C2B Podcast 23 - Hyperkalemia

Hyperkalemia Intro

Potassium is primarily an intracellular ion responsible for maintenance of the resting membrane potential for normal cell conduction. Serum measured potassium is typically between 3.5 and 5.0 mEq/L. Serum K greater than 5.0 mEq/L is generally considered the threshold for hyperkalemia. Potassium is mostly excreted via the kidneys, and the "classic" hyperkalemia patient is one who has missed several dialysis appointments complaining of paralysis or diffuse weakness.

Causes of HyperK

Most commonly, renal failure.  Transcelluar shift  DKA Acidosis  Other acid-base disturbances Medications  RAAS or ACE inhibitors

Effects of HyperK 

Most drastically affect cardiac myocytes  Conduction between myocytes is depressed, leading to slower conduction and widened QRS complexes, however, the rate of repolarization is increased.  Leads to ominous “sine wave” pattern on ECG.  Arrythmogenic  May produce classic tall, “peaked” T waves on ECG. Stepwise ECG changes in hyperkalemia: 5.5-6.5 mEq/L - Peaked T Waves 6.5-7.5 mEq/L - P waves amplitude becomes smaller and PR intervals prolong 7.5-8.0 mEq/L - QRS becomes wide ECGs are not always sensitive for hyperkalemia. Patients may have a critical K with no changes on the ECG.  Skeletal muscle tissue is also sensitive to hyperkalemia, and patients may present with weakness or paralysis as a result.  Nondescript symptoms such as muscle cramps, diarrhea, vomiting, nausea, and focal paralysis may also be present - but are also not reliable findings. 

Management 

Prioritized by a strategy of: Stabilization of cardiac cell membranes  Shifting potassium back into the cells  Eliminating potassium Calcium (Chloride or gluconate) administered to stabilize cell membranes  Stabilizing effect is transient and relatively short lived  Calcium Chloride contains roughly 3 times the amount of elemental calcium as compared to Ca gluconate, but is associated with severe complications if extravasation occurs.  Effects (narrowing of QRS complex, return of more hemodynamic stability) occurs within minutes  Calcium Chloride - generally, 1 gram is administered over 3 minutes. Calcium Gluconate - 1 gram over 2-3 minutes  Repeat either q5min Albuterol / Beta 2 agonists These act on beta 2 receptors to assist in moving potassium back into the intracellular space  Albuterol - 10-20mg (inhalation), with most effect noted in 30 minutes  IV Insulin  Drives K back into the cells (shift) Generally administered with dextrose unless the patient’s BGL is below 250mg/dL 10 units IVP followed by 25G dextrose Incidence of hypoglycemia is high, and this therapy should be administered cautiously Dialysis  Treating reversible cause d/c RASS or ACE inhibiting medicaitions  Volume administration