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Pharmacology for Nurses

5.1 Fluid Volume

Pharmacology for Nurses5.1 Fluid Volume

Learning Outcomes

By the end of this section, you should be able to:

  • 5.1.1 Define fluid volume.
  • 5.1.2 Discuss the process of fluid volume deficit and excess as it relates to the body.
  • 5.1.3 Describe cellular compartments and their role in fluid balance.
  • 5.1.4 Explain the importance of blood and blood products.

Fluid volume is a critical component of the body’s homeostasis, allowing for proper functioning of numerous physiological processes. Disruptions to fluid volume can occur due to a variety of factors and can have serious consequences if left untreated. Maintaining an appropriate balance of fluids and electrolytes is essential for optimal health.

Fluid Volume Introduction

Fluid volume refers to the total amount of fluid present in the body, which includes both intracellular (inside cells) and extracellular (outside cells) fluids. The body is composed of approximately 60 percent water, which is distributed throughout the body in various compartments, including blood vessels, tissues, and organs.

The fluid volume in the body is tightly regulated through a complex system of feedback mechanisms that help to maintain a balance of fluids and electrolytes. These mechanisms, which are discussed in Introduction to Homeostasis, help to ensure that the body’s cells receive the appropriate amount of nutrients and oxygen and that waste products are removed efficiently. Figure 5.2 shows how diffusion works across cell membranes to create a balance.

Maintaining, monitoring, and regulating fluid volume in the body is essential for proper bodily functions and an important aspect of medical care, especially when looking at fluid imbalances, which will be discussed in the next section.

The simple diffusion of small uncharged molecules across the plasma membrane is shown. A red horizontal arrow pointing towards the right indicates the progress of time. The uncharged molecules are shown in blue and are present in higher numbers in the extracellular fluid. A few uncharged molecules cross the lipid bilayer to the cytoplasm and their number increases with time.
Figure 5.2 The structure of the lipid bilayer allows substances, such as oxygen and carbon dioxide, and molecules, such as lipids, to pass through the cell membrane by simple diffusion. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Fluid Imbalances

A fluid imbalance occurs when there is an abnormal distribution of fluids between the intracellular fluid (ICF) and the extracellular fluid (ECF) compartments within the body. An abnormal distribution of fluids between the ICF and ECF compartments can disrupt cellular function and result in fluid imbalance in the form of either a deficit or an excess (Brinkman et al., 2023). These fluid imbalances will be discussed in more detail in the subsequent sections.

A fluid imbalance can be caused by a variety of factors including medical conditions, such as kidney and heart disease, medication use, and lifestyle factors, such as diet and exercise.

Treatment for the imbalance typically involves addressing the underlying cause and restoring the balance of fluids and electrolytes in the body. This may include oral or intravenous fluids, electrolyte replacement, and other interventions as necessary.

Fluid Volume Deficit

Fluid volume deficit, also known as hypovolemia, is a condition that occurs when there is a decrease in the body’s fluid volume. This can be due to a loss of sodium from the body, decreased fluid intake, or a combination of both. Several conditions and diseases can lead to fluid volume deficit, such as dehydration, diabetes insipidus, and hemorrhage. Certain drugs, including diuretics, blood pressure drugs (e.g., angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs), which inhibit aldosterone), and laxatives (which increase fluid loss through stools), can lead to hypovolemia (Melendez-Rivera & Anjum, 2022).

Manifestations of fluid volume deficit include:

  • Postural dizziness
  • Fatigue
  • Confusion
  • Muscle cramps
  • Chest pain
  • Abdominal pain
  • Postural hypotension
  • Tachycardia

The diagnosis of fluid volume deficit involves a comprehensive approach that includes a thorough physical examination, a detailed client history, and laboratory tests such blood chemistry panels, electrolyte panels, complete blood cell counts, and urinalysis.

Treatment of fluid volume deficit involves replenishing fluids and electrolytes through oral rehydration therapy or intravenous (IV) fluid replacement, depending on the severity of the deficit.

Fluid Volume Excess

Fluid volume excess, also known as hypervolemia, is a condition that occurs when there is an abnormal increase in the body’s total fluid volume. This can be due to increased fluid intake, decreased fluid output, or a combination of both. Several conditions and diseases can lead to fluid volume excess, including heart failure, liver disease, and kidney disease (Ekinci et al., 2018). Certain drugs such as nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids (which can lead to fluid retention by affecting the kidneys’ ability to eliminate sodium and water), hormonal therapies such as estrogen replacement (which can lead to fluid retention), and diabetes drugs such as thiazolidinediones can cause fluid retention as an adverse effect.

