English and Metric Conversion

Introduction

Imagine you are in your first job, working at an emergency clinic on a Sunday afternoon. Things have been a little quiet today, but that is about to change …

A client rushes into your clinic lobby with her 2-year-old Yorkshire Terrier. She came home about 15 minutes ago and the dog was eating a dark chocolate bar it got out of an open cabinet. She thinks it ate about half of the bar. She has the wrapper with her to show you. You weigh the dog and it is 12 pounds. These are the questions going through your mind:

• The wrapper says it was 8 ounces of 70% dark chocolate. Did the dog get a toxic dose? You know dark chocolate has about 150 mg/oz of theobromine and the toxic dose is 100 mg/kg.
• If it did get a toxic dose, you want to give it 0.04 mg/kg apomorphine as an intramuscular injection to induce vomiting. How much do you give? The ampule you have on the shelf is 10 mg/ml.

While you are waiting for the dog to vomit, your next case is a 14 year old cat that has been vomiting and has an elevated BUN and Creatinine. On physical examination, you determine the cat has bilaterally small kidneys and appears about 7% dehydrated. The cat weighs 7.5 pounds and is thin. This is what you ask yourself as you make a treatment plan for the cat:

• How much IV fluid will I need to give the cat (in addition to its maintenance needs) to do this?

These are the type of questions you will encounter every day in veterinary practice. Change the species, the toxin, or the medication and the same skills are needed across many disciplines. In order to answer them, you need to be comfortable with some basic mathematical conversions and units.

In this lesson, you will start with simple calculations of weight and volume.

Pounds to Kilograms

Remember the following weight conversions:

• 1 kilogram (kg) = 2.2 pounds (lb)
• 1 lb = 0.45 kg

Volume and Mass

Remember the following conversions:

• 1000 grams (g) = 1 kg
• 1 Liter (L) of fluid = 1000 milliliters (ml)
• 1 kg = 1 L of fluid, therefore 1000 g = 1000 ml → 1g = 1 ml of fluid

Calculating Fluid Deficits

(See Table 5 in the American Animal Hospital Association’s 2013 Fluid Therapy Guidelines for a sample dehydration assessment)

Fluid deficits are often expressed in % of body weight; the formula is as follows: Given Y% fluid deficit, (Y ÷ 100) x body weight (kg) = volume of fluid deficit (L).

Wrapping Up

In this lesson, you learned about the importance of accurately converting units of weight and practiced converting to metric. In the next lesson, you will learn and practice the skills needed to calculate drug doses and amounts.