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A volume expander is a type of
intravenous therapy Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutri ...
that has the function of providing volume for the
circulatory system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. It may be used for
fluid replacement Fluid replacement or fluid resuscitation is the medical practice of replenishing bodily fluid lost through sweating, bleeding, fluid shifts or other pathologic processes. Fluids can be replaced with oral rehydration therapy (drinking), intravenous ...
or during surgery to prevent nausea and vomiting after surgery.


Physiology

When blood is lost, the greatest immediate need is to stop further blood loss. The second greatest need is replacing the lost volume. This way remaining red blood cells can still oxygenate body tissue. Normal human blood has a significant excess oxygen transport capability, only used in cases of great physical exertion. Provided blood volume is maintained by volume expanders, a rested patient can safely tolerate very low hemoglobin levels, less than 1/3 that of a healthy person. The body detects the lower hemoglobin level, and compensatory mechanisms start up. The
heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...
pumps more blood with each beat. Since the lost blood was replaced with a suitable fluid, the now diluted blood flows more easily, even in the small vessels. As a result of chemical changes, more oxygen is released to the tissues. These adaptations are so effective that if only half of the red blood cells remain, oxygen delivery may still be about 75 percent of normal. A patient at rest uses only 25 percent of the oxygen available in their blood. In extreme cases, patients have survived with a hemoglobin level of 2 g/dl, about 1/7 the normal, although levels this low are very dangerous. With enough blood loss, ultimately red blood cell levels drop too low for adequate tissue oxygenation, even if volume expanders maintain circulatory volume. In these situations, the only alternatives are blood transfusions, packed red blood cells, or oxygen therapeutics (if available). However, in some circumstances,
hyperbaric oxygen therapy Hyperbaric medicine is medical treatment in which an ambient pressure greater than sea level atmospheric pressure is a necessary component. The treatment comprises hyperbaric oxygen therapy (HBOT), the medical use of oxygen at an ambient pressure ...
can maintain adequate tissue oxygenation even if red blood cell levels are below normal life-sustaining levels.


Types

There are two main types of volume expanders: crystalloids and colloids. Crystalloids are
aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be r ...
s of mineral salts or other water-soluble molecules. Colloids contain larger insoluble molecules, such as
gelatin Gelatin or gelatine (from la, gelatus meaning "stiff" or "frozen") is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also ...
;
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
itself is a colloid. There is no evidence that colloids are better than crystalloids in those who have had trauma, burns, or surgery. Colloids are more expensive than crystalloids. As such, colloids are not recommended for volume expansion in these settings.


Crystalloids

The most commonly used crystalloid fluid is ''normal saline'', a solution of
sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35. ...
at 0.9% concentration, which is close to the concentration in the blood ( isotonic). ''
Ringer's lactate Ringer's lactate solution (RL), also known as sodium lactate solution, Lactated Ringer’s, and Hartmann's solution, is a mixture of sodium chloride, sodium lactate, potassium chloride, and calcium chloride in water. It is used for replacing flu ...
'' or ''Ringer's acetate'' is another isotonic solution often used for large-volume fluid replacement. The choice of fluids may also depend on the chemical properties of the medications being given.


Normal saline

''Normal saline'' (NS) is the commonly used term for a solution of 0.9% w/v of
NaCl Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/ ...
, about 300
mOsm Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L ...
/L. Less commonly, this solution is referred to as ''physiological saline'' or ''isotonic saline'', neither of which is technically accurate. NS is used frequently in
intravenous drip Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
s (IVs) for patients who cannot take fluids orally and have developed or are in danger of developing
dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
or
hypovolemia Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the los ...
. NS is typically the first fluid used when hypovolemia is severe enough to threaten the adequacy of blood circulation, and has long been believed to be the safest fluid to give quickly in large volumes. However, it is now known that rapid infusion of NS can cause
metabolic acidosis Metabolic acidosis is a serious electrolyte disorder characterized by an imbalance in the body's acid-base balance. Metabolic acidosis has three main root causes: increased acid production, loss of bicarbonate, and a reduced ability of the kidneys ...
.


Ringer's solution

Lactated Ringer's solution Ringer's lactate solution (RL), also known as sodium lactate solution, Lactated Ringer’s, and Hartmann's solution, is a mixture of sodium chloride, sodium lactate, potassium chloride, and calcium chloride in water. It is used for replacing f ...
contains 28 mmol/L lactate, 4 mmol/L K+ and 1.5 mmol/L Ca2+. It is very similar – though not identical – to
Hartmann's Solution Ringer's lactate solution (RL), also known as sodium lactate solution, Lactated Ringer’s, and Hartmann's solution, is a mixture of sodium chloride, sodium lactate, potassium chloride, and calcium chloride in water. It is used for replacing f ...
, the ionic concentrations of which differ slightly. Ringer's lactate contains calcium, which may combine with citrate (that is used as a preservative in some blood products) and form a precipitate; therefore, it is not to be used as a diluent in blood transfusions.


1/3 NS 2/3D5

2/3 1/3 is no longer recommended as a maintenance intravenous fluid in children as it is hypotonic and isotonic fluids are preferred.


Glucose (dextrose)

Intravenous sugar solution Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...
s, such as those containing
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
(also called dextrose), have the advantage of providing some energy, and may thereby provide the entire or part of the energy component of
parenteral nutrition Parenteral nutrition (PN) is the feeding of nutritional products to a person intravenously, bypassing the usual process of eating and digestion. The products are made by pharmaceutical compounding companies. The person receives a nutritional mi ...
. Types of glucose/dextrose include: * D5W (5% dextrose in water), which consists of 278 mmol/L dextrose * D5NS (5% dextrose in normal saline), which, in addition, contains normal saline.


Plasma-lyte

Plasma-Lyte Plasma-Lyte is a crystalloid solution for intravenous infusion, with varying electrolyte formulation depending on market. Generally the solution has a composition that mimics human physiological plasma electrolyte concentrations, osmolality and ...
A and Plasma-Lyte 148 are buffered crystalloid solutions that may be infused intravenously, or used in conjunction with blood products.


Comparison table


Colloids

Colloids preserve a high
colloid osmotic pressure Oncotic pressure, or colloid osmotic-pressure, is a form of osmotic pressure induced by the proteins, notably albumin, in a blood vessel's plasma (blood/liquid) that causes a pull on fluid back into the capillary. Participating colloids displac ...
in the blood, while, on the other hand, this parameter is decreased by crystalloids due to hemodilution. Therefore, they should theoretically preferentially increase the
intravascular volume Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the int ...
, whereas crystalloids also increase the interstitial volume and
intracellular volume The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion ...
. However, there is no evidence to support that this results in less mortality than crystalloids. Another difference is that crystalloids generally are much cheaper than colloids. Common colloids used in the medical context include
albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water- soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Album ...
and fresh frozen plasma.


Hydroxyethyl starch

''Hydroxyethyl starch'' (HES/HAES, common trade names: Hespan, Voluven) is controversial. Its use in those who are very ill is associated with an increased risk of death and kidney problems. Therefore, HES/HAES is not recommended in people with known inflammatory conditions such as renal impairment.


Gelofusine

''Gelofusine'' is a colloid volume expander which may be used as a
blood plasma Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the int ...
replacement when a significant amount of blood is lost due to extreme hemorrhagia, trauma, dehydration, or a similar event. It is an intravenous colloid that behaves much like blood filled with albumins. As a result, it causes an increase in blood volume, blood flow, cardiac output, and
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
transportation.


References

{{Intravenous therapy Blood substitutes Intravenous fluids