Chem: Section 4.3- Renal Electrolytes

ions that carry a positive charge

cation

ions that carry a negative charge

anion

increase in blood alkalinity (increase in pH); can be due to an accumulation of alkaline substances or a loss of acidic substances

alkalosis

increase in blood acidity (decrease in pH); can be due to an accumulation of acidic substances or a loss of alkaline substances

acidosis

pressure that develops when you have 2 solutions of different concentrations separated by a membrane

osmotic pressure

What is the purpose of sodium?

maintains osmotic pressure due to its high concentration in extracellular fluid

What causes hypernatremia (increase in sodium)?

losing more water than sodium or gaining more sodium than water

- *Dehydration* from severe diarrhea, extensive burns, or excessive sweating without fluid replacement

- Inability to ingest sufficient amounts of water (dehydration)

- *Diabetes Insipidus* (ADH deficiency- ADH should retain water, so if it is deficient, you're losing water)

- *Conn's syndrome* (excess of aldosterone so Na is staying in the body)

What are the 3 types of hyponatremia (decrease in sodium)?

depletional, dilutional, artifactual

true loss of body sodium

depletional hyponatremia

greater proportion of water to sodium, so it appears as if the sodium concentration is low

dilutional hyponatremia

proteins and triglycerides displace the liquid in the body, since Na is confined to the water space, it appears low

artifactual hyponatremia, "pseudo-hyponatremia"

What causes depletional hyponatremia?

Hypoaldosteronism, Addison's disease, diuretics, GI losses associated with diarrhea or vomiting, or skin damage with burns or trauma

How does Addison's disease cause depletional hyponatremia?

Addison's disease is a decrease in cortisol which comes from the same source as aldosterone (adrenal gland), so aldosterone is decreased too

What causes dilutional hyponatremia?

overhydration and anything that results in edema-- chronic renal disease, congestive heart failure, cirrhosis

How are the effects of aldosterone and ADH similar?

both excrete potassium since water and sodium are retained, both increase sodium and water concentration in the blood, therefore decreasing them in the urine

What is the role of aldosterone?

distal tubular reabsorption of sodium is enhanced followed by water

(sodium first, followed by water)

What is the role of anti-diuretic hormone (ADH)?

collecting ducts increase renal water reabsorption, therefore concentrating the urine

(water first, sodium follows)

What is the purpose of potassium?

Regulates many cellular processes and maintaining cardiac rhythm, contributes to neuromuscular conduction. Imbalances may cause cardiac arrhythmias and neuromuscular weakness.

What is the primary cause of hyperkalemia (increased K)? What are some other causes?

*Primary cause is renal failure because kidneys regulate K*

Other causes:

- use of certain diuretics (lose water/sodium, so K increases)

- Hypoaldosteronism or hypocortisolism (lose water/sodium, so K increases)

- Imbalances caused by an ion shift

- Iatrogenic causes (medical causes, e.g. IV with K)

- Increased dietary intake of K+ (rare)

What are the S/S of hyperkalemia?

hyperkalemia decreases the resting membrane potential of cells, so *normal activity is suppressed*

Fatigue, muscle weakness and tingling, nausea and vomiting, bradycardia (low HR), arrhythmias, cardiac arrest from cardiac ischemia (not getting enough O2), respiratory weakness

What causes hypokalemia (decreased K)?

- renal tubular acidosis (water retained to balance this acid, thus decreasing K)

- hyperaldosteronism (Conn's)

- hypercortisolism, certain diuretics

What are the S/S of hypokalemia? At first and prolonged

*increases the resting membrane potential of cells, resulting in muscle excitability (system never shuts off)*

Constipation, muscle cramps or spasms, tetany, tachycardia (rapid HR), and arrhythmias.

When the hypokalemia is *prolonged*, symptoms may include fatigue, muscle weakness, and possible cardiac arrest (because body is so tired)

Explain the effects of hemolysis on K+ results, and the reason for the effect

Potassium will be falsely elevated because intracellular substances spill out into the plasma when RBCs are lysed

What is Diabetes Insipidus? What are the associated Na and K levels in both blood and urine?

is an ADH deficiency (retains water), *massive* amounts of water are lost

plasma: high Na *and* K

urine: *normal* Na and K

What is Conn's Syndrome? What are the associated Na and K levels in both blood and urine?

Conn's syndrome is too much aldosterone (retains sodium), so too much sodium is retained.

