1) Hyponatremia is an electrolyte disturbance in which the sodium concentration in the plasma is lower than normal, specifically below 135 mEq/L. The large majority of cases of hyponatremia occurring in adults result from an excess amount or effect of the water retaining hormone known as Antidiuretic Hormone ( ADH).
@ Hyponatremia is most often a complication of other medical illnesses in which either fluids rich in sodium are lost (for example because of diarrhea or vomiting), or excess water accumulates in the body at a higher rate than it can be excreted (for example in polydipsia (rarely) or syndrome of inappropriate antidiuretic hormone, SIADH). Regarding sodium loss as a cause of hyponatremia, it is important to note that such losses promote hyponatremia only in an indirect manner. In particular, hyponatremia occurring in association with sodium loss does not reflect inadequate sodium availability as a result of the losses. Rather, the sodium loss leads to a state of volume depletion, with volume depletion serving as a signal for the release of ADH. As a result of ADH-stimulated water retention, blood sodium becomes diluted and hyponatremia results.
@ There may also be spurious hyponatremia (pseudohyponatremia or factitious hyponatremia) if other substances expand the serum and dilute the sodium (for example, high blood sugar (hyperglycemia) or if a blood constituent leads to the creation of a sodium-free phase in the blood thereby causing the blood plasma volume to be overestimated (e.g. extreme hypertriglyceridemia).
- The diagnosis of hyponatremia relies mainly on the medical history, clinical examination and blood and urine tests.
- Treatment can be directed at the cause (for example, corticosteroids in Addison’s disease) or involve restriction of water intake, intravenous saline or drugs like diuretics. Correcting the salt and fluid balance needs to occur in a controlled fashion, as too rapid correction can lead to severe complications such as heart failure.
- Symptoms:
@ Patients with low-level, chronic water intoxication are often asymptomatic, but may have symptoms related to the underlying cause.
@ Typical symptoms include nausea, vomiting, headache and malaise. As the hyponatremia worsens, confusion, diminished reflexes, convulsions, stupor or coma may occur. Since nausea is, itself, a stimulus for the release of ADH, which promotes the retention of water, a positive feedback loop may be created and the potential for a vicious cycle of hyponatremia and its symptoms exists.
@ When these people consume large quantities of water without an adequate increase in sodium, the hyponatremic condition worsens.
- Causes:
@ One approach to determining causes of hyponatremia
An abnormally low plasma sodium level is best considered in conjunction with the person’s plasma osmolality and extracellular fluid volume status.
@ Indeed, correct ascertainment of volume status, as well as determination of the presence or absence of edema, are both critical in establishing the cause of hyponatremia. As described above, a state of volume depletion leads to increased blood levels of ADH and thus water retention. The greater the amount of water that is retained, the more the blood sodium will become diluted to cause worsening degrees of hyponatremia. The presence of edema indicates that blood volume has been lost insofar as fluid from the blood has shifted out into the peripheral tissues to cause the edema. In other words, edema is usually reflecting a state of blood volume depletion. As a result, edematous states are also associated with increased blood levels of ADH, water retention, and hyponatremia. In all cases of volume depletion-associated hyponatremia, it is important to note that retention of water per se, such as that promoted by ADH, does not correct the volume depleted state.
@ In addition to volume depletion, there are other causes of increased ADH levels (and ultimately, therefore, of hyponatremia). These include nausea, pain, and opiate drugs such as codeine and morphine. Such factors often play a role in the hyponatremia that is frequently seen in hospitalized patients.
-> The treatment of hyponatremia usually depends on the underlying cause.
2) Hypernatremia is an electrolyte disturbance that is defined by an elevated sodium level in the blood. Hypernatremia is generally not caused by an excess of sodium, but rather by a relative deficit of free water in the body. For this reason, hypernatremia is often synonymous with the less precise term, dehydration.
@Water is lost from the body in a variety of ways, including perspiration, insensible losses from breathing, and in the feces and urine. If the amount of water ingested consistently falls below the amount of water lost, the serum sodium level will begin to rise, leading to hypernatremia.
- Etiology:
@ Hypovolemic
o Inadequate intake of water. This is the most common cause of hypernatremia.
o Excessive losses of water from the urinary tract, which may be caused by osmotic diuretics.
o Water losses associated with extreme sweating.
o Severe watery diarrhea.
@ Euvolemic
o diabetes insipidus, which involves either inadequate production of the hormone, vasopressin, from the pituitary gland or impaired responsiveness of the kidneys to vasopressin.
@ Hypervolemic: uncommon.
- Symptoms:
@ Clinical manifestations of hypernatremia can be subtle, consisting of lethargy, weakness, irritability, and edema. With more severe elevations of the sodium level, seizures and coma may occur.
@ Severe symptoms are usually due to acute elevation of the plasma sodium concentration to above 158 mEq/L (normal is typically about 135-145 mEq/L). Values above 180 mEq/L are associated with a high mortality rate, particularly in adults. However such high levels of sodium rarely occur without severe coexisting medical conditions.
- Treatment:
@ The cornerstone of treatment is administration of free water to correct the relative water deficit. Water can be replaced orally or intravenously.
@ However, overly rapid correction of hypernatremia is potentially very dangerous. The body (in particular the brain) adapts to the higher sodium concentration. Rapidly lowering the sodium concentration with free water, once this adaptation has occurred, causes water to flow into brain cells and causes them to swell. This can lead to cerebral edema, potentially resulting in seizures, permanent brain damage, or death. Therefore, significant hypernatremia should be treated carefully by a physician or other medical professional with experience in treatment of electrolyte imbalances.