Chapter4(2)  Potassium Disorders
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Chapter4(2) Potassium Disorders 1.Normal potassium metabolism: (1) Balance of potassium intake and excretion : K + intake : 50-200mmol/day from vegetable and fruit K + excretion : kidney:approximately 90% of dietary potassium

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Chapter4(2) Potassium Disorders

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Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

Chapter4(2) Potassium Disorders

1.Normal potassium metabolism: (1) Balance of potassium intake and excretion:K+intake : 50-200mmol/day from vegetable and fruit

K+ excretion:

kidney:approximately 90% of dietary potassium

GI tract: only about 10 %


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

Major organ of excretion potassium: kidney Regulative site: renal distal tubuleHormone of major regulated: ADS

Only the potassium output remains equivalent to intake every 24 hours, then to ensureTotal body potassium 50-55mmol/kg B.W


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

Distal and collecting tubule secretion

(Principal cells)

Regulated by:

1 Na+-K+ ATPase

2 Electrochemical gradient of across the apical membrane

3 permeability of the apical membrane


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

Factors of affecting renal handling potassium

Aldosterone Activates Na+-K+ ATPase   Sodium channels in the luminal membrane Na+reabsorption

 Potassium channels in the luminal membrane

Intracellular potassium content  Secretion 

Urine flow rate Secretion 

Distal delivery of sodium  Secretion 

Acid-base balance: Acute acidosis Secretion


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

(2) Balance of potassium distribution:

It is depended Na+—K+—ATPase on the cellular membrane(pump leak).

consumption of1 ATP→pumping3 Na+ out offand2 K+ intothe cell

Total body potassium approximately 98% in ICF50-55mmol/kg B.W approximately 2% inECF

ICF (3500mmol ): 150-160mmol/L

ECF (70 mmol ): serum potassium 3.5-5.5mmol/L


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

Influence factor of potassium distribution between ICF and ECF(1)Function of the Na+-K+ pump: anoxia → Na+-K+ ATPase ↓[K+]e: Na+-K+ ATPase ↑

(2)Influence of acid-base balance: H+-K+ exchanges across the cellular menbrane Acidosis company with hyperkalemia Alkalosis company with hypokalemia

(3) Influence of hormone: Insulin----K+ into cell Aldosterone----increases excretion of K+Catecholamines : -R net influx into the cells

-R plasma K+

(4) Rate of cell breakdown: crush syndrome

(5) Plasma osmolality:


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

  • Function of the Potassium

  • The Intracellular and extracellular potassium gradient is of major importance in maintenance resting cell membrane potential(Em)

  • The abundant pool of intracellular potassium is necessary for maintenance of osmolality and hence the volume of body cells.

  • Essential for enzymatic reactions that regulate protein synthesis,growth,and metabolic processes


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

The relationship between serum potassium and total body potassium

The clinical signs and symptoms are major depended on concentration ofserum potassium.


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

  • Disorders of potassium homeostasis

  • Hypokalemia: Serum potassium 3.5 mmol/L ( Potassium depletion: ICF or total potassium  )

  • Hyperkalemia: Serum potassium 5.5 mmol/L


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

  • Hypokalemia

  • Concept:

  • Serum potassium<3.5mmol/L


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

(2)Causes:a. Inadequate intake: Inability to eat; Fast and anorexia; Administration of K+ -free parenteral solutionsb. Excessive losses:Gastrointestinal losses – Vomiting; Diarrhea; suction; Fistula.Renal losses – Polyurine phase of acute renal failure,Diuretic therapy (except triamterene and spironolactone).Increased mineralocorticoid levels – primary and second aldosteronism Cushing’s syndromeTreatment with glucocorticoid hormonesc. Intracellular shift:AlkalosisInsulin treatmentFamilial hypokalemic periodic paralysis Barium poisoning


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

(3)Effect on body:a. Effect on neuromuscular irritabilityAcute Hypokalemia:[K+]I/[K+]e → | Em |↑(more negative) → ( Em-Er )↑→ Irritability↓→ Hyperpolarized blockNerve system manifestation: Depression, apathy, coma .Muscle system manifestation: striated muscle----Fatigue ,weakness, flaccid paralysis smooth muscle----vessel dilation; decreased intestinal motion, abnormal distension,constipation and paralytic ileus.

Chronic hypokalemia: The intracellular K+ moves into ECF to maintain nearly normal RMP. So it has no above mentioned manifestation.