Plasma: High Na, low K

Urine: Low Na, high K

What is Hypoaldosteronism? What are the associated Na and K levels in both blood and urine?

decreased aldosterone (retains sodium), so sodium is lost

Plasma: low Na, high K

Urine: high Na, low K

What is Addison's Disease? What are the associated Na and K levels in both blood and urine?

aka hypocortisolism; is a disease of the adrenal gland, so both cortisol and therefore aldosterone are decreased

Plasma: low Na, high K

Urine: high Na, low K

What is Cushing's Disease? What are the associated Na and K levels in both blood and urine?

aka hypercortisolism; cortisol is over produced, therefore aldosterone is too

Plasma: high Na, low K

Urine: low Na, high K

What is the purpose of chloride in the body?

maintenance of fluid balance and osmotic pressure (works with sodium); also chloride shift and isohydric shift

What causes hypochloremia?

decreased Cl

loss of gastric contents from prolonged vomiting or nasogastric suctioning

What causes hyperchloremia?

increased Cl

anything that causes hypernatremia causes hyperchloremia to a lesser extent

What is the purpose of bicarbonate in the body?

part of the extracellular buffer system (is a base), maintains acid-base balance

What causes increased and decreased levels of bicarbonate in the body?

Decreased: metabolic acidosis (because decreased base)

Increased: metabolic alkalosis (because gaining base)

What is the most common method used for the analysis of electrolytes?

*Ion-selective electrodes (ISEs)*: electrode covered by a membrane that is specific and selective to a certain ion

What is the ISE for sodium?

glass membrane with lithium aluminum silicate or other composite silicon dioxide glass

What is the ISE for potassium?

liquid membrane with valinomycin

What is the ISE for CO2/HCO3?

gas permeable silicone membrane for CO2, glass membrane of silicon dioxide/lithium and calcium oxide for H+

What is the ISE for chloride?

solid-state membrane with silver chloride

What are some interferences for ISEs?

- hemolysis (false increase in K due to intracellular substances spilling out, false decrease in extracellular substances)

- indirect interference: increased lipids or proteins can displace the liquid containing sodium and chloride making them appear falsely decreased

- use closed container, test immediately

How do you calculate the anion gap?

cations - anions

*(Na + K) - (Cl + HCO3)*

note: sometimes K is left out because it is mostly intracellular, that is ok

What would cause an increased anion gap?

an accumulation of acids: uremia, lactic acidosis, ketoacidosis, *ingestions of toxic substances (methanol, ethylene glycol, salicylates)*, large doses of antibiotics (produce acid products when metabolized), increased net protein charge

What would cause a decreased anion gap?

Not often seen, hypoalbuminemia is the only true cause of decreased anion gap. Usually a calibration or measurement error.

What is the formula for calculating plasma osmolality?

(1.86 x sodium) + (glucose/18) + (BUN/2.8) +9

Explain the freezing point depression measurement steps.

Sample is supercooled to -10C, stirring wire is vibrated to initiate the freezing to a slush stage, and the heat of fusion warms the solution, causing a equilibrium in temperature between freezing and thawing state. The resistance of the slush against the wire is measured and is directly proportional to the # of particles in the solution.

What is the osmolal gap and its purpose?

Osmolal gap: difference between measured osmolality and calculated osmolality

Used to diagnose poisonings and to estimate blood alcohol levels, usually performed on an ER patient

What will happen to each of the following when the patient is dehydrated?

sodium

potassium

chloride

bicarbonate

BUN:creatinine ratio

specific gravity

Increase in sodium (not following water yet, dehydration is temporary)

Decrease in potassium (opposite sodium)

Increase in chloride (same as sodium)

Decrease in bicarbonate (lose bicarb when we sweat)

Increase in BUN:creatinine ratio (retain more BUN, e.g. 30:1)

Increase in specific gravity (increased conc of urine)

What is sweat chloride analysis? What is it used to diagnose?

diagnostic test for cystic fibrosis performed on newborns to children less than 5 years of age; pilocarpine induces sweating and chloride is measured

>60 mmol/L is diagnostic level

a disorder of the exocrine glands characterized by excessive mucus secretions which precipitate and obstruct organ passages

cystic fibrosis

What are the major contributors to osmolality?

*sodium*, chloride, glucose, urea, proteins, ethyl alcohol when present