3 Potassium Imbalances

Potassium and its clinical importance

Potassium is the major intracellular cation and is essential for skeletal-muscle contraction and cardiac electrical conduction. A common adult reference range is $3.5\text{–}5.0\ \mathrm{mEq/L}$ ($3.5\text{–}5.0\ \mathrm{mmol/L}$), although laboratory ranges vary.

Both low and high serum potassium can cause dangerous dysrhythmias. ECG findings are not reliable enough to estimate the potassium level or rule out danger, so assess the patient as well as the laboratory result.

Low potassium: causes and urgency

Hypokalemia is a serum potassium level below $3.5\ \mathrm{mEq/L}$. Severe hypokalemia is often defined as $2.5\ \mathrm{mEq/L}$ or lower. Severe hypokalemia, or hypokalemia accompanied by symptoms or ECG changes, requires urgent assessment and treatment.

Common causes include:

• Renal losses: loop or thiazide diuretics, mineralocorticoid excess, and some renal disorders.

• Gastrointestinal losses: diarrhea, vomiting, or laxative use.

• Shift of potassium into cells: insulin, beta agonists, or alkalosis.

• Low intake: poor nutrition or starvation.

Low magnesium can contribute to potassium loss and make hypokalemia difficult to correct.

Low potassium: manifestations and ECG findings

Hypokalemia may cause fatigue, muscle weakness, or cramps. Severe cases may cause paralysis or respiratory weakness. Cardiac effects include dysrhythmias; risk is greater in people with heart disease or those taking digoxin.

Typical ECG findings include flattened or inverted T waves, ST-segment depression, and prominent U waves. A prolonged QT may also occur. Severe cases can involve ventricular dysrhythmias. These ECG changes may be absent, and their severity does not consistently match the potassium level.

Low potassium: nursing assessment and treatment

Assess for weakness, cramps, respiratory effort, vital signs, cardiac history, medication use, and ongoing gastrointestinal losses. Review potassium, magnesium, and renal function, and assess the ECG as indicated.

Address the cause and replace potassium as prescribed. Oral replacement is generally preferred when the patient can take it and the deficit is not severe. IV replacement is reserved for severe or symptomatic cases, or when oral treatment is not feasible.

Safety during IV replacement: Never administer potassium by IV push. Use the prescribed dilution and infusion rate, an infusion pump, and cardiac monitoring when indicated by the concentration, rate, symptoms, or local policy. Check the IV site and promptly report pain or signs of infiltration. Follow institutional medication-safety guidance.

Recheck potassium as ordered and monitor magnesium, renal function, ECG, and clinical response. Use extra caution in renal impairment because replacement can cause hyperkalemia.

High potassium: causes and urgency

Hyperkalemia is an elevated serum potassium level, but definitions differ among references and laboratories. The UK Kidney Association classifies $5.5\text{–}5.9\ \mathrm{mEq/L}$ as mild, $6.0\text{–}6.4\ \mathrm{mEq/L}$ as moderate, and $6.5\ \mathrm{mEq/L}$ or higher as severe. Acute severe hyperkalemia, symptoms, or ECG changes require emergency assessment.

Common causes include impaired kidney excretion, such as acute or chronic kidney disease; potassium-retaining medicines; and potassium release from damaged cells, such as in rhabdomyolysis, burns, or tumor lysis. Acidosis, reduced insulin, and excess potassium intake can also contribute, especially when kidney function is impaired.

A falsely high result may occur because of sample hemolysis or collection problems. If a result does not fit the clinical picture, promptly alert the clinician and obtain a repeat sample as directed. Do not delay emergency care if the patient is unstable or has concerning ECG changes.

High potassium: manifestations and ECG findings

Hyperkalemia may cause muscle weakness or, when severe, paralysis. It can also be nearly symptom-free until cardiac toxicity develops.

ECG changes may include tall, peaked T waves; PR prolongation; reduced or absent P waves; and QRS widening. Severe progression may produce a sine-wave pattern, ventricular fibrillation, or asystole. Changes do not occur in a predictable sequence in every patient, and a normal ECG does not exclude clinically important hyperkalemia.

High potassium: emergency response and treatment

Treat suspected severe hyperkalemia as an emergency. Promptly notify the responsible clinician or activate the emergency response system according to the patient’s condition and local policy. Obtain an ECG and initiate continuous cardiac monitoring when indicated; monitor vital signs and muscle strength.

Review the potassium result, kidney function, medication list, recent potassium intake, and possible sample hemolysis. Withhold potassium-containing products or medications only as directed by the authorized clinician or protocol.

Prepare to administer prescribed emergency therapies:

• IV calcium stabilizes the cardiac membrane but does not lower serum potassium.

• Insulin with glucose and inhaled beta agonists shift potassium into cells. Monitor blood glucose closely after insulin.

• Other therapies remove potassium from the body. Dialysis may be needed in severe renal impairment or persistent hyperkalemia.

After treatment, reassess the ECG, potassium, glucose, and clinical status. Potassium-shifting therapies can wear off before potassium is eliminated, so recurrence is possible.

Comparing the two potassium imbalances

Both imbalances can cause muscle weakness and life-threatening cardiac dysrhythmias. Hypokalemia commonly results from gastrointestinal or renal losses, low intake, or movement of potassium into cells. Hyperkalemia most often reflects impaired excretion, medicines, or release from damaged cells.

• Hypokalemia: weakness or cramps may progress to paralysis or respiratory weakness. Typical ECG clues include flattened T waves, ST depression, and prominent U waves. Priorities include assessing symptoms and ECG, replacing potassium safely, and monitoring potassium, magnesium, and renal function.

• Hyperkalemia: weakness may progress to paralysis. Typical ECG clues include peaked T waves, PR prolongation, diminished P waves, and widened QRS; severe cases may develop a sine-wave pattern. Severe, symptomatic, or ECG-changing hyperkalemia calls for urgent escalation, monitoring as indicated, and preparation for ordered stabilization, potassium-shifting, and potassium-removal therapies.

ECG patterns are not universal or reliable measures of potassium severity. Correct the underlying cause, assess the patient along with the laboratory result, and monitor closely during treatment. Follow local protocols and prescribed orders, especially for IV potassium and emergency hyperkalemia therapies.