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Potassium Disorders

Potassium Disorders. Jerry Hladik, MD UNC-Chapel Hill. Case 1. A 62 year old male presents to the emergency room with a 2 day history of weakness. His recent history is significant for gouty arthritis for which he was taking over the counter ibuprofen. 106 76 7.8 15 10. 100.

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Potassium Disorders

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  1. Potassium Disorders Jerry Hladik, MD UNC-Chapel Hill

  2. Case 1 A 62 year old male presents to the emergency room with a 2 day history of weakness. His recent history is significant for gouty arthritis for which he was taking over the counter ibuprofen. • 106 76 • 7.8 15 10 100 Normal Values 140 104 10 4 24 1 100

  3. Case 2 A 56 year old female presents with a 2 day history of weakness. On physical exam she is diffusely weak and is unable to sit up. The blood pressure is 210/105 mmHg. There is no edema. • 96 20 • 1.9 32 1.4 100 140 104 10 4 24 1 100 Normal values

  4. Outline • Potassium distribution in the ECF and ICF and factors that alter K distribution. • Renal tubular potassium regulation and excretion • Differential diagnosis of hyperkalemia and hypokalemia

  5. Physiologic Effects of Potassium • Major determinant of the resting membrane potential • Hypokalemia • may precipitate cardiac arrhythmias • Hyperkalemia • life threatening cardiac conduction disturbances and arrhythmias

  6. Transcellular K+ Distribution 3Na+ ATPase 2K+ K+cell = 140-160 mEq/L K+e = 4-5 mEq/L

  7. Relationship Between [K+]serum and Total Body Potassium in 70 kg Adult 6 5 Serum [K+] mEq/L 4 3 2 -150 mEq Normal +150 mEq Total Body Potassium

  8. Potassium Distribution ECF 80 mEq 2% ICF 3920 mEq 98%

  9. Potassium Content in Fruits and Vegetables Amount of PotassiumMilligrams mEq Potato with skin 844 mg 20 3 Oz. Dried Fruit 796 mg 20 10 Dried Prunes 626 mg 16 1 Banana 451 mg 11 Tomato 254 mg 6.5 1 Kiwi 252 mg 6.5 8 Oz. Glass of 250 mg 6.5 Orange Juice 1Grapefruit 158 mg 4

  10. A 24 y.o male returns home to visit his mother. For breakfast she serves orange juice (of which he drinks 3 large glasses), and a bowel of fruit comprised of 2 bananas, 1 grapefruit, and 1 kiwi. What would happen to the serum potassium concentration if all of the ingested potassium remained in the extracellular space? Ingested Potassium = 52 mEq Extracellular Potassium = 80 + 52 = 132 mEq Serum K Concentration = 132 mEq/15 L = 8.8 mEq/L !

  11. Components of Potassium Homeostasis ICF Distribution 90% Kidney Insulin Excretion Aldosterone ECF Intake 10% Colon

  12. Renal Tubular Potassium Handling Filtered load 600-700 mEq per day K+ Reabsorption 20-30% K+ Secretion K+ Reabsorption 60-70% Urinary Excretion 90mEq/day

  13. Urinary Potassium Excretion • Normal kidneys have the capacity to excrete 500-600 mEq per day (average K+ excretion 40-100 mEq/day). • The key site of renal potassium excretion regulation occurs at the cortical collecting duct.

  14. Cortical Collecting Duct - Principle Cells Na+ Peritubular capillary Na+ 3Na+ ATPase 2K+ Tubular lumen K+ R-Aldo Aldosterone Cl-

  15. Cortical Collecting Duct Na+ Tubular lumen Peritubular Capillary Na+ 3Na+ Principle Cell ATPase 2K+ K+ Aldosterone R-Aldo Cl- ATPase 3Na+ H+ ATPase Intercalated Cell H2O 2K+ T HCO3- OH- + CO2 K+ NH4+ ATPase Cl- H+ H+ + NH3 NH3

  16. Mechanisms Leading to Hyperkalemia • Impaired entry into cells • Increased release from cells • Decreased urinary excretion

  17. Hyperkalemia – Redistribution: ICFECF • H+ • Glucose • Insulin • Digoxin • β-blockers • Cell injury 3Na+ ATPase 2K+ K+

  18. Factors that Impair Urinary K+ Excretion • Collecting duct lumen relatively more electropositive • Decreased flow and sodium delivery to the CCD • Decreased aldosterone production or activity

