Wednesday, October 20, 2010

Treatment of Hyperkalemia

continuous cardiac monitoring is mandatory if the patient has severe hyperkalemia (serum potassium > 6.5 MEq/L) or cardiac arrhythmias.
a patient with mild-moderate hyperkalemia (serum potassium < qid =""> the patient can be discharged and followed-up in 48 - 72 hours.
a patient with moderate hyperkalemia (serum potassium 6.0 - 6.5 mEq/L) should probably be admitted to hospital for supervised lowering of the serum potassium with a potassium-binding resin.
treat hyperkalemia more emergently if the serum potassium is > 6.5 meq/L or if there are any ECG changes suggestive of hyperkalemia => use sodium polystyrene sulfonate as first line therapy +/- insulin/glucose +/- calcium gluconate.

The following drug order sequence is recommended for life-threatening hyperkalemia (absent P waves + widened QRS complex, and/or serum potassium > 8 meq/L, and/or significant cardiovascular symptoms or arrhythmias, and/or severe neuromuscular symptoms)

1) Calcium gluconate
(there is no "correct" dose)
- 10 ml of 10% calcium gluconate solution over 10 minutes IV (rule of "tens") is a common approach.
(* calcium should preferably be administered in large veins because it is sclerosing)
- works in 1 - 3 minutes and lasts 30 - 60 minutes
- repeat dose in 5 - 10 minutes if no ECG change/improvement
(* calcium only antagonises potassium's deleterious electrical effect on the myocardium and it does not decrease the serum level of potassium - it is used temporarily until the serum potasium can be decreased by insulin + glucose administration)
- special warnings:-

* calcium should be given slowly over 20 - 30 minutes in a digitalised patient by diluting the calcium in 100 ml of normal saline and giving the calcium by an infusion pump - high risk of increased myocardial toxicity in the digitalised patient
* calcium is contra-indicated in digoxin-toxic patients and hypercalcemic states
* don’t give calcium in solutions containing bicarbonate

2) Insulin + Glucose
used to drive potassium into the cells
- 10 units insulin by rapid IV bolus + 50ml of 50% dextrose IV over 20 - 30 minutes; or the insulin can be mixed with 100 ml of 20% dextrose solution and administered IV over 20 - 30 minutes

- glucose should not be given to diabetics without first giving insulin - because insulin is needed to move potassium into the cells; also avoid giving 50% glucose by rapid IV bolus injection.
- onset occurs within 15 - 60 minutes and effect lasts 4 - 6 hours.

3) Albuterol by nebuliser
- 10 - 20mg in 4 ml saline over 10 - 20 minutes (large doses required)
- decreases serum potassium by about 0.5 - 1.0 meq/L

4) Bicarbonate
- only indicated when the patient is significantly acidotic (serum bicarb < depleted =""> use 3 amps of bicarb in 1L of 5DW at desired rehydration rate

5) Kayexalate - sodium polystyrene sulfonate
- defer if the patient is going to be dialysed within 2 hours to avoid a "colonic laundry"
- po route preferred if possible (greater degree of cation exchange)
- 15 - 50g in 100cc of 70% sorbitol po (or use commercial preperation)
- onset within 1 - 2 hours and lasts 4 - 6 hours
- use a retention enema if po administration is not preferable/possible

6) Lasix
- 40 - 80 mg of lasix IV to all patients who can produce urine

7) Dialysis
- primary therapy when renal function is absent
- prompt dialysis may also be required in patients with ARF + associated rhabdomyolysis (large potasssium load)
- also used for intractable hyperkalemia unresponsive to conservative pharmacological measures

8) Treat any underlying cause of the hyperkalemia

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