What are the reasons for low blood sodium levels in newborns?

Patient's question:

Low milk intake, sodium level 128, receiving intravenous fluids in the hospital

Doctor's answer:

Analysis of the condition: The causes of hyponatremia include: ① During fluid loss, if the loss of solutes exceeds the loss of water, it results in hypotonic dehydration; ② The extracellular fluid volume remains relatively normal, but due to endocrine disorders, there is abnormal loss of electrolytes. For example, inappropriate secretion of antidiuretic hormone syndrome (SIADH) or disorders of thyroid and adrenal cortex function; ③ Excess extracellular fluid volume, such as excessive administration of hypotonic fluids or impaired renal water excretion, leading to dilution of extracellular sodium, also known as dilutional hyponatremia.
Advice: The symptoms of hyponatremia vary depending on the rate of decline in blood sodium levels. If the change in cell volume causes hypotonic dehydration, it may manifest as severe circulatory failure, cold limbs, weak pulse, oliguria, and sunken fontanelle. As hyponatremia progresses, fluid shifts inward into the cells, which can lead to symptoms of cerebral edema, such as drowsiness, lethargy, coma, and convulsions. Accompanying hyponatremia may be neuromuscular excitability changes, such as hypotonia and diminished tendon reflexes. Based on your child's condition, the blood sodium level is slightly low. Treatment should identify the underlying cause and also include symptomatic management.