Sect. 4 PPIII - Electrolytes

50-60%

In adult males, total body water constitutes how much of body weight?

45-50%

In adult females, total body water constitutes how much body weight?

**hint: lower due to increase percentage of adipose tissue (has lower water content)

Intracellular and Extracellular

Total body water can be divided into 2 major components:

Intracellular (ICF)

Fluid found in cells

water contained in cells represents ~66% of total body water

Extracellular (ECF)

Fluid found outside cells

makes up ~33% of total body water

Interstitial and Intravascular

Two types of Extracellular fluid:

intrestitial fluid

immediately surrounds cells (cushions)

intravascular fluid

fluid found in blood vessels

Cation

ions that carry positive charge

Anion

ions that carry negative charge

Alkalosis

increased in blood alkaline (blood more basic)

due to accumulation of alkaline substance or due to loss of acidic substance

Acidosis

increased blood acidity (blood more acidic)

due to accumulation of acids or loss of base (bicarbonate)

Osmotic pressure

pressure that must be applied to prevent osmotic movement across a selectively permeable membrane

osmosis

diffusion of water through a selectively permeable membrane

flow from low to high & requires energy

diffusion

flow from high to low & does not require energy

Sodium (Na+), Potassium (K+), Chloride (Cl-), Bicarbonate (HCO3-)

4 major electrolytes

Sodium (Na+) and Potassium (K+)

Which electrolytes are cations

**hint: positively charged

Sodium (Na+)

Cation found in greater concentration extracellularly

Potassium (K+)

Cation found in greater concentration intracellularly

Na-K-ATPase Pump

Cation measurement is maintained by:

moves 3 Sodium (Na+) out of cell and 2 Potassium (K+) into cell

Chloride (Cl-) and Bicarbonate (HCO3-)

Which electrolytes are anions

**hint: negatively charged

Sodium (Na+)

plays a major role in maintaining osmotic pressure, due to high concentration in extracellular fluid

levels maintained by renal reabsorption in the renal tubules

Aldosterone & Anti-diuretic hormone (ADH)

Sodium balance is maintained by (2):

Aldosterone

Hormone produced by adrenal cortex that stimulates the kidney to retain sodium ions and water

distal tubular reabsorption of sodium is enhanced followed by water

↑ Na+ = ↑ H2O = ↓ K+

Anti-diuretic Hormone (ADH)

Hormone produced by the posterior pituitary gland that stimulates the collecting ducts to increase renal water reabsorption, which concentrates the urine

↑ H2O = ↑ Na+ = ↓ K+

Vasopressin

aka ADH

true

T or F:

Extremely high/low Na+ concentrations in plasma will cause severe osmotic pressure changes that can induce serious consequences to several organs

brain

Which organ is most affected by high/low Na+ concentrations in plasma?

Hypernatremia

increase Na+ in blood

most commonly due to depletion of water exceeding that of sodium (losing lots of H2O makes Na+ look high)

conditions with Hypernatremia

dehydration from severe diarrhea, extensive burns, excessive sweating without fluid replacement

inability to ingest sufficient amount of water (dehydration)

diabetes insipidus (deficiency of ADH = increase H2O loss)

Conn's syndrome (excess of aldosterone = increase Na+ reabsorption)

Hyponatremia

decrease Na+ in blood

reflection of the ratio of Na+ to volume in plasma only, tells us nothing directly about the total body content

Depletional, Dilutional, Artifactual

3 types of Hyponatremia

Depletional Hyponatremia

true loss of total body Na+

Conditions: Hypoaldosteronism, Addison's disease, use of diuretics, GI loss associated with diarrhea/vomiting, or skin damage with severe burns/trauma

Dilutional Hyponatremia

results from conditions in which there is greater proportion of water to sodium than normal (Na+ appears low when it's not)

Conditions: Overhydration and Chronic Renal Disease and other diseases (Congestive heart failure and Cirrhosis) that are characterized by increased fluid retention resulting in edema

Artifactual Hyponatremia

refers to analytical errors that reveal a falsely low Na+

Conditions: Conditions in which volume of plasma contains a significant amount of non-aqueous components (↑ protein/triglycerides)

Substances in high levels replace certain amount of H2O, and since Na+ is confined to the H2O space, the Na+ appears low when it's actually normal

