<prompt> Acute hyponatremia becomes symptomatic at -135 mEq125mEq120mEq1 l0mEq  <response>: Ans. is b i.e., 125 mEq Serum level of sodium at which symptoms develop Acute 125 meqL Chronic 120 meqLo Hyponatremia is commonly defined as a serum sodium 135 mmolL 135 mEqL. Neurological symptoms occur at different levels of low sodium, depending not only on the absolute value but also on the rate of fall.o In patients with hyponatremia that develops over hours, life-threatening seizures and cerebral edema may occur at values as high as 125 mmolL.o In contrast, some patients with more chronic hyponatremia that has slowly developed over months to years may be asymptomatic even with serum levels 110 mmol.Acute or hyperacute hyponatremiao The hyponatremia developed within the previous 24 hours, it is called acute. o If the hyponatremia developed over just a few hours due to a marked increase in water intake self-induced water intoxication, as may be seen in marathon runners, psychotic patients, and users of ecstasy, it is called hyperacute. Chronic hyponatremiao If it is known that the hyponatremia has been present for more than 48 hours, or if the duration is unknown such as in patients who develop hyponatremia at home, it is called chronic. Mild to moderate hyponatremiao Mild hyponatremia is usually defined as a serum sodium concentration between 130 and 135 meqL.o Moderate hyponatremia is often defined as a serum sodium concentration between 121 and 129 meqL.Severe hyponatremiao Severe hyponatremia can be defined as a serum sodium of 120 meqL or less.Symptoms of hyponatremia Absent symptomso Patients with hyponatremia are frequently asymptomatic, particularly if the hyponatremia is chronic and of mild or moderate severity ie, serum sodium 120 meqL.o However, such patients may have subclinical impairments in mentation and gait.Mild to moderate symptomso Mild to moderate symptoms of hyponatremia are relatively nonspecific and include headache, nausea, vomiting, fatigue, gait disturbances, and confusion.o In patients with chronic hyponatremia ie, 48 hours duration, these findings are not associated with impending herniation; however, in patients with more acute hyponatremia, such symptoms should be considered ominous and may evolve without warning to seizures, respiratory arrest, and herniation.Severe symptomso Severe symptoms of hyponatremia include - Seizures Obtundation Coma Respiratory arrest. 