Fluid Replacement in Adults: Guidelines, Formula

Instructor: Lindsay Townsend

Lindsay is a masters degree prepared Advanced Practice Registered Nurse currently expanding her career in nurse education.

In this lesson, you will learn about evaluating adult patients for fluid replacement, types of fluid replacement, fluid replacement guidelines, and formulas.

A Dehydrated Patient

Angie is a Registered Nurse in the Intensive Care Unit admitting a new patient. Mrs. Robbins is an elderly woman who has had nausea and vomiting for three days. She's being admitted for dehydration and electrolyte disturbances.

As Angie is admitting Mrs. Robbins, she questions her orders for fluid replacement. Her orders state to begin oral fluid replacement with a commercially available oral solution. Angie doesn't think this is correct for Mrs. Robbins because she is still complaining of severe nausea.

What would be the best plan for this patient's fluid replacement? Let's take a look at fluid replacement and figure it out!

A 1 liter bag of lactated ringers, a crystalloid used for fluid replacement
fluid bag

Indications for Fluid Replacement

Fluid replacement is the medical practice of restoring circulating volume that has been lost due to dehydration. Dehydration can occur from excessive sweating, vomiting, diarrhea, bleeding, and burns. You should also look for physical symptoms of decreased circulating volume, such as:

  • Tachycardia
  • Weak pulse
  • Increased respiratory rate
  • Pale, clammy skin
  • Dry mucous membranes (mouth, eyes)
  • Decreased skin turgor
  • Decreased urine output
  • Changes in mental status

You must have an accurate history of the patient, including the reason for the dehydration, and any comorbidities such as kidney and heart problems. Lab results, including a complete metabolic panel (CMP) and complete blood count (CBC), will also help guide therapy.

Methods of Fluid Replacement

Oral Fluid Replacement

Fluid replacement can be accomplished either with oral or intravenous solutions. Recent studies suggest that oral rehydration works just as well as intravenous hydration. Appropriate oral solutions should have a proper balance of sugars and electrolytes to replace what has been lost, as well as to promote water absorption in the gut. Clear liquids such as ginger ale, apple juice, and broth are not recommended for oral rehydration. They lack the proper electrolyte content, and can also cause water malabsorption and can worsen diarrhea.

There are contraindications to oral hydration, such as bowel obstructions, vomiting, inability to tolerate oral therapy, and altered mental status. In these instances, intravenous hydration is the correct choice.

Intravenous Fluid Replacement

An intravenous catheter being used to administer intravenous fluids
intravenous fluid

Intravenous fluid replacement is accomplished by placing an intravenous cannula into a vein in the body, commonly referred to as an IV. Then, intravenous fluid is administered through the IV. There are many different types of intravenous fluids, although the most common are crystalloid or colloid. Choosing one depends on your patient, the reason for their dehydration, and their medical history.

Crystalloids are balanced mineral solutions and work by increasing the circulating volume. Examples include 0.9% (normal) saline, lactated ringers, and dextrose solutions. Colloids are either synthetic (like Hetastarch) or naturally derived (albumin or red blood cells), and increase the osmotic pressure in the circulating volume, theoretically remaining in the circulation better than crystalloids.

General accepted practice states that fluid replacement should begin with crystalloid therapy unless known active hemorrhaging is occurring. In the case of active bleeding, fluid replacement should begin with O-negative packed red blood cells unless this therapy will be delayed.

Which Method is Best?

Now that we've looked at the methods of fluid replacement, let's check in on Mrs. Robbins. Because she is still nauseated, Angie knows that she won't be able to tolerate oral fluids and needs intravenous fluid replacement instead. Angie calls Mrs. Robbins' admitting provider and explains that Mrs. Robbins is still nauseated, and receives an order for intravenous fluid replacement and nausea medication.

Formula for Fluid Replacement

Once you have determined a patient needs intravenous fluid replacement, you should begin with a crystalloid bolus of 500 ml over 15 minutes. Then re-assess your patient for an improvement in their vital signs. Maintenance fluids should be prescribed at 25-30 milliliters per kilogram per day.

For example, Mrs. Robbins weighs 65 kilograms. After her initial bolus, you would calculate her maintenance as: 65 kg x 25 mL = 1,625 milliliters per day. Now, you need to divide this number by 24 to determine the milliliters per hour Mrs. Robbins should receive: 1,625 milliliters / 24 hours = 68 milliliters per hour.

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