Chapter 24 - Fluid and electrolyte homeostasis and imbalances

body fluid

serves as a lubricant and as a solvent for the chemical reactions that we call metabolism; fluid transports oxygen, nutrients, chemical messengers and waste products to their destination (plays role in regulation of body temp)

body fluid pt 2

water within the body and the particles dissolved in it, contained in two major compartments….

1. extracellular (outside the cells) - 1/3

2. intracellular (inside the cells) - 2/3

(in infants there is more extracellular fluid than intracellular)

intracellular fluid composed of

(rich in)

• potassium, magnesium ions, inorganic and organic phosphates and proteins

• low in sodium and chloride ions

extracellular fluid composed of

(rich in)

• sodium, chloride, bicarbonate ions

• low in potassium, magnesium, and phosphate ions

• lies between the cells (interstitial compartment) in the blood vessels (vascular compartment), in dense CT and bone and in several minor compartments that are termed transcelllar fluids

3 important fluid compartments

1. vascular compartments - fluid inside blood vessels (blood plasma)

2. interstitial compartments - fluid between and around cells

3. intracellular compartments - fluid inside cells

interstitial compartments

fluid between and around cells

fluid homeostasis

process viewed as the net result of four subprocesses…

1. fluid intake

2. fluid absorption

3. fluid distribution

4. fluid excretion

fluid intake

entry of fluid into body by any route (ex. drinking, eating water contained in food)

fluid absorption

entry of fluid into bloodstream or body tissues

• by GI tract; water drank is absorbed by intestines (fluid must be absorbed before reaching vascular compartment, bloodstream)

• by intravenously (IV); fluid being delivered directly into bloodstream

fluid distribution

how the fluid distributes into other fluid compartments after reaching vascular compartments (bloodstream)

• filtration

• osmosis

• diffusion

filtration

fluid movement between blood vessels and surrounding tissues (between vascular and interstitial compartments)

• occurs by hydrostatic pressure (PUSHES fluid) and colloid osmotic pressure (PULLS fluid toward proteins)

capillary hydrostatic pressure

PUSHES vascular fluid against the inside capillary wall

interstitial colloid osmotic pressure

PULLS fluid out of capillaries towards proteins outside in tissues

capillary colloid osmotic pressure

PULLS fluid into blood vessels toward plasma proteins

interstitial hydrostatic pressure

PUSHES fluid from tissues back into blood vessels (capillaries)

osmosis

fluid movement between interstitial and intracellular compartments: fluid movement between outside and inside of cells

• cell membranes contain aquaporin’s that allow water ti pass through

• water moves from an area with fewer dissolved particles to an area with more dissolved particles (trying to balance particle concentration)

osmoality

measures how concentrated the dissolved particles are in a fluid

• high dissolved particles = more concentrated (water moves toward side with higher osmoality until balance to try and dilute it)

• low dissolved particles = more diluted

diffusion

particles move from high concentration to low concentration (particles spread out)

fluid excretion

how body normally gets rid of excess water

• urinary tract - through urine (kidneys)

• bowls - through feces

• lungs - water vapor as you breathe

• skin - through sweating and evaporation

fluid loss

through abnormal routes - ways body can lose extra fluid due to illness, injury, or medical procedures

• emesis - vomiting

• GI tubes - a nastrogastric (NG) tube may remove stomach fluids

• hemorrhage - excessive bleeding

• wound drainage - fluid leaks from wounds or surgical drains

• paracentesis - a procedure that removes fluid from abdominal cavity

regulatory mechanisms

these are the ways your body controls how much water you take in, keep and eliminate

1. thirst mechanisms and hypothalamus

2. kidneys regulate output

3. hormones that control fluid balance

thirst mechanisms and hypothalamus

(hypothalamus is part of brain that helps control thirst)

when body needs more water…

1. blood becomes more concentrated and blood volume decreases

2. hypothalamus detects change

3. it triggers thirst, making you drink

kidneys regulate output

kidneys control how much water leaves your body through urine (kidneys are the bodies water control system)

