Today, methods of infusion have changed dramatically, and small-volume parenteral fluids may be administered as a secondary infusate or in a volume-controlled reservoir for electronic drug delivery.

An infusion is usually regarded as an amount of fluid > 100 mL designated to be infused parenterally because the volume must be administered over a long period. However, when medications are administered as a piggyback (secondary to and delivered with the initial infusion) small-volume (50 to 100 mL) parenteral infusion, a shorter period (usually 30 to 60 minutes) may be required, whereas volumes of 150 to 200 mL may require > 1 hour. Today, methodologies have changed to be consistent with the clinical needs of patients, and alternate delivery systems are readily available.

IV fluids are mistakenly referred to as IV solutions. The term solution is defined in the United States Pharmacopeia (USP) as a liquid preparation that contains one or more soluble chemical substances usually dissolved in water. Solutions are distinguished from injections, for example, because they are not intended for administration by infusion or injection. Moreover, methods of preparation may vary widely. The USP refers to parenteral fluids as injections, and methods of preparation must follow standards for injection. IV injections must meet the tests, standards, and all specifications of the USP applicable to injections. This includes quantitative and qualitative assays of infusions, including tests for pyrogens and sterility (McEvoy, 2007).

Each fluid container must be carefully examined to detect cracks. The fluid must be examined for cloudiness or particles. The final responsibility falls on the pharmacist and the nurse who administers the fluid. Tests to detect particulate matter, and standards for an acceptable limit of particles, have been established by the USP. A large-volume injection for singledose infusion meets the requirements of the test if it contains not more than 50 particles per milliliter that are ≥ 10.0 µm and not more than 5 particles per milliliter that are ≥ 25.0 m in effective linear dimension.

The pH indicates hydrogen ion concentration or free acid activity in solution. All IV fluids must meet the pH requirements set forth by the USP. Most of these requirements call for a fluid that is slightly acid, usually ranging in pH from 3.5 to 6.2. Dextrose requires a slightly acid pH to yield a stable fluid. Heat sterilization, used for all commercial fluids, contributes to the acidity. It is important to know the pH of the commonly used IV fluids because it
may affect the stability of an added drug and cause the drug to deteriorate. The acidity of dextrose fluids has been criticized for its corrosive effect on veins.

The cell wall separates the intracellular compartment from the extracellular compartment. The capillary endothelium and the arterial and venous walls divide the extracellular compartment into the intravascular and interstitial compartments. Water flows freely through cell and vessel calls and is distributed throughout these compartments. (Grocott, Mythen, & Gan, 2005).

Osmosis is the process by which a solvent, usually water, moves through a semipermeable membrane from a solution of lower concentration to a solution of higher concentration. The osmotic pressure exerted by particles in solution is determined by the number of particles per volume of fluid versus the mass or size of the particles (Phillips, 2005).

Capillary pressure has a tendency to force fluid and dissolved substances through the capillary pore into the interstitial spaces.

A change in water content causes cells to swell or shrink. Tonicity refers to the tension or effect that the osmotic pressure of a solution, with impermeable solutes, exerts on cell size due to water movement across the cell membrane.

Solutions are classified according to the tonicity of the fluid in relation to normal blood plasma. The osmolality of blood plasma is 290 mOsm/L. Fluid that approximates 290 mOsm/L is considered isotonic. IV fluids with an osmolality significantly > 290 mOsm (+50 mOsm) are considered hypertonic, whereas those with an osmolality significantly < 290 mOsm (−50 mOsm) are hypotonic.

Parenteral fluids usually range from approximately one-half isotonic (0.45% sodium chloride) to 5 to 10 times isotonic (25% to 50% dextrose). The tonicity of the fluid infused into the circulation affects fluid and electrolyte metabolism and may result in disastrous clinical disturbances (see Table 9-1 for more information on the effects of isotonic, hypertonic, and hypotonic fluids).

Knowing the osmolality of the infusion and the physical effect it produces alerts the nurse to potential fluid and electrolyte imbalances. The choice of veins used for an infusion is affected by the tonicity of the fluid; hyperosmolar fluids, for example, must be infused
through veins that carry a large blood volume to dilute the fluid and prevent trauma to the vessel.

The tonicity of the fluid also affects the rate at which it can be infused. Hypertonic dextrose infused rapidly may result in diuresis and dehydration.

Because of the direct and effective role osmolality plays in IV therapy, the nurse involved in administering IV fluids needs to be familiar with various terms and calculations. For instance, the osmotic pressure is proportional to the total number of particles in the fluid. The milliosmole (mOsm) is the unit that measures the particles or the osmotic pressure. By converting milliequivalents to milliosmoles, an approximate osmolality may be determined.

A significant number of solutions are available premixed. Premixed solutions have been sterilized following the admixture process, ensuring longer shelf life. The pH has already been adjusted to enhance stability, and the correct amount of medication has been added to the proper volume and type of solution.

Care should be taken in selecting premixed solutions when multiple types are available. For example, premixed solutions with potassium chloride are available in several concentrations. Other premixed solutions include heparin sodium, theophylline, lidocaine hydrochloride, and dopamine hydrochloride. Antibiotics are often premixed in small-volume parenterals. In addition to premixed solutions, some products allow the medication container to be connected to the IV solution. In general, premixed solutions tend to increase cost.

Sodium chloride injection (0.9%), USP (normal saline), contains 308 mOsm/L (sodium, 154 mEq/L; chloride, 154 mEq/L). It has a pH between 4.5 and 7.0 and is usually supplied in volumes of 1,000, 500, 250, and 100 mL. The term normal (or physiologic) is misleading because the chloride in normal saline is 154 mEq/L, compared with the normal plasma chloride value of 103 mEq/L, whereas the sodium is 154 mEq/L, or approximately 9% higher than the normal plasma value of 140 mEq/L. Because normal saline lacks the other electrolytes present in plasma, the isotonicity of the fluid depends on the sodium and chloride ions, resulting in a higher concentration of these ions (USP, 2012).

Dextrose 5% in 0.9% sodium chloride (normal or isotonic saline solution), which contains 252 mOsm dextrose (chloride, 154 mEq/L; sodium, 154 mEq/L), has a pH of 3.5 to 6.0 and is available in volumes of 1,000, 500, 250, and 150 mL. When normal saline is infused, the addition of 100 g dextrose prevents both the formation of ketone bodies and the increased demand for water the ketone bodies impose for renal excretion. The dextrose prevents catabolism and, consequently, loss of potassium and intracellular water.

Dextrose 10% in 0.9% sodium chloride contains 504 mOsm/L dextrose (sodium, 154 mEq/L; chloride, 154 mEq/L), has a pH of 3.5 to 6.0, and is usually supplied in volumes of 1,000 and 500 mL.

These infusions include 3% sodium chloride (sodium, 513 mEq/L; chloride, 513 mEq/L) and 5% sodium chloride (sodium, 850 mEq/L; chloride, 850 mEq/L).