Review of Medical Calculations in Pharmacology

hello pharmacology students this is Dr. Herndon this is the first of two videos on the review of medical calculations our learning objectives for today are to recognize and be able to use different systems of measurement, you should be able to convert metric units of measurement, you should be able to convert from one system of measurement to another system of measurement and you should understand when decimal points should be used and when they should not be used when you're writing down or recording drug doses or drug amounts. ok so there are three systems of measurement which I'm going to be talking about here The metric system which is probably the most commonly used, the Apothecary system and the household system all three of these have different units that measure weight, volume, and length; the metric system is probably the most commonly used system of measurement in the calculation of drug dosages and fluid rates and constant rate infusions. We often will use these units for weight: kilogram, the gram the milligram, and the microgram keep in mind that different units of metric measurements differ from one another by a power of a thousand so for instance a kilogram is greater than a gram and a gram is greater than a milligram and a milligram is greater than a microgram, and they're by a thousand, so here, one kilogram is equivalent to a thousand grams, and one gram is equivalent to a thousand milligrams, and down here one milligram is equivalent to a thousand micrograms, so we can use these we can use these conversions when we are working with the metric system down here the liter and the milliliter are volume measures, again same thing with liter and milliliter right here: one liter is equivalent to a thousand milliliters. And I want you to look down at the bottom here the "cc": the "cc" stands for cubic centimeter it just so happens that within one cubic centimeter is held one milliliter of fluid or water ok so these two are you'll often see them used as equivalencies sometimes you'll see syringes labeled and cc's instead of mls I one ml or one cc is equivalent to one gram (of water). If you are confused and you don't know off the top of your head all these conversions it's perfectly fine to use a common conversion table and i've posted one on Canvas though you can find them on the web anywhere if you have a favorite version or something that's perfectly fine you can also go on to Plumb's Veterinary Drugs, and in the Appendix you'll find a conversion chart. Ok, there's two ways to convert metric units the first way is to use a conversion factor which is what we kind of just did so here's an example: if we need to convert 3,000 milligrams to grams, so we want to know how many grams is equivalent to three thousand milligrams three thousand milligrams I know that I'm going to have to cancel out my milligrams and that my answer is going to be in grams I'm gonna put that on top because i know that these are going to cancel out so the question becomes what's your conversion factor right here you can look this up so happens that a thousand milligrams is equivalent to one gram, so our problem this one is kind of easy because we could just cancel out our zeroes right here, right? so 3 times 1 divided by 1 equals three, and there's our units and grams. Different way to do metric conversions are by using this little system of arrows right here, some people like this, and this helps you, it's a visual to help you determine which direction you're going to move your decimal point in. When you're converting and you're moving the decimal point, you're going to move your decimal point three places because remember these units differ by a power of a thousand. let's do an example. For the microgram you can use mcg or mu-g, I like to use mcg and i'll tell you why. Because the mu is nice, but every once in awhile it can look strange, maybe somebody doesn't write it right, and it may actually end up looking more like milligrams (mg), ok, so i like to use three letters for microgram myself let's do this example so the question reads here and I need . 