Normal serum sodium levels are 134-145 mmol/L. Hypernatremia is defined as a serum sodium level exceeding 145 mmol/L. Think “fried food is salty”. Hypernatremia can be caused by too much sodium in the blood, but it also is caused by too little free water in the body. You must first assess the patient’s volume status before knowing how to treat appropriately. Hypernatremia signs can be very subtle, with changes in the level of consciousness typically being the earliest indicator. Sodium is closely related to blood pressure and blood volume. It is also necessary for muscle and nerve function.