IV Fluids

 INTRODUCTION
Intravenous fluids are chemically prepared solutions that are administered
to the patient. They are tailored to the body’s needs and used to replace lost
fluid and/or aid in the delivery of IV medications. For patients that do not
require immediate fluid or drug therapy, the continuous delivery of a small
amount of IV fluid can be used to keep a vein patent (open) for future use.
IV fluids come in different forms and have different impacts on the body.
Therefore, it is important to have an understanding of the different types of
IV fluids, along with their indications for use.
How Intravenous Fluids Are Created
There are several types of IV fluids that have different effects on the body.
Some IV fluids are designed to stay in the intravascular space (intra, within;
vascular, blood vessels) to increase the intravascular volume, or volume of
circulating blood. Other IV fluids are specifically designed so the fluid leaves
the intravascular space and enters the interstitial and intracellular spaces. Still
others are created to distribute evenly between the intravascular, interstitial,
and cellular spaces. The properties that an IV solution has within the body
depends on how it is created and the specific materials it contains. It also determines the best type of IV solution to use in relation to the patient’s needs.
The majority of an IV solution is sterile water. Chemically, water is
referred to as a “solvent.” A solvent is a substance that dissolves other
materials called “solutes.” Within IV solutions, the solutes can be molecules
called electrolytes (charged particles such as sodium, potassium, and
chloride) and/or other larger compounds such as proteins or molecules.


Together, the  solvent (water) and  solutes (electrolytes, proteins, or other
molecules dissolved in the water) create the IV solution. Consider a cup of
coffee to which sugar is added for sweetness. The coffee is the solvent,
which dissolves the solute sugar.
Intravenous Fluids
IV fluids come in four different forms:
• Colloids
• Crystalloids
• Blood and blood products
• Oxygen-carrying solutions
Understanding these IV fluids is important because each has a different
impact on the body and particular indications for use:
• Colloid Solutions. Colloid solutions are IV fluids that contain solutes in
the form of large proteins or other similarly sized molecules. The proteins and molecules are so large that they cannot pass through the walls
of the capillaries and onto the cells. Accordingly, colloids remain in
the blood vessels for long periods of time and can significantly increase
the intravascular volume (volume of blood). The proteins also have the
ability to attract water from the cells into the blood vessels. However,
although the movement of water from the cells into the bloodstream
may be beneficial in the short term, continual movement in this direction can cause the cells to lose too much water and become dehydrated.
Colloids are useful in maintaining blood volume, but their use in the
field is limited. Colloids are expensive, have specific storage requirements, and have a short shelf life. This makes their use more suitable in
the hospital setting. However, familiarity is important because in a
mass casualty incident the EMT may be required to assist with the administration of colloids either in a field hospital or during the transport
of critically injured patients. Commonly used colloid solutions include
plasma protein fraction, salt poor albumin, dextran, and hetastarch. To
learn more about colloidal solutions, the EMT should consult a critical
care or paramedic textbook.
• Crystalloid Solutions. Crystalloid solutions are the primary fluid used
for prehospital IV therapy. Crystalloids contain electrolytes (e.g.,
sodium, potassium, calcium, chloride) but lack the large proteins and
molecules found in colloids. Crystalloids come in many preparations
and are classified according to their “tonicity.”
A crystalloid’s tonicity describes the concentration of electrolytes
(solutes) dissolved in the water, as compared with that of body plasma
(fluid surrounding the cells). When the crystalloid contains the same
amount of electrolytes as the plasma, it has the same concentration and
is referred to as “isotonic” (iso, same; tonic, concentration). If a crystalloid contains more electrolytes than the body plasma, it is more concentrated and referred to as “hypertonic” (hyper, high; tonic, concentration).


Consider the example of coffee and sugar. The more sugar that is added
to the coffee, the more concentrated the sugar becomes relative to the
amount of coffee, and the sweeter tasting the coffee becomes.
Conversely, when a crystalloid contains fewer electrolytes than the
plasma, it is less concentrated and referred to as “hypotonic” (hypo, low;
tonic, concentration). The less sugar a cup of coffee contains, the lower
its concentration or tonicity, and the less sweet the coffee may taste.
Depending on their concentration, crystalloids can affect the distribution of water within the body. To better understand this, the EMT must
first know what  total body water (TBW) is. TBW describes the entire
amount of water contained within the body and accounts for approximately 60% of body weight. It is distributed among the intracellular and
extracellular compartments. The intracellular space is the space within all
the body cells (intra, within; cellular, cell). The extracellular space is the
space outside the cells (extra, outside;  cellular, cells). The extracellular
compartment can be further divided into the intravascular space (space
within the blood vessels) and the interstitial space (space between the cells
but not within the blood vessels) 
The different compartments are separated by membranes through
which the body water can easily pass. As a general rule, body water is
pulled toward the solution with a higher concentration of dissolved
molecules. The movement of water across a semipermeable membrane
that selectively allows certain structures to pass while inhibiting others
(i.e., a capillary wall or cellular wall) is known as osmosis. The osmotic
movement of water occurs as the body attempts to create a balance between the different solute concentrations that exist on either side of a
semipermeable membrane. What this means is that the water will easily
cross the semipermeable membrane from the side that has a lower concentration of particles to the side that has a higher concentration of
particles. The net movement of water stops when each side of the membrane becomes equal in its concentration of water and particles. With
this in mind, isotonic, hypertonic, and hypotonic IV fluids cause the
following shifts of body water:
• Isotonic. Isotonic crystalloids have a tonicity  equal to the body
plasma. When administered to a normally hydrated patient, isotonic
crystalloids do not cause a significant shift of water between theblood vessels and the cells. Thus, there is no (or minimal) osmosis
occurring
• Hypertonic. Hypertonic crystalloids have a tonicity higher than the
body plasma. The administration of a hypertonic crystalloid causes
water to shift from the extravascular spaces into the bloodstream,
increasing the intravascular volume. This osmotic shift occurs as the
body attempts to dilute the higher concentration of electrolytes contained within the IV fluid by moving water into the intravascular
space .
• Hypotonic. Hypotonic crystalloids have a tonicity lower than the
body plasma. The administration of a hypotonic crystalloid causes
water to shift from the intravascular space to the extravascular
space, and eventually into the tissue cells. Because the IV solution
being administered is hypotonic, it creates an environment where
the extravascular spaces have higher concentrations of electrolytes.
The osmotic change results in the body moving water from the intravascular space to the cells in an attempt to dilute the electrolytes.