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

b. Effect on heartserum [K+]↓→ reducing potassium conductance↓→ |Em|↓→ (Em-Er)↓→ irritability↑ serum [K+]↓→ reducing potassium conductance↓→ decrease K+ outward and accelerating Na+ inward in 4 phase → automaticity↑ serum [K+]↓→ |Em|↓→ inward of Na+ in phase 0 ↓ → conductivity↓ early stage or mild serum [K+]↓→ accelerating of Ca2+ inward in phase2 → contractivity↑ severe serum [K+]↓→ Ca2+ transport disorder ; ATP decreased; myocardium degeneration → contractivity↓ ECG: low T wave ; high U wave ; prolonged Q-T interval ; fallen S-T segment


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

Hyperkalemia

Tall, peaked T-wave(5.5-6.5)

Wide flat P-wave/Prolonged PR interval/Widened QRS complex /Deep S-wave (6.5-8.0)

Ventricular fibrillation. Sine-wav: proceed to asystole (absence of heartbeat)(8.0)

Hypokalemia

Shallow T-wave /Prominent U-wave (2.5-3.5)

ST depression/

Tall “P” waves

(1.5-2.5)

Ventricular Tachycardia (1.5)


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

c. Effects on kidneyHypokalemia → damage of renal tubules → inability to concentrate urine refractoriness to ADHpolyuria, nocturia, low specific gravity urine ,thirst

prolonged severe hypokalemia: oliguria


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

d. Effects on acid-base balance

Hypokalemia:more K+ move out of cells metabolic alkalasismore H+ and Na+ of ECF move into cells H+of ECF↓→ with more H+ are secreted from kidney abnormal acidic urine


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

(4) Principle of treatmenta. In mild hypokalemia:

replenishment of KCl by the oral route is preferable because it is safer than I.V. administration.b. In severe hypokalemia:

adding KCl to glucose water intravenously at a final concentration of 40 mmol/L, and infusing KCl at a rate of 10-20 mmol/h, since KCl is an irritating substance. Usually the repair of hypokalemia needs several days. Never give KCl solution by direct intravenous injection to patients.


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

  • Hyperkalemia

  • Concept :Hyperkalemia is defined as a serum K+ level greater than 5.5 mmol per liter .( serum potassium >5.5mmol/L )


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

(2)Causes:A. Diminished renal excretiona. reduced GFR: oliguria phase of acute renal failure terminal phase of chronic renal failure b. reduced tubular secretion of K+ addison’s disease; hypoaldosteronism application of potassium sparing diuretic(spironolactone ,triamterene). B. Increasedinput of potassiumexcessive or rapid parenteral infusion of KCl solutionC. Extracellularshiftsa. acidosis b. cell destruction(trauma, burns, hemolysis, tumor lysis, rhabdomyolysis c. Familial hyperkalemic periodic paralysis


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

(3)Effects on body :A. Effects on neuromuscular irritability

a. mild serum [K+] ↑→ [K+]I/[K+]e↓→ |Em|↓( as partial depolarization)→ (Em- Er)↓→ irritability↑→ Excitation( Diarrhea,intestinal colic,paresthesia)

b. severe serum [K+]↑→ [K+]I/[K+]e↓↓→ |Em|↓↓→|Em|≤ |Et| → Na+channel inactive → irritability↓→ Depolarized block(weakness, paralysis, mental confusion and coma。)


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

b. Effect on hearta. Mild serum [K+] ↑→ [K+]I/[K+]e↓→ |Em|↓( as partial depolarization)→ (Em- Er)↓→ irritability↑b. Severe serum [K+]↑→ [K+]I/[K+]e↓↓→ |Em|↓↓→|Em|≤ |Et| → Na+channel inactive → irritability↓Serum [K+] ↑ →increased potassium conductance → accelerating K+ outward and decreased Na+ inward in 4 phase → autodepolarization ↓ → automaticity↓ Serum [K+] ↑ → [K+]I/[K+]e↓→ |Em|↓ → inward of Na+ in 0 phase ↓ → decreased velocity and extent of depolarization → conductivity↓ Serum [K+] ↑ → depression Ca2+ inward in 2 phase → contractivity↓clinic signs and symptom :sinus bradycardia, heart block, asystole and heart arrest.


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

ECG:

tall peaked and tent-shaped T wave; disappearance of P wave ; prolonged P-R interval; widening of QRS complex


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

c. effect on acid-base balanceserum K+↑→K+ of ECF move into cells and H+of ICF move out of cell; decreased secretion of H+ due to intensive exchange between Na+ and K+ by distal tubules → metabolic acidosis with abnormal alkali urine


Chapter42 potassium disorders 1 normal potassium metabolism 1 balance of potassium inta

(4) Principles of treatmenta. Treating primary disease b. Restriction of potassium intake c. Shift of K+ from ECF into cell (insulin+glucose) d. Increased in K+ excretion from body (furosemide, ethacrynic acid) e. Antagonizing the effects of hyperkalemia on heart (Ca2+ or NaHCO3)


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