5 grams of drug A, but I have 250 milligram tablets, well that's really asking us anything but what I can see here is I have milligrams in one side and grams in the other side; how am I going to do any kind of dose calculation? I'm gonna have to use the same units. Remember, when you're doing dose calculations, you need your units to be the same. ok, so I'm going to convert grams to milligrams we're going to milligrams, so here's our arrow, we know that grams is greater than milligrams which means we're going to move our decimal point three places to the right let me write this out down here with more zeroes so you can see. There's 0.5 grams, (but i just added some zeroes) so if we're going to move this decimal point right here three places to the right, we're going to go from here: one, two, three and it's going to end up right there so our answer is going to be 500 milligrams, so 0.5 grams equals 500 milligrams. Alright, let's try one more just for practice. Again, this isn't really asking you to do a conversion, but you can see if you need three hundred thousand micrograms of a drug but you have a hundred fifty milligram tablets you're gonna have to get your units the same so you can work with this in a formula. So I'll convert 300,000 micrograms to milligrams, and we're going to use these arrows, which one do we use? We're going to use this one, between micrograms and milligrams. Milligrams are greater than micrograms, micrograms are less than milligrams, or smaller than. So, we're going to have our arrow this direction, so this in this case we're going to move our decimal point three places to the left: one, two, three, and it's going to go right there, so our answer is three hundred micrograms. Alright, here's a practice problem for you; pause the video, try the problem, come back and we'll go over it. Ok, the question reads how many micrograms are there and three milligrams let's start by writing down three milligrams, you can do it either way, however you want to do it. I'm going to do it using a conversion factor. So i know that i have to have my milligrams on the bottom to cancel them out, and I'm trying to convert to micrograms right there. So I know that in one milligram there are thousand micrograms, and you can get this from a chart, that's fine cancel, cancel; three times a thousand = three thousand micrograms Alright, here's a problem for you; pause the video, try it and then when you come back I'll go over the question all right I hope you tried it. This is one of my daughter's little guinea pigs, her name is Misty, she's very very cute. So the question is: how many kilograms does a 230 Gram guinea pig weigh? so let's do it this way: how about if we just use the arrows? So we want to know how many kilograms is equivalent to 230 grams? So i know that a kilogram is larger than a gram, so my decimal point will move three places to the left, we're going to start here 1, 2, 3, = 23 kilograms. The other way to do it would have been to use dimensional analysis or a conversion factor. 1,000 grams equals 1 kilogram, and then you do the math cancel, cancel, a hundred into twenty-three goes 0.23 times. ok. The second system of measurement that we're going to be using and you will see used a little bit in pharmaceutical calculations is called the Apothecary system. The grain, which is the basic unit of weight. A grain just happens to be equivalent to one grain of wheat, that shows you how old this system is, and grain just happens to be equivalent to about sixty five milligrams, not exactly. When we are writing grain make sure you put the "gr", grain is "gr", before the number, this is important right here. You can also use fractions when we're looking at grains, and grain one half means a half of the green so half of a grain would be half of sixty five milligrams. The DRAM is a volume unit of measurement that's equivalent to four mls. The minim is equal to a drop. The fluid ounce here is a unit of measurement which equals 30 mils, or two tablespoons. So again, you don't have to memorize all these conversions, you can look them up on a chart. ok and the third system of measurement we have here that you'll see used is called the household system and you can see I have some measuring spoons here because anybody who's worked in the kitchen has used the household system. This first one here, you're going to use this all the time when we're doing fluid drip rates, the drop, which is abbreviated "gtt" . 1 ml has 15 standard size drops in it but we have different sized fluid administration sets which are calibrated to different drop sizes ok so we have drop sets it they have little tiny drops, so there's more drops per mil, and then bigger drops - fewer drops per ml. Down here - the teaspoon and the table spoon are very commonly used measurements. It just so happens that a tablespoon is equal to 15 mls and a teaspoon is equal to 5 mls (you can look that up). Down here, very important, the household system uses the pound to measure weight. you can see the pound is most commonly abbreviated lb but sometimes you'll see hashtag used. The hashtag is used to record pounds; I use the hashtag a lot when I'm writing pounds; if you see me writing something like this 20 hashtag means 20 pounds, ok? The conversion from metric to household system of weight measure is one kilogram is equivalent to 2.2 pounds; you're going to use this all the time. Say you are converting a weight from pounds to kilograms, 2.2 pounds here is equivalent to one kilogram, so the problem becomes weight in pounds