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76 terms

Unit 5: Fluid & Electrolytes

p99-113; 118-119; Module 3 on Evolve
STUDY
PLAY
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
filtration:
fluid moves out of capillary into interstitial spaces
reabsorption:
fluid moves back into capillary from interstitial spaces
CAPILLARY HYDROSTATIC PRESSURE:
blood pressure: facilitates the outward movement of water from the capillary to the interstitial space
CAPILLARY OSMOTIC PRESSURE:
osmotically attracts water from interstitial spaces back into the capillary
INTERSTITIAL HYDROSTATIC PRESSURE:
facilitates inward movement of water form interstitial spaces into capillary
INTERSTITIAL OSMOTIC PRESSURE:
osmotically attracts water from capillary into interstitial spaces
NET FILTRATION:
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
...
SODIUM
is responsible for ECF osmotic balance
POTASSIUM maintains
ICF osmotic balance
EDEMA:
excessive accumulation of fluid within interstitial spaces
CAUSES OF EDEMA:
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)
LOCALIZED EDEMA:
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)
GENERALIZED EDEMA:
manifested by a more uniform distribution of fluid in interstitial spaces (dependent edema)
EDEMA IS ASSOCIATED WITH:
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
ALDOSTERONE
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
NORMAL SERUM SODIUM CONCENTRATION: maintained by
kidneys; narrow range: 136-145 mEq/L
ALDOSTERONE:
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
VASOCONSTRICTION INCREASES
BLOOD FLOW
ALDOSTERONE PUTS OUT
SODIUM
Natriuretic hormones (peptides):
promote urinary excretion of sodium & water/decreased BP
Electrolytes carry electric charges when in water
...
TONICITY:
The ability of a solution to cause a cell to gain or lose water
isotonic
(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)
HYPERNATREMIA:
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)
SODIUM GAINS cause
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
hyperchloremia:
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:
hyponatremia
potassium:
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:
KIDNEYS