Of the different types of IV solutions, crystalloids are the mainstay of
IV therapy in the prehospital setting. The particular type of IV solution
selected beyond this depends on the patient’s needs. For instance, based
on the osmotic movement of water as described previously, a person
with a low volume of blood may benefit from a hypertonic or isotonic
crystalloid solution that will increase blood volume, whereas a hypotonic crystalloid would be more appropriate for a person suffering from cellular dehydration. The EMS system’s medical director will determine
which crystalloids will be used for prehospital IV therapy.
The most common isotonic solutions used in prehospital care are
• Lactated Ringer’s. Lactated Ringer’s (LR) is an isotonic crystalloid
that contains sodium chloride, potassium chloride, calcium chloride, and sodium lactate in sterile water.
• Normal saline solution. Normal saline solution (NSS) is an isotonic
crystalloid that contains 0.9% sodium chloride (salt) in sterile water.
• 5% Dextrose in water. 5% Dextrose in water (D5W) is packaged
as an isotonic carbohydrate (sugar solution) that contains glucose
(sugar) as the solute. D5W is useful in keeping a vein open by delivering a small amount of the fluid over a long period of time
and/or supplying sugar, which is used by the cells to create energy.
However, once D5W enters the body, the cells rapidly consume
the glucose. This leaves primarily water and causes IV fluid to
become hypotonic in relation to the plasma surrounding the cells.
Accordingly, the now hypotonic solution causes an osmotic shift of
water to and from the bloodstream and into the cells.
In the prehospital setting, LR and NSS are commonly used for fluid
replacement because of their immediate ability to expand the volume of
circulating blood. However, over the course of about 1 hour, approximately two-thirds of these IV fluids eventually leave the blood vessels
and move into the cells. Some authorities recommend that for every
1 liter of blood lost, 3 liters of an isotonic crystalloid be administered
for replacement. This is only a guide, and the volume of IV fluid administered should be based on medical direction or local protocol, as
well as the patient’s clinical response to fluid administration.
• Blood and Blood Products. Blood and blood products (e.g.,
platelets, packed red blood cells, plasma) are the most desirable
fluids for replacement. Unlike colloids and crystalloids, the hemoglobin (in the red blood cells) carries oxygen to the cells. Not only
is the intravascular volume increased, but the fluid administered can
also transport oxygen to the cells. Blood, however, is a precious
commodity and must be conserved to benefit the people most in
need. Its use in the field is generally limited to aeromedical services
or mass casualty incidents. The universal compatibility of O-negative
blood makes it the ideal choice for administration in emergent situations. To learn more about blood and blood products, consult a
critical care or paramedic textbook.
• Oxygen-Carrying Solutions. Oxygen-carrying solutions are synthetic
fluids that carry and deliver oxygen to the cells. These fluids, which remain experimental, show promise for the prehospital care of patients
who have experienced severe blood loss or are otherwise suffering
from hypovolemia. It is hoped that oxygen-carrying solutions will
be similar to crystalloid solutions in cost, storage capability, and ease
of administration, and be capable of carrying oxygen, which
presently can only be accomplished by blood or blood products.


Intravenous Fluid Packaging
Most IV fluids are packaged in soft plastic or vinyl bags of various sizes
(10, 50, 100, 250, 500, 1,000, 2,000, and 3,000 milliliters) (Figure 3.5).
The EMT will most likely be using 250-, 500-, and 1,000-milliliter bags.
Some IV solutions are premixed with medications that are not compatible
with plastic or vinyl and must be packaged in glass bottles. Glass bottles
are not common to prehospital IV therapy but may be encountered during
interfacility or critical care transports.
Every IV fluid container must contain a label. The label provides important information that you must examine before administering the fluid
to a patient. This information includes
• Type of IV fluid (by name and by type of solutes contained within).
• Amount of IV fluid (expressed in milliliters or “mL”).
• Expiration date.
Always carefully read the label to ensure you are administering the
correct IV solution. Many different IV fluids are packaged in similar containers, including those containing premixed medications. Administering an inappropriate IV fluid may be detrimental or even fatal to the patient, resulting
in disciplinary and/or legal action. Like any other medication, IV solutions
have a shelf life and must not be used after their expiration date.
The IV fluid container contains a medication injection site and administration set port. Both ports are located on the bottom of the IV bag when holding it upright. The medication injection port permits the injection of
medication into the fluid for use by advanced life support (ALS) or hospital
personnel after the EMT has initiated the IV. The administration set port
receives the spike from the IV administration set (IV tubing)