Potassium - HYPOkalaemia





K+ = the main intracellular cation

Thus, even a small drop could indicate a significant deficit

1 mmol/L drop in K+
≈ 100 to 300 mmol drop in total body K+

Severity

Hypokalaemia is when K+ < 3.5 mmol/L

Severity of hypokalaemia:

  • Mild: 3 to 3.5 mmol/L
  • Moderate: 2.5 to 3 mmol/L
  • Severe: < 2.5 mmol/L

Causes

Hypokalaemia can be due to:

  • Decreased intake
  • Increased loss
  • Intercompartmental shift

Decreased intake

  • Anorexia nervosa
  • Alcoholism

Increased loss

  • GIT loss
    • Vomiting
    • NGT suction
    • Diarrhoea
    • Pyloric stenosis
  • Renal loss
    • Drugs
      • Diuretics (thiazide, loop)
      • Licorice
    • Osmotic diuresis
      • Mannitol
      • Hyperglycaemia
    • Hyperaldosteronism
      • e.g. Conn's
    • Mineralocorticoid excess
      • e.g. Cushing's
    • Renal tubular acidosis (type 1 and 2)
  • Others
    • Mg2+ depletion
    • Leukaemia

Intercompartmental shift

  • Alkalosis
    • 0.1 ↑ in pH
      → 0.6 mmol/L ↓ in K+
  • Insulin
  • Beta2-agonist
    • e.g. Salbutamol
  • Steroid

S&S

S&S include:

  • Respiratory

    • Respiratory muscle weakness

  • CVS

    • Arrhythmias
      • Torsades de pointes
      • Atrial tachycardia
    • ECG changes

  • D (CNS)

    • Coma

  • Muscular dysfunction

ECG changes

  • Prolonged PR
  • ST segment depression
  • T wave flattening
  • T wave inversion
  • Prominent U wave

NB:

  • LITFL and ECGPedia agreed only on:
    • U wave
    • Flat T wave
  • OHA2 listed all 5 changes above

Muscular dysfunction

  • Muscle weakness
  • Muscle cramps
  • Fatigue
  • Hyporeflexia
  • Hypotonicity
  • Rhabdomyolysis
    • Reported cases when < 2 mEq/L

Rx

Includes:

  • Minimise further potassium loss
    • esp if GI loss or drug-induced
  • K+ replacement
  • Correct Mg2+ and PO4 deficiencies

Potassium replacement

  • K+ can be given IV or PO

?? Each 10 mmol given will increase K+ by 0.1 mmol/L in the short term
→ Depends on rate of intercompartmental equilibration @@ Need source

PO route

Safer and preferred route

Up to 200 mmol per day

e.g. chlorvescent, span K

IV route

  • Use IV route if ECG changes

  • via Peripheral veins

    • Concentration < 10 mmol/L
    • Maximum rate < 10 mmol/hr

  • via CVL

    • Concentration < 40 mmol/L
    • Rate up to 20 mmol/hr
      • Up to 40 mmol/hr if severe
    • ECG monitoring needed

Others

  • Hypokalaemia exacerbates digoxin toxicity

  • Paediatric maximum IV infusion rate = 0.4 mmol/kg/hr

  • Consider keeping K+ > 4 mmol/L ... if post MI

AMx

Issues

Hypokalaemia can lead to:

  • Cardiac arrhythmia
  • Prolonged response to non-depolarising NMBDs
    ... due to muscle weakness