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Factors that influence body fluid

Age – increase risk with age (skeletal muscle mass decreases as adipose tissue increases), after age 60 water content drops to 45% when 60% in huge healthy adult, infant or small child is also at risk
Gender - Men have more body fluid
Body fat – if pt obese then have less body water because fat cells contain little water


fluid compartments

Intracellular space and Extracellular space (Intravascular space, Interstitial space, Transcellular space)


Intracellular space –

fluid in the cells; 2/3 of body fluid


Extracellular space –

fluid outside the cells 1/3 of body fluid


Intravascular space –

fluid within the blood vessel; contains plasma; approx 3 L of the average 6 L blood volume is plasma (plasma – liquid portion of blood, 20%)


Interstitial space –

contains fluid that surrounds the cell and totals ~ 11-12 L in adult (Lymph is an example of Interstitial fluid) 80%


Transcellular space –

smallest division of the ECF compartment; contains ~ 1L of fluid at any given time (examples: cerbrospinal, pericardial, synovial, intraocular, and pleural fluids; sweat, and digestive secretions)


When a (hypotonic) solution is placed next to (hypertonic) solution, fluid shifts from

the hypotonic (less concentration) solution into a more concentrated (hypertonic) compartment to equalize the concentration



solutes move from high concentration to low concentration, This requires no energy – natural tendency, Ex. Exchange of O2 and CO2 in the lung



movement of water to dilute volume


Normal movement of fluids through the capillary wall into tissues depends on

Hydrostatic pressure (the pressure exerted by the fluid on the walls of the blood vessel) at both the arterial and the venous ends of the vessel and the osmotic pressure exerted by the protein of the plasma. The direction of fluid movement depends on the differences in these two opposing forces (hydrostatic versus osmotic pressure).



hydrostatic pressure in the capillaries tends to filter fluid out of the intravascular compartment into the interstitial fluid. Movement of water and solutes occurs from an area of high hydrostatic pressure to an area of low hydrostatic pressure.
higher pressure on arterial side – hydrostatic pressure (produced by contracting of heart) – pushes fluid out into capillary beds
Other side (venus side) onconic pressure pulls fluid back in, helped by albumin, exert pressure in plasma, draws in the waste and prevents water from being trapped


Sodium-Potassium Pump

active transport, so needs energy to help regulate
Sodium higher concentration outside cell
Potassium higher concentration inside cell
Larger molecules



(Antidiuretic Hormone) – release hormone from hypothalamus; when water levels low, released then increase reabsorption of water; stops excretion of excess water, when this occurs has increase urine concentration, increases blood volume (so retains water in the body and to constrict blood vessels)



(Renin-Angiotension-Aldosterone System) – purpose absorption of salt, water follows salt so increasing fluid volume



reabsorbs salt and water follows salt



(Atrial Natriuretic Peptide) – senses fluid volume, if increased the releases for diaphoresis of water; inhibits ADH, so increased urinary output of water; right atrium; direct opposite of RAAS; watch urinary output because of potential UTI; in diabetes insipidus – higher diuretic effect


serum samples drawn from

when reading lab results, these are serum samples which is drawn from the extra cellular space, more specifically intravascular space (differs from Interacellular space) therefore it is telling you how much of the solute is outside of the cell



reflects the concentration of fluid that affects the movement of water between fluid compartments by osmosis; Measures the solute concentration per kilogram in blood and urine


urine specific gravity

how concentrated the urine is, the higher the urine specific gravity the higher the concentration, measures the kidney’s ability to excrete or conserve water, Urine normal range = 1.010 – 1.025


three processes involved in balancing electrolytes

1. Distribution
2. Intake and absorption )
3. Output


Isotonic solutions

NS, D5W, Ringers Lactate (LR)
The solute concentration is about equal to that of serum. Therefore, it stays in the intravascular space after administration.
Same osmolality as intravascular space (so no net charge)