divided by 2.2 equals the weight in kilograms. It's important that you always confirm what units you're using either for the pets weight: is it pounds? or is it kilograms? and for the medication strength that you're using. You want to make sure that you confirm units before you start doing your calculations. here's another point: Death by Decimal Point. It's kind of an ugly sounding phrase, but the point to make here is that you need to double check your decimal places. If you are off, if you converted incorrectly, so let's say you were supposed to give 0.025 ml of something, and instead you're giving 0.25 mils of something. Suddenly you're giving ten times the amount of a drug. Depending on the drug, that could have very serious consequences. So it's important to check, and double check, and triple check, and ask somebody else, ask a senior vet tech, or ask the veterinarian to check your math. Very important. Another word about decimals, and this is an important point right here., you need to know where to put your decimal point and when to use zero, and when not to use a zero. If you're writing a value less than 1, so your writing .25 milligrams, you always want to have your place holder zero in front of your decimal point, okay? Otherwise it could potentially get washed away by a drop of water or it could end up being scribbled and you don't see it, because let's say all of a sudden the drop of water comes and just washes it away. Well, suddenly you have a very different drug dose. You started out with needing .25 milligrams, the decimal point got wiped away, and then suddenly you recording a dose that's a hundred times larger. That could have devastating consequences. Likewise, if you're writing a whole number, let's say you're writing a whole number 25 milligrams, you don't need to put your decimal and placeholder zero afterwards, that's not necessary. You could end up losing this decimal point somehow, maybe it's scribbled, maybe it's a pencil and it just got washed out, who knows? Or, it just doesn't show up that well and all the sudden you have something that's very different than what you need and what you started with. So, you need 25 milligrams of a drug and all of a sudden you're recording in an animal's medical record that you need 250 milligrams of a drug. Big difference. So be careful with your zeros and your decimals. Ok conversions: I have put a conversion table on Canvas, you can also find conversion tables, there's one in the Plumbs Veterinary Drug online in the Appendix, you can find them all over the internet too; if you have some kind of favorite jar or if you have an aap or something like that that's perfectly fine. But you should be able to convert between metric units, what we were just working on, and you also should be able to easily convert between different units of measurement. Here are some more common ones: converting between tablespoons and mls or teaspoons to mls or vice versa; between ounces and mls; grains to milligram, this is grains over here, grains to milligrams, milligrams to grains; pounds to kilograms- we do that all the time. Again, you're going to need a conversion chart. Some of these you'll eventually memorize. Alright, so let's practice the first one is asking 20 mls is how many teaspoons? I've given you the conversion here so you don't have to look it up. I'm going to do it this way: 20 mls, I know that I put mls on the bottom I can cancel out my units there it is right here five mls is equivalent to one teaspoon cancel, cancel, 20 / 5 equals 4 and our units are in teaspoons. Here are two practice problems for you. Pause the video, try them, I've given you the conversions. When you restart the video I'll go over the answers. ok let's go over the answers. First question asks - half a grain is equivalent to how many milligrams? I've given you the conversion - one grain equals 65 milligrams Easy to set up knowing what units you need to end up with, I'm going to put grain down here not here otherwise it'll look like gram. milligrams up on the top - 65 milligrams is equivalent to one grain. Cancel units, so the problem becomes 65 times a half or 65 / 2 which equals 32 . 5 milligrams. Second problem 45 milliliters is equivalent to how many ounces? Here's your conversion, same thing I can cancel, ounces on the top, 30 mils is equivalent to one ounce cancel units, so this problem becomes 45 x 1 / 30 which equals 1.5 ounces. Alright we're finished with part one of medical calculations, go ahead and take the calculations quiz number one that is in the calculations module on Canvas, make sure you have some sort of conversion chart that you have available while you're doing this. Okay, when you're finished with that, then go ahead and watch part 2 of medical calculations and then there is a quiz number two that's associated with that Thanks!

