Barry Schoenborn is a longtime technical writer and is the coauthor of Technical Math For Dummies.

Barry Schoenborn is a longtime technical writer and is the coauthor of Technical Math For Dummies.

Medical Dosage Calculations For Dummies

John Wiley & Sons

Chapter One

In This Chapter

* Looking at the basics of medical math and dosage calculations

* Taking a look at healthcare careers and the need for math

* Remembering the importance of compassion, empathy, and other important skills

If you're a healthcare professional (or planning to be one), you're in one of the most important careers around today. In essence, you help healthy people stay healthy, you help sick people get well, and you help people with critical health conditions live.

Of course, nursing and all health professions involve more than just calculating and administering medications. They're vocations for comforting the sick and injured — clearly they involve much more than just "pushing meds."

However, being a successful healthcare provider means being an able mathematician. After all, the field of medicine relies extensively on administering medications, and you must be able to calculate meds correctly before you dispense them.

In any healthcare education program, medical dosage calculations come up in practically every course (or they should). In addition, most schools of nursing have one course devoted entirely to medical dosage calculations.

In this chapter, we introduce you to the math you need to know to perform basic and complex medical dosage calculations. We also provide an overview of the different careers available in the healthcare field (and show you how they all utilize medical math). Finally, we go beyond math and focus on the other essential components of being a good healthcare provider.

DID YOU KNOW?

Florence Nightingale had a great gift for mathematics. She was a pioneer in presenting information visually — especially health statistics. She has been recognized for developing a form of the pie chart now known as the polar area diagram.

Knowing What Math You Need to Know in Healthcare

In healthcare, you need to know the following three kinds of dosing math:

• School math: The math you learn in order to pass tests while getting an education
  • NCLEX (National Council Licensure Examination) math: The math you learn to get your license
    • Real-world math: The math you use to handle your job

      It's true; you'll sometimes find questions on tests in school or in practicing for the NCLEX that may never come up in real life, but you still need to be prepared for those questions. Similarly, real life will surely present you with math problems that you never practiced in school. In this section, we cover the math concepts and calculation methods you need to know to be prepared for just about any scenario in healthcare.

      REMEMBER

      Never despair about medical dosage calculations. Each principle in this book is easy if you look at it the right way. Medical dosing math isn't harder than you think; it's actually easier!

      Nailing down basic arithmetic

      Nursing and related professions require basic math skills, but don't worry if math hasn't always been your favorite subject in school. The best part about medical math is that it's easy to identify just how much math you need to know.

      Basic math is essentially just arithmetic — addition, subtraction, multiplication, and division. And you mostly use multiplication and division in your dosage calculations. But don't forget that counting is math, too. For example, when you count out 4 tablets, you're doing addition (1 + 1 + 1 + 1 = 4).

      In case you missed some of what you need to know math-wise in school, we cover the most important principles in Chapters 2 through 4.

      Fiddling with fractions in four forms

      Medical dosage calculations use fractions 90 percent of the time (or 9/10 of the time or in a 9:1 ratio). In case you're wondering, all those phrases mean the same thing.

      The four forms a fraction can take are

      • Common fraction (also called a vulgar fraction):

        100 units/50 mL

        • Decimal fraction: 0.56 mL
          • Percent fraction: 0.9% normal saline (NS)
            • Ratio: 1:9

              Of these four types, you use only two (common fractions and decimal fractions) to do most of the work in your dosage calculations.

              Conquering the calculation methods

              A word to the wise about the complex math used in this book: There isn't any. All the math used in medical dosage calculations is very simple. For example, one of the most common calculations you see in dosing problems is unit conversion. To convert units, you just have to know how to use some simple formulas, called conversion factors, like 1 kg (kilogram) = 2.2 lb (pounds). You use conversion factors mostly to convert mass (weight) and liquid volumes. Chapter 4 explains everything you need to know about units and conversion.

              As far as figuring out drug dosage and administration, you use the following three basic calculation methods: the formula method, the ratio-proportion method, and the dimensional analysis method. Chapter 8 walks you through each method and shows you when and how to use it.

              EXAMPLE

              The following problem is an example of some of the math you have to do when calculating medical dosages. It uses the ratio-proportion method (see Chapter 8 for more details).

              If 250 mg are in 5 mL and you need to give 333 mg, what's the dose in mL?

