Potassium/Mg Imbalances Flashcards
What is the role of potassium in the body? (3)
- Intracellular functions, such as protein and glycogen synthesis, cell growth and metabolism
- Determines the resting membrane potential across the cell membrane
- Helps maintain blood pressure
Potassium homeostasis is affected by? (4)
- Dietary intake
- GI and urinary excretion
- Hormones
- Insulin – drives potassium into liver, muscle, and fat cells
- Epinephrine/norepinephrine – stimulate potassium uptake by cells
- Aldosterone – promotes urinary potassium excretion - Acid-base balance
- Excessive hydrogen ions -> ↑ acidity -> ↑ serum potassium (H+ ions move into cells in exchange for K+ ions)
- Metabolic alkalosis -> ↓ hydrogen ions in serum -> ↓ serum potassium
Hypokalemia is anything under 3.5 mmol/L
What is mild, moderate, and severe?
- Mild = 3.1-3.5 mmol/L
- Moderate = 2.5-3 mmol/L
- Severe = <2.5 mmol/L
Hypokalemia may result from?
May result from a total-body potassium deficit or intracellular shift of potassium
- Potassium Deficit: inadequate dietary intake, excessive GI or renal potassium loss
– Excessive K+ loss is commonly due to thiazide or loop diuretics
– May also be due to vomiting or diarrhea
How does hypomagnesemia contribute to hypokalemia?
Promotes renal potassium loss
What are the symptoms of mild hypokalemia?
Generally asymptomatic
What are the symptoms of moderate hypokalemia? (4)
- Muscle cramping
- Myalgias
- Weakness
- Malaise
What are the symptoms of severe hypokalemia? (6)
- Impaired muscle contraction
- ECG changes (ST depression, T-wave inversion)
- Heart block
- Atrial flutter
- Paroxysmal atrial tachycardia
- Ventricular fibrillation
How might mild, asymptomatic hypokalemia be managed?
May respond to increased dietary K+ intake
How might moderate or refractory hypokalemia be managed?
- Oral replacement preferred
- Estimation: 10 mmol potassium should increase serum potassium by 0.1 mmol/L
- Chronic loop or thiazide diuretics: 40-100 mmol of potassium per day should correct mild-moderate hypokalemia
– Divide the total daily dose to TID (with food) to decrease GI intolerance
– Liquid potassium elixir may be bitter tasting but will give a more rapid increase in serum potassium
How might severe hypokalemia be managed? (2)
- CAUTION: Overly rapid administration of IV potassium can cause cardiac conduction abnormalitities – continuous ECG monitoring should be performed if high doses need to be given quickly
- High concentrations of potassium can cause phlebitis if administered through a peripheral vein – requires a central line into a large vein (e.g. superior vena cava) - Generally safe up to 20 mmol/hour IV
When might potassium-sparing diuretics be used for hypokalemia?
Potassium-sparing diuretics may also help prevent loop or thiazide diuretic-associated hypokalemia
- Spironolactone especially effective with hyperaldosteronism
- Amiloride or triamterene are second-line agents (act by unclear mechanisms)
Most common cause/contributor to hyperkalemia is?
Renal disease
Hyperkalemia is defined as >5 mmol/L.
What are mild, moderate, and severe ranges?
- Mild = 5.1-5.9
- Moderate = 6-7
- Severe >7
What are some potential causes of hyperkalemia? (4)
-
Increased potassium intake
- Consumption of potassium-rich foods (usually with decreased potassium excretion, as in stage 4 or 5 CKD)
- Potassium-containing salt substitutes -
Decreased potassium excretion
- Acute or chronic kidney disease -> impaired potassium excretion and hyperkalemia
- Adrenal insufficiency, Addison disease -> ↓ aldosterone production -> hyperkalemia
- Drugs: ACEI/ARBs, potassium-sparing diuretics, NSAIDs, trimethoprim-sulfamethoxazole, cyclosporine, tacrolimus -
Tubular Unresponsiveness to Aldosterone
- Autoimmune diseases like lupus, amyloidosis -
Extracellular redistribution of potassium
- Acidosis
- Diabetes
- CKD
How to treat asymptomatic, mild hyperkalemia?
Decrease dietary K+ intake, monitor
How to treat moderate, symptomatic hyperkalemia, ECG changes, or severe hyperkalemia? (3)
Immediate treatment
1. Calcium gluconate 1g IV to stabilize myocardium
2. Promote intracellular potassium shift of K+
- Insulin (+ dextrose to prevent hypoglycemia) e.g insulin Lispro 10 units IV + 25 g dextrose
- Beta-2 agonists (salbutamol) via nebulizer or MDI
- Sodium bicarbonate
3. Eliminate excess potassium from the body
- Loop diuretics
- Oral cation exchange resins (e.g. sodium polystyrene sulfonate or Kayexelate)
- If severe/refractory -> hemodialysis
Magnesium is important for what in the body?
Important for cellular function, and as a cofactor for numerous biochemical processes
Where in the body is magnesium mostly found in? (2)
- Primarily intracellular
- Found in bone (67%) and muscle (20%)
What are the symptoms of hypomagnesemia? (2)
- Neuromuscular - tetany, muscle twitches
- Cardiac - heart palpitations, ECG changes, cardiac arrhythmias
What are a couple of potential causes of hypomagnesemia? (2)
- Decreased intestinal Mg absorption e.g. ulcerative colitis, chronic diarrhea, pancreatic insufficiency, chronic PPI use
- Renal magnesium wasting e.g. due to thiazide or loop-diuretics
How is hypomagnesemia treated? (2)
- Oral supplementation preferred, except in severe deficiency
- Many different forms available (liquids, tablets)
- Most common adverse effect = diarrhea
Hypermagnesemia is uncommon, but when is it generally seen?
Generally seen in CKD with excess magnesium consumption (e.g., vitamins and antacids)
Symptoms of hypermagnesemia are rare until serium magnesium is > 2 mmol/L. What are the symptoms? (4)
- Muscle weakness
- Lethargy
- Confusion
- Dysrhythmias
In mild cases of hypermagnesemia, how to treat hypermagnesemia?
Identify and correct the cause
How to treat severe hypermagnesemia? (2)
- IV calcium to antagonize cardiac effects of hypermagnesemia
- Loop diuretics to increase magnesium elimination
