Mrs. Bush, a 70-year-old woman, is admitted to the hospital. Her history states that she has been suffering from diarrhea for three weeks. On admission, she complains of severe fatigue and muscle weakness. A blood chemistry study yields the following information: Na⁺ 142 mEq/L; K⁺ 1.5 mEq/L; Cl⁻ 92 mEq/L; Pco₂ 32 mm Hg.
Which electrolytes are within normal limits? Which are so abnormal that the patient has a medical emergency?
Which of the following represents the greatest danger to Mrs. Bush?
a. A fall due to her muscular weakness
b. Edema
c. Cardiac arrhythmia and cardiac arrest.

Verified step by step guidance

1. Identify the normal reference ranges for the electrolytes and blood gas values given: typically, Na⁺ (sodium) is 135-145 mEq/L, K⁺ (potassium) is 3.5-5.0 mEq/L, Cl⁻ (chloride) is 98-106 mEq/L, and Pco₂ (partial pressure of carbon dioxide) is 35-45 mm Hg.
2. Compare Mrs. Bush's values to these normal ranges: Na⁺ is 142 mEq/L (within normal limits), K⁺ is 1.5 mEq/L (significantly low), Cl⁻ is 92 mEq/L (low), and Pco₂ is 32 mm Hg (slightly low).
3. Recognize that severe hypokalemia (very low potassium) is a medical emergency because potassium is critical for normal muscle and cardiac function, and such a low level can cause life-threatening cardiac arrhythmias.
4. Understand that while muscle weakness and risk of falls are concerns, the greatest immediate danger is cardiac arrhythmia and cardiac arrest due to the hypokalemia.
5. Conclude that the normal electrolyte here is sodium, the most abnormal and dangerous electrolyte disturbance is potassium, and the greatest danger to Mrs. Bush is option c: cardiac arrhythmia and cardiac arrest.

Key Concepts

Electrolyte Normal Ranges and Imbalances

Electrolytes like sodium (Na⁺), potassium (K⁺), and chloride (Cl⁻) have established normal blood ranges essential for bodily functions. Deviations can cause symptoms and complications; for example, normal potassium is typically 3.5–5.0 mEq/L, and severe hypokalemia (like 1.5 mEq/L) can be life-threatening. Understanding these ranges helps identify which values are normal or critical.

Clinical Consequences of Hypokalemia

Hypokalemia, or low potassium levels, can cause muscle weakness, fatigue, and most critically, cardiac arrhythmias. Potassium is vital for normal cardiac electrical activity, and severe deficiency increases the risk of dangerous heart rhythms and cardiac arrest, making it a medical emergency requiring prompt treatment.

Interpreting Acid-Base and Electrolyte Disturbances in Diarrhea

Prolonged diarrhea leads to loss of fluids and electrolytes, often causing hypokalemia and metabolic acidosis or respiratory compensation (reflected in Pco₂). Recognizing how diarrhea affects electrolyte balance and acid-base status is crucial for diagnosing the underlying problem and prioritizing treatment to prevent complications.