1. dehydrated = kidneys conserve water = less urine, darker

2. too much water = kidneys eliminate extra water = more urine, lighter

hormones that control fluid balance

1. ADH (anti-diuretic) - tells kidneys to retain more water (saves water)

2. aldosterone - tells kidneys to retain sodium; water follows (saves water and sodium)

3. natriuretic - helps kidneys eliminate sodium and water (ANP / BNP)

fluid imbalances

when body has too much, too little fluid or abnormal concentration of water and electrolytes (fluid homeostasis is disturbed by pathophysiological processes)

falls into two major categories…

1. imbalances of extracellular fluid volumes (saline imbalance)

2. imbalances of body fluid concentration (water imbalance)

extracellular fluid volume

EVC imbalance involves a change in amount (volume)of the extracellular fluid; disorders of isotonic salt water (concentration is normal, just too much or too little of it)

• volume deficit

• volume excess

volume deficit

not enough sodium containing fluid in extracellular compartment (removal of fluid)

• low BP, increase in HR, decrease in urine output

volume excess

retains to much sodium and water fluids in body / extracellular compartment

• edema and rapid weight gain

body fluid concentration

imbalance of how concentrated or diluted your body fluids are (abnormal serum sodium concentration = reflects the osmolality of the blood), normal serum sodium concentration is 135-145 mEq/L

both volume and concentration (clinical dehydration)

combo of 2 fluid disorders (ECV deficit and hypernatremia); has too small a volume of fluid in extracellular compartment and body fluids are too concentrated

• occurs in individuals who have vomiting and diarrhea and do not know how to (or are unable to) replace the water / salt that is exiting the body

• removal of the saline portion of fluid = ECV deficit

• removal of extra water from body = hypernatrima

key electrolytes

1. sodium (Na+)

2. potassium (K+)

3. calcium (Ca2+)

4. magnesium (Mg2+)

5. phosphate (PO₄^3-)

electrolytes

ionized salts dissolved in water, minerals that have an electrical charge when dissolved in water

(maintain fluid balance, helps muscles contract, send nerve signals, maintain normal heartbeat, regulate acid-base balance)

found in: ICF and ECF

four processes that control electrolyte concentration…

1. intake

2. absorption

3. distribution

4. excretion - kidney is major regulatory of electrolyte excretion

sodium

an electrolyte that helps control fluid balance, nerve signals and muscle function

two types of sodium imbalances…

1. hyponatremia

2. hypernatremia

135 -145 mEq/L

normal sodium level

hyponatremia

sodium level is less than 135 mEq/L, too much water in body relative with sodium (too little sodium)

causes:

1. excessive water intake

2. diuretics - certain water pills cause kidney to lose sodium

3. vomiting

4. syndrome of inappropriate antidiuretic hormone - too much ADH causes the kidneys to retain water = diluting sodium

what happens to cells during hyponatremia

water moves into cells through osmosis (causing cell to swell)

hypernatremia

sodium lvls is more than 145 mEq/L, too much sodium in body relative to water (too little water)

causes:

1. water deficit - not drinking enough water or losing too much through sweating, diarrhea, or excessive urination

2. sodium gain

what happens to cells during hypernatremia

water moves out of cells through osmosis (causing cell to shrink)

calcium

an electrolyte that helps with muscle contractions, nerve function, strong bones and teeth, blood clotting, normal heart function

two types of calcium imbalances…

1. hypocalcemia

2. hypercalcemia

calcium in plasma

presents in three forms…

1. calcium ions are bound to plasma proteins (albumin)

2. bound to small inorganic ions (citrate)

3. rest are unbound

4.5 - 5.5 mEq/L

or 9 - 11 mg/dL

normal total serum calcium concentration

hypocalcemia

occurs if the serum calcium concentration drops less than 9 mg/dL or 4.5 mEq/L

• low calcium causes nerves and muscles to become OVERACTIVE

causes of hypocalcemia

1. hypoparathyroidism - parathyroid glands do not produce enough parathyroid hormone (PTH), which normally raises blood calcium

