2 Sodium Imbalances
Learn how sodium and water balance causes hyponatremia and hypernatremia, how to assess their effects and likely causes, and why correction must be carefully monitored.
and water balance
is the major positively charged ion in extracellular fluid and helps regulate water distribution. A blood result reflects the balance between and water, rather than simply the amount of salt a person has eaten. is a serum below , while is above . The rate of change and the patient’s symptoms matter as much as the result itself.
Water shifts across cell membranes in response to concentration differences. In , water tends to move into brain cells and can cause swelling. In , water moves out of brain cells, causing them to shrink. Both imbalances can therefore produce serious neurologic symptoms.
can develop when the body loses more than water, retains excess water, or both. Assessing fluid-volume status helps guide evaluation and treatment.
: and water are lost, but loss is greater. Causes include vomiting, diarrhea, sweating, burns, and diuretic use.
: Total body water rises while total body is relatively unchanged. Causes include syndrome of inappropriate antidiuretic hormone secretion (), excessive water intake, some medications, adrenal insufficiency, and hypothyroidism.
: Both and water increase, but water increases more. Common associated conditions include heart failure, cirrhosis, and kidney disease.
Symptoms are often neurologic and may initially be subtle. Nausea, headache, fatigue, weakness, muscle cramps, and unsteadiness can progress to confusion, reduced alertness, seizures, or coma. A rapid fall in may cause severe symptoms even when the result is not as low as it might be in a gradual, chronic imbalance.
Assessment and care
Assess airway, breathing, circulation, and neurologic status. Check level of consciousness, orientation, headache, behavior, strength, and seizure activity. New confusion, a seizure, or reduced consciousness requires urgent escalation.
Assess fluid status by reviewing vital signs, mucous membranes, edema, lung sounds, intake and output, and daily weight. Look for losses such as vomiting or diarrhea and signs of fluid overload. Follow serum trends and ordered serum and urine osmolality or urine tests. Review kidney, heart, liver, adrenal, and thyroid conditions, recent fluid administration, and medications that may contribute.
Use seizure and fall precautions when indicated. Keep the environment safe and assist with mobility when a patient is weak, confused, or unsteady.
Treatment depends on the cause and volume status. The prescribed fluid plan may include fluid restriction, isotonic intravenous fluid for selected patients with volume depletion, or carefully monitored hypertonic saline for severe neurologic symptoms. Do not independently choose or adjust intravenous fluids.
Monitor at the ordered frequency and promptly report a change faster than the prescribed target. Overly rapid correction, particularly of chronic , can cause and permanent neurologic injury. A commonly cited limit is no more than an rise in the first 24 hours; the treating team may set a stricter target for some patients.
usually indicates too little body water relative to . Causes include inadequate access to water or impaired thirst; fever and sweating; vomiting or diarrhea; excessive urine losses, including or osmotic diuresis; and, less commonly, excessive administration. Older adults and people who depend on others for fluids may be especially vulnerable.
Thirst is common, but a person who cannot communicate or obtain water may not be able to report it. Neurologic findings can include restlessness, irritability, weakness, confusion, muscle twitching or increased reflexes, seizures, and coma. Volume depletion may also cause dry mucous membranes, low blood pressure, tachycardia, and reduced urine output. Findings depend on the cause and volume status.
Assessment and care
Assess stability and neurologic status, including vital signs, mental status, thirst, and signs of dehydration or fluid overload. Escalate promptly for seizures, declining consciousness, or circulatory instability.
Identify likely water and losses by reviewing intake and output, urine volume, gastrointestinal losses, fever, sweating, tube-feeding and intravenous-fluid plans, medications, and the patient’s ability to access water. Monitor ordered laboratory tests and trends, including serum , glucose, kidney function, and other ordered electrolytes. Report unexpectedly large urine volumes or a poor response to prescribed fluids.
If the patient is alert, can swallow safely, and has no fluid restriction, offer water as permitted. Assist patients who cannot obtain fluids independently.
Prescribed replacement may involve oral or enteral water, intravenous free-water replacement, and treatment of the cause. If the patient is in shock or severely volume depleted, clinicians generally restore circulation first and then correct the water deficit. The fluid type and rate require individualized orders.
Chronic , or of unknown duration, is generally corrected gradually to reduce the risk of cerebral edema. Monitor and neurologic status at the prescribed frequency and report a faster-than-planned fall.
Applying assessment priorities
For a patient with heart failure, low serum , ankle edema, and crackles, edema and crackles suggest a pattern. The care team may consider fluid restriction and treatment of the underlying heart failure.
For an older adult with limited access to drinking water who becomes confused and has high serum , assess stability and neurologic status, escalate the new confusion, evaluate volume status and intake and output, and follow prescribed water replacement and laboratory monitoring. Gradual correction may be needed if the imbalance is chronic or its duration is unknown.