Disorder of potassium metabolism Zhao Mingyao BMC ZZU

Disorder of potassium metabolism Zhao Mingyao BMC. ZZU.

Disorder of potassium metabolism [K+]s mmol/L 3. 5 ~ 5. 5 < 3. 5 > 5. 5 Status Normal level Hypokalemia Hyperkalemia ?

Function of K+ enzyme activity cellular electricity cellular osmolality acid-base balance . H+ K+ Na+

Part 1 General introduction 1. Potassium content and distribution Source: fruit, vegetable, coffee

50~55 mmol/Kg×BW K+ 3. 5~ 5. 5 mmol/L ECF 1. 4% K+ 140~160 mmol/L ICF 90% Potassium content and distribution

2. Maintenance of K+ balance

intake ECF ICF K+ K+ pump 3. 5~ 5. 5 mmol/L channel 140~160 mmol/L kidney 90% GI tract 10% Direction of K+ shifting Skin? Maintenance of K+ balance

(1) The control of K+ transfer between intra- & extracellular compartments • The Na+/K+ATPase (membrane pump ) • Permeability of ion channels

ICF ECF K+ pump channel Insulin, β-adrenergic agonist, ADS, [K+]s↓, exercise, p. H ↓, ECF osmolanity ↑ K+ shifts between ICF and ECF

(2) Regulation of renal K+ excretion ?

tubular lumen tubular cell ICF K+ Na+ - -- kidney 90% K+ Na+-K+ ATPase Na+ K+ ADS, guanylin, [K+]s, urinary flow rate, p. H, distal delivery of sodium, impermeable anion Regulation of renal K+ excretion

Part 2 Hypokalemia • Defined as [k+]s < 3. 5 mmol/L • may or may not be associated with K deficit?

1. Causes (1)K+ Intake↓ (2)K+ redistribution p. H↑, some drugs, Familial Hypokalemic Periodic Paralysis (3)K+ loss infant －by gastrointestinal tract adult － by kidney: diuretics, renal tubular acidosis, ADS ↑, Mg 2+ ↓

2. Effect on body (1)Neuromuscular irritability ↓ hyperpolarization impeding

Nernst equation：Em∝ -60 lg[K+]icf / [K+]ecf (mv) +35 Millivolts 0 -60 Threshold -90 Milliseconds ~ Effects on Neuromuscular Excitability

30 0 mv Action potential (AP) -30 -60 TMP RMP -90 -120 Normal Low [K+] High [K+] The effects of [K+]s concentration on cellular membrane excitability

Acute Hypokalemia [K+]i / [K+]e ↑ RMP more negative than normal ( Em - Et ↑) hyperdepolarization block, excitability↓ muscle weakness, flaccid paralysis, smooth muscle symptoms

(2) Effect on heart Excitability ↑ ---- Et-Em ↓ Conductivity ↓ ---- Em ↓, phase 0, rapid Na+ inward flow ↓ Automaticity ↑ ---- slow K+ outward flow ↓ Contractility ↑ ---- Ca 2+ inward flow ↑

normal a low [K+]e v Threshold potential repolarization normal prolonged Effects of low [K+]s on the AP of the myocardial cell

Typical feature of ECG during hypokalemia < 2. 5 mmol/L + U wave(ECG) aura sign of cardiac asystole

Cardiac arrhythmias due to increased excitability shortened ERP (effective refractory period ) prolonged SNP (supranormal period) increased automaticity decreased conductivity

The conducting system of the heart

(3) Miscellaneous effect • Metabolic alkalosis • Paradoxical acidic urine

3. Principle of prevention & treatment oral slow: ≤ 10 mmol of K/h low concentration: KCl≤ 40 mmol/L limited total amount/d: 40~120 mmol K+/day urine existence (iv instillation: Never inject ! )

Part 3 Hyperkalemia • Defined as [k+]s >5. 5 mmol/L • Except false phenomena?

1. Causes (1)K+ Intake ↑ (2)K+ shift into ECF ↑ p. H ↓, some drugs (β-R antagonist), cell injury, familial hyperkalemic periodic paralysis (3)Renal K+ excretion ↓ GFR ↓ ↓, ADS ↓(Addison`s disease), diuretics with blocking ADS

2. Effect on body (1) Neuromuscular irritability ↑, then↓ ( Partial depolarization? Excitation ↑) Depolarization impeding

(2) Effect on heart Excitability ↑, then↓ ---- Et-Em ↓, closing Conductivity ↓ ---- Em, phase 0, rapid Na+ inward flow ↓ Automaticity ↓ ---- slow K+ outward flow ↑ Contractility ↓ ---- Ca 2+ inward flow ↓

Typical feature of ECG during hyperkalemia > 7. 5 mmol/L + tent-like T wave aura sign of cardiac asystole

ECG K+ 7. 8 mmol/L absent "P ", tall tented "T" and widening of QRS

（3）Effect on acid and base • Metabolic acidosis • Paradoxical alkaline urine ( due to K+↑ or ? )

3. Principle of prevention and treatment ①Limit origination: intake ↓ ② Sodium and calcium salt opposite the toxicity of hyperkalemia ③ Shifted into cell (transient, such as GI fluid, p. H ↑) ④ Remove K+ out of body Na+-K+ cation exchange resin enema hemodialysis