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Unit 5: Fluid & Electrolytes

p99-113; 118-119; Module 3 on Evolve
Total Body Water:
sum of fluids within cells; 60% of body weight
Intracellular fluid:
all fluid WITHIN cells; 2/3 of TBW (40% of body weight)
Extracellular fluid:
all fluid OUTSIDE cells; 1/3 of TBW; divided into 2 main compartments (Interstitial & Intravascular)
Interstitial fluid:
fluid that is in spaces between cells and outside the blood vessels
Intravascular fluid:
blood plasma
Other compartments of ECF:
lymph and transcellular fluids (synovial, intestinal, cerebrospinal); sweat, urine, pleural, peritoneal, pericardial, intraocular)
Normal water losses:
sweat, urine (most), stool (least), skin, lungs
Normal water gains:
drinking water, food with water, water of oxidation (least)
Hydrostatic pressure:
PUSHES water
Osmotic pressure:
PULLS water
fluid moves out of capillary into interstitial spaces
fluid moves back into capillary from interstitial spaces
blood pressure: facilitates the outward movement of water from the capillary to the interstitial space
osmotically attracts water from interstitial spaces back into the capillary
facilitates inward movement of water form interstitial spaces into capillary
osmotically attracts water from capillary into interstitial spaces
movement of fluid back and forth across capillary wall (best described as Starling's forces)
ARTERIAL end of capillary:
hydrostatic pressure > capillary oncotic pressure - fluid moves into interstitial space
VENOUS end of capillary:
capillary oncotic pressure > capillary hydrostatic pressure - fluids are attracted back into capillary
Water moves between ICF & ECF primarily as a function of osmotic forces
is responsible for ECF osmotic balance
POTASSIUM maintains
ICF osmotic balance
excessive accumulation of fluid within interstitial spaces
INCREASED capillary hydrostatic pressure; LOWERED plasma oncotic pressure; INCREASED capillary membrane permeability; lymphatic channel obstruction
Pathophysiology of Edema #1: Venous obstruction (DVT) >
increased hydrostatic pressure behind obstruction > fluid pushed from capillaries into interstitial spaces
Common causes of DVT:
thrombophlebitis, hepatic obstruction, tight clothing around extremities, prolonged standing, CHF, renal failure
Interventions for DVT: Slow IV rate, girdle, "spanx"
pathophysiology of edema #2: lost or diminished plasma albumin production contributes to decreased plasma oncotic pressure >
decreased attraction of fluid within capillary causes filtered capillary fluid to remain in interstitial spaces > edema (low oncotic pressure=edema)
Causes of low plasma albumin production:
liver disease, protein malnutrition, serous drainage of open wounds, hemorrhage, burns, cirrhosis of liver
Pathophysiology of edema #3: capillaries become more permeable >
proteins escape from vascular space and produce edema through decreased capillary oncotic pressure & interstitial fluid protein accumulation (direct trauma to capillary membranes)
Causes of capillaries becoming more permeable:
inflammation, immune responses, trauma (burns, crushing injuries) neoplastic disease, allergic reactions
Pathophysiology of edema #4: lymphatic system normally absorbs interstitial fluid and a small amount of proteins;
lymphatic channels blocked or surgically removed > cause proteins and fluid to accumulate in interstitial spaces (lymphedema)
usually limited to a site of trauma or within a particular organ system; includes cerebral edema, pulmonary edema, pleural effusion, pericardial effusion (membrane around heart), ascites (in peritoneal space)
manifested by a more uniform distribution of fluid in interstitial spaces (dependent edema)
weight gain, swelling, puffiness, tight-fitting clothes/shoes, limited movement of affected joints, symptoms associated with underlying condition
Kidneys and hormones have central role in maintaining
sodium and water balance
Water balance is regulated primarily by
antidiuretic hormone: posterior pituitary gland secretes ADH or vasopressin
Sodium is regulated by renal effects of
ADH is secreted when
plasma osmolality increases or circulating blood volume decreases & blood pressure drops
WATER BALANCE: water deficit/sodium excess > increased plasma osmolality >
stimulated hypothalamic osmoreceptors > cause thirst, signal posterior pituitary gland to release ADH > stimulated water drinking, ADH increases permeability of renal tubular cells to water > water reabsorbed into blood from distal tubules and kidneys > urine concentration increases > reabsorbed water decreases plasma osmolality returning it to normal
SODIUM: accounts for 90%
of ECF cations; OUTSIDE!
