Question 15.2

College answer

c)    Potassium level                                              
 
d)    Counteract cardiotoxic effects of hyperkalaemia                     
•    Calcium chloride 
•    Sodium bicarbonate 
        Shift potassium into the cells 
•    Dextrose and insulin 
•    Beta agonists 
      Remove potassium (and water) 
•    Urgent haemodialysis 
 

Discussion

Classical ECG features of hyperkalemia:

• Broad QRS complexes 
• Peaked T waves 
• No typical bundle branch block pattern 
• Left axis deviation
• Long PR interval (if P waves are even visible)
• Absent P waves (merged with QRS)
• Absent T-waves (merged with QRS)
• Ultimately, a "sine wave" ECG.

Montague (2008) found that these were generally unreliable.  The ECG used here is not from the college paper, but rather represents the ECG of an end stage renal failure patient presenting with syncope. The serum potassium level was 7.9.

Management of hyperkalemia is discussed elsewhere. In brief, it consists of the following strategies:

Stabilize myocardial cell membrane:

• Calcium chloride (10%): 6.8 mmol (10ml) over 2-5 minutes
• Hypertonic saline (3%): apparently, this has been show to reverse the ECG changes of hyperkalemia, only when there is concurrent hyponatremia.

 Shift potassium into cells:

• Sodium bicarbonate: 50-100mmol/L, over 5 minutes
• 50ml of 50% dextrose with 10 units of Actrapid insulin
• Salbutamol: 2-4 ×salbutamol nebs (5mg each)

Promote potassium excretion:

• Frusemide 40 to 80 mg IV
• Cation-exchange resin: AHA recommend "kayexelate", which is the same sodium polystyrene sulfonate which is marketed as "Resonium" in Australia.
  "15 to 50 g per oral or per rectum" is recommended in the AHA text, along with sorbitol (to promote rapid transit, one assumes). Oh's Manual suggests a flat dose of 50g, and does not mention sorbitol.
• Dialysis is ultimately the most effective clearance mechanism