Electrolyte abnormalities

Question 1

List the ECG findings in hypokalaemia.

See ecgweekly - 13 Aug 18 for examples

Answer 1

• Inc’d amplitude and duration of p-waves
• Widespread ST depression -> STE in aVR
• Down-up (inverse Wellens) T-waves
• Presence of U-waves
• T-U wave fusion -> apparent
• VEBs -> VF/VT
• Easily confused with (L)MCA occlusion -> look for long QT!

Question 2

What is normal K+?

Classify low K+ as mild, moderate and severe.

List the common clinical manifestations of hypokalaemia.

Answer 2

• Normal K+: 3.5-5mmol/L
• Mild hypoK+: 3-3.5mmol/L
  
  • Likely asymptomatic
• Moderate hypoK+: 2.5-3mmol/L
  
  • Fatigue, muscle cramps, weakness, constipation
  • ECG changes - U-waves, T-wave flattening, STD, long QTc
• Severe hypoK+: <2.5mmol/L
  
  • Life-threatening arrhythmias -> CHB, VF, VT
  • Marked muscle (inc’g diphragm) weakness -> respiratory failure
  • Ascending paralysis
  • Rhabdomyolosis

Question 3

List the common causes of hypokalaemia. (think of the categories!)

Answer 3

• Dec’d intake
  
  • Poor diet
  • Starvation
• Inc’d loss
  
  • GI - diarrhoea, vomiting
  • Skin - ++sweating
  • Burns
  • Renal - nephrogenic DI
  • Endocrine disease - hyperaldosteronism, Conn’s syndrome, Cushing’s disease
  • Drugs - diuretics, laxatives
  • Dialysis
• Intra-cellular shift
  
  • Insulin
  • beta-agonists
  • alkalosis - met’c and resp’y

Question 4

List the treatment options for replacement of K+ in mild, moderate and severe hypo+.

Answer 4

• Mild/moderate:
  
  • Oral short acting KCl - ii tabs po bd/tid (2x 14mmol bd/tid) AND/OR
  • Oral long acting KCl - ii tabs po bd/tid (2 x 8mmol bd/tid)
• Severe