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Fluid Resuscitation
Lindee Abe, APRN
Fluid resuscitation has been a staple of emergency medicine treatment for decades. Research has shown that more fluids does not always equal better outcomes for most patients. As practice has shifted over the years to favor using less fluids, it has become even more important for clinicians to select the right fluid for the right patient. Most practitioners have their own “fluid of choice” based on their routine practice. How often do we individualize the type of fluid selection for our patients? Likewise, Are we giving the right fluid? We should be approaching fluid selection similar to how we approach antihypertensive medication selection for each patient. Therefore, we should individualize the patient’s treatment plan based on their condition, comorbidities, and interactions with other medications.
Body Composition
The first thing to understand about fluid resuscitation is the pathophysiology of the fluid make-up of the body. Extracellular fluid composes one-third of our body and intracellular fluid is two-thirds. Of that extracellular fluid, approximately 80% is in the interstitial space and 20% in the plasma. The osmolality of plasma is 275 to 295 mOsm/kg. When comparing the different types of fluids, we reference this baseline.
There are two main groups of fluids: colloids and crystalloids. We use Crystalloids most frequently. Each also has their place in treating patients. The main difference between the two is that colloids contain proteins and polysaccharides and crystalloids contain electrolytes. Also, colloid fluids are more expensive and not as readily available as crystalloids.
Colloids
These fluids also contain insoluble particles and have a high osmotic pressure that prevents the passage of fluid from the vascular space to the interstitial space. There are also two subcategories for colloids: synthetic and nonsynthetic. Synthetic colloids include gelatins, dextrans and also starches. Albumin is the predominant nonsynthetic colloid. It is also the most commonly used colloid fluid. Albumin 5% has an osmolarity of 310 mOsmol/L and albumin 25% has an osmolarity of 312 mOsmol/L. It is usually given along with with crystalloid fluids. Therefore, Albumin is not considered a first line therapy for most conditions. It is also considered a blood product and shares the same associated risks. Blood products are also considered colloids.
Crystalloids
Crystalloids are further classified into three different categories based on osmolarity. These categories include isotonic, hypotonic, and hypertonic osmolarities. Isotonic fluids are the most commonly used. They also simulate the natural osmolality found in our extracellular fluid. Isotonic solutions are further classified as balanced vs. unbalanced solutions. The electrolyte composition of the fluid defines it balance state.
Isotonic Fluids
Normal Saline
Isotonic fluids will have an average osmolarity of 275 mOsm/L to 310 mOsm/L. The most frequently used of this group is generally Normal Saline (0.9% Normal Saline). Normal Saline has a pH of 5.5 and osmolarity of 308 mOsm/L. The sodium concentration is 154 mEq/L and chloride is 154 mEq/L. Likewise, this makes Normal Saline an unbalanced solution based on the electrolyte make-up. Due to the high chloride content, Normal Saline can lead to a metabolic acidosis and decreased renal clearance. However, the effect on the GFR is more common with large quantities of Normal Saline.
Lactated Ringer’s
This solution is a balanced solution. Lactated Ringer’s (LR) has a pH of 6.6 and osmolarity of 275 mOsmol/L. It contains 130 mEq/L of sodium, 109 mEq/L of chloride, potassium of 4 mEq/L, 3 mEq of calcium, and also 28 mEq/L of lactate. Lactate is added to this solution and it is then metabolized in bicarbonate. This makes LR beneficial in acidosis. Lactated Ringer’s also does not last as long in the body as normal saline, which could be an advantage in those patients where fluid overload is a concern. Lactated Ringer’s is also usually the solution of choice in the OR.
Plasmalyte
Plasmalyte is also a balanced isotonic solution. It is less commonly used than LR due to its limited availability and price. It costs twice as much as Lactated Ringer’s. Plasmalyte has a pH of 5.5 and osmolarity of 294 mOsmol/L. It contains 140 mEq/L of sodium, 98 mEq/L of chloride, 5 mEq/L of potassium, 3 mEq/L of magnesium, 27 mEq/L of acetate, and also 23 mEq/L of gluconate. Plasmalyte is safe to give with blood products. This is one of its advantages. LR should be avoided when blood products are also being given.
Hypertonic Fluids
3% Normal Saline
The primary hypertonic solution is 3% Normal Saline. 3% Normal Saline has a pH of 5.0 and osmolarity of 1027 mOsmol/L. It also contains 513 mEq/L of sodium and 513 mEq/L of chloride. Hypertonic solutions are often given to patients who have cerebral edema. Further, if your goal is to shift intracellular fluid into the extracellular space, hypertonic fluids are a good choice. Hypertonic saline can have similar outcomes to mannitol when reducing intracranial pressure.
Hypotonic Fluids
1/2 Normal Saline
The primary hypotonic solution used is ½ Normal Saline, or 0.45% Normal Saline. 0.45% Normal Saline has a pH of 5.6 and osmolarity of 154 mOsmol/L. It contains 77 mEq/L of sodium, 77 mEq/mL of chloride. If your goal is to shift extracellular fluid into the Intracellular space, hypertonic fluids are a good choice. In fact, it has the opposite effect as hypertonic solutions. Likewise, avoid these fluids in patients with increased intracranial pressure.
Dextrose Solutions
There is also one additional group that contains both isotonic and hypotonic solutions: dextrose solutions. Dextrose solutions can contain both 5% and 10% dextrose solution. These solutions are different from the others. The fluid osmolality decreases as dextrose is metabolized. Below is a table to provide a quick reference and comparison of the different types of solution.
Summary
Ordering IV fluids should be based on a clear treatment goal. You should also consider any contraindications to the fluids you are giving. Remember that some of these fluids also interfere with other parenteral medications.
References:
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https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018090sS116lbl.pdf.
Mason A, Malik A, Ginglen JG. Hypertonic Fluids. [Updated 2021 Sep 6]. In: StatPearls
[Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK542194/
Najem O, Shah MM, De Jesus O. Serum Osmolality. [Updated 2022 Jan 24]. In: StatPearls
[Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:
https://www.ncbi.nlm.nih.gov/books/NBK567764/.
Nall, R. (2020 Jan 9). Ringer’s Lactate Solution: What It Is and How It’s Used. Retrieved from
https://www.healthline.com/health/lactated-ringers#vs-saline.
RxList. (2021 Mar 02). Hypertonic Saline. Retrieved from https://www.rxlist.com/hypertonicsaline-drug.htm#description.
Stanford Health Care. (2017 Mar). Guidelines for Intravenous Albumin Administration at
Stanford Health Care. Retrieved from https://stanfordhealthcare.org/content/dam/SHC/healthcare-professionals/medical-staff/medstaff-weekly/20170315-guidelines-for-intravenous-albuminadministration.pdf.
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