Hyponatremia in neurosurgical patients

Hyponatremia is the most common electrolyte disturbance seen in a neurosurgical ICU. The most common cause is impaired excretion of water, which may be due to many causes. The hyponatremia itself is of importance only because of its effect on ECF osmolality, which, when low, causes cellular swelling and dysfunction. While a low serum sodium is most commonly associated with an increased ECF, it may also be associated with a normal or low ECF. In any of these situations, however, the symptomatology will be the same. On the other hand, the examination of the patient and the laboratory examinations will help in determining whether it is an instance of overhydration or underhydration. The urgency and type of treatment are dictated by the severity of the patient's symptoms.