              To find out, follow these steps:

              1. Set up the following proportion:

              known equivalent/known equivalent = known equivalent/desired equivalent

              250 mg/5 mL = 333 mg/x mL

              2. Cross-multiply and solve.

              250x = 5 x 333 250x = 1,665 x = 6.66

              The answer is 6.66 mL. You'd give 6.7 mL to provide the needed 333 mg.

              TIP

              Calculations with multiple steps may look complex, but they aren't because the math involved in each step is fairly simple. For example, when you calculate a weight-dependent dosage that you must administer intravenously, your calculations typically follow this pattern:

              • Convert the patient's weight from lb (pounds) to kg (kilograms).
                • Determine the number of mg (milligrams) of the med to give for that body weight.
                  • Because the med is in a liquid suspension, calculate the mL that contain the number of mg you need to give.
                    • Because IV meds are often ordered to be dosed per min (minute) but are infused in mL/hr (milliliters per hour), calculate the flow rate by converting from mL/min (milliliters per minute) to mL/hr so you can program an electronic infusion pump.

                      Living in a metric world

                      Dosing medications — whether you're working in a hospital, clinic, rehab center, or home setting — is built on the metric system. Don't start panicking, yet. Because the metric system is based on a system of tens, it's easy to learn and to use.

                      For a long time, medicine used an older system (once called the English system) with units like lb (pounds) and fl oz (fluid ounces). Medicine also used the apothecaries' system with units such as the grain, dram, and scruple. The United States still commonly uses its household system, which includes units like fl oz (fluid ounces) and Tbsp (tablespoons), but it does so mostly in the kitchen, not the hospital.

                      Because the older systems haven't disappeared completely, be aware that you sometimes have to convert units from one system to units of another. (See Chapter 4 for tons more details on units and conversion.)

                      Tools of the Trade for Dosing Meds

                      This probably goes without saying, but accurate dosing is vital in the healthcare profession. It's a good thing the math isn't hard, because there's no room for error. After all, medicine relies primarily on medications to get healing done, so errors in dosage calculations can mean critical errors in patient health and safety.

                      Following are three tools of the trade that help you do medical dosing calculations accurately every time:

                      • Undivided attention: Anyone who works in healthcare knows how busy the day can get. When you're dealing with medications, especially when you're performing medical dosage calculations, your undivided attention is paramount to reducing the chance of any dosing error. Take the time to double-check your calculations. The most important mathematical tool you have is your mind.
                        • Calculator: When you're dealing with decimals, percentages, and complex calculations, you often need more than your fingers and a pen and paper. You need a calculator to do more complex calculations. Portable computer-based calculation programs like MedCalc also work well.
                          • Medication reference guides: It's impossible to keep straight all the medications and dosages out there. So you need to use the many excellent reference guides available in book form, smartphone apps, and on the Internet. Use them to research medication names, dosages, possible drug interactions, and clinical applications of the drugs.

                            Surveying Healthcare Careers (They All Use Medical Math!)

                            In this section, we introduce you to various types of healthcare professions. Each of these professions requires knowledge of medical math in some form or another.

                            REMEMBER

                            No one is an island. It's important to work as a team. Nurses, doctors, pharmacists, patients, and parents of young patients need to be on the same page. It's not unusual for a nurse or doctor to call a pharmacist for dosing assistance, especially when it comes to giving complicated medications, like those used in chemotherapy. Being on the same page and working as a team are critical to providing both optimal and safe care, with a reduced likelihood of errors.

                            Looking at the classic nursing careers

                            A career in nursing takes numerous forms. Some are based on your level of education, while others are based on where you do the work. No matter what initials come after your name, however, you still need to know all about medications and to be able to do dosing calculations.