hello pharmacology students this is Dr. Herndon this is the first of two videos on the review of medical calculations our learning objectives for today are to recognize and be able to use different systems of measurement, you should be able to convert metric units of measurement, you should be able to convert from one system of measurement to another system of measurement and you should understand when decimal points should be used and when they should not be used when you're writing down or recording drug doses or drug amounts. ok so there are three systems of measurement which I'm going to be talking about here The metric system which is probably the most commonly used, the Apothecary system and the household system all three of these have different units that measure weight, volume, and length; the metric system is probably the most commonly used system of measurement in the calculation of drug dosages and fluid rates and constant rate infusions. We often will use these units for weight: kilogram, the gram the milligram, and the microgram keep in mind that different units of metric measurements differ from one another by a power of a thousand so for instance a kilogram is greater than a gram and a gram is greater than a milligram and a milligram is greater than a microgram, and they're by a thousand, so here, one kilogram is equivalent to a thousand grams, and one gram is equivalent to a thousand milligrams, and down here one milligram is equivalent to a thousand micrograms, so we can use these we can use these conversions when we are working with the metric system down here the liter and the milliliter are volume measures, again same thing with liter and milliliter right here: one liter is equivalent to a thousand milliliters. And I want you to look down at the bottom here the "cc": the "cc" stands for cubic centimeter it just so happens that within one cubic centimeter is held one milliliter of fluid or water ok so these two are you'll often see them used as equivalencies sometimes you'll see syringes labeled and cc's instead of mls I one ml or one cc is equivalent to one gram (of water). If you are confused and you don't know off the top of your head all these conversions it's perfectly fine to use a common conversion table and i've posted one on Canvas though you can find them on the web anywhere if you have a favorite version or something that's perfectly fine you can also go on to Plumb's Veterinary Drugs, and in the Appendix you'll find a conversion chart. Ok, there's two ways to convert metric units the first way is to use a conversion factor which is what we kind of just did so here's an example: if we need to convert 3,000 milligrams to grams, so we want to know how many grams is equivalent to three thousand milligrams three thousand milligrams I know that I'm going to have to cancel out my milligrams and that my answer is going to be in grams I'm gonna put that on top because i know that these are going to cancel out so the question becomes what's your conversion factor right here you can look this up so happens that a thousand milligrams is equivalent to one gram, so our problem this one is kind of easy because we could just cancel out our zeroes right here, right? so 3 times 1 divided by 1 equals three, and there's our units and grams. Different way to do metric conversions are by using this little system of arrows right here, some people like this, and this helps you, it's a visual to help you determine which direction you're going to move your decimal point in. When you're converting and you're moving the decimal point, you're going to move your decimal point three places because remember these units differ by a power of a thousand. let's do an example. For the microgram you can use mcg or mu-g, I like to use mcg and i'll tell you why. Because the mu is nice, but every once in awhile it can look strange, maybe somebody doesn't write it right, and it may actually end up looking more like milligrams (mg), ok, so i like to use three letters for microgram myself let's do this example so the question reads here and I need . 5 grams of drug A, but I have 250 milligram tablets, well that's really asking us anything but what I can see here is I have milligrams in one side and grams in the other side; how am I going to do any kind of dose calculation? I'm gonna have to use the same units. Remember, when you're doing dose calculations, you need your units to be the same. ok, so I'm going to convert grams to milligrams we're going to milligrams, so here's our arrow, we know that grams is greater than milligrams which means we're going to move our decimal point three places to the right let me write this out down here with more zeroes so you can see. There's 0.5 grams, (but i just added some zeroes) so if we're going to move this decimal point right here three places to the right, we're going to go from here: one, two, three and it's going to end up right there so our answer is going to be 500 milligrams, so 0.5 grams equals 500 milligrams. Alright, let's try one more just for practice. Again, this isn't really asking you to do a conversion, but you can see if you need three hundred thousand micrograms of a drug but you have a hundred fifty milligram tablets you're gonna