FLUIDS AND ELECTROLYTES Flashcards
Thid-Spacing
Third-spacing is the accumulation and sequestration of trapped extracellular fluid in an actual or potential body space as a result of disease or injury.
The trapped fluid represents a volume loss and is unavailable for normal physiological processes.
Fluid may be trapped in body spaces such as the pericardial, pleural, peritoneal, or joint cavities; the bowel; the abdomen’ or within soft tissues after trauma or burns.
Assessing the intravascular fluid loss caused by third-spacing is difficult The loss may not be reflected in weight changes or intake and output records and may not become apparent until after organ malfunction occurs
EDEMA
Edema is an excess accumulation of fluid in the interstitial space’ it occurs as a result of alterations in oncotic pressure, hydrostatic pressure, capillary permeability, and lymphatic obstructions.
Localized edema occurs as a result of traumatic injury from accidents or surgery, local inflammatory processes, or burns.
Generalized edema, also called anasarca, is an excessive accumulation of fluid in the interstitial space throughout the body and occurs as a result of conditions such a cardiac, renal, or liver failure.
BODY FLUID
Body fluids transport nutrients to the cells and carry waste products from the cells.
Total body fluid (intracellular and extracellular) amounts to about 60% body weught in the adult, 55% in the older adult, and 80% in the infant.
Thus infants and older adults are at a higher risk for fluid-related problems than younger adults; children have a greater proportion of body water than adults,, and the other older adult has the least proportion of body water.
Body fluids consist of water and dissolved substances.
The largest single fluid constituent of the body is water.
Some substances, such as glucose, urea, and creatining, do not dissociate in solution; that is, they do not separate from their complex forms into simpler substances when they are in solution.
Other substances do dissociate; for example, when sodium chloride is in a solution, it dissociates, or separates, into 2 parts or elements.
INFANTS AND OLDER ADULTS NEED TO BE MONITORED CLOSELY FOR FLUID IMBALANCES.
Body fluid transport - DIFFUSION
Diffusion is the process whereby a solute (substance that is dissolved) may spread through a solution or solvent (solution in which the solute is dissolved).
Diffusion of a solute spreads the molecules from an area of higher concentration to an area of lower concentration.
A permeable membrane allows substances to pass through it without restriction.
A selectively permeable membrane allows some solutes to pass through without restriction but prevents other solutes from passing freely.
Diffusion occurs within fluid compartments and from one compartment to another if the barrier between the compartments is permeable to the diffusing substances.
BODY FLUID TRANSPORT - OSMOSIS
Osmosis is the movement of solvent molecules across a membrane in response to a concentration gradient,
usually from a solution of lower to one of higher solute concentration.
Osmotic pressure is the force that draws the solvent from a less concentrated solute through a selectively permeable membrane into a more concentrated solute, thus tending to equalize the concentration of the solvent.
If a membrane is permeable to water but not to all solutes present, the membrane is a selective or semipermeable membrane.
When a more concentrated solution is on one side of a selectively permeable membrane and a less concentrated solution is on the other side, a pull called osmotic pressure draws the water through the membrane to the more concentrated side, or the side with more solute.
BODY FLUID TRANSPORT - Filtration
Filtration is the movement of solutes and solvents by hydrostatic pressure.
The movement is from an area of higher pressure to an area of lower pressure.
BODY FLUID TRANSPORT - Hydrostatic pressure
Hydrostatic pressure is the force exerted by the weight of a solution.
When a difference exists in the hydrostatic pressure on two sides of a membrane, water and diffusible solutes move out of the solution that has the higher hydrostatic pressure by the process of filtration.
At the arterial end of the capillary, the hydrostatic pressure is higher than the osmotic pressure; therefore, fluids and diffusible solutes move out of the capillary.
At the venous end, the osmotic pressure, or pull, is higher than the hydrostatic pressure, and fluids and some solutes move into the capillary.
The excess fluid and solutes remaining in the interstitial spaces are returned to the intravascular Compartment by the lymph channels.
BODY FLUID TRANSPORT - Osmolality
Osmolality refers to the number of osmotically active particles per kilogram of water; it is the concentration of a solution.
In the body, osmotic pressure is measured in milliosmoles (mOsm).
The normal osmolality of plasma is 275 to 295 mOsm/kg (275 to 295 mmol/kg).
Movement of body fluid
Cell membranes and capillary walls separate body compartments.
Cell membranes are selectively permeable; that is, the cell membrane and the capillary wall allow water and some solutes free passage through them.
Several forces affect the movement of water and solutes through the walls of cells and capillaries; for example, the greater the number of particles within the cell, the more pressure exists to force the water through the cell membrane out of the cell.
If the body loses more electrolytes than fluids, as can happen in diarrhea, then the extracellular fluid contains fewer electrolytes or less solute than the intracellular fluid.
Fluids and electrolytes must be kept in balance for health; when they remain out of balance, death can occur.
Isotonic solutions
When the solutions on both sides of a selectively permeable membrane have established equilibrium or are equal in concentration, they are isotonic.
Isotonic solutions are isotonic to human cells, and thus very little osmosis occurs; isotonic solutions have the same osmolality as body fluids.
Hypotonic solutions
When a solution contains a lower concentration of salt or solute than another, more concentrated solution, it
is considered hypotonic.
A hypotonic solution has less salt or more water than an isotonic solution; these solutions have lower osmolality than body fluids.
Hypotonic solutions are hypotonic to the cells; therefore, osmosis would
continue in an attempt to bring about balance or equality.
Hypertonic solutions
A solution that has a higher
concentration of solutes than another, less concentrated solution is hypertonic; these solutions have a higher osmolality than body fluids.
Osmotic pressure
The amount of osmotic pressure is determined by the concentration of solutes in solution.
When the solutions on each side of a selectively permeable membrane are equal in concentration, they are isotonic.
A hypotonic solution has less solute than an isotonic solution, whereas a hypertonic solution contains more solute.
Active transport
If an ion is to move through a membrane from an area of lower concentration to an area of higher concentration, an active transport system is necessary.
An active transport system moves molecules or ions against concentration and osmotic pressure.
Metabolic processes in the cell supply the energy for active transport.
Substances that are transported actively through the cell membrane include ions of sodium, potassium, calcium, iron, and hydrogen; some of the sugars; and the amino acids.
Body fluid intake
Water enters the body through 3 sources—orally ingested liquids, water in foods, and water formed by oxidation of foods.
About 10 mL of water is released by the metabolism of each 100 calories of fat, carbohydrates, or proteins.