4 Electrolyte Assessment and Replacement

Assessment and safe replacement

Electrolyte disorders can affect neurologic function, muscle strength, cardiac conduction, and fluid balance. Treatment depends on the cause, symptoms, kidney function, and whether the imbalance represents a true body deficit or a shift between body compartments. Reference ranges vary by laboratory, so interpret results using the patient’s values and local protocols.

Assess mental status, muscle strength, reflexes, vital signs, intake and output, volume status, renal function, relevant medications, and recent gastrointestinal or urinary losses. Review laboratory trends rather than relying on a single value. Obtain an ECG when an imbalance is severe, symptomatic, or likely to affect cardiac conduction, and check related electrolytes because abnormalities commonly occur together.

Oral replacement is generally preferred when the patient is stable and can take and absorb medication. IV replacement is reserved for severe or symptomatic abnormalities, inability to use the oral route, or situations requiring urgent treatment. Renal impairment increases the risk of accumulation, so replacement and monitoring must be adjusted.

Use prescribed replacement protocols, verify the correct product and route, and reassess laboratory values and symptoms after treatment.

Sodium disorders

Sodium is the major extracellular cation and is closely linked to water balance. Hyponatremia can cause headache, confusion, seizures, or coma as water shifts into brain cells. Hypernatremia reflects too little body water relative to sodium and can cause thirst, irritability, confusion, seizures, or coma as water leaves brain cells.

Managing low sodium

Determine volume status and the cause. Hypovolemic hyponatremia may require isotonic saline. Dilutional hyponatremia may require fluid restriction and treatment of the underlying condition. Severe neurologic symptoms may require carefully controlled hypertonic saline in a closely monitored setting.

Avoid overly rapid correction. A commonly used limit is no more than $8\ \text{mmol/L}$ in $24$ hours; targets should be individualized for patients at high risk of complications.

Managing high sodium

Replace water orally or enterally when safe, or use IV fluid selected according to volume status. If the duration is chronic or unknown, lower sodium gradually because rapid correction can cause cerebral edema. A commonly cited limit is about $0.5\ \text{mmol/L}$ per hour.

During active correction, monitor neurologic status, serum sodium, fluid intake and output, and signs of volume overload or depletion. Follow the prescribed laboratory schedule closely, and notify the prescriber about worsening neurologic symptoms or a sodium change that exceeds the planned rate.

Potassium disorders

Potassium is essential for skeletal muscle and cardiac electrical activity. Hypokalemia may cause weakness, cramps, ileus, and dangerous dysrhythmias. Hyperkalemia can cause weakness and life-threatening conduction changes, sometimes with few early symptoms.

Managing low potassium

Oral potassium is generally preferred when appropriate. IV potassium is used for severe or symptomatic deficiency or when oral treatment is not feasible. Never administer IV potassium by direct injection or rapid, undiluted infusion. Use an infusion pump and follow institutional limits for concentration and rate. Routine IV infusion rates are commonly limited to $10\ \text{mEq/hour}$; faster replacement requires specific orders and continuous cardiac monitoring.

For IV replacement, verify the solution and pump settings, assess the IV site, and recheck potassium as ordered. Review kidney function, urine output, medications, and ECG findings. Check magnesium when potassium is low: potassium may remain difficult to correct until magnesium deficiency is treated.

Managing high potassium

Stop exogenous potassium and address the cause. Urgent treatment may stabilize the myocardium, shift potassium into cells, and remove potassium from the body. Severe cases may require dialysis. IV calcium protects the heart when indicated but does not lower serum potassium; other treatment is needed to shift or remove potassium.

Calcium disorders

Calcium supports bone, muscle contraction, nerve signaling, and cardiac function. Hypocalcemia can cause tingling, cramps, hyperreflexia, tetany, seizures, and QT prolongation. Hypercalcemia may cause constipation, weakness, confusion, kidney stones, and a shortened QT interval.

Interpret total calcium in the context of albumin. Ionized calcium may be needed when results or symptoms are unclear; a normal total calcium does not rule out abnormal ionized calcium.

Managing calcium disorders

For low calcium, treat the cause and check magnesium, phosphate, kidney function, and vitamin D status as appropriate. Oral calcium is used for many stable cases. IV calcium gluconate may be required for tetany or other severe symptoms; give it slowly with ECG monitoring as directed and watch the IV site for infiltration. Correct accompanying magnesium deficiency when present.

For high calcium, treat the cause. Hydration with isotonic saline is often part of treatment, but must be individualized for patients with heart or kidney failure. Severe cases may require calcium-lowering medication or dialysis.

Monitor muscle symptoms, mental status, cardiac rhythm when indicated, calcium trends, and fluid status.

Magnesium disorders

Magnesium contributes to neuromuscular function and cardiac rhythm. Hypomagnesemia may cause tremor, weakness, hyperreflexia, tetany, seizures, or dysrhythmias and often occurs with low potassium or calcium. Hypermagnesemia, particularly with impaired kidney function or magnesium-containing medicines, can cause diminished reflexes, hypotension, respiratory depression, and cardiac arrest.

Managing magnesium disorders

Oral magnesium may be used for stable deficiency. IV magnesium sulfate is used for severe symptoms or when oral treatment is not possible. Monitor serum magnesium and renal function, especially with repeated IV doses, and replete associated potassium or calcium as indicated.

For high magnesium, stop magnesium sources and support breathing and circulation. Severe toxicity may be treated with IV calcium; diuresis or dialysis may be needed depending on kidney function and severity.

With IV magnesium, monitor blood pressure, respiratory status, reflexes, urine output, and laboratory results as ordered. Be especially alert to toxicity in patients with renal impairment.

Phosphate disorders

Phosphate is important for cellular energy, oxygen delivery, and bone. Hypophosphatemia may cause weakness; severe deficiency can impair respiratory and cardiac muscle function and cause neurologic or blood-cell complications. Hyperphosphatemia is commonly associated with kidney dysfunction and may lower calcium, causing tetany. Chronic elevation can contribute to soft-tissue calcification.

Managing low phosphate

Address the cause, such as poor intake, refeeding, or ongoing losses. Oral phosphate is often used when replacement is needed and the patient can tolerate it. IV phosphate is reserved for severe deficiency, serious symptoms, or inability to use the oral route. Closely monitor phosphate, calcium, potassium, and renal function during IV replacement because treatment can cause hypocalcemia and other complications.

Managing high phosphate

Treat the cause, commonly reduced kidney excretion. Management may include limiting dietary phosphate and prescribed phosphate binders taken with meals. Severe acute cases may require dialysis.

Monitor for muscle weakness and breathing difficulty in severe deficiency, and review kidney function and related calcium results. Confirm whether a phosphate replacement contains potassium or sodium because this affects the patient’s electrolyte and fluid plan.