Plasma Expanders and How They Help Maintain Fluid Balance

Plasma Expanders and How They Help Maintain Fluid Balance

Plasma expanders are fluids that are administered intravenously to increase the volume of plasma in the bloodstream. When a person experiences severe blood loss from injury or surgery, their circulating blood volume decreases. Volume expanders help replace this lost volume in order to maintain adequate circulation and oxygen delivery throughout the body. They enable doctors to temporarily expand the volume of plasma while the body replaces the lost blood on its own.

Types of Plasma Expanders

There are a few main types of volume expanders that are commonly used:

- Dextran is a polysaccharide volume expander derived from sugar cane or sugar beet. Dextran solutions attract and hold water molecules inside blood vessels to increase plasma volume. It remains in circulation for up to 12 hours before being cleared by the kidneys. Possible side effects include allergic reactions, coagulation disorders, and kidney injury.

- Hydroxyethyl starch (HES) is a man-made volume expander. HES solutions function similarly to dextran by attracting and retaining water in the blood vessels. HES is eliminated by the kidneys within 24 hours. Serious side effects can include acute kidney injury, bleeding complications, and allergic reactions.

- Albumin is a plasma protein produced naturally by the liver. Intravenous albumin solutions expand plasma volume by increasing the concentration of albumin molecules in the blood. As a natural human protein, albumin is generally well-tolerated. However, it carries a higher risk of allergic reactions and viral infections if sourced from human blood plasma. Synthetic albumin produced in laboratories aims to reduce these risks.

- Crystalloid solutions like saline (normal saline or NS) expand plasma volume through their sodium content, which attracts water into the bloodstream during distribution. Saline is essentially salt water and functions as an extracellular fluid replenisher. It is considered the safest type of volume expander but also has the shortest intravascular retention time of only 30 minutes.

Workings

Volume expanders work primarily through increasing the colloid osmotic pressure in blood vessels. Colloids are large molecules like proteins that remain within blood vessels instead of filtering into tissues. The higher concentration of colloid molecules in volume expanders creates an osmotic gradient that pulls water from surrounding cells and tissues into the circulatory system.

This increases both the hydrostatic pressure inside blood vessels and the viscosity and oncotic pressure of blood. More volume enhances blood flow and perfusion of vital organs. volume expanders also help regulate fluid balance by drawing extra fluids back into the circulation from swollen tissues or body cavities. This is especially important after extensive blood loss, severe burns, or multi-organ injuries.

Monitoring and administration

Plasma expanders are administered intravenously through a controlled infusion, usually over a period of 30 minutes to 2 hours depending on the solution and individual patient circumstances. Close monitoring is necessary during and after administration to check for adverse effects like allergic reactions.

Vital signs including blood pressure, heart rate, breathing rate and urine output are observed frequently. Hemoglobin levels, platelet counts, clotting times and other blood tests help evaluate the efficacy and safety of treatment. X-rays may verify resolution of pulmonary edema if fluid overload was present.

Fluid balance, fluid intake and output are carefully calculated and documented to avoid complications. The expanding plasma volume is temporary, lasting from 30 minutes up to 24 hours maximum depending on the expander used. Repeated doses may be needed during resuscitation from ongoing bleeding or fluid loss through other means.

Limitations and risks

While volume expanders effectively increase intravascular volume and perfusion in emergencies, they do carry risks that must be weighed against benefits for each patient. Allergic reactions to foreign proteins can potentially cause dangerous anaphylaxis. There is also a theoretical increased risk of blood clots or electrolyte abnormalities from unnaturally high colloid concentrations.

Kidney damage, bleeding issues, and fluid imbalances leading to pulmonary or cerebral edema are serious potential complications. Using the minimum effective dose for the shortest time possible helps reduce adverse effects. Natural human products like albumin are less antigenic but carry supply and contamination concerns.

The fluid-expanding capacity of plasma volume substitutes is relatively short-term. They buy time for the body’s natural clotting and volume regulation mechanisms to replenish losses from injury, but do not provide a lasting solution on their own. Judicious fluid resuscitation rather than rapid volume expansion is recommended to avoid overloading the circulation.

Volume expanders remain an important rescue treatment for severe hypovolemic, hemorrhagic, or distributive shock. Careful consideration of fluid status, hemodynamics, and individual risk factors guides appropriate selection and dosage. With diligent monitoring and temporary use as an adjunct, they can make the lifesaving difference for patients suffering critical volume depletion.