Hyperkalemia for USMLE Step 1 and USMLE Step 2

PHYSIOLOGY
Normal potassium level is anywhere between 3.5 to 5.0meq per liter. Any amount above this is considered hyperkalemia and any amount below this is considired hypokalemia.

Potassium levels are maintained by the sodium-potassium ATPase pump that maintains more potassium inside the cell rather than outside. The resting membrane potential of excitatory cells is most important such as the muscle and neurons.

When you eat a banana the food goes into the intestine and eventually goes into the blood. Potassium is absorbed with glucose and so insulin helps lower glucose levels, but also maintains low levels of potassium to prevent hyperkalemia.

The muscle has beta 2 receptors and during exercise the muscle release potassium. However, the beta 2 receptors also actiave sodium potassium ATPase channels also helping prevent hyperkalemia during periods of exercise.

The potassium also makes it way to the adrenal gland and causes release of aldosterone which acts on the principal cells in the distal convulated tubules. On these cells more potassium is released into the urine preventing hyperkalemia by increase sodium channels and increase sodium potassium ATPase channels.

ETIOLOGY PF HYPERKALEMIA
INCREASE POTASSIUM RELEASE FROM CELL CAUSES HYPERKALEMIA
Catabolism - burns, trauma, rhabdomyolysis, tumor lysis syndrome
Cellular Shift - Acidosis, Hyperosmolality, Insulin deficiency,
Drugs - Digitalis, Beta-blockers, RBC Transfusion

DECREASE URINARY EXCRETION CAUSING HYPERKALEMIA
Aldosterone - anything that inhibits aldosterone will cause hyperkalemia
Addison's, Spironolactone, eplereonone, triamterene, amiloride, ACE inhibitors, NSAIDs
RTA Type 4 - Decrease Sodium reabsorption in principal cells. Obstructive uropathy, lupus nephritis, sickle cell disease
Acute Kidney injury - Low GFR and oliguria causes decrease potassium filterin causing hyperkalemia

SPURIOUS CAUSES OF HYPERKALEMIA
Hemolysis, thrombocytosis, leukocytosis, tourniquet

CLINICAL ASPECTS OF HYPERKALEMIA
Muscle weakness - ascending legs, trunks arm
ECG Changes - Hyperacute T waves, No P Waves,
Arrythmias - Sinus bradycardia, V. Tachycardia, Ventricular Fibrillation, Systole, LBBB, RBBB, Bifasicular Block, AV Block
Decease Urine Acid Secretion - Potassium is necessary for Ammonia secretion which is necessary for proton secreiton

MANAGEMENT OF HYPERKALEMI
First check for ECG Changes.
If there is ECG Changes, Potassium greater than 7meq or symptomatic then ive Calcium gluconate right away to stabilize the heart.

Then give IV insulin and glucose. Beta 2 agonist, Diuretic, K Binding resins, Hemodialysis, Sodium Bicarbonate if there is acidosis.

If the hyperkalemia is betwen 5 to 6 than change diet or stop drugs that are causing hyperkalemia.

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