical equations for serum osmolality calculation acquire relevance in health services where serum is not available, and situations in which calculation of the osmolal gap is necessary, but the variability of the formulas is a significant bias. Conclusion: The measurement of serum osmolality is useful in cases of dehydration, sodium and potassium disorders, glucose alteration, exogenous poisoning, adrenal insufficiency, neurological injury, physical exercise and others.

RESUMO Introdução: A osmolalidade sérica constitui um parâmetro laboratorial importante para compreensão de diversas desordens clínicas, como os distúrbios eletrolíticos, as intoxicações exógenas e o status de hidratação. Objetivo: Este trabalho visa atualizar os conhecimentos acerca do exame de osmolalidade por meio da pesquisa de artigos científicos publicados até a presente data. Materiais e métodos: A pesquisa foi realizada no banco de dados do PubMed. Este artigo de atualização aborda os principais conceitos, aspectos históricos, aspectos fisiológicos e aplicações clínicas do exame de osmolalidade sérica. Foi também realizado um levantamento das diferentes fórmulas propostas para o cálculo da osmolalidade sérica. Discussão: A medida da osmolalidade sérica é pertinente nas alterações do equilíbrio intra e extracelular, sendo um bom indicador para avaliar as concentrações de solutos no sangue. As fórmulas matemáticas para o cálculo da osmolalidade sérica são úteis quando a medida laboratorial não está disponível, bem como nas situações em que o cálculo do gap osmolal se faz necessário, mas a variabilidade das fórmulas é um viés significativo. Conclusão: A medida da osmolalidade sérica é útil na avaliação de diversas condições clínicas, como na desidratação, nos distúrbios dos íons sódio e potássio, nas disglicemias, nas intoxicações exógenas, na insuficiência adrenal, nas lesões neurológicas, nos exercícios físicos, entre outras.

Uncoventional Views on Certain Aspects of Toxin-Induced Metabolic Acidosis

This discussion will highlight the following 9 specific points that related to metabolic acidosis caused by various toxins. The current recommendation suggests that alcohol dehydrogenase inhibitor fomepizole is preferred to ethanol in treatment of methanol and ethylene glycol poisoning, but analysis of the enzyme kinetics indicates that ethanol is a better alternative. In the presence of a modest increase in serum osmolal gap (<30 mOsm/L), the starting dose of ethanol should be far less than the usual recommended dose. One can take advantage of the high vapor pressure of methanol in the treatment of methanol poisoning when hemodialysis is not readily available. Profuse sweating with increased water ingestion can be highly effective in reducing methanol levels. Impaired production of ammonia by the proximal tubule of the kidney plays a major role in the development of metabolic acidosis in pyroglutamic acidosis. Glycine, not oxalate, is the main final end product of ethylene glycol metabolism. Metabolism of ethylene glycol to oxalate, albeit important clinically, represents less than 1% of ethylene glycol disposal. Urine osmolal gap would be useful in the diagnosis of ethylene glycol poisoning, but not in methanol poisoning. Hemodialysis is important in the treatment of methanol poisoning and ethylene glycol poisoning with renal impairment, with or without fomepizole or ethanol treatment. Severe leucocytosis is a highly sensitive indicator of ethylene glycol poisoning. Uncoupling of oxidative phosphorylation by salicylate can explain most of the manifestations of salicylate poisoning.

Correlation of Urine Ammonium with Urine Osmolal Gap in High Anion Gap Matabolic Acidosis: Comparison to Urine Anion Gap / 대한내과학회지

OBJECTIVES: Urine anion gap(UAG) and urine osmolal gap(UOG) were proposed as indirect measures of urine ammonium(NF4+). While the former is known to have its usefulness limited to hyperchloremic metabolic acidosis, the latter is reported to have its correlation with urine NE4+ in ketoacidosis. This study was undertaken to evaluate the correlation of urine NH with IJOG in high anion gap metabolic acidosis(AGMA) and to compare it with UAG. METHODS: We measured urine NH' by enzymatic determination, UOG(=0.5 X [urine osmolality-{2 X (Na++K+)+urea+glucose)]), and UAG(=Na++K+-Cl-) in 18 patients(serum AG=24.4+/-1.6mmol/L ) with AGMA. RESULTS: When they were grouped into those with acute disorders(n=11) and those with chronic disorder(n=7), urine Nk4+ concentration was higher (p40mmol/d) had the UOG>40mmol/L. CONCLUSION: In contrast to the UAG, the UOG has a significant correlation with urine NH4+ in AGMA.

The Changes of Arterial Ketone Body Ratio and Osmolal Gap during Hemorrhagic Shock in Rabbit / 대한마취과학회지

The ratio of acetoacetate to 8-hydroxybutyrate (ketone body ratio) in the blood may reflects the mitochondrial free NAD+/NADH ratio in the liver. Also arterial ketone body ratio will reflects the energy status of the hepatocytes, because mitochondrial free NAD+/NADH ratio is closely related to oxidative phosphorylation. Arterial ketone body ratio and osmolal gap, the difference between measured osmolality and calculated osmolality, were measured 30 min after the induction of hemorrhagic shock with mean arterial blood pressure at 40 mmHg in ten rabbits. Arterial ketone body ratios decreased significantly (p<0.05) from 0.74+/-0.17 to 0.38+/-0.09 and osmolal gap increased significantly (p<0.05) from 17.7+/-5.9 mOsm/Kg to 32.8+/-12.3 mOsm/Kg at 30 min after the induction of hemorrhagic shock. These results suggest that in hemorrhagic shock, decreased arterial ketone body ratio which reflects the inhibition of the TCA cycle is associated with increase of osmolal gap.