Manifestations of fluid volume excess include:

  • Shortness of breath
  • Crackles in the lungs
  • Swelling in the legs, ankles, and feet
  • Weight gain
  • High blood pressure
  • Fatigue

To diagnose fluid volume excess, the provider must take a comprehensive approach. This involves a physical examination, a detailed client history, and various laboratory tests such as blood chemistry panels, electrolyte panels, complete blood cell counts, and urinalysis. Additionally, imaging studies like a chest x-ray and echocardiogram may also be necessary to assess the heart and lungs.

Treatment of hypervolemia involves addressing the underlying cause, restricting fluid and sodium intake, and increasing urine output through diuretic drugs. In severe cases, hospitalization may be required for monitoring and treatment.

Fluid Replacement

Fluid volume replacement is a medical treatment that involves replenishing lost fluid and electrolytes, specifically sodium in the body, typically through IV infusion. This treatment is commonly used to address fluid volume deficit and conditions that result in body fluid loss.

Fluid volume replacement works by restoring the balance of fluid and electrolytes that are essential for maintaining proper bodily function. Electrolytes are electrically charged minerals such as sodium, potassium, chloride, phosphate, magnesium, and calcium, which play roles in regulating cellular function and maintaining the body’s fluid balance (Melendez-Rivera & Anjum, 2022).

Fluid volume replacement usually involves various types of fluids or a combination of fluids containing electrolytes and other nutrients. The specific type of fluid used depends on the client’s condition and individual needs. Fluid replacement and types of intravenous fluid replacement solutions will be discussed in more detail in subsequent sections.

Fluid volume replacement is administered by health care professionals, and the treatment is closely monitored to ensure that the client’s fluid and electrolyte levels are being properly balanced.

Blood and Blood Products

Blood is a vital component of fluid balance. Blood circulates through the body and is composed of various cells including red blood cells, white blood cells, and platelets (see Figure 5.3), as well as a liquid component called plasma. Blood plays an important role in:

  • Oxygen transport: Blood transports oxygen from the lungs to the body’s tissues. Red blood cells contain hemoglobin, which binds with oxygen and carries it throughout the body.
  • Nutrient transport: Blood carries nutrients such as glucose, amino acids, and fatty acids to the body’s cells, where they are used for energy and cellular function.
  • Waste removal: Blood transports waste products such as carbon dioxide to the lungs and urea to the kidneys, where they are removed from the body.
  • Immune defense: White blood cells play a crucial role in the body’s immune system, defending against infections and diseases.
  • Blood clotting: Blood contains platelets and clotting factors that help stop bleeding and promote the healing of injured tissues.
  • Hormone regulation: Blood helps regulate hormone levels in the body, which controls many important functions such as metabolism, growth, and development.
Different types of blood cells and cellular components are depicted. Red blood cells are disc-shaped and indented in the middle. Platelets are long and thin, and about half the length red blood cells. White blood cells are divided into neutrophils, monocytes, lymphocytes, eosinophils, and basophils and are about twice the diameter of red blood cells and spherical. Monocytes and eosinophils have U shaped nuclei. Eosinophils contain granules, but monocytes do not. Basophils and neutrophils both have irregularly shaped, multi-lobed nuclei and granules. Red blood cells are the most prevalent; white blood cells are the least prevalent.
Figure 5.3 White blood cells (including basophils, eosinophils, lymphocytes, monocytes, and neutrophils), red blood cells, and platelet blood components are shown in this diagram. (credit: modification of work from Biology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Blood products are derived from donated human blood and are used for a variety of medical purposes, including fluid volume replacement. The most commonly used forms of blood products for fluid replacement are packed red blood cells (PRBCs), platelets, plasma, and cryoprecipitated anti-hemophilic factor (cryo) (American Red Cross, n.d.).

When a person experiences severe blood loss or fluid volume deficit, fluid volume replacement is necessary to restore their blood volumes and prevent shock. Blood and blood products are administered intravenously to replenish lost fluids/blood, maintain the body’s blood pressure and hormonal balance, and restore the body’s oxygen-carrying capacity (Lotterman & Sharma, 2022). Blood and blood products will be discussed in more depth in the next section of this chapter.


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