Human serum albumin is the most abundant protein in human blood plasma, representing approximately 50% of the total protein content. Synthesized exclusively by the liver, this globular protein plays a central role in maintaining the body’s fluid balance and circulatory health. When a patient’s natural production is compromised, or rapid plasma volume expansion is necessary, a therapeutic infusion of human albumin solution may be required. Determining the precise amount involves recognizing its physiological actions and using a complex, individualized calculation to ensure the correct concentration and dose are delivered.
Albumin’s Essential Functions in the Body
The primary physiological role of albumin is its contribution to colloid osmotic pressure (oncotic pressure). Albumin molecules are too large to easily pass through blood vessel walls, remaining within the bloodstream. These proteins generate an osmotic pull that draws fluid from surrounding tissues back into the blood vessels. This action is responsible for 70% to 80% of the total oncotic pressure, which prevents excessive fluid leakage and maintains stable blood volume.
A second major function of albumin is acting as a versatile transport vehicle. The protein has multiple binding sites that allow it to carry hormones, fatty acids, bilirubin, and various therapeutic drugs. Albumin helps solubilize and distribute these compounds throughout the body, ensuring they reach target tissues or the liver for metabolism. This transport capacity is significant for hydrophobic substances that do not mix well with water-based plasma.
When liver disease, severe inflammation, or other conditions reduce circulating albumin levels, these essential functions are impaired. Administering therapeutic albumin aims to restore the fluid-balancing mechanism and the transport capacity to support overall homeostasis.
Medical Situations Requiring Albumin Treatment
Albumin administration is indicated when its unique properties offer a clinical advantage over other intravenous fluids. Indications fall into two categories: rapid volume expansion and specialized replacement therapy. For patients experiencing hypovolemic shock or severe trauma, albumin quickly restores circulating blood volume. In severe burns, it is typically given after the initial 24 hours to maintain plasma volume and address massive protein loss through damaged skin.
A common specialized use is in patients with advanced liver disease undergoing large-volume paracentesis, which is the removal of ascites fluid from the abdomen. Removing more than five liters can cause a significant drop in blood volume and circulatory dysfunction. Infusing albumin prevents this complication by pulling fluid back into the vessels and stabilizing circulation. This therapy is also standard for complications of liver failure, such as spontaneous bacterial peritonitis and hepatorenal syndrome.
In spontaneous bacterial peritonitis, albumin is given at a high dose to reduce the risk of kidney impairment. The use of albumin in severe hypoalbuminemia (serum levels below 2.0 g/dL) is generally reserved for patients exhibiting clinical complications like significant edema or respiratory distress. Low albumin levels alone are not always an indication for infusion, as the underlying cause must also be addressed.
Determining the Appropriate Dosage
Calculating the correct albumin dose depends on the specific clinical goal and the patient’s condition. The initial decision involves selecting the appropriate concentration: typically 5% or 25% human albumin solution. The 5% solution is iso-oncotic, similar in osmotic pressure to normal plasma, and is primarily used for volume expansion. The 25% solution is hyperoncotic, providing five times the protein per volume, making it highly effective at drawing interstitial fluid back into the circulation with minimal fluid load.
The hyperoncotic 25% solution is preferred when fluid or sodium restriction is necessary, such as in patients with compromised heart or kidney function. The target clinical endpoint dictates the dosage strategy. For example, volume expansion for shock aims to stabilize blood pressure and heart rate, not necessarily raise the serum albumin level. Treatment for severe hypoalbuminemia, conversely, might involve a calculated dose over several days to replace the total body deficit.
Dosing for specific conditions follows established guidelines. For large-volume paracentesis, the standard recommendation is 6 to 8 grams of albumin for every liter of ascites fluid removed. For spontaneous bacterial peritonitis, a specific regimen is used, often involving an initial dose of 1.5 grams per kilogram of body weight, followed by a second dose on the third day. The total daily dose should not exceed 2 grams of albumin per kilogram of body weight.
Administering Albumin and Tracking Patient Response
Albumin is administered intravenously, and the infusion rate must be controlled to prevent adverse effects. The hyperoncotic 25% solution must be infused slowly, typically at a maximum rate of 1 to 2 milliliters per minute. The 5% solution can generally be infused faster, often up to 5 to 10 milliliters per minute. Rapid infusion, especially of the 25% solution, can quickly shift large amounts of fluid into the circulation, risking circulatory overload.
The primary concern during administration is the potential for fluid overload, which can lead to pulmonary edema, particularly in patients with pre-existing heart problems. Continuous monitoring involves tracking vital signs like blood pressure and heart rate, and observing for signs of respiratory distress. Urine output is also monitored as a measure of kidney function and overall fluid balance.
Serious risks include allergic or anaphylactic reactions, which necessitate immediate cessation of the infusion. Clinicians also monitor serum electrolyte levels, as large volumes of albumin can sometimes lead to imbalances. The goal of monitoring is to confirm the dose achieved the desired clinical effect—such as blood pressure stabilization or improved urine output—without causing harmful fluid shifts or circulatory compromise.