Pharmacology of Volume Expanders and Blood Products

Vasopressors: Vasopressin

When fluid resuscitation alone is insufficient to maintain blood pressure, vasopressors may be required. Vasopressin (antidiuretic hormone) is a peptide hormone synthesized in the hypothalamus and released by the posterior pituitary.

In clinical practice, vasopressin acts via V1 receptors on vascular smooth muscle to cause vasoconstriction, and V2 receptors in the renal collecting ducts to promote water retention. It is primarily used as a second-line vasopressor in cases of catecholamine-resistant vasodilatory shock, such as septic shock. It also serves as an alternative to epinephrine during cardiopulmonary resuscitation (CPR).

Warning: High doses of vasopressin can cause ischemic complications in the skin, digits, mesenteric, or cardiac tissues.

Blood Products and Colloids

For patients experiencing significant blood loss (hemorrhagic shock), crystalloids may not be enough to restore oxygen-carrying capacity or clotting ability. In these instances, blood products are indicated.

Packed Red Blood Cells (PRBCs)

PRBCs are used to restore oxygen-carrying capacity and expand volume in patients suffering from hemorrhagic shock.

Fresh Frozen Plasma (FFP)

FFP is utilized to treat coagulopathy (clotting disorders) and thrombocytopenia by providing essential clotting factors.

Albumin

Albumin is a colloid solution that is highly effective at maintaining plasma oncotic pressure. Because it pulls fluid into the intravascular space more effectively than crystalloids, it allows for hemodynamic stabilization with smaller infusion volumes. It is indicated for hypovolemia, burns, acute nephrosis, and ARDS.

Nursing Implications and Monitoring

The administration of volume expanders requires vigilant nursing assessment to prevent complications such as fluid overload or electrolyte imbalances.

Key Nursing Responsibilities:

• Monitor Vital Signs and Perfusion: Frequently assess blood pressure, heart rate, and urine output to evaluate the efficacy of the fluid or medication.
• Assess for Fluid Overload: Watch for signs of pulmonary edema, such as dyspnea (shortness of breath) and jugular venous distention (JVD).
• Transfusion Reactions: When administering blood products or albumin, monitor for fever, chills, urticaria (hives), hypotension, or anaphylaxis. If a reaction is suspected, stop the infusion immediately and notify the provider.
• Laboratory Monitoring: Regularly check hematocrit, coagulation profiles, electrolytes, and serum albumin to ensure appropriate replacement.

Dosage Calculation Example

In clinical settings, nurses must often calculate infusion rates.

Problem: A nurse receives an order for $1000\text{ mL}$ of Normal Saline to be infused at $65\text{ mL/hr}$. The IV drip factor is $10\text{ gtts/mL}$. What is the drip rate in drops per minute (gtts/min)?

Solution: To find the drops per minute, use the following formula: $\text{gtts/min} = \frac{\text{Total Volume (mL)}}{\text{Time (min)}} \cdot \text{Drop Factor (gtts/mL)}$

First, convert the hourly rate to minutes: $\frac{65\text{ mL}}{60\text{ min}} \cdot 10\text{ gtts/mL}$

Calculate the result: $\begin{aligned} \frac{65}{60} &= 1.0833 \\ 1.0833 \cdot 10 &= 10.833 \end{aligned}$

Rounding to the nearest whole number, the nurse will titrate the IV to $11\text{ gtts/min}$.