                            Each type of nurse needs education, testing, and usually licensing. The basic types are

                            • Registered nurse, or RN: An RN usually has a degree (an AS, ASN, AAS, or AND) or a diploma from a hospital-based school of nursing. But you can also obtain other nursing degrees, including Bachelor of Science in Nursing, Master of Science in Nursing, Doctor of Nursing Science, and Doctor of Nursing Practice. To be an RN, you must pass exams and be licensed. Education and other requirements vary widely, and state law regulates what you can do as an RN. RNs are the largest healthcare occupation in the United States; according to the U.S. Bureau of Labor Statistics, there are about 2.3 million registered nurses.
                              • Nurse practitioner, or NP: If you're an NP, you're an RN with an advanced education. NPs are certified and licensed, but the duties permitted vary according to different states. Often, NPs do many tasks that doctors do (for example, they take histories and manage chronic conditions, such as diabetes). The NP's ability to prescribe drugs varies according to state law. These days, NPs are very common in the offices of family practice physicians. In fact, it's almost essential for the doctors to have one.
                                • Public health nurse, or PHN: Public health nursing is a specialized form of nursing that combines nursing and public health principles. A PHN knows about community health, health maintenance, and disease prevention. Counties and school districts employ one or more PHNs.
                                  • Licensed practical nurse, or LPN: An LPN is known as a licensed vocational nurse (LVN) in California and Texas. If you're an LPN/LVN, you're well-educated, you've passed exams, and you're licensed. You work under the supervision of an RN. You do many nursing tasks, but you can't do other tasks, depending on what the law and hospital policy allow. The U.S. Bureau of Labor Statistics estimates that about 700,000 persons are employed as LPNs/LVNs.
                                    • Certified nursing assistant, or CNA: This certification lets you assist patients with activities of daily living and give care under the supervision of an RN or an LPN/LVN. According to law and hospital policy, this care may include answering patients' call signals, observing patients' conditions, measuring and recording food and liquid intakes and outputs, taking vital signs, and reporting changes to the nursing staff. After the CNA completes a certificate training program (sometimes just one course at a community college), he's required to take a state certification exam.

                                      In the United States, a certified nursing assistant may be called a nursing assistant certified (NAC), patient care assistant (PCA), state tested nurse aid (STNA), or nursing assistant-registered (NA/R).

                                      Probing other medical careers

                                      In addition to nursing, several other medical careers, including the following, require an understanding of medical dosage math:

                                      • Physician assistant, or PA: Like the NP, a PA is a midlevel practitioner who can work in a physician's office, hospital, or rehabilitation center. PAs are licensed and work under the supervision of a physician. California requires PAs to complete an American Academy of Physician Assistants accredited, formal education program and pass a national exam to get a license. PAs can prescribe medications and other medical treatments. You can bet they need to know their math!
                                        • Medical assistant: A medical assistant typically works in a physician's or other health practitioner's office. Medical assistants are tested and certified. You find them in the offices of virtually any specialty, from family practice and internal medicine to cardiology, the heart doctor, and nephrology (ne-frall-a-gee), the kidney doctor. In an office setting, they're often multitasking — recording heights and weights, taking vital signs, recording and trending blood chemistries, and reviewing patient medication dosages and frequency.
                                          • Pharmacist, or PharmD (Doctor of Pharmacy): Pharmacists know pharmacology (drugs and drug action) and are also excellent mathematicians. They're responsible for filling prescription orders from doctors and other healthcare professionals. In the United Kingdom, pharmacists are called chemists. In a hospital setting, pharmacists use basic math, different systems of measurement, conversions, and more as they make up many medications.
                                            • Physician, or MD (Doctor of Medicine) or DO (Doctor of Osteopathic Medicine): When physicians, also called doctors, write prescriptions, they're doing basic math calculations. Some specialties require more math than others. For example, an oncologist (ahn-kall-a-gist) — a doctor who specializes in cancer — needs to do math calculations when dosing chemotherapy. The calculations are often based on the patient's body mass index (or BMI), a vital mathematical calculation based on height and weight. One of the authors, Rich, is an internist and nephrologist. Because nephrology relies a lot on numbers, he's always doing math.

                                              Doctors come in many varieties. For example, a dentist (DDS) is a Doctor of Dental Surgery. A foot doctor (DPM) is a Doctor of Podiatric Medicine.

                                              • Home healthcare aide, or HCA: HCAs, also called home health aides (HHAs), are not nurses. They're in a special category. HCAs must complete a certificate training program and pass an examination from the National Association for Home Care. They're usually certified by the state. HCAs usually help in elder care settings and convalescent hospitals. They often assist disabled people in their homes. See the section "Offering help at home" for more details.

                                                (Continues...)

                                                
                                                Excerpted from Medical Dosage Calculations For Dummiesby Richard Snyder Barry Schoenborn Copyright © 2011 by John Wiley & Sons, Ltd. Excerpted by permission of John Wiley & Sons. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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