To understand how iv therapy works to restore fluid and electrolyte balance, lets review some basics of fluids & electrolytes.
Intracellular – 55% of the total body fluid Extracellular:2 formsIntravascular (blood plasma) – liquid component of the blood. Surrounds RBCs & accounts for most of the blood volumeInterstitial ECF – transcellular fluid contains secretions from the salivary glands, pancreas, liver & sweat glandsGeneral composition of extracellular fluid:More Na+ , Cl- , HCO3 - Less K+, Ca++, Mg++, PO4-3, SO4-2General composition of intracellular fluid:More K+, PO4-3, Mg++, SO4-2 Less Na+ , Cl- , HCO3-
Maintaing fluid balance involves these organs.This balancing act affected by Fluid volumeDistribution of fluids in the bodyConcentration of solutes in the fluid
This balancing act affected by Fluid volumeDistribution of fluids in the bodyConcentration of solutes in the fluid
Daily fluid gains & lossesIntake – water of oxidation (combined water & oxygen in the respiratory system) – 300 – 400mlLungs (respiration)Skin (perspiration)Kidneys (urine)Intestines (feces)
ADH – referred as to water – conserving hormone – affects fluid volume & water concentration by regulating water retention.
Aldosterone acts to retain sodium and water. Its secreted when the serum sodium level is low, the potassium is high, or the circulating volume of fluid decreases.
Before carefully assessing a patient before and during IV therapy, you can identify fluid imbalances early – before serious complications develop.
Electrolytes are associated with electricity. These vital substances are chemical compounds that dissociate in solution into electrically charged particles called ions. Like wiring for the body, the electrical charges of ions conduct current that’s necessary for normal cell function
Fluids and electrolytes are usually discussed in tandem, especially where IV therapy is concerned, because fluid balance and electrolyte balance are interdependent. any change in one alters the other, and any solution given IV can affect a patient’s fluid and electrolyte balance.
Two ECF components – ISF & intravascular fluid – have identical electrolyte compositions. Pores in the capillary walls allow electrolytes to move freely between the ISF and plasma, allowing for equal distribution of electrolytes in both substances. The protein contents of ISF and plasma, however, ISF doesn’t contain proteins because protein molecules are too large to pass through capillary walls. Plasma has a high concentration of proteins.
Body fluids in constant motion although separated by membranes, they continually move between the major fluid compartments.
The sodium – potassium pump – it moves sodium ions out of cells to the ECF and potassium ions into cells from ECF. This pump balances sodium and potassium concentrations.
Lower serum – fluid overloadHigher serum – hemoconcentration and dehydration
Contain different electrolytes because the cell membranes separating the two compartments have selective permeability. Contain different solutes, concentration levels are about equal when balance is maintained.
FLUID MOVEMENT A mechanism that regulates fluid and electrolyte balance. Body fluids are in constant motion. Nutrients , waste products, and other substances get into and out of cells, organs, and systems. Influenced by membrane permeability and colloid osmotic and hydrostatic pressures.
Osmosis Movement of water across a semipemeable membrane from an area of low solute concentration (less concentrated) to an area of high solute concentration (more concentrated).
Capillary filtration and reabsorption Filtration – movement of substances from an area of high hydrostatic pressure to an area of lower hydrostatic pressure Hydrostatic pressure – pressure at any level on water at rest due to weight of the water above it. Pushes fluids and solutes through capillary wall pores and into the ISF. Capillary Reabsorptionby the osmotic or pulling force of albumin (Colloid Osmotic/Oncotic Pressure) - pulling force of albumin in the capillaries, attracting water in from the interstitial space
Osmolarity Concentration of a solution. Expressed in milliosomols of solute per liter of solution (mOsm/L) Same osomolarity as other body fluids about 300 mOsm/L
Three Main Types of IV Solutions Isotonic Hypotonic Hypertonic
Isotonic Solutions(240-340mOsm) Solution has the same solute concentration (or osmolality) as normal blood plasma (290mOsm) and other body fluids Solution stays where it is infused, inside the blood vessel Expands the intravascular compartment Does not affect the size of the cells Solution maintains body fluid balance
Isotonic Solutions Nursing considerations Monitor patient for signs of fluid overload especially in patients with CHF and hypertension.
Hypotonic Solutions Solution has a lower osmolarity than serum (less than 240 mOsm/L) Solution causes a fluid shift out of the blood vessels into the cells and interstitial spaces Solution hydrates cells while reducing fluid in the circulatory system Ex.: ½ NSS (0.45% NaCl)
Hypotonic Solutions Nursing considerations Administer cautiously Solution can lower blood pressure Do not give if these solutions if the patient is at risk for: ICP from cerebrovascular accident Head trauma Neurosurgery
Hypertonic solutions Solution has an osmolarity higher than serum(>340mOsm/L) Causes the solute concentration of the serum to increase pulling fluid from the cells and the interstitial compartment into the blood vessels Reduces the risk of edema, stabilizes blood pressure, and regulates urine output
Hypertonic Solutions Nursing considerations Monitor your patient for circulatory overload Solution can be irritating to the vein
Two Main Groups of IV Solutions Crystalloids Colloids
Crystalloids Are isotonic and remain isotonic in the vasculature and are therefore effective volume expanders for a short period of time. Ideal for patients who need fluid volume replacement Ex.: Lactated Ringer’s (LR), Normal Saline (NS)
Colloids Used to increase vascular volume rapidly drawing fluid from the interstitial and intracellular compartments into the vascular compartment. They work well in reducing edema (as in pulmonary or cerebral edema) while expanding the vascular compartment. Examples: albumin, mannitol, dextran, hetastarch, gelafundin, Haesteril
Colloids Dextran Polysaccharide fluid Albumin Natural plasma protein from donor plasma Mannitol Sugar alcohol substance Hetastarch Synthetic colloid made from starch