Disorders of potassium balance

1. Disorders of potassium balance Zhao Chenghai Pathophysiology

2. Outline • Potassium balance • Disorders of potassium balance • Hypokalemia • Hyperkalemia

3. Potassium balance

4. Potassium balance • Distribution of potassium • Gains and losses of potassium • Mechanisms of regulation • Functions of potassium

5. Distribution of potassium • The intracellular concentration of potassium ranges from 140 to 150 mmol/L. • The extracellular concentration of potassium (3.5-5.0mmol/L) is considerable less.

6. Gains and losses • Food is the main source of potassium intake. • The kidneys are the main source of potassium elimination.

7. Mechanisms of regulation • Renal regulation • Transcellular shift between the intracellular and extracellular compartments

8. Renal regulation • Secretion of potassium by distal and collecting tubules. • Aldosterone --- a sodium-potassium exchange system. Sodium is transported back into blood. Potassium is secreted into tubular filtrate. Mineralocorticoid hormone Plasma potassium levels control aldosterone secretion by adrenal gland.

9. Transcellular shifts • Sodium-potassium ATPase • Both insulin and epinephrine increase the activity of sodium-potassium pump. (An increase in potassium level stimulates insulin release. --- a feedback mechanism) • Potassium channels • ECF osmolality↑→H2O leaves cell→ ICF K+↑→ K+ moves out of cell through K+ channels →ECF K+ • Exercise • Potassium-hydrogen exchange to maintain electrical neutrality • In acidosis • In alkalosis

10. Functions of potassium • Maintain the osmotic integrity of cells • Osmotic pressure in ICF • Maintain acid-base balance • Through potassium-hydrogen exchange • Contribute to the reactions that take place in cells • Transform carbohydrates into energy • Convert amino acid to protein • Change glucose into glycogen • Play a critical role in the excitability of skeletal, cardiac, and smooth muscle.

11. Resting membrane potential (RMP) RMP≈-59.5lg[K+]i/[K+]e Excitability of muscle cells can be affected by the distance between RMP and threshold potential.

12. Hypokalemia Hypokalemia refers to a decrease in plasma potassium level below 3.5 mmol/L.

13. Causes of hypokalemia • Inadequate intake • inability to obtain or ingest food • Diet deficient in potassium • Excessive renal, gastrointestinal and skin losses • Diuretic therapy (thiazide and loop diuretics) • Increased aldosterone level (primary aldosteronism, stress-cortisol) • burn, sweating increase, vomiting and diarrhea • Transcellular shift • Administration of insulin (to treat diabetic ketoacidosis) • β-adrenergic agonist----albuterol (bronchodilator) • Alkalosis

14. Manifestations of hypokalemia • Neuromuscular manifestations • Muscle flabbiness, weakness and fatigue • Muscle cramps and tenderness • Paresthesia and paralysis • Impaired kidney’s ability to concentrate the urine • polyuria, urine with low osmolality, polydipsia (ECF osmolality↑) • Gastrointestinal manifestations • Anorexia, nausea, vomitting, • Constipation, abdominal distension, paralytic ileus • Cardiovascular manifestations • Arrhythmias, increased sensitivity to digitalis toxicity • Metabolic alkalosis

15. ECG changes in hypokalemia • Depression of the ST segment • Flattening of the T wave • Appearance of a prominent U wave • Prolongation of PR interval

16. Treatment of hypokalemia • Increasing the intake of foods high in potassium content • Oral potassium supplements • Giving potassium intravenously when rapid replacement is needed. • Only if the renal function is adequate

17. Hyperkalemia • Hyperkalemia refers to an increase in plasma levels of potassium in excess of 5.0mmol/L.

18. Causes of hyperkalemia • Decreased renal elimination • Decreased renal function-renal failure • Treatment with potassium-sparing diuretics • Decreased aldosterone level • Adrenal insufficiency (addison’s disease) • Treatment with ACEI • Angiotensin II receptor blocker • Excessively rapid administration • Movement of potassium from the intracellular to extracellular compartment • Tissue injury such as burns and crushing injuries • Extreme exercise or seizures • Acidosis

19. Manifestations of hyperkalemia • Gastrointestinal manifestations • Anorexia, nausea, vomitting, intestinal cramps, diarrhea • Cardiovascular manifestations • Ventricular fibrillation and cardiac arrest • Neuromuscular manifestations • Paresthesias • Weakness • Muscle cramps

20. ECG changes in hyperkalemia • Appearance a peaked T wave • Widening of the QRS complex • Prolongation of the PR interval • Disappearance of the P wave

21. Treatment of hyperkalemia • Decreasing intake or absorption of potasssium. • Using calcium to antagonize the potassium. • Using insulin and glucose • Increasing potassium excretion • hemodialysis • peritoneal dialysis

22. Case1 • A 40-year-old man with advanced acquired immunodeficiency syndrome (AIDS) presents with an acute chest infection. Investigation confirm a diagnosis of P.carinii pneumonia. Although he is treated appropriately, his serum sodium level is 118mmol/L. Tests of adrenal function are normal. • What type of disorders happened to this man? • What is the likely cause of this electrolyte disturbance?

23. Case 2 • A 70-year-old woman who is taking furosemide (a loop diuretic) for congestive heart failure complains of weakness, fatigue, and cramping of the muscles in her legs. Her serum potassium is 2.0mmol/L, and her serum sodium is 140mmol/L. She also complains that she notices a “strange heart beat” at times. • What is the likely cause of this woman’s symptoms? • What would be the treatment for this woman?

24. Case 3 • A 76-year-old woman was brought to the hospital because she was lethargic and refused to drink fluid. Her blood pressure is 100/60 mmHg. Serum sodium level is 170mmol/L, potassium level is 4.3mmol/L. • What kind of electrolyte disturbance happened to this woman? • What is the cause of this kind of disorder? • What is the most severe outcome of this disorder?