have to get your units the same so you can work with this in a formula. So I'll convert 300,000 micrograms to milligrams, and we're going to use these arrows,  which one do we use? We're going to use this one, between micrograms and milligrams. Milligrams are greater than micrograms, micrograms are less than milligrams, or smaller than. So, we're going to have our arrow this direction, so this in this case we're going to move our decimal point three places to the left: one, two, three, and it's going to go right there, so our answer is three hundred micrograms. Alright, here's a practice problem for you; pause the video, try the problem, come back and we'll go over it. Ok, the question reads how many micrograms are there and three milligrams let's start by writing down three milligrams, you can do it either way, however you want to do it. I'm going to do it using a conversion factor. So i know that i have to have my milligrams on the bottom to cancel them out, and I'm trying to convert to micrograms right there. So I know that in one milligram there are thousand micrograms, and you can get this from a chart, that's fine cancel, cancel; three times a thousand = three thousand micrograms Alright, here's a problem for you; pause the video, try it and then when you come back I'll go over the question all right I hope you tried it. This is one of my daughter's little guinea pigs, her name is Misty, she's very very cute. So the question is: how many kilograms does a 230 Gram guinea pig weigh? so let's do it this way: how about if we just use the arrows? So we want to know how many kilograms is equivalent to 230 grams? So i know that a kilogram is larger than a gram, so my decimal point will move three places to the left, we're going to start here 1, 2, 3, = 23 kilograms. The other way to do it would have been to use dimensional analysis or a conversion factor. 1,000 grams equals 1 kilogram, and then you do the math cancel, cancel, a hundred into twenty-three goes 0.23 times. ok. The second system of measurement that we're going to be using and you will see used a little bit in pharmaceutical calculations is called the Apothecary system. The grain, which is the basic unit of weight. A grain just happens to be equivalent to one grain of wheat, that shows you how old this system is, and grain just happens to be equivalent to about sixty five milligrams, not exactly. When we are writing grain make sure you put the "gr", grain is "gr", before the number, this is important right here. You can also use fractions when we're looking at grains, and grain one half means a half of the green so half of a grain would be half of sixty five milligrams. The DRAM is a volume unit of measurement that's equivalent to four mls. The minim is equal to a drop. The fluid ounce here is a unit of measurement which equals 30 mils, or two tablespoons. So again, you don't have to memorize all these conversions, you can look them up on a chart. ok and the third system of measurement we have here that you'll see used is called the household system and you can see I have some measuring spoons here because anybody who's worked in the kitchen has used the household system. This first one here, you're going to use this all the time when we're doing fluid drip rates, the drop, which is abbreviated "gtt" . 1 ml has 15 standard size drops in it but we have different sized fluid administration sets which are calibrated to different drop sizes ok so we have drop sets it they have little tiny drops, so there's more drops per mil, and then bigger drops - fewer drops per ml. Down here - the teaspoon and the table spoon are very commonly used measurements. It just so happens that a tablespoon is equal to 15 mls and a teaspoon is equal to 5 mls (you can look that up). Down here, very important, the household system uses the pound to measure weight. you can see the pound is most commonly abbreviated lb but sometimes you'll see hashtag used. The hashtag is used to record pounds; I use the hashtag a lot when I'm writing pounds; if you see me writing something like this 20 hashtag means 20 pounds, ok? The conversion from metric to household system of weight measure is one kilogram is equivalent to 2.2 pounds; you're going to use this all the time. Say you are converting a weight from pounds to kilograms, 2.2 pounds here is equivalent to one kilogram, so the problem becomes weight in pounds divided by 2.2 equals the weight in kilograms. It's important that you always confirm what units you're using either for the pets weight: is it pounds? or is it kilograms? and for the medication strength that you're using. You want to make sure that you confirm units before you start doing your calculations. here's another point: Death by Decimal Point. It's kind of an ugly sounding phrase, but the point to make here is that you need to double check your decimal places. If you are off, if you converted incorrectly, so let's say you were supposed to give 0.025 ml of something, and instead you're giving 0.25 mils of something. Suddenly you're giving ten times the amount of a drug. Depending on the drug, that could have very serious consequences. So it's important to check, and double check, and triple check, and ask somebody else, ask a senior vet tech