Potassium - HYPERkalaemia





K+ = the main intracellular cation

Range

  • Mild: 5.5 to 6 mmol/L
  • Moderate: 6 to 7 mmol/L
  • Severe: > 7 mmol/L

Causes

Can be divided into the following:

  • Increased intake
  • Decreased urinary excretion
  • Release from cells
    • Intercompartmental shift
    • Tissue injury
  • Measurement error

Increased intake

  • IV administration
  • Rapid blood transfusion

Decreased urinary excretion

  • Renal failure
  • Adrenocortical insufficiency
    • Hypoaldosterone
    • Addison's
  • Obstructive uropathy
  • Drugs
    • K+ sparing diuretics
    • ACE inhibitors (aldosterone inhibition)
    • Cyclosporin

Intercompartmental shift of K+

  • Acidosis
  • Acute digoxin toxicity

Tissue injury

  • Rhabdomyolysis
  • Trauma, burns
  • Malignant hyperthermia
  • Suxamethonium
    • esp in burns or denervation injuries
  • Intense physical activity

Measurement error

  • Haemolysed sample

S&S

S&S include

  • Respiratory failure
  • N&V
  • Muscle weakness
  • Fatigue
  • Diarrhoea

ECG changes:

ECG changes usually varies with severity of hyperkalaemia...
... but NOT always


Earliest ( > 5.5 mmol/L)
→ Repolarisation abnormalities

  • Peaked T waves (usually the earliest change)


Early ( > 6.5 mmol/L)
→ Progressive paralysis of atria

  • Widened P wave and flattened
  • Prolonged PR interval
  • ?? ST depression


Later ( > 7.0 mmol/L)
→ Conduction abnormality and bradycardia

  • Loss of P wave
  • Widened QRS → Shortened QT interval
  • Prominent S wave
    • "Slurring" or "notching"
  • High grade AV block
  • Conduction block
  • Sinus bradycardia or slow AF


Late stage ( > 9 mmol/L)
→ Cardiac arrest

  • Sinusoidal shape
  • VT/VF
  • Asystole


ECG changes are potentiated by

  • Acidosis
  • Low Ca2+
  • Low Na+

Rx

Rx includes:

  • Stop any administration of K+
  • Give calcium
  • Shift K+ intracellularly
  • Remove K+ from body

Calcium

Does NOT alter K+ level

Reduces cardiac effect of hyperkalaemia

  • Stablise myocardial membrane
  • Decrease risk of serious arrhythmia

Indications:

  • Symptomatic hyperkalaemia
  • Significant ECG changes

Dose:

  • Calcium chloride 10%
    • 0.1 to 0.2 mL per kg
    • Up to 10 mLs
  • Calcium gluconate 10%
    • 0.3 to 0.5 mL per kg
    • Up to 30 mLs

Caution:

  • Avoid extravasation

NB:

  • Caution against calcium Rx in hyperkalaemia caused by digoxin
    • Due to "stone heart theory"
      • Inhibition of Na/K ATPase pump by digoxin
      • Can cause accumulation of Ca+ in myocardium
      • Thus cardiac tetany
    • The risk has been disputed by study

Shifting K+ intracellularly

Temporising measure only

Options include:

  • Hyperventilation
  • Sodium bicarbonate
  • Insulin
  • Beta-agonist
    • e.g. Salbutamol NEB

Sodium bicarbonate 8.4%

Use if acidosis

Dose ≈ 1 mL/kg

Least effective of all if used alone

Hyperventilation

Use if IPPV

Aim for PaCO2 of 25 to 30 mmHg

Insulin

[ACC/AHA recommended regime]

Insulin 10 iu ... inglucose 50% 50ml (1 bottle)

  • Infused IV over 15 to 30 min

Alternative recipe: 50 iu in 50mL of D50 - Gives 10 mL (10 iu) at a time - Up to 2 boluses (i.e. 20 mL / 20 iu in total) - I have used it on a couple of occasions and it does not seem to cause hypoglycaemia

Beta agonist

Salbutamol 5 mg NEB Q1H

Up to 20 mg

Removing K+ from body

Definitive Rx

Options include:

  • Forced diuresis
  • Resonium
  • Dialysis

Forced diuresis

Promotes urinary excretion

Frusemide 40 to 80 mg IV + NS

Resonium

  • Promotes excretion in faeces
  • Available in PO or NGT or rectal

NB:

  • Slow, NOT useful in emergency
  • Net loss of K+
  • Net gain of Na+

Others

Supportive measurements like fluids, pacing, and pressors do NOT work on arrhythmias in the setting of hyperkalemia → Must treat the hyperkalemia first.