Electrolyte Disturbances
Abstract
Electrolyte disturbances affect many patients with neurologic conditions. The most common electrolyte disturbances in these patients are an imbalance of sodium or glucose. Such disturbances can have serious negative effects on neurologic function; therefore, it is important for nurses to understand the causes, signs, and treatment of these abnormalities.
Keywords: antidiuretic hormone, cerebral salt wasting, diabetes insipidus, hypernatremia, hyponatremia, syndrome of inappropriate antidiuretic hormone
5.1 Electrolyte Balance
Sometimes, brain injury can cause electrolyte imbalances. Any electrolyte (sodium, potassium, chloride, or carbon dioxide) can be thrown out of balance, but in nerologic disorders, a patient’s level of sodium is most likely to be affected.
Another type of metabolic disorder that is commonly found in conjunction with electrolyte imbalance is impaired glucose tolerance or excessively high or low serum concentrations of glucose. Glucose, a simple sugar, is measured as part of the metabolic panel that includes the electrolyte panel. Although glucose is not an electrolyte per se, patients with neurologic conditions often have glucose imbalance along with electrolyte imbalances.
Electrolyte and glucose imbalances can exacerbate neurologic injury, causing further decline. The best way to manage these imbalances is to detect and treat them early.
5.2 Sodium
The definition of the normal sodium level may vary slightly by institution. Sodium levels within the “normal” or laboratory “reference” range of 135 to 145 mEq/L are generally considered acceptable.
5.2.1 Antidiuretic Hormone
Antidiuretic hormone (ADH), also called vasopressin, is a peptide hormone that is active in the blood vessels and kidneys. It causes more absorption of water into the blood. In turn, this dilution reduces the concentration of serum sodium.
Produced by the posterior portion of the pituitary gland, called the hypothalamus, and released into systemic circulation
Release of ADH is regulated by
Baroreceptors in the carotid sinus (and aortic arch)
Plasma osmolality (Box 5.1 Osmolality)
Prompts decreases in blood pressure and blood volume
Box 5.1 Osmolality
Osmolality is defined as the number of particles present per kilogram weight of solvent
Normal serum osmolality is 275 to 295 mOsm/kg
Functions of Antidiuretic Hormone
Increases rate of water reabsorption
Dilutes circulating blood
Reduces and concentrates urine
Plays a key role in maintaining osmolality and serum–urine sodium levels
Deficiency of ADH can lead to diabetes insipidus (DI), discussed later in this chapter
5.2.2 Hyponatremia
Hyponatremia is a condition in which the level of serum sodium is too low. In most institutions, hyponatremia is diagnosed in patients whose level of serum sodium is less than 135 mEq/L. There may be several causes of hyponatremia. It can be
Relatively common in patients with neurologic disorders
Associated with cerebral edema, which increases intracranial pressure (ICP); see Chapter 3: Principles of Intracranial Pressure (Box 5.2 Clinical Alert: Hyponatremia)
Caused by volume overload (then referred to as hypervolemic hyponatremia), as seen in congestive heart failure
In neurosurgical patients, hyponatremia usually manifests as a syndrome of inappropriate ADH (SIADH) or as cerebral salt wasting. The etiologies of these two types of hyponatremia and their respective treatments differ vastly (Box 5.3 Conditions Associated with Hyponatremia and ▶ Table 5.1).
Box 5.2 Clinical Alert: Hyponatremia
Hyponatremia is associated with cerebral edema
Patients with cerebral edema or those at risk for it may be maintained at a higher serum sodium level
Box 5.3 Conditions Associated with Hyponatremia
Most disorders of the central nervous system, including
Cerebral trauma
Tumors
Strokes
Infectious processes (e.g., abscess, meningitis, and encephalitis)
Pulmonary disease, including
Carcinoma
Chronic obstructive pulmonary disease
Pneumonia
Some drugs, including
Anesthesia
Selective serotonin reuptake inhibitors (e.g., Paxil [paroxetine hydrochloride], Zoloft [sertraline hydrochloride], and Celexa [citalopram hydrobromide])
Some opiates
Carbamazepine (prescribed for epileptic patients or for those with nerve pain)
Syndrome of Inappropriate Antidiuretic Hormone
Electrolyte imbalance caused by excessive ADH release from the pituitary gland
Hyponatremia with high urine osmolality
Can occur in hypervolemic patients (patients with elevated blood volume) or in normovolemic patients (patients with normal blood volume)
Associated with intracranial trauma, abnormalities, or malignancies.
Table 5.1 Comparison of syndrome of inappropriate antidiuretic hormone and cerebral salt wasting
Comparative factor
SIADH
Cerebral salt wasting
Serum sodium value
Below 134 mg/dL
Below 134 mg/dL
Urine sodium value
Normal or increased
Increased
Serum osmolality
Decreased
Normal or increased
Urine osmolality
Increased
Normal or increased
Intravascular volume
Normal or increased
Decreased
Fluid restriction
Restrict free water, approximately 1 L every 24 h
Never
Treatment
Fluid restriction; may add salt supplements, such as salt tablets and hyperosmolar saline solution (3%). May also add demeclocycline or furosemide (Lasix)
Volume replacement, salt supplements, or hyperosmolar saline solutions (3%)
Associated neurologic disorder
Could be related to any neurologic disorder, including brain tumor, stroke, trauma, and infectious process
Subarachnoid hemorrhage
Abbreviation: SIADH, syndrome of inappropriate antidiuretic hormone.
Clinical Manifestations of Syndrome of Inappropriate Antidiuretic Hormone
Confusion
Lethargy
Seizures
Decreased level of consciousness (LOC)
Cerebral edema and signs of increased ICP
Signs of fluid overload
Possible weight gain
Cerebral Salt Wasting
Manifests as hyponatremia with hypovolemia (decreased blood volume)
Associated with subarachnoid hemorrhage, with or without vasospasm
Clinical Manifestations of Cerebral Salt Wasting
Confusion
Lethargy
Seizures
Decreased LOC
Cerebral edema and signs of increased ICP
Possible orthostatic hypotension
Possible weight loss
Symptoms may range from vague to severe (Box 5.4 Hyponatremia)
Box 5.4 Hyponatremia
In the presence of intracranial disease or trauma, even mild hyponatremia may cause symptoms
Patients with chronic hyponatremia may not have symptoms right away
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