Factors that influence amount and distribution of body fluids

• Age
  • Infants: 70-80% of body weight is h20; risk for fluid related problems bc of a greater % of their body weight is h20
  • Elderly: <!-- /* Font Definitions */ @font-face {font-family:"Courier New"; panose-1:2 7 3 9 2 2 5 2 4 4; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 0 0 0 1 0;} @font-face {font-family:"Comic Sans MS"; panose-1:3 15 7 2 3 3 2 2 2 4; mso-font-charset:0; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 0 0 0 1 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:none; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman"; mso-ascii-font-family:"Courier New"; mso-fareast-font-family:"Times New Roman"; mso-hansi-font-family:"Courier New"; mso-bidi-font-family:"Times New Roman"; layout-grid-mode:line;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> 50% of body weight is H₂O r/t decrease in lean body mass; risk for fluid related problems bc they have less fluid reserve.
    
• Sex
  • Men: more body fluid than women bc fewer fat cells; 60% of body weight is h20
  • Women: 50% of body weight is h20
• Racial/Ethnic Origin
  • African Americans more fat cells= less body
    

Measurement of fluid loss

2% mild deficit

5% moderate deficit

8% or > severe deficit

Determined by the weight of patient (same time of day, scale, & clothing).

Sudden weight loss or gain is an excellent indicator of fluid loss or gain

Electrolytes

• substances that, when in solution, separate (or dissociate) into electrically charged particles called ions.  Some ions are positively chared (cations); others, negatively charged (anions)

Body Fluid Compartments

The body holds fluid in two basic areas, or compartments-- inside the cells and outside the cells:

1. Intracellular fluid
2. Extracellular fluid

Intracellular Fluid (ICF)

• Fluid within the cell
• Contains 2/3's (25L) of total body h20
  

Extracellular Fluid (ECF)

• Fluid outside the cell
• Contains 1/3 (15L) of total body fluid
• Subdivided into
  • Intravascular
  • Interstitial

Intravascular Fluid

Interstitial Fluid

• Fluid that surrounds the cells
• Includes: lymph, blood, bone and connective tissue
  

Transcellular Fluid

Fluid Spacing

Term used to classify the distribution of body h20

• First spacing
  • normal distribution of fluid in ECF and ICF compartments
    
• Second spacing
  • Abnormal accumulation of interstitial fluid-- edema
    
• Third spacing
  • Fluid accumlates in areas that normally have no fluid or only have minial amount of fluid- i.e.: ascites
    

Regulation of body fluid compartments

1. Filtration
2. Diffusion
3. Active transport
4. Osmosis
5. Hydrostatic pressure
6. Homeostasis

Filtration

• within the vascular system
• movement of fluids through capillaries results from blood pushing against the walls of the capillary.  That pressure, called hydrostatic pressure, forces fluids and solutes through the capillary wall.  
• When hydrostatic pressure inside a capillary is greater than the pressure in the surrounding interstitial space, fluids and solutes inside the capillary are forces out into the interstitial space.  When pressure inside the capillary is less than the pressure outside of it, fluids and solutes move back into the capillary
• Does not require energy
  

Diffusion

• within the cells
• Solutes move from an area of higher concentration to an area of lower concentration, which eventually results in an equal distribution of solutes within the two areas
• Diffusion is a form of passive transport bc no energy is required to make it happenl it just happens

• Facilitated Diffusion: Diffusion across a cell membrane that requires the assistance of a transport system or membrane alterning system. *Diffusion is important in the transport of gases and the movement of most electrolytes, atoms, & molecules through cell membranes
  

Active transport

• solutes move from an areas of lower concentration to an area of higher concentration
• requires energy to make it happen
• The energy required for a solute to move against a concentration gradient comes from a substance calledadenosine triphosphate , or ATP.
• Ex: Sodium-potassiumm ATPhase pump
  

Osmosis

• passive movement of fluid (solvent) across a semi-permeable membrane from an area of lesser concentration to an area of great concentration
• it attempts to equalize concentrations of molecules on both sides of the membrane
• no energy required
• measurement: osmols per kilogram (mOmsm/kg)

Osmolarity

• describes the concentration of solution
• measured in milliomoles per liter (mOsm/L)

3 types of solutions

1. isotonic
2. hypotonic
3. hypertonic

Isotonic

• both sides of the membrane are in equilibrium
• Ex: 0.9% sodium chloride in water and Ringer's lactate in water = these solutions dont change the osmolarity of plasma

Hypertonic

• has a higher solute concentration than another solution= fluid from seco
  
• osmolarity >300 mOsm/L
• fluid from the second solution would shift into the hypertonic solution until the two solutions had equal concentrations
• Ex: Mannitol IV solution
  

Hypotonic

• has a lower solute concentration than another solution= fluid from the hypotonic solution would shift into the second solution until the two solutions had equal concentrations
• osmolatity < 270 mOsm/L
• Ex: Dextrose IV solutions
  

Hydrostatic pressure

• is a water pushing pressure bc it is the force that pushes water outward from a confined space through a membrane
• if hydrostatic pressure is same in both fluid spaces= equilibrium
• If hydrostatis pressure is not the same= disequilibrium
• Edema develops when there is a change in hydrostatic pressure such as patients with heart failure
  

