In this review, let’s go over isotonic IV (intravenous) solutions.
Isotonic IV solutions have the same osmolarity as the blood, meaning they have the same concentration of solutes within the fluid being administered than the blood. With these fluids, there will be an equal transfer of water, so our cells will stay the same inside and out. Therefore, we can use these fluids to expand extracellular fluid volume, hence increasing our plasma.
Now, why would we want to expand extracellular fluid? If a patient is experiencing fluid loss in this space, such as through vomiting or diarrhea, they need some sodium and chloride back. They may also be experiencing hypovolemic shock, burns, or preparing for surgery, where we know they will be losing a lot of blood and extracellular fluid.
Some fluids that are considered isotonic include normal saline, lactated Ringer’s solution (also called LR), and *5% dextrose in water (D5W). There is an asterisk by D5W, which I will explain shortly. Although it is isotonic initially, it acts as a hypotonic solution once administered.
Here are some key points to remember about isotonic solutions:
Normal saline replaces water, sodium, and chloride, and it is the only solution we use to administer with blood. No other solutions should be used with blood products. With this type of solution, you must watch out for fluid overload, especially in patients with kidney and heart failure. Their heart and kidneys may not be functioning optimally, and administering too much fluid can overwhelm them, potentially leading to complications.
It is essential to monitor the patient’s blood pressure to ensure they are not hypertensive. Additionally, you should check their breathing and lung sounds to ensure there are no crackles, which could indicate pulmonary edema due to fluid buildup in the lungs. Pay attention to their extremities, particularly the lower limbs, to check for any edema. Because we are administering sodium and chloride, you also need to monitor sodium and chloride levels, ensuring they do not increase excessively, as too much fluid could cause elevated levels.
Next is 5% dextrose in water (D5W). This solution replaces water and glucose. As I pointed out earlier, it starts out as isotonic but ends up as a hypotonic solution. Why is this?
In this solution, dextrose will be metabolized by the body. What remains is not very concentrated and is essentially free water, leading to low osmolarity and making it hypotonic. Therefore, due to the components of this fluid, it is not suitable for fluid resuscitation situations and can actually cause an increase in blood glucose, leading to hyperglycemia.
However, it can help with hypernatremia, where there is too much sodium in the blood. Because it becomes hypotonic, it can help dilute the blood, thereby decreasing sodium levels.
Lastly, with lactated Ringer’s solution (LR), this fluid contains water, potassium, sodium chloride, calcium, and lactate. Lactate can help increase the blood’s pH by converting to bicarbonate, which is beneficial in cases of metabolic acidosis.
However, it is not suitable for patients with liver disease because the liver converts lactate to bicarbonate, nor is it appropriate for patients experiencing lactic acidosis, as there is already a high amount of lactic acid in the body.
Because this fluid contains potassium, you should monitor for hyperkalemia, or high potassium levels in the blood, especially if your patient has renal insufficiency.
You may be interested in IV Fluid Types and IV Fluid Quiz.
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References:
Dengue Clinical Case Management E-learning. (2023). Crystalloid IV Solutions: Intravenous Fluids. Retrieved from https://www.cdc.gov/dengue/training/cme/ccm/page70749.html.
Merriam-Webster. (n.d.). Osmolarity. In Merriam-Webster.com dictionary. Retrieved March 08, 2023, from https://www.merriam-webster.com/dictionary/osmolarity
NCI Dictionary: Osmotic. National Cancer Institute. (n.d.). Retrieved March 8, 2023, from https://www.cancer.gov/publications/dictionaries/cancer-terms/def/osmotic