CRYSTALLOID SOLUTIONS: COMPOSITION, TYPES AND EXAMPLES - CHEMISTRY - 2025

The crystalloid solutions are those formed by dissolving an electrolyte and other small molecules soluble in water, used in routine clinical procedures as adjusting the liquid volume of the circulatory system. In simple chemical terms: these solutions are nothing more than dilute, aqueous solutions of mineral salts.

Crystalloid solutions play an important role in clinical therapies as intravenous fluids for bleeding, dehydration, hypovolemia, and infections. Usually, its salt concentration is isotonic, which means that the number of its dissolved ions is comparable to that of blood plasma.

A crystalloid solution can be prepared simply by dissolving salt and other solutes in water at a moderate concentration. Source: Rillke / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

Crystalloid solutions therefore do not cause osmotic alterations, but rather provide an adequate volume of fluid so that the blood continues to be irrigated through the circulatory system. In this way, the heart is able to pump the diluted blood and can supply the oxygen to the tissues.

An example of a crystalloid solution is normal saline, which contains NaCl at a concentration of 0.9%. However, depending on the clinical case, other solutions can be chosen, with different components, concentrations and types of tonicity.

Composition of crystalloid solutions

All crystalloid solutions are sterile water-based or microorganism-free, so this is your solvent of choice. Otherwise, they could not be healthily integrated into our body and it would cause any type of undesirable reaction. As a solution or solution, it also has solutes, which are essentially mineral salts or strong electrolytes.

The salts can be various, as long as they provide Na ⁺, Ca ²⁺, K ⁺ and Cl ^- ions in moderate concentrations. In addition to inorganic salts, they can also have highly water-soluble organic solutes such as acetates, gluconates, and lactates. Also, some of these solutions contain glucose (dextrose).

The concentrations of these salts or solutes are very varied, and are expressed either in percentages, milligrams per deciliters (mg / dL), molarities or osmolarities. The choice of one or the other will depend on clinical criteria.

Types

It was said at the beginning that crystalloid solutions are frequently used to add volume of fluid to the circulatory system. In the process, depending on its tonicity, the blood plasma undergoes or not osmotic changes, which promote or favor certain desired states in the patient.

Thus, the only thing that distinguishes one crystalloid solution from another is not the chemical nature of its solute, but its tonicity; that is, if it is a hypertonic, isotonic or hypotonic solution.

Hypertonic

A hypertonic crystalloid solution is one whose saline concentration is higher than that found in blood plasma. Therefore, the water migrates from inside the cells to the plasma, which has increased its tonicity by the presence of the hypertonic crystalloid solution. An example of this type of solution is 3% NaCl, which is significantly more concentrated than 0.9% normal saline.

These solutions are contraindicated for most clinical cases, except for those with neurological sequelae.

Isotonic

An isotonic crystalloid solution is one whose saline concentration is comparable or identical to that of blood plasma and that of the cell interior. Therefore, there is no water exchange between the two media. An example of this type of solution is 0.9% NaCl, already mentioned above.

Hypotonic

And finally, a hypotonic crystalloid solution is one whose saline concentration is lower than that of the blood plasma and that of the compartment or intracellular space. This time the water moves into the cell until it reaches equilibrium. An example of this type of solution is NaCl 0.45%.

As with hypertonic crystalloid solutions, hypotonic ones are contraindicated for most clinical cases, especially those where there is a risk of cerebral edema.

Examples of crystalloid solutions

Some examples of crystalloid solutions will be mentioned and described below. The difference between one and the other will lie in the identity of their electrolytes or dissolved salts.

Normal saline solution

The normal saline solution has a composition of 0.9% NaCl, it is isotonic and it is also the most recurrent crystalloid solution, since it is used to treat countless common cases of dehydration; such as those caused by diarrhea, shock, vomiting, bleeding, among others. However, its use is avoided in patients with kidney or heart problems.

Lactate solution

Also known as Ringer's or Hartmann's solution (although these differ slightly in their ionic concentrations), it is one that is composed of a mixture of sodium chloride, sodium lactate, calcium chloride, and potassium chloride.

Its saline composition is the one that most closely resembles that of blood plasma, so it is of the isotonic type. It is used as a liquid or adjusting fluid for cases of burns, trauma, electrolyte imbalance, metabolic acidosis. However, it is contraindicated for patients suffering from hypercalcemia.

Lactate is metabolized in our body and ends up transforming into bicarbonate. This solution can also contain the gluconate anion, as well as certain amounts of magnesium, Mg ²⁺.

Glucose solution

Also known as a crystalloid dextrose solution, it comes in two strengths: 5 and 10% (D5 or D10, respectively). This is initially hypotonic, but it becomes isotonic once the glucose is absorbed, providing water to the kidneys. Although it provides a significant amount of calories, it is contraindicated for patients suffering from hyperglycemia.

Unlike the other crystalloid solutions, these are sweet. The sweetest ones have concentrations above 10% (D20, D30, D50, etc.), and are intended for patients with pulmonary and cerebral edema. On the other hand, they reduce protein catabolism, protect the liver, and help combat circulatory collapse.

Hypertonic and hypotonic saline solutions

Hypertonic saline solutions (3 and 5% NaCl) are used to deliver fluid to burn patients, induce hyperosmolarity, and relieve kidney failure. On the other hand, hypotonic saline solutions (0.45% NaCl or lower concentrations) control hypernatremia, and are contraindicated for patients with burns.

Therefore, one has the opposite effects to the other; when the hypertonic solution is indispensable, the hypotonic is disapproved, and vice versa.

The mechanism behind all crystalloid solutions are based on the osmotic and water balance between intra and extracellular fluids.

References

1. Lewis SR et al. (August 3, 2018). Colloids or crystalloids for fluid replacement in critically people. The Cochrane Collaboration. Recovered from: cochrane.org
2. Epstein EM, Waseem M. (November 29, 2019). Crystalloid Fluids. In: StatPearls. Treasure Island (FL): StatPearls Publishing 2020 -. Recovered from: ncbi.nlm.nih.gov
3. Wikipedia. (2020). Volume expander. Recovered from: en.wikipedia.org
4. Elsevier BV (2020). Crystalloid. ScienceDirect. Recovered from: sciencedirect.com
5. Sheila Bouie. (2020). Crystalloids: Definition & Examples. Study. Recovered from: study.com