Chemical Pathology/ Abnormal Electrolytes Flashcards
What is hyperkalemia?
Serum potassium concentration >5 mEq/L
What factors place chronic kidney disease patients at risk for hyperkalemia?
They have reduced potassium excretion by the kidneys, are prone to metabolic acidosis, and are more likely to be on medications (RAS antagonists) that have hyperkalemia as a possible side effect.
What type of renal tubular acidosis causes hyperkalemia?
Type IV
In general, what are the causes of hyperkalemia?
- Decreased potassium excretion: renal failure, renal hypoperfusion (heart failure, volume depletion), aldosterone deficiency or insensitivity, medications (ACEIs, potassium-sparing diuretics, NSAIDs)
- Excessive release of intracellular potassium (acidosis, trauma, tumors, hemolysis, infection)
Hyperkalemia needs to be treated emergently when what factors are present?
- Electrocardiogram changes (peaked T wave, loss of P wave, widened QRS)
- rapid rise in potassium
- potassium >6 mEq/L
- renal failure
- moderate to severe acidosis
What medications are used to meet the following goals when treating emergent hyperkalemia?
–> Myocardial stabilization and prevention of fatal arrhythmia
Intravenous (IV) calcium gluconate or calcium chloride (does not lower potassium)
What medications are used to meet the following goals when treating emergent hyperkalemia?
–> Cellular uptake of potassium
- IV insulin (glucose is added to prevent hypoglycemia)
- IV sodium bicarbonate
- nebulized beta-adrenergic (such as albuterol)
What medications are used to meet the following goals when treating emergent hyperkalemia?
—>Elimination of potassium
Furosemide or dialysis depending on the patient’s renal function
What is the medical treatment of nonemergent hyperkalemia?
Sodium polystyrene sulfonate (PO or PR)
What is hypokalemia?
Serum potassium concentration <3.5 mEq/L
In a stable patient, oral potassium chloride powder (diluted in liquid) may be used to treat most cases of hypokalemia . What is the approximate treatment dose for the following potassium level?
–>Less than 3.0 mEq/L
20 mEq PO every 2 hours for four doses
In a stable patient, oral potassium chloride powder (diluted in liquid) may be used to treat most cases of hypokalemia . What is the approximate treatment dose for the following potassium level?
—> 3.0 to 3.5 mEq/L
20 mEq PO every 2 hours for two doses
What are some common causes of hypokalemia?
- vomiting (bulimia, infection, hyperemesis gravidarum)
- diarrhea (infection, excessive laxative use)
- thiazide and loop diuretics
- hyperaldosteronism
- type I and II renal tubular acidosis
In the acute setting of hyperglycemia requiring intense insulin therapy, why is it necessary to administer potassium along with insulin?
Insulin promotes potassium uptake into the cells and decreases serum potassium.
Why does vomiting cause hypokalemia even though gastric fluid has little potassium?
Loss of hydrogen ions (acidic gastric fluid) → metabolic alkalosis → alkalosis causes potassium shift into cells
What are the symptoms of hypokalemia?
- weakness
- fatigue
- muscle cramps
- constipation
- arrhythmias (severe cases)
What is hypernatremia?
Serum sodium concentration >145 mEq/L. Total sodium may actually be normal or less than normal depending on the patient’s volume status.
What is the difference between hypovolemia (aka volume depletion) and dehydration?
- Hypovolemia refers to the loss of extracellular fluid volume (water plus sodium and other solutes) with resulting decreased tissue perfusion.
- Dehydration is a kind of hypovolemia but involves a disproportionately greater loss of free water to sodium, causing hypernatremia
What are the common causes of hypervolemic hypernatremia?
- Hyperaldosteronism (eg, idiopathic adrenal hyperplasia, Conn syndrome)
- Excess sodium administration by physicians (eg, hypertonic intravenous fluid, parenteral nutrition, bicarbonate administered as NaHCO 3 ) or caregivers (eg, errors preparing infant formula)
What is diabetes insipidus (DI) and how does it cause hypernatremia?
- Normally when the body senses dehydration, ADH (antidiuretic hormone) is released.
- The kidneys then concentrate the urine in order to retain more water.
- In DI, there is either no production of ADH (central ADH) or there is ADH insensitivity (nephrogenic DI).
- Inappropriately dilute urine is produced causing an elevation of serum sodium.
What is the major complication of treating hypernatremia too rapidly, especially if the patient has chronic hypernatremia?
Cerebral edema
What is hyponatremia?
Serum sodium concentration <135. Total sodium may actually be normal or higher than normal depending on the patient’s volume status.
What is the mechanism of hyponatremia in patients with diabetic ketoacidosis (or hyperglycemia nonketotic coma)?