Homeostasis

• ability to maintain internal balance

Regulations of Body Fluids

• Hypothalamus (regulated by kidney)
  • regulated primarily through thirst mechanism.  Thirst occurs as a result of even small losses of fluid.  Losing body fluids or eating highly salty foods (hypotension) leads to an increase in extracellular fluid osmolality.  This increase leads to drying of the mucous membranes in the mouth, which in turn stimulates the thrist center in the hypothalamus.
  • Sensitivity of the thirst mechanism decreases in the elderly
    
  • Ex: hypovolemic patient
    
• Hormonal Regulation of Body Fluids
  1. aldosterone
  2. antidiuretic hormone (ADH)
     
  3. natriuretic peptide (NP)
     
  • 3 main hormones that help control the balance of fluid and electrolytes:

Aldosterone

• secreted by the adrenal cortex
• stimulated by either a decrease in sodium in ECF or and increase in sodium in the urine.  Maintains sodium by preventing sodium loss.  Water will follow the sodium and as a result of this relationship (h2o & Na), aldosterone secretion also helps regulate water balance
  
• To help the body maintain a balance of sodium and water as well as a healthy blood volume and BP, special cells (juxtaglomerular cells) near each glomerulus secrete an enzyme called renin.  Through a complex series of steps, renin leads to the production of angiotensin II, a powerful vasoconstrictor. 
  
• Angiotensin II causes peripheral vasoconstriction and stimulates the production of aldosterone.
• Aldosterone acts on the distal tubules of the nephrons to reabsorb Na for the urine back in the blood which increases osmolarity.  It also helps prevent blood K levels from becoming too high
• Aldosterone secretion is stopped when blood osmolarity or sodium levels are greater than normal levels
  

Antidiuretic hormone (ADH)

• aka: vasopressin
• The hypothalamus produces ADH, but the posterior pituitary gland stores and releases it
• Special cells in the hypothalamus called osmoreceptors are sensitive to charges in osmolarity.  Increase in osmolarity and sodium levels shrinks the osmoreceptors causing the release of ADH. 
  
• ADH acts on the kidney tubules and collecting ducts, making them more permeable to water.  As more water is reabsorbed the osmolarity is decreased.  The osmoreceptors begin to swell and ADH is inhibited.
  

Natriuretic Peptides

• hormones secreted by special cells that line the atria and ventricles of the heart
• secreted in reponse to increases in blood volume and BP
• when secreted the kidneys reabsorption of sodium is inhibited; at the same time the glomerular filtration is increased = increase in urinary output with high Na content = decreased circulating blood volume and decreased blood osmolarity

Organs involved in Regulation of Body Fluids

1. Kidneys
2. Heart and Blood Vessels
3. Lungs
4. Pituitary gland
5. Adrenl glands
6. Thyroid gland
7. GI tract
8. Skin

Kidneys

*Most important factor for F&E!

• Filters plasma automatically in response to the hormones: aldosterone & ADH
• Major functions of kidney:
  • regultion of ECF volume and osmolaity
    
  • regulation of electrolyte levels in ECF
  • regulation of pH of ECF
  • excretion of metabolic wastes & toxic substances
    • Average urine output: 1500mL/day= 60mL/hour
    • Output <30mL/hr= renal alteration

Heart and Blood Vessels

• circulates blood through the kidneys hydrostatic pressure
• failure of the heart to provide the hydrostatic pressure interferes with:
  • renal perfusion
  • urine formation
  • F&E balance

Lungs

• regulated by medulla
• removes ~300mL of h20/day

Pituitary Gland

• ADH stored in pituitary gland
• ADH is the "water conserving hormone"
  • causes re-absorption of H20 in renal tubules
    
• ADH is secreted when there is a high solute concentration= decrease urine output
  
• Low concentration of solute= ADH secretion decreased.  results increase urine ouput
• Factors which stimulate ADH secretions:
  • stress
  • pain
  • trauma
  • CHF
  • Drugs (nicotine, morphine)
    

Adrenal Glands

• secrete aldosterone= promotes Na retention in exchange for K and H ions

Thyroid Gland

• produces calcitonin
• regulates calcium levels
• inhibits bone re-absorption of Ca

GI tract

• accounts for most water intake
• small amount water secreted in feces

Skin

• water loss is regulated by the SNS which activates sweat glands
• Sensible water loss= excessive perspiration; observable
  
• Insensible water loss= continuous; nonobservable

Functions of body fluids

• transporation of nutrients to the cell
• carry waste products from the cell
• a medium for chemical reaction

= maintain homeostasis

Normal loss of body fluids

• lungs= 500mL
• skin= 300mL
• GI tract= 200mL
• kidneys= 1500mL
  

Abnormal losses of body fluids

• burn or wound exude
• hemorrhage
• vomitting and diarrhea
• hyperventilation
• suction of gastic or intestinal tube
• colostomy
  
• loss in 3rd space

Abnormal Gains of fluid

• run away IV
• renal failure
• tube feeding too rapid

Replenishment of body fluids

• ingestion of liquids
• ingestion of food (h20 product of metabolism)
• hospitalized patient
  • IC; NG or Gastroostomy

calculation of fluid gain or loss

• WEIGHT= best indicator of fluid volume loss or gain
• 1L h20 weighs 2.2lbs (1kg)
• *when weighing patient must be the same time of day, scale, and clothing