The electrolyte disturbance hyponatremia or hyponatraemia exists in humans when the sodium level in the plasma falls below 135 mmol/l. At lower levels water intoxication may result, an urgently dangerous condition. Hyponatremia is an abnormality that can occur in isolation or, as most often is the case, as a complication of other medical illnesses. In the case of other mammals, particularly agricultural animals, different indications are relevant. The following refers to humans; an introduction to the sodium deficiency is appended for bovines.
Symptoms
Most patients are asymptomatic of the hyponatremia, but usually have symptoms related to the underlying cause.
Severe hyponatremia may cause osmotic shift of water from the plasma into the brain cells. Typical symptoms include nausea, vomiting, headache and malaise. As the hyponatremia worsens, confusion, stupor or coma may occur.
Causes
An abnormally low plasma sodium level is best considered in conjunction with the person's plasma osmolarity and extracellular fluid volume status.
Most cases of hyponatremia are associated with reduced plasma osmolarity.
A recent surge in death from hyponatremia has been attributed to the abuse of MDMA (ecstacy).
Pseudohyponatremia
A normal or high plasma osmolarity with hyponatremia is called pseudohyponatremia. Pseudohyponatremia may be caused if high lipid levels in the plasma interfere with the sodium assay, or if a different solute (such as glucose) is abnormally abundant.
When the plasma osmolarity is low, the extracellular fluid volume status may be in one of three states:
- Low volume. Loss of water is accompanied by loss of sodium.
- Normal volume.
- SIADH (syndrome of inappropriate antidiuretic hormone)
- Some cases of psychogenic polydipsia
- High volume. There is retention of water.
Severe hyponatremia may result from a few hours of heavy exercise in high temperature conditions, such as hiking in desert areas, or from endurance athletic events when electrolytes are not supplied. (Such an incident notably happened to long-distance athlete Craig Barrett in 1998).
Animals: bovines
Sodium deficiency exits in grazing animals where soil sodium levels have been depleted by leeching. This is more common in mountainous regions. Agricultural science research conducted in the northern Thai highlands in the 1970s found that an endemic sodium deficiency masked all other nutrient deficiencies across all seasons and reduced productivity. Sodium supplementation increased liveweight gain by around 30% and also reproductive rates by around 30%. Simple salt supplementation is now recommended in this region and neighbouring mountains as both a herd management tool and for increased productivity (see sources below).
See also
Sources