CHLORIDE: major anion in
ECF; proportional to changes in sodium; provides electroneutrality in relation to sodium
kidneys; narrow range: 136-145 mEq/L
maintains hormonal regulation of sodium balance; secreted when sodium levels DECREASE or potassium levels INCREASE
RENIN-ANGIOTENSIN-ALDOSTERONE system: circulating blood volume/pressure reduced > renin is released > angiotensin-converting enzyme (ACE) in pulmonary vessels converts angiotensin I to angiotensin II > stimulates secretion of aldosterone (puts out sodium) >
causes vasoconstriction > sodium & water reabsorption > increased blood volume > elevated systemic blood pressure > restores renal perfusion > restoration inhibits further release of renin
Natriuretic hormones (peptides):
promote urinary excretion of sodium & water/decreased BP
Electrolytes carry electric charges when in water
The ability of a solution to cause a cell to gain or lose water
(used of solutions) having the same or equal osmotic pressure; normal range 280-294 mOsm
Losses of isotonic fluids:
hemorrhage, severe wound drainage, excessive diaphoresis, decreased urine output, symptoms of hypovolemia (tachycardia, flattened neck veins, normal/decreased BP)
isotonic fluid volume deficit:
SAME concentration, just less total amount (hypovolemic)
isotonic fluid excess
aka hypervolemia; fluid overload; still SAME concentration
causes of hypervolemia:
excessive administration of IV fluids, hypersecretion of aldosterone, effects of drugs, excessive intake, ineffective regulation (heart/renal failure)
pathophysiology of hypervolemia:
causes diluting effect which leads to decreased hematocrit and plasma protein concentration, weight gain, edema, hypervolemia, JVD, bounding pulse, pulmonary congestion, HTN
hypertonic alterations:
alterations in Na concentration
hypertonicity develops
when osmolality of ECF is elevated above normal (>294 mOsm)
occurs when serum sodium levels exceed 145 mEq/L (HIGHER AMOUNTS OF SODIUM THAN WATER IN ECF)
Hypernatremia: water leaves cells
and moves into ECF causing cells to shrink
hypernatremia: water leaves cells in order to
dilute the blood (cells shrink due to too much Na/too little water)
intracellular dehydration
manifestations of hypernatremia:
fever, thirst, dry mucous membranes, restlessness, muscle twitching, hyperreflexia, convulsions
most common cause of dehydration:
increase renal clearance of free water as reults of impaired tubular function or inability to concentrate urine
manifestations of dehydration:
thirst, dry skin, elevated temperature, weight loss, concentrated urine, tachycardia, weak pulse, postural hypotension
occurs when too little sodium or too little bicarbonate
hypotonic alterations:
too much water, too little salt
hypertonicity = hypernatremia
hypotonic causes:
sodium deficit/water excess, vomiting, diarrhea, NG suction, excessive perspiration, diuretics, excessive administration of D5W (water intoxication), increased ADH secretion, heart failure
pathophysiology of hypotonicity:
osmotic pressure of ECF decreases > water moves into cells where osmotic pressure is greater > plasma volume decreases > symptoms of hypovolemia
hypoosmolar hyponatremia:
renal excretion of water is impaired during acute oliguric renal failure, severe CHF, or cirrhosis > TBW and sodium levels increase > TBW exceeds increase in sodium
manifestations of hyponatremia:
legthargy, confusion, apprehension, depressed reflexes, seizures, coma, cerebral edema, muscle cramps, nausea
water excess is usually accompanied by:
major intracellular electrolyte (98% in ICF); normal range 3.5-5.0 mEq/L; active transport
functions of potassium:
required for glycogen and glucose deposition in liver & skeletal muscle cells; maintains resting membrane potential; maintains normal cardiac rhythms; skeletal/smooth muscle contractions
most efficient regulator of potassium: