What is the method for calculating fluid replacement in patients with dehydration?

From the Guidelines

To calculate fluid replacement, first determine the patient's maintenance fluid needs using the 4-2-1 rule: 4 mL/kg/hr for the first 10 kg of body weight, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr for each additional kg, as recommended by the 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea 1. The 4-2-1 rule is a widely accepted method for calculating maintenance fluid needs, and it is essential to consider the patient's weight and age when determining the appropriate fluid replacement.

• For example, a 70 kg adult would need 40 mL/hr (first 10 kg) + 20 mL/hr (next 10 kg) + 50 mL/hr (remaining 50 kg) = 110 mL/hr or approximately 2,640 mL/day.
• Then, assess for any existing fluid deficits by evaluating clinical signs of dehydration, weight loss, or laboratory values, as outlined in the 2017 guidelines 1.
• Calculate ongoing losses from sources like vomiting, diarrhea, fever (add approximately 10-15% to maintenance for each degree Celsius above normal), or excessive sweating.
• The total fluid replacement equals maintenance needs plus deficit replacement plus ongoing losses, and it is crucial to distribute correction over 24-48 hours to avoid rapid fluid shifts, as recommended by the guidelines 1.
• Isotonic solutions like 0.9% normal saline or lactated Ringer's are typically used for initial rehydration, while maintenance fluids often contain some dextrose and lower sodium concentration.
• Monitor the patient's response through vital signs, urine output (goal >0.5 mL/kg/hr), electrolyte levels, and clinical improvement to adjust the plan as needed, as emphasized in the guidelines 1. It is also important to note that the 2017 guidelines recommend the use of reduced osmolarity oral rehydration solution (ORS) as the first-line therapy for mild to moderate dehydration in infants, children, and adults with acute diarrhea from any cause 1.
• The guidelines also provide recommendations for the administration of ORS, including the use of nasogastric administration in infants, children, and adults with moderate dehydration who cannot tolerate oral intake 1.
• In severe dehydration, intravenous rehydration should be continued until pulse, perfusion, and mental status normalize, and the remaining deficit can be replaced by using ORS 1.
• Once the patient is rehydrated, maintenance fluids should be administered, and ongoing losses in stools should be replaced with ORS until diarrhea and vomiting are resolved 1.

From the FDA Drug Label

Plasbumin-25 is hyperoncotic and on intravenous infusion will expand the plasma volume by an additional amount, three to four times the volume actually administered, by withdrawing fluid from the interstitial spaces, provided the patient is normally hydrated interstitially or there is interstitial edema. If the patient is dehydrated, additional crystalloids must be given, or alternatively, Albumin (Human) 5%, USP (Plasbumin®-5) should be used.

The calculation of fluid replacement is not directly provided in the drug label. However, it is mentioned that Plasbumin-25 will expand the plasma volume by three to four times the volume actually administered.

• To calculate the required fluid replacement, the patient's hydration status and interstitial fluid volume should be considered.
• If the patient is dehydrated, additional crystalloids must be given, or alternatively, Albumin (Human) 5% should be used 2.
• The total dose of albumin should not exceed the level of albumin found in the normal individual, i.e., about 2 g per kg body weight in the absence of active bleeding 2.

From the Research

Calculating Fluid Replacement

To calculate fluid replacement, it is essential to consider the type of infusion solution used. There are two main types:

• Crystalline fluids (such as NaCl 0.9% and lactated Ringer's solution)
• Colloidal fluids made of hydroxyethyl cellulose, albumin or gelatine 3

Factors to Consider

When choosing a fluid replacement solution, the following factors should be considered:

• The patient's condition (e.g., septic patients with hypoalbuminaemia may require albumin-based infusions) 3
• The risk of complications (e.g., anaphylaxis, renal insufficiency, and increased bleeding tendency associated with colloidal solutions) 3
• The composition of the solution (e.g., lactated Ringer's solution is closer to plasma than NaCl 0.9%) 3

Solution Composition

The composition of the solution can affect the outcome of fluid replacement therapy. For example:

• Lactated Ringer's solution does not cause hyperchloremic acidosis and may lead to less renal insufficiency than NaCl 0.9% 3
• Hydroxyethyl cellulose (HEC) is associated with higher mortality and renal impairment, making it a less justifiable choice 3