2. vitamin D deficiency - intestines cannot absorb calcium as efficiently

3. pancreatitis - inflammation of the pancreas

hypercalcemia

occurs when the serum calcium concentration rises above 11 mg/dL or 5.5 mEq/L

• high calcium causes nerves and muscles to become LESS ACTIVE

causes of hypercalcemia

1. hyperparathyroidism - too much PTH increases calcium lvls in blood

2. bone metastases - cancer spreads to bones, causing calcium to be released into bloodstream

3. prolonged immobilization - not moving for a long time = increase in bone breakdown and calcium release

potassium

ann electrolyte that helps control muscle contractions, nerve signals, normal heartbeat, digestive system movement (especially important for heart, abnormal K+ can cause dangerous heart rhythms)

two types of potassium imbalances…

1. hypokalemia

2. hyperkalemia

3.5 - 5.0 mEq/L

normal concentration of potassium ions in plasma

hypokalemia

K+ levels are less than 3.5 mEq/L, low potassium causes muscles to become WEAKER and LESS responsive

• muscles hyper polarize: inside of muscle cells become more negatively charges making it harder for them to respond to electrical signals to activate and contract normally

causes:

1. diuretics - water pills that cause kidneys to eliminate too much potassium

2. vomiting / diarrhea

hyperkalemia

K+ levels is greater than 5.0 mEq/L, too much potassium in the blood interferes with normal muscle and heart electrical activity

• muscles hypo polarize: inside of muscle cells become less negatively charged = interference with electrical signaling and eventual muscle weakness

causes of hyperkalemia

• increase of potassium intake - excessive K+ administration through IV fluids

• decrease in potassium excretion

  • renal failure - kidneys cannot eliminate potassium effectively

  • oliguria - decrease in urine production

  • K+ sparing diuretics - cause body to retain K+

  • meds that decrease aldosterone activity

  • nephrotoxic meds - drugs that damage kidney

magnesium

an electrolyte that helps control muscle contraction / relaxation, nerve function, normal heart rhythm, bone health, energy production

two types of magnesium imbalances…

1. hypomagnesemia

2. hypermagnesemia

1.5 - 2.5 mEq/L

normal serum magnesium concentration

hypomagnesemia

magnesium levels are less than 1.5 mEq/L, low magnesium makes nerves and muscles OVERACTIVE

causes:

1. decreased mg2+ intake or absorption

2. decreased physiologic availability of mg2+

3. increase in mg2+ excretion

4. loss of magnesium by abnormal route - emesis (vomiting)

what happens to muscles during hypomagnesemia

decrease in levels of magnesium = nerves becoming more excited and reacting easy

hypermagnesemia

levels of magnesium are greater than 2.5 mEq/L, high mg2+ levels SLOW DOWN nerve and muscle activity

causes:

• increased mg2+ intake or absorption

• decrease in mg2+ excretion

  • adrenal insufficiency: decrease in adrenal hormone production can contribute to mg2+ retention

what happens to muscle during hypermagnesemia

high levels of magnesium depress neuromuscular excitability (nerves and muscles become less responsive)

phosphate

an electrolyte that helps body produce energy (ATP), build strong bones / teeth with calcium, sport muscle / nerve function, maintain acid / base balance

two types of phosphate imbalances…

1. hypophosphatemia

2. hyperphosphatemia

2.5 - 4.5 mg/dL

normal phosphate levels

hypophosphatemia

phosphate levels less than 2.5 mg/dL. decrease in phosphate causes cells to have difficulty producing enough energy

causes:

1. decrease intake and absorption

2. phosphate shifts from the blood into cells - lowering concentration in blood

3. increase in excretion

hyperphosphatemia

phosphate levels are greater than 4.5 mg/dL, too much phosphate can bring calcium levels down

causes:

• increase in phosphate intake and absorption

• phosphate shifts from inside the cell to the blood - when cells are damaged or destroyed they release phosphate into the bloodstream

