POTASSIUM DISORDERS

Distribution of Potassium (K) in the Body

Potassium (K) is a vital electrolyte in the human body, primarily found within cells. Approximately 98% of the body’s potassium is intracellular, while only about 2% is extracellular. The normal serum potassium concentration ranges from 3.5 to 5.0 mEq/L. The distribution of potassium is crucial for various physiological functions, including maintaining cellular membrane potential, nerve conduction, muscle contraction, and acid-base balance.

The intracellular concentration of potassium is significantly higher than that of sodium, which is mainly found in the extracellular fluid. This gradient is maintained by the sodium-potassium ATPase pump (Na+/K+ pump), which actively transports sodium out of cells and potassium into cells against their concentration gradients. This mechanism is essential for maintaining resting membrane potential and overall cellular function.

Causes of Hypokalemia

Hypokalemia refers to a lower-than-normal level of potassium in the blood (<3.5 mEq/L). Several factors can lead to hypokalemia:

1. Inadequate Dietary Intake: Insufficient consumption of potassium-rich foods such as fruits (bananas, oranges), vegetables (spinach, potatoes), and legumes can contribute to low levels.
2. Excessive Losses:
   • Renal Losses: Conditions such as hyperaldosteronism or diuretic use can lead to increased renal excretion of potassium.
   • Gastrointestinal Losses: Vomiting, diarrhea, or excessive laxative use can result in significant loss of potassium.
3. Transcellular Shifts: Conditions like metabolic alkalosis or insulin administration can cause potassium to shift from the extracellular space into cells.
4. Certain Medications: Some medications, particularly loop diuretics (e.g., furosemide) and thiazide diuretics, can induce hypokalemia by promoting renal excretion.
5. Hormonal Influences: Increased levels of hormones such as aldosterone can enhance renal excretion of potassium.

Causes of Hyperkalemia

Hyperkalemia refers to elevated levels of potassium in the blood (>5.0 mEq/L). Causes include:

1. Decreased Renal Excretion: Chronic kidney disease or acute kidney injury impairs the kidneys’ ability to excrete potassium effectively.
2. Excessive Intake: High dietary intake or intravenous administration of potassium can lead to hyperkalemia, especially in individuals with compromised renal function.
3. Cellular Release:
   • Conditions that cause cell lysis (e.g., hemolysis, rhabdomyolysis) release intracellular potassium into the bloodstream.
   • Metabolic acidosis can also promote a shift of potassium from inside cells to outside.
4. Medications: Certain medications like ACE inhibitors and angiotensin receptor blockers may reduce renal excretion and contribute to hyperkalemia.
5. Hormonal Factors: Adrenal insufficiency (Addison’s disease) leads to decreased aldosterone production, resulting in reduced renal excretion.

Diagnosis and Management

Diagnosis:

• Diagnosis begins with a thorough clinical history and physical examination.
• Serum electrolytes are measured through blood tests; abnormal levels indicate either hypokalemia or hyperkalemia.
• An ECG may be performed; changes such as peaked T-waves may indicate hyperkalemia while flattened T-waves may suggest hypokalemia.
• Further tests may include urine analysis to assess renal losses or imaging studies if an underlying condition is suspected.

Management:

• For hypokalemia:
  • Mild cases may be managed with dietary modifications or oral potassium supplements.
  • Severe cases (<2.5 mEq/L) often require intravenous potassium replacement under careful monitoring due to risks associated with rapid infusion.
• For hyperkalemia:
  • Immediate management includes stabilizing cardiac membranes using calcium gluconate or calcium chloride if ECG changes are present.
  • Insulin and glucose administration can help drive potassium back into cells temporarily.
  • Sodium bicarbonate may be used if acidosis is present.
  • In severe cases or when other treatments fail, dialysis may be necessary for rapid removal of excess potassium from the body.

In both conditions, addressing underlying causes—such as adjusting medications or treating kidney disease—is essential for long-term management.