Displacement or Pseudo-Hyponatremia

2 other names for Artifactual Hyponatremia

Potassium (K+)

the major intracellular cation

responsible for regulating many cellular processes & maintaining cardiac rhythm and contributes neuromuscular condition

cardiac arrythmias and neuromuscular weakness

Imbalances of potassium (K+) may cause (2):

**hint: responsible for regulating many cellular processes & maintaining cardiac rhythm and contributes neuromuscular condition

98%

About what percent of K+ is found intracellularly?

hemolysis

K+ is the #1 analyte affected by:

Hyperkalemia

increase K+ in blood; decreases the resting membrane potential of cells

caused by: Certain diuretics, Hypoaldosteronism or Hypocortisolism (Addioson's disease), imbalance caused by an ion shift, iatrogenic causes

decreased renal excretion in acute or chronic renal failure

major cause of Hyperkalemia

**hint: Kidneys are the only significant route of K+ elimiation

conditions with Hyperkalemia

Fatigue, muscle weakness and tingling, nausea/vomiting

Most severe on cardiac & lung function:

Bradycardia

Arrhythmias/Heart Palpitations

Cardiac arrest from cardiac ischemia

Respiratory weakness

Muscle weakness/paralysis & digestive problems (diarrhea/gas/pain)

Hypokalemia

decrease K+ in blood; increases resting membrane potential of cells

caused by: Renal loss (renal tubular acidosis), Hyperaldosteronism (Conn's syndrome), Hypercortisolism (Cushing's Disease/Syndrome), certain diuretics, GI deficiency/loss from severe vomiting/diarrhea/nasogastric suctioning/laxatives/malabsorption

conditions with Hypokalemia

S/S:

Constipation

Muscle cramps or spasms, tetany

Tachycardia (rapid HR)

When prolonged, body shuts down -- fatigue, muscle weakness/paralysis, and possible cardiac arrest

Diabetes Insipidus

deficiency of ADH leads to increased H2O loss

Plasma Na+: increased

Plasma K+: increased

Urine Na+: Normal (progressive disease)

Urine K+: Normal (progressive disease)

Conn's Syndrome

excess of aldosterone (hyperaldosteronism) so water and sodium retained

Plasma Na+: increased

Plasma K+: decreased

Urine Na+: decreased

Urine K+: increased

Hypoaldosteronism

decrease of aldosterone; leads to decrease Na+ production

Plasma Na+: decreased

Plasma K+: increased

Urine Na+: increased

Urine K+: decreased

Addison's Disease (Hypocortisolism)

decrease in cortisol (comes from adrenal gland same as aldosterone) = aldosterone decreased

Plasma Na+: decreased

Plasma K+: increased

Urine Na+: increased

Urine K+: decreased

Cushing's Disease (Hypercortisolism)

increase in cortisol (comes from adrenal gland same as aldosterone) = aldosterone increased

Plasma Na+: Increased

Plasma K+: decreased

Urine Na+: decreased

Urine K+: increased

Chloride (Cl-)

one of the major extracellular anion that helps maintain electrical neutrality with Na+

major function includes: maintenance of fluid balance and osmotic pressure

Chloride Shift

the movement of chloride (Cl-) ions into the red blood cells as bicarbonate (HCO3-) ions move out

to maintain the electrochemical equilibrium

moves opposite to bicarbonate ions during acid-base compensation (maintains electrical neutrality)

Isohydric Shift

hemoglobin acts as a buffer by binding H⁺ ions generated, preventing acidosis and maintaining acid-base balance in the blood

HCl

Cl- exists in gastric contents associated with H+ as:

Hypochloremia

decrease Cl- in blood

loss of gastric contents from prolonged vomiting or nasogastric suctioning can lead to Cl- being removed from HCl

caused by: Diuretic use/abuse (loss of H2O = ↓Na+ = ↓Cl-

Hyperchloremia

increase Cl- in blood

conditions: Conn's syndrome, Cushing's disease, Diabetes insipidus, dehydration from severe dehydration, extensive burns, excessive sweating without fluid replacement; dehydration due to decreased water intake

same as hypernatremia but to lesser extent

Bicarbonate (HCO3-)

major component of extracellular buffer system that is produced from CO2 as it reacts with water in plasma

CO2 + H20

regulated by kidneys through increased/decreased tubular reabsorption as they function to maintain acid-base homeostasis

metabolic acidosis

low pH (acidic), low HCO3-

metabolic alkalosis

high pH (basic), high HCO3-

Cl-

The levels of HCO3- concentration tend to vary reciprocally with ____ as the body maintains normal electroneutrality

Ion-Selective Electrodes (ISEs)

most common methodology for analysis of electrolytes

only free unbound ions are measured

ISE for sodium

contains lithium aluminum silicate or other composite silicon dioxide glass compound

ISE for potassium

liquid membrane containing valinomycin

ISE for CO2/HCO3-

compound (2 membranes separated by buffer)

1st membrane: gas permeable silicone membrane; once diffusion occurs, gas reacts with buffer to produce H+ in proportion to amount of total CO2 in plasma

2nd membrane: H+ ions are then detected by an additional glass membrane made of silicon dioxide/lithium and calcium oxide glass that selects for H+

ISE for Cl-

solid-state membrane containing silver chloride

heparinized plasma; contains less K+ than serum

Specimen: Venous serum or lithium-heparinized whole blood or plasma, or heparinized arterial whole blood

Which is the specimen of choice for electrolyte analysis and why?

avoid hemolysis and refrigeration

When collection a specimen for electrolyte analysis, what should we avoid?

**hint: we don't want excess K+

intracellular substances spill out into plasma

Interferences with Electrolyte Analysis:

Hemolysis can cause false increase in intracellular substances due to:

**hint: releases K+

dilution of plasma when RBCs burst spilling their contents

Interferences with Electrolyte Analysis:

Hemolysis can cause false decrease in extracellular substance due to:

Indirect / Dilutional effect of Na+

Interferences with Electrolyte Analysis:

Diluting specimen before analysis:

Increase levels of proteins can displace some of the plasma within dilution, causing false decreased levels of Na+ and sometimes Cl-

Cystic Fibrosis (CF)

A generalized disorder of the exocrine glands characterized by excessive mucus secretion, which precipitates and obstruct organ passages (lungs & digestive function (pancreas))

Sweat Chloride Analysis

test performed on newborn infants and pediatric patients for diagnosis of cystic fibrosis (CF)

increased Na+ and Cl- levels

one key feature of CF is an abnormal sweat chloride pattern mainfested by:

N:

Reference range for cystic fibrosis (CF):

Anion Gap

Difference between the concentrations of serum cations and anions: determined by measuring the concentrations of Na+/K+ cations & Cl-/HCO3- anions.

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

Reference range: 10 - 20 mmol/L

increased Anion Gap

causes build up of acids

Uremia (phosphate, sulfate)

Lactic acidosis

Ketoacidosis (uncontrolled DM)

Ingestion of toxic substances (Methanol, Ethylene glycol, Salicylates)

Large dose of antibiotics

Increased net protein charge (albumin has neg charge; more albumin = slight acidosis)

decreased Anion Gap

not very common

Indication of technical problems (especially when Na+ and K- electrodes are in need of calibration/maintaince)

Lab measurement error (overestimation of Na+/underestimation of Cl-)

True decreased anion may occur occasionally

hypoalbuminemia

True decreased anion may occur occasionally due to:

**hint: less albumin = slight alkalosis

Osmolality

concentration of solutes in solvent (# of particles)

mOsm/kg

units for Osmolality

sodium, chloride, glucose, urea, proteins, ethyl alcohol

6 major contributors to osmolality

Osmolality formula

Freezing Point Depression Procedure

1. Thermistor probe and stirring machine comes in contact with sample & supercooled to -10C

2. Stirring wire vibrated to initiate freezing slush stage and heat of fusion warms solution to cause equilibrium between freezing and thawing state

3. Resistance of stirring wire at slush stage is proportional to particles in solution (variable resistance is measured) which is a reflection of particles in solution that affect FPD

serum free of cells or gross hemolysis

preferred specimen for Freezing Point Depression

urine & gastric acids can also be measured

increased Osmolality levels

dehydration (retaining protein)

uremia

diabetes mellitus (increased glucose)

alcohol intoxication (increased ethyl alcohol)

salicylate intoxication

excessive electrolytes IVs

Osmolal Gap

the difference between measured (FPD) osmolality and calculated osmolality; calculates unmeasured particles in solution

OG = MO - CO

OG >15 is considered critical

diagnose poisoning and estimate blood alcohol levels

What is Osmolal Gap used to diagnose?

**hint: high levels indicate an abnormal concentration of an unmeasured substance such as isopropanol, methanol, ethylene glycol, or acetone; leads to acidosis