Even though glucose is not an electrolyte, it acts as a solute. So in a hyperglycemic state, serum osmolality is high. This draws fluid out of the intracellular compartment into the extracellular fluid. Serum sodium is diluted.
Describe the mechanism behind hypervolemic hypoosmolar hyponatremia.
In an edematous state (ie, CHF) there is a misperceived volume status. Total body water is increased, but effective circulatory volume is low. In response, the renin-angiotensin-aldosterone system activates (increases sodium and water retention) and ADH is released (increases water retention). Their net effect causes hyponatremia and further exacerbates volume overload.
What is the most common iatrogenic cause of hypovolemic hypoosmolar hyponatremia, especially in the elderly?
Thiazide diuretics
What is the major complication of treating hyponatremia too rapidly, especially if the patient has chronic hyponatremia?
Central pontine myelinolysis
When a patient develops the syndrome of inappropriate antidiuretic hormone (SIADH), do the following increase or decrease?
–> Serum sodium
Decreases
When a patient develops the syndrome of inappropriate antidiuretic hormone (SIADH), do the following increase or decrease?
–> Serum osmolality
Decreases
When a patient develops the syndrome of inappropriate antidiuretic hormone (SIADH), do the following increase or decrease?
–> Urine osmolality
Increases
What is pseudohyponatremia?
Elevated triglycerides or proteins → a decreased proportion of the serum is composed of water (and the sodium in it) → if the lab measures sodium concentration in whole serum (vs. serum water), sodium appears to be too low
What is the normal range for serum calcium concentration?
9-10.5 mg/dL
Lab values for calcium may be falsely low in patients with hypoalbuminemia (lab measures protein-bound calcium, not ionized [free] calcium). What is the formula for corrected total calcium in the setting of hypoalbuminemia?
Corrected total calcium (mg/dL) = total calcium (mg/dL) + 0.8 × (4-serum albumin [g/dL])
Does hypocalcemia occur with low or high magnesium levels?
Low
Does hypocalcemia occur with low or high phosphorus levels?
High
What is the most common symptom of hypocalcemia?
Neuromuscular instability (nerve and muscle twitching, muscle cramping, tingling)
What is Chvostek sign?
It is a sign of tetany seen in hypocalcemia. Tapping the facial nerve where it emerges just anterior to the ear causes spasm of the ipsilateral facial muscles.
What is the ECG hallmark of hypocalcemia?
Prolonged QTc interval
What are the two most common causes of hypercalcemia ?
- Hyperparathyroidism
- Malignancy
What are the symptoms of hypercalemia?
Multisystem symptoms including “stones, bones, moans abdominal groans, and psychic overtones”: kidney stones, bone pain and osteoporosis, muscle weakness and fatigue, abdominal discomfort, mental dysfunction
In metabolic acidosis/alkalosis and respiratory acidosis/alkalosis, are hydrogen, bicarbonate, and carbon dioxide level high or low?
Of the above(shown in the attached table) acid-base disturbances, for which is hyperventilation the compensatory mechanism?
Metabolic acidosis
Of the above(in the attached table) acid-base disturbances, for which is hypoventilation the compensatory mechanism?
Metabolic alkalosis
How is anion gap calculated? g
Difference between measured cations and measured anions: [Na] − [Cl] − [HCO 3] = anion gap
What is the typical acid-base disturbance(s) in Diabetic ketoacidosis?
Increased anion gap metabolic acidosis
What is the typical acid-base disturbance(s) in Opiate overdose?
Respiratory acidosis
What is the typical acid-base disturbance(s) in Chronic renal failure?
Increased anion gap metabolic acidosis
What is the typical acid-base disturbance(s) in Vomiting?
Metabolic alkalosis
What is the typical acid-base disturbance(s) in Salicylate intoxication?
Respiratory alkalosis and increased anion gap metabolic acidosis
What is the typical acid-base disturbance(s) in Lactic acidosis?
Increased anion gap metabolic acidosis
What is the typical acid-base disturbance(s) in Pulmonary embolism?
Respiratory alkalosis
What is the typical acid-base disturbance(s) in Chronic renal failure?
Increased anion gap metabolic acidosis
What is the typical acid-base disturbance(s) in Neuromuscular disorder (ALS, multiple sclerosis, Guillain-Barré)?
Respiratory acidosis
What is the typical acid-base disturbance(s) in Prolonged diarrhea?
Normal anion gap metabolic acidosis
What is the typical acid-base disturbance(s) in Methanol, formaldehyde, or ethylene glycol intoxication?
Increased anion gap metabolic acidosis
What is the typical acid-base disturbance(s) in Renal tubular acidosis?
Normal anion gap metabolic acidosis