Hypotonic solutions

½ NS
The solute concentration is less than that of serum. Therefore, it shifts out of the intravascular compartment after administration.
Less solute per sterile water, draw in water from intracellular to cellular
(swelling of the cell)


Hypertonic solutions

D5 ½ NS, D5 NS, D10 W
The solute concentration is higher than that of serum. Therefore, it draws fluid into the intravascular spaces after administration. Although a hypertonic solution has more solutes than an adjacent solution it has less fluid.
Draw in fluids from tissue because of large molecules
(skinning of the cell)



the loss of water alone with increased serum sodium levels



loss of volume (water and solutes) at the same time (ex. Hemorage, GI loss, N/V/D, GI fistula, sweating, osmotic diruresis, GI suctioning, edema); become volume depleted more rapidly with low fluid intake


hypovolemia s/s

flattened neck veins, decrease neck pressure, postural hypotension, oliguria (decrease urine output), weakness, rapid heart rate, leg/abdominal cramping, cool clammy skin (r/t peripheral vasoconstriction), tachycardia, acute weight loss, concentrated urine, thirst, decreased skin turgor, can have renal failure, increased temperature, decreased central venous pressure, anorexia, muscle weakness


hypovolemia assessment

Monitor I&O, weigh daily, assess vitals, breath sounds, conciseness
labs: kidney function, electrolytes, serum and urine osmolarity


hypovolemia treatment

Replace fluids – give isotonic first because main concern is circulation, once volume restored then changed to hypotonic solution
Correct causes



Increase in water and electrolytes (most commonly sodium – more water more salt), Occurs when aldosterone is stimulated so in CHF


hypervolemia patho

simple fluid overload, renal failure, chirrhosis, holding on to fluid or fluid expansion
Contributing factors: CHF, renal failure, chirrhosis of liver; consumption of excess table salt or sodium-containing fluids


hypervolemia s/s

distentded neck veins, increase volume, increase central venous pressure, tachycardia, edema, crackles, increase bp, increase weight, bounding pulse, shortness of breath, wheezing


hypervolemia assessment

(want increase urinary output so increase ADH); Lab: BUN and hematocrit – both may decrease because of plasma dilution
In Chronic renal failure – serum osmolality and sodium decrease due to excessive retention of water
Urine sodium is increased if kidneys are attempting to excrete excess volume
Chest XR may show pulmonary congestion
Hypervolemia occurs when aldosterone is chronically stimulated – cirrhosis, CHF, nephrotic syndrome – which means urine sodium will not be increased


hypervolemia treatment

Pharmacologic therapy – diuretics are prescribed when dietary restriction of sodium alone is insufficient to reduce edema by inhibiting the reabsorption of sodium and water
Hemodialysis – used to remove nitrogenous wastes and control potassium and acid-base balance, and to remove sodium and fluid
Nutritional therapy – dietary restriction of sodium


Sodium =

135-145 mEq/L


Potassium =

3.5 – 5.0 mEq/L


Calcium =

9.0 – 10.5 mg/dL


Magnesium =

1.5 – 2.5 mEq/L


Phosphorus =

2.5 – 4.5 mg/dL


Chloride =

96 – 106 mEq/L


Most abundant electrolyte in ECF

Sodium; Na accounts for 90% of ECF cations (positively charged ions).
important functions, including regulation of osmolality (interstitial and intravascular fluid volume), working with potassium and calcium to maintain neuromuscular irritability for conduction of nerve impulses, regulation of acid-base balance, participation in cellular chemical reactions, and membrane transportation. Imbalances occur frequently.


Important ICF electrolyte

K+ is major intracellular El+ - - - 98% of body’s K+ is inside the cells.
Influences both skeletal and cardiac muscle activity. The significant role of potassium in maintaining the resting membrane potential.
Commonly associated with various diseases, injuries, medications – diuretics, laxatives, antibiotics, TPN, and chemotherapy
To maintain K+ balance, renal system must function because 80% K+ is excreted by kidneys
Other 20% lost through bowels and sweat glands