  19. Effect of Amiloride Tubular lumen • Predict changes in the following: • Relative lumen charge • Renal K+ excretion • Serum potassium • Renal H+ excretion • Arterial pH Aldosterone

  20. Hyperkalemia: Decreased Renal Excretion • Volume depletion decreased flow in CCD • Decreased renin-AII-aldo production • NSAIDS  renin • ACEI  AII • Heparin  aldosterone production • Spironolactone  aldosterone activity • Inhibition of CCD Na+ channel • Amiloride, triamterene, trimethoprim, pentamidine

  21. ECG Changes due to Hyperkalemia

  22. ECG Changes of Hyperkalemia Serum K+ (mEq/L) ECG 9 Sinoventricular V-fib 8 Atrial standstill Intraventricular block 7 Tall T wave. Depressed ST segment 6 Tall T wave. Shortened QT interval

  23. Effect of i.v. Ca2+ on Membrane Potentials in Hyperkalemia +30 0 i.v. Calcium - 30 Et Em Em -60 Et Et -90 Em Normal K+e K+e

  24. Treatment of Hyperkalemia Therapy Mechanism of Action Calcium Stabilization of Membrane Potential Insulin Increased K+ entry into Cells Beta-2 Agonists Bicarbonate (if pHa<7.2 in setting of acidosis) Dialysis Potassium removal Cation Exchange Resin (sodium polystyrene = Kayexalate)

  25. Differential Diagnosis of Hypokalemia • Increased entry into cells • Inadequate intake or GI losses • Urinary losses

  26. Hypokalemia: Redistribution: ECFICF • Insulin • β-2 agonists • Alkalosis • Barium • poisoning • Hypokalemic • periodic • paralysis 3Na+ ATPase 2K+ K+

  27. Factors that Enhance Urinary K+ Excretion • Lumen of CCD more electronegative • Enhanced flow and sodium delivery to the CCD • Increased aldosterone

  28. Sites of Action of Diuretics Thiazide Diuretics Loop diuretics Blood Lumen (Defect = Bartter’s) Na+ Cl- Lumen Blood Na+ K+ 2Cl-- Thiazide diuretics Loop diuretics (Defect = Gitelman’s)

  29. Interpretation of Urinary K+ in the Setting of Hypokalemia GI Losses or prior Renal K Loss or Diuretic Therapy Current Diuretic Use 24o Urine K < 20 mEq > 30 mEq FeK < 6 % > 10 %

  30. Metabolic Alkalosis in Vomiting 35 Volume Depletion 30 Serum [HCO3-] 25 20 7.0 UpH 5.5 4.0 50 U[Cl-] 30 10 Early Maintenance Phase Generation Phase Late Maintenance Phase

  31. Tubular lumen Peritubular Na+ Capillary Na+ 3Na + ATPase 2K + K+ R - Aldo Aldosterone 3Na + H+ ATPase ATPase H O 2K + 2 T HCO - OH - + CO 3 2 Cl - Effect of Gastric Loss of HCl, Na+/H2O (Volume) Predict changes in the following: 1. Relative lumen charge 2. Renal K+ excretion 3. Serum potassium 4. Renal H+ excretion 5. Arterial pH HCO3-

  32. Aldosterone Escape Aldosterone 110 Mean arterial Pressure 100 90 21 ECF Vol (L) 18 15 20 15 Urine [Na+] mEq/L 10 200 Na+ balance 0 -200 Days 8 10 12 14 16 18 2 4 6

  33. Urine Na+ and Cl- in the Differential Diagnosis of Metabolic Alkalosis and Hypokalemia Urine Electrolytes Na+ Cl- Condition (meq/L) Vomiting Alkaline urine >15 <15 Acidic urine <15 <15 Diuretic Drug active >15 >15 Remote use <15 <15 Hyperaldosteronism >15 >15

  34. Case 2 A 56 year old female presents with a 2 day history of weakness. On physical exam she is diffusely weak and is unable to sit up. The blood pressure is 210/105 mmHg. There is no edema. • 96 20 • 1.9 32 1.4 100 140 104 10 4 24 1 100 Normal values

  35. Case 2 Continued Urine [Na+] = 75 mEq/L Urine [Cl-] = 100 mEq/L FeK = 20% What is the most likely diagnosis?

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