Hyperkalemia mnemonic and other electrolyte mnemonics, with where each one misleads

What the letters stand for

MURDER for high potassium: muscle cramps or weakness, urine changes such as oliguria, respiratory distress from weak breathing muscles, decreased cardiac contractility, ECG changes, and reflex changes. CATS for low calcium: convulsions, arrhythmias, tetany, and spasms with stridor, which warns of laryngospasm. Review books vary slightly, but these are the versions most students meet.

FRIED SALT for high sodium: fever and flushed skin, restlessness, increased fluid retention and blood pressure, edema, decreased urine output and dry mouth, skin flushed, agitation, low-grade fever, and thirst. SALT LOSS for low sodium: stupor or coma, anorexia with nausea, lethargy, tendon reflexes decreased, limp muscles, orthostatic hypotension, seizures with headache, and stomach cramping.

When nurses reach for them

These mnemonics earn their place at the bedside when a lab result comes back and the nurse has to decide what to look for. A high potassium means cardiac monitoring and a check of muscle strength. A low calcium means asking about tingling around the lips, fingers and feet and watching the airway.

They also help in the other direction. Confusion in an older adult who cannot reach water, or tetany after neck surgery, should prompt the nurse to ask whether a lab has been drawn. MSD Manuals notes that thirst is the major symptom of hypernatremia and that people with impaired thirst or limited access to water are most at risk.

Worked scenario: a high potassium in a client who feels fine

Hypothetical scenario, not a real exam item: a client with chronic kidney disease has a potassium of 6.8 reported by the lab. He is chatting, denies weakness and says he feels fine. Options: recheck the level with morning labs since he has no symptoms, place him on a cardiac monitor and notify the provider, offer a banana, or document and continue routine care.

Monitoring and notifying is the best answer. MSD Manuals describes hyperkalemia as often silent until cardiac effects appear, with the ECG moving from peaked T waves toward a widened QRS, a sine wave and arrest. Waiting for morning is the tempting distractor because MURDER teaches you to expect symptoms. The banana adds potassium.

Where these mnemonics mislead

FRIED SALT puts edema and fluid retention at its center, yet MSD Manuals explains that hypernatremia reflects too little body water relative to sodium and is only rarely linked to volume overload, as with hypertonic sodium solutions. Most clients are dry, thirsty and confused, not swollen. SALT LOSS has its own problem: severe hyponatremia can cause hyperreflexia, not only decreased reflexes.

MURDER implies the ECG tracks the number, but MSD Manuals notes that potassium levels vary widely among clients with similar ECG changes. A falsely high result can come from hemolysis, a long tourniquet or fist clenching. CATS leans on tetany, while MSD Manuals notes Chvostek sign is present in up to 10 percent of healthy people and often absent in chronic hypocalcemia.

Related exam trap: correcting too fast

Once the imbalance is found, the trap moves to treatment speed. Rapid correction of chronic hypernatremia risks cerebral edema, and rapid correction of hyponatremia risks osmotic demyelination, which can leave a client paralyzed. An answer that pushes sodium back to normal as fast as possible is wrong even though it sounds proactive.

Calcium has a lab trap too. Total calcium falls when albumin falls, so a low total calcium in a malnourished client may not mean true hypocalcemia. MSD Manuals recommends correcting for albumin or measuring ionized calcium. If a question gives a low calcium with a low albumin and no symptoms, the corrected value is the point.

Sources and further reading

MSD Manual Professional Edition: Hyperkalemia. Threshold, often asymptomatic until cardiac effects, ECG progression, levels varying among clients with similar ECG changes, and pseudohyperkalemia from hemolysis, tourniquet or fist clenching.

MSD Manual Professional Edition: Hypernatremia. Thirst as the major symptom, CNS signs, at-risk groups, water deficit as the usual mechanism, rare volume overload, and cerebral edema with rapid correction.

MSD Manual Professional Edition: Hyponatremia. Neurologic symptoms including hyperreflexia in severe cases, and osmotic demyelination with rapid correction.

MSD Manual Professional Edition: Hypocalcemia. Paresthesias, tetany, laryngospasm and seizures, QT prolongation, Chvostek and Trousseau signs in healthy people, and correcting total calcium for albumin.