VETgirl December 2024 BEAT e-Magazine

QUARTERLY BEAT / DECEMBER 2024

AAHA Recommended Daily Maintenance Fluid Rate Non-Linear Formulas Dog: 132 x BW kg 0.75 = mL/day Cat: 80 x BW kg 0.75 = mL/day

HOW TO CALCULATE FLUID RATES

Figure 1. Courtesy of Danelia de Kock.

CALCULATOR TIP If you have a scientific calculator, use the exponent function “x^y“ for solving a number raised to the power of 0.75; to access this function using your smartphone’s calculator, turn your phone sideways when you are in the calculator app. When using a calculator that does not have an exponent function, raising a number to the power of 0.75 is the same as raising the number to the power of 3 and then taking the square root twice. For example, 10^0.75 = 10 x 10 x 10, then take the square root, and take the square root again. The daily maintenance fluid rate in mL/day can be converted into the hourly maintenance fluid rate in mL/hour by using the unit conversion factor 1 day = 24 hours (shortcut: mL/day divided by 24 = mL/hour). DEHYDRATION FLUID RATE This is the additional fluid rate necessary to rehydrate a patient within a certain period of time, usually over an 8 to 24 hour time period.

ONGOING LOSSES FLUID RATE This is the additional fluid rate necessary to account for abnormal losses occurring through conditions such as vomiting, diarrhea, polyuria, excessive panting, sweating, and blood loss. Ongoing losses need to be measured or estimated, which can sometimes prove challenging. Since a patient’s ongoing losses will change with the patient’s response to treatments, I recommend reassessing the patient’s ongoing losses every 4 to 6 hours and adjusting the fluid rate as indicated. Alternatively, you can estimate the patient’s anticipated total daily losses, divide by 24 hours, and add this to the patient’s hourly rate. When calculating ongoing losses, you can measure the weight of soiled bedding materials using the equivalents of 1 kg = 1 L or 1 g = 1 mL, but for fluids containing solids (i.e., diarrhea) this number would need to be adjusted further, perhaps by visual inspection, for an estimation of solids content. The ongoing losses fluid rate in mL/hour is calculated by dividing the estimated ongoing losses in mL by the time period (in hours) within which the ongoing losses are to be corrected. TOTAL FLUID RATE The maintenance, dehydration, and ongoing losses fluid rates are added together to obtain the total fluid rate for your patient.

DR. DANELIA DE KOCK

Vetpocket TM Co-Founder

Looking for a refresher on how to calculate your patient’s fluid rates? Look no further! In this VETgirl article, Dr. Danelia de Kock , BS Math reviews maintenance rates, patient dehydration, and ongoing losses rates for dogs and cats, to help you put together the puzzle pieces and formulate an IV fluid therapy tailored to your patient’s needs!

In veterinary medicine, appropriately managing a patient's intravenous (IV) fluid therapy is crucial for helping ensure their recovery and overall well-being. Not only is it important to use the appropriate fluid rate for a patient, but also to use the appropriate fluid type. In veterinary medicine, we often use balanced isotonic crystalloids as our “maintenance fluids”, but this is a misnomer, as TRUE maintenance fluids are hypotonic in nature. Regardless of what type of fluid is used (e.g., maintenance versus replacement; isotonic, hypotonic, or hypertonic; crystalloid versus colloid), the clinician must be able to appropriately calculate fluid rates. It is important to remember to always tailor IV fluid therapy to the individual patient’s needs, that fluid therapy guidelines are ever evolving, that fluids are drugs and therefore come with risks, and to avoid adverse effects such as electrolyte derangements or fluid overload. Fluid rate formulas are based on fluid estimates needed to maintain normal patient fluid balance. Therefore, these formulas provide estimates, which are meant to be used as starting points and as guidelines only, and then adjusted as indicated for each individual patient’s needs. A patient’s fluid rate needs to be carefully calculated, and the patient regularly monitored to ensure an appropriate volume of fluids is being administered - do not administer too little or too much, as both can result in deleterious outcomes.

these types of discussions with the patient’s owner, allowing all parties involved to be on the same page concerning any potential risks of IV fluid therapy. Note: In order to solve some of the below formulas, the patient’s body weight needs to be in kilograms (kg). Body weight can be converted from pounds (lb) to kg by using the unit conversion factor 1 kg = 2.2 lb (shortcut: lb divided by 2.2 = kg). MAINTENANCE FLUID RATE This is the fluid rate necessary to maintain the daily metabolic needs of a normal patient, including losses such as through normal urine output and through moisture content of feces. Note that several different maintenance fluid rate formulas exist, and that there isn’t a definitive consensus on which formula to use. Non-linear formulas (such as Figure 1.) are generally considered to be more accurate than linear formulas (e.g., 50-60 mL/kg/day), as linear formulas may underestimate or overestimate fluid needs for patients outside a certain weight range. An additional, important note is that part of the maintenance fluid rate formula accounts for the average urine output of normal healthy patients which is ~1 to 2 mL/kg/hr or ~24 to 48 mL/kg/day. However, patients with renal disease can have variable urine output rates ranging from polyuria to anuria, so maintenance fluid rate formulas do not apply to patients with renal dysfunction. In these patients, tailoring IV fluid therapy to the individual patient's needs is especially important.

Dehydration Fluid Rate Formula BW kg x % dehydration = L of fluid deficit

Total Fluid Rate Formula Maintenance Fluid Rate + Dehydration Fluid Rate + Ongoing Losses Fluid Rate

Figure 2. Courtesy of Danelia de Kock.

Recall that x% = x/100, for example 5% = 5/100 = 0.05.

The fluid deficit can be converted into mL by using the unit conversion factor 1 L = 1,000 mL (shortcut: L multiplied by 1,000 = mL). The dehydration fluid rate in mL/hour is calculated by dividing the fluid deficit in mL by the time period (in hours) to correct the fluid deficit.

Note: Once a patient is rehydrated and/or the ongoing losses are under control, it is important to adjust (lower) your fluid rate. Figure 3. Courtesy of Danelia de Kock

BLOG HIGHLIGHTS

Patients with comorbidities such as cardiac or renal disease, and cats, are at an increased risk for fluid overload. Always have

VETGIRL BEAT EMAGAZINE | VETGIRLONTHERUN.COM

Made with FlippingBook - Online Brochure Maker