The Metric System

A primary function of government since the very beginning of governments is to derive a set of weights and measurements to facilitate the progress of commerce.  The differences between a shekel and a lira have been the center of controversy and even war for thousands of years.  In the 18th century, French scientists seeking to devise a logical system of weights and measures (as opposed to measurements derived from the length of a persons arm, for example) came up with the metric system.  Over 200 years, the metric system has pretty much made its way around the globe.  According to the United States Metric Association, there are only 3 countries in the world that do no use the metric system (which are the United States, Burma, and Liberia).  In the United States, the U.S. Department of Commerce, National Institute of Standards & Technology governs weights and measures.   Since people get sick everywhere, the weights and measures of the medical community is the metric system.  The metric system has a system of measuring everything (except time) and is based on the ‘Base 10’ concept:

The Metric System Making Things Smaller

1 gram = 10 decigrams = 100 centigrams = 1000 milligrams
1 liter = 10 deciliters = 100 centiliters = 1000 milliliters

The Metric System Making Things Bigger

10 grams  = 10 decagrams
10 liters = 10 decagrams

The following are prefixes.  Like a telephone number, you put the prefix in front of the unit of measurement

Since medications are generally given by weight or by volume, we use the metric system equivalents for weight and volume.  The metric system has an answer for everything, including temperature, time, distance, mass, and volume. For the sake of this lecture, we are only going to discuss mass and volume.

Weight  =  Grams (English use Grammes)
Volume = Liters (English use Litres)

Volume gets confusing for some because we often use 1 liter or 1000 cc’s or ml’s.  Volume is defined as the amount of space that something takes up. We should all be familiar with the liter, which is the unit for measuring volume. Most soft drinks are sold in 2 liter bottles. On the ambulance we might give a patient a 200 ml bolus of normal saline or give 1000 ml of normal saline. We might give 4 ml of a particular medication in order to give 40 mg.

cc = cubic centimeter or the volume of water in one cm2
ml = 1:1000 of a liter (we made the liter smaller by putting milli- in front of it)

1 cc = 1 ml (yes, they are the same and are used interchangeably)

1000 cc’s = 1 liter = 1000 ml’s

At this point, you know that the metric system is organized by 10’s. Being an American, you are probably saying that why doesn’t the rest of the world just learn to play by our rules? Well, the metric system is so well organized that it is hard not to fall in love with it. In order to convert grams to kilograms, all you need to do is multiply the number x 1000. You see, a kilo means 1000. So a kilogram means you have 1000 grams. How easy was that? Can you convert pounds to ounces so easily? Given the simplicity, the scientific and medical communities have adopted this system as their primary source of measurement. Now lets look at the most common metric measurements.

Mass is defined as anything that has weight and takes up space. The metric system measures mass in grams

Looks easy enough. The most common problem is when you try to convert mass from the English system of measurement (pounds, ounces, etc.). There are 2.2 poinds in every kg. Therefore if somebody weighed 220 pounds, then he or she would weigh 100 kg.

A microgram is one-millionth of a gram. You can give any medication measured in grams as a microgram. Commonly carried is dopamine, dobutamine, and sometimes epinephrine is given as a drip.   Micrograms often use the following abbreviation: µg,

Which is bigger, a cc or a ml?

What is difference between a cubic center (cc) and a milliliter (ml)? Absolutely nothing. In fact the term cc’s and ml’s are almost completely interchangeable. As you know, a ml is one thousandth of a liter. A cubic centimeter is the amount of volume in a theoretical cube, each edge being 1 cm in length. The volume of a cc is 1 ml.