What is hypernatremia?
Hypernatremia is the state where the sodium levels in the blood are higher than normal. It is more correctly defined as a blood sodium concentration exceeding 145 mmol/L. Hypernatremia is a problem that arises when the body loses water without the equivalent loss of electrolytes like sodium. In other words, hypernatremia is mainly a consequence of losing excessive amounts of water and not often due to acquiring excess sodium from outside sources.
Hypernatremia may arise with various diseases with copious water loss, as a result of impaired thirst sensation or difficulty accessing water. The high sodium levels “drains” water out of cells which has a host of complications primarily in the cardiovascular system and central nervous system. Attempting to rapidly administer water alone can also have consequences in hypernatremia and lead to complications such as brain swelling (cerebral edema).
Why does hypernatremia occur?
Sodium is a mineral that occurs widely in nature. Most of us know it in the form of table salt – sodium chloride – whee sodium is bonded with chlorine. Sodium is one of the major electrolytes in the body fluids and determines the osmolality (solute concentration) of the blood. The body is constantly acting to maintain the osmolaltity in the blood and tissue fluid by retaining excess water when the sodium levels are too high or passing out more water when the sodium levels are too low.
Water-salt regulation is mainly achieved by vasopressin or antidiuretic hormone (ADH) which acts on the kidneys. The thirst sensation also plays a role in this regard prompting a person to drink more water or less thereby maintaining the water-salt balance in the body. In fact the thirst sensation is so important that if it is functioning normally and water is accessible, it is almost impossible for hypernatremia to arise.
Effects of Excess Sodium
Hypernatremia is usually associated with water loss which reduces the blood volume in the body. In order for the heart to maintain the blood pressure within acceptable levels, it has to work harder until the volume can be restored. The effects of hypernatremia on the circulatory system is seen as hypotension (low blood pressure) and tachycardia (rapid heart rate).
Since the osmolality of blood and tissue fluid (extracellular fluids) are higher than within a cell (intracellular), hypernatremia can draw water out of the cell and into the surrounding tissue fluid. Normal cell functions are affected by the loss of intracellularland cells literally shrink to some degree. In order to compensate, the cell increases its internal solutes and this “sucks” some water back into the cell. Its an adaptive response to maintain cellular function and is somewhat effective given the hyperosmolality of the extracellular fluids.
However, there is a risk that these cells will then “suck” in excess water once the water levels are restored in the body. Normally the cells can still adapt to these changes but if water is introduced too suddenly, then the cell will swell. Although it will normalize again with time, there is a serious risk when it affects the brain cells leading to cerebral edema.
What are the symptoms of hypernatremia?
The initial symptoms that may be seen are not due to hypernatremia but rather the underlying cause. This includes symptoms like :
- Polyuria – passing of large volume urine in a day marked by frequent urination.
- Polydipsia – excessive thirst although this is often impaired for hypernatremia to arise.
- Profuse vomiting.
- Severe diarrhea.
- Excessive perspiration.
The actual symptoms of hypernatremia depends on the severity of the condition, how rapidly it developed (onset) and for how long it persisted (duration). Generalized symptoms include :
- Weight loss
Symptoms of dehydration, due to the lower than normal blood volume, includes :
- Hypotension – significant drop when standing up from a sitting or lying position (postural or orthostatic hypotension)
- Tachycardia – rapid heart rate
- Oliguria – low urine output or even a total absence of urine (anuria)
- Dry skin (lack of sweat), dry mouth (lack of saliva) and dry eyes (lack of tears)
- Abnormal skin turgor – the skin lacks its normal firmness and tension
Symptoms of central nervous system dysfunction includes :
- Slurred speech
- Nystagmus – rapid eye movements that are involnutary
- Myoclonic jerks – rapid involuntary twitches to more violent muscle jerks
What are the causes of hypernatremia?
The cause of hypernatremia is extensive. It is a consequence of many medical conditions, extreme physiological states, the use of certain medication and lifestyle factors. Overall hypernatremia is uncommon and mainly seen among :
- Infants, especially newborns (neonates)
- Elderly people
- Debilitated patients
- Disabled patients
- Hospitalized patients
A brief overview of the causes of hypernatremia is discussed below.
Reduced water intake
This occurs in a person who has an impaired thirst sensation, does not recognize the thirst sensation as a need for water or cannot access water.
- Physical disability
- Geriatric hypodipsia
- Hypothalamic lesions affecting the thirst centers
Loss of water through kidneys
- Diabetes insipidus (central or nephrogenic)
- Uncontrolled diabetes mellitus
Loss of water through the skin
- Excessive physical activity
- Very hot weather
Loss of water through the gut
- Severe or persistent diarrhea
- Profuse vomiting
- Nasogastric aspiration
Substances that causes water loss
- Intravenous antibiotics (containing sodium)
- Medication that affect vasopressin (ADH) secretion or action on the kidneys
Increased sodium intake
- Sodium poisoning, even with table salt
- Tube feeding
- Hypertonic saline
- Sodium chloride tablets
- Seawater consumption
How is hypernatremia diagnosed?
The signs and symptoms are usually not clearly indicative of hypernatremia. Often the condition is missed in debilitated and hospitalized patients as other more likely causes of the presenting symptoms are first considered. Hypernatremia is a blood sodium level exceeding 145 mmol/L. Diagnostic investigations are therefore necessary to conclusively diagnose hypernatremia. This include tests such as :
- Blood urea and electrolytes
- Blood osmolality
- Urine electrolytes
- Urine osmolality
Other tests and scans may be conducted to identify the possible causes and complications of hypernatremia :
- Blood glucose level
- Blood vasopressin (ADH) level
- Blood lithium level
- Magnetic resonance imaging (MRI) and computed tomography (CY) scan of the brain
What is the treatment for hypernatremia?
Hypernatremia is a state that arises as a result of different factors – pathological, physiological and sometimes lifestyle. It is therefore important that the underlying cause is identified and treated immediately to prevent recurrence of the condition or complications associated with excessively high blood sodium levels. Treatment of hypernatremia itself needs to be undertaken carefully after the patient’s condition is assessed.
Acute hypernatremia can be treated rapidly since it is has only occurred over a 24 hour period and the cells have not undergone an adaptive response as yet. Therefore the risk of cerebral edema is less likely. However, chronic hypernatremia which develops over a period longer than 48 hours has to be treated gradually as there is a major risk of cerebral edema with rapid fluid administration.
Fluid replacement should be done in the clinical setting as it needs to be carefully monitored. The fluid can be administered via one of the following routes :
- Through the mouth (orally) which is preferred if the patient is conscious and able to swallow properly.
- Into the gut (enterally) through a nasogastric tube for patients who are unable to swallow or unconscious.
- Into the bloodstream (parenterally) as a last resort for patients who are unconscious, have severe diarrhea or are vomiting profusely.
The tonicity of the fluid depends on the individual condition and underlying cause of hypernatremia. The patient’s electrolyte levels need to be monitored and the tonicity and rate of fluid replenishment may need to be altered accordingly.