  • tumor lysis syndrome - large #s of cancer cells break down rapidly, releasing phosphate

  • crush injuries - damaged muscle cells release phosphate

  • rhabdomyolysis - muscle tissue breaks down releasing its contents into blood

• decrease in excretion

CM of hyponatremia

• Mild - central nervous system dysfunction​

  • Malaise (feeling unwell), Anorexia, Nausea, Vomiting​

  • Headache​

• Severe - central nervous system dysfunction​

  • Confusion, Lethargy, Seizures, Coma​

  • Fatal cerebral herniation​ (brain swelling that can cause fatal herniation)

CM of hypernatremia

• Mild​

  • Thirst, Oliguria (decreased urine output), Confusion, Lethargy​

• Severe​

  • Seizures, Coma, Death​

CM of hypokalemia

Altered muscle function (smooth, skeletal, cardiac muscles). Smooth and skeletal muscle hyperpolarized​

• Abdominal symptoms​

  • Distention​

  • Diminished bowel sounds​

  • Paralytic ileus​

• Skeletal muscle symptoms​

  • Bilateral muscle weakness; usually begins in legs​

  • Respiratory paralysis ​

• Cardiac symptoms​

  • Ectopic beats​ - extra or abnormal heartbeat

  • Alterations in conduction​ - electrical signal do not travel normally through the heart

  • Dysrhythmias - severe enough to cause sudden cardiac death​

• Polyuria​ - excessive urintation

CM of hyperkalemia

Muscle dysfunction - smooth muscle and skeletal muscle hypopolarized ​

• Early, mild​

  • Intestinal cramping, diarrhea​

• Late, more severe​

  • Muscle weakness: ascending, beginning in lower extremities​

• Cardiac dysrhythmias, cardiac arrest​

CM of hypocalcemia

Increased neuromuscular excitability: ​

• Positive Chvostek sign (tapping facial nerve near cheek causes facial muscle twitch), paresthesias, muscle twitching and cramping, hyperactive reflexes, carpal spasm, pedal spasm, tetany (sustained painful muscle contraction), laryngospasm (throat muscle tighten), seizures, and cardiac dysrhythmias.​

CM of hypercalcemia

• Anorexia, nausea, emesis, constipation, fatigue, polyuria (feeling unusually tired), muscle weakness, diminished reflexes, headache, confusion, lethargy, personality change, and cardiac dysrhythmias.​

• Renal calculi, pathologic fractures.​

CM of hypomagnesemia

Increases neuromuscular excitability. ​

• Insomnia, hyperactive reflexes, muscle cramps, muscle twitching, grimacing (involuntary facial muscle contractions), positive Chvostek sign, positive Trousseau sign (inflating BP cuff = hands and wrist spasms), nystagmus (involuntary repetitive eye movements), dysphagia (difficulty swallowing), ataxia, tetany, and seizures ​

• Cardiac dysrhythmias​

CM of hypermagnesemia

Depresses neuromuscular excitability​

• Decreased deep tendon reflexes, lethargy, hypotension, flushing (skin = red and warm), diaphoresis (excessive sweating), drowsiness, flaccid paralysis (muscles become limp and unable to move), respiratory depression, bradycardia, cardiac dysrhythmias, and cardiac arrest.​

CM of hypophosphatemia

Generalized cellular adenosine triphosphate (ATP) deficiency.​

• Anorexia, malaise, paresthesias, hemolysis, diminished reflexes, muscle aches, muscle weakness, respiratory failure caused by weak diaphragm muscles, confusion, stupor (decreased alertness), seizures, coma, cardiac dysrhythmias, and impaired cardiac function.​

CM of hyperphosphatemia

• Increased neuromuscular excitability​

  • Causes hypocalcemia signs and symptoms ​

• Excess phosphate salts may deposit in soft tissues ​

  • Depends on area where salts precipitate​

  • May cause aching and stiffness of joints​

  • Itching​

  • Conjunctivitis​