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Jerry Hladik, MD UNC-Chapel Hill
Potassium Disorders Jerry Hladik, MD UNC-Chapel Hill
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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. 100 Normal Values 100
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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 20 100 100 Normal values
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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
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Physiologic Effects of Potassium
Major determinant of the resting membrane potential Hypokalemia may precipitate cardiac arrhythmias Hyperkalemia life threatening cardiac conduction disturbances and arrhythmias
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Transcellular K+ Distribution
3Na+ ATPase 2K+ K+cell = mEq/L K+e = 4-5 mEq/L
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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
![Relationship Between [K+]serum and Total Body Potassium in 70 kg Adult](http://slideplayer.com./slide/9066366/27/images/7/Relationship+Between+%5BK%2B%5Dserum+and+Total+Body+Potassium+in+70+kg+Adult.jpg "6. 5. Serum. [K+] mEq/L mEq. Normal mEq. Total Body Potassium.")
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Potassium Distribution
ECF 80 mEq 2% ICF 3920 mEq 98%
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Potassium Content in Fruits and Vegetables
Amount of Potassium Milligrams mEq Potato with skin 844 mg 20 3 Oz. Dried Fruit 796 mg 20 10 Dried Prunes 626 mg 16 1 Banana mg 11 Tomato 254 mg 6.5 1 Kiwi mg 8 Oz. Glass of mg 6.5 Orange Juice 1Grapefruit mg 4
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Ingested Potassium = 52 mEq
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 = = 132 mEq Serum K Concentration = 132 mEq/15 L = 8.8 mEq/L !
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Components of Potassium Homeostasis
ICF Distribution 90% Kidney Insulin Intake ECF Excretion Aldosterone 10% Colon
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Renal Tubular Potassium Handling
Filtered load mEq per day K+ Reabsorption 20-30% K+ Secretion K+ Reabsorption 60-70% Urinary Excretion 90mEq/day
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Urinary Potassium Excretion
Normal kidneys have the capacity to excrete mEq per day (average K+ excretion mEq/day). The key site of renal potassium excretion regulation occurs at the cortical collecting duct.
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Cortical Collecting Duct - Principle Cells
Na+ Peritubular capillary Na+ 3Na+ ATPase 2K+ Tubular lumen K+ R-Aldo Aldosterone Cl-
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Cortical Collecting Duct
Na+ Tubular lumen Peritubular Capillary Na+ 3Na+ Principle Cell ATPase 2K+ K+ R-Aldo Aldosterone Cl- ATPase H+ 3Na+ ATPase Intercalated Cell H2O 2K+ T OH- + CO2 HCO3- K+ NH4+ ATPase Cl- H+ + NH3 H+ NH3
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Mechanisms Leading to Hyperkalemia
Impaired entry into cells Increased release from cells Decreased urinary excretion
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Hyperkalemia – Redistribution: ICFECF
Glucose Insulin Digoxin β-blockers Cell injury 3Na+ ATPase 2K+ K+
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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
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Effect of Amiloride Predict changes in the following:
Tubular lumen Predict changes in the following: Relative lumen charge Renal K+ excretion Serum potassium Renal H+ excretion Arterial pH Aldosterone
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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
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ECG Changes due to Hyperkalemia
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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
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Effect of i.v. Ca2+ on Membrane Potentials in Hyperkalemia
+30 i.v. Calcium - 30 Et Em Em -60 Et Et -90 Em Normal K+e K+e
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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)
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Differential Diagnosis of Hypokalemia
Increased entry into cells Inadequate intake or GI losses Urinary losses
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Hypokalemia: Redistribution: ECFICF
Insulin β-2 agonists Alkalosis Barium poisoning Hypokalemic periodic paralysis 3Na+ ATPase 2K+ K+
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Factors that Enhance Urinary K+ Excretion
Lumen of CCD more electronegative Enhanced flow and sodium delivery to the CCD Increased aldosterone
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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)
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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 %
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Metabolic Alkalosis in Vomiting
35 Volume Depletion 30 Serum [HCO3-] 25 20 7.0 UpH 5.5 4.0 50 U[Cl-] 30 10 Generation Phase Early Maintenance Phase Late Maintenance Phase
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Effect of Gastric Loss of HCl, Na+/H2O (Volume)
ATPase Tubular lumen Peritubular Capillary OH - + CO 2 HCO 3 T Cl H O H+ 3Na + 2K K+ Na+ R Aldo Aldosterone Predict changes in the following: 1. Relative lumen charge 2. Renal K+ excretion 3. Serum potassium 4. Renal H+ excretion 5. Arterial pH HCO3-
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Aldosterone Escape Days 8 10 12 14 16 18 Aldosterone 2 4 6 15 20 15 10
110 Mean arterial Pressure 100 90 21 ECF Vol (L) 18 15 20 Urine [Na+] mEq/L 15 10 200 Na+ balance -200 Days 2 4 6 8 10 12 14 16 18
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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
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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 20 100 100 Normal values
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Case 2 Continued Urine [Na+] = 75 mEq/L Urine [Cl-] = 100 mEq/L
FeK = 20% What is the most likely diagnosis?
![Case 2 Continued Urine [Na+] = 75 mEq/L Urine [Cl-] = 100 mEq/L](http://slideplayer.com./slide/9066366/27/images/35/Case+2+Continued+Urine+%5BNa%2B%5D+%3D+75+mEq%2FL+Urine+%5BCl-%5D+%3D+100+mEq%2FL.jpg "FeK = 20% What is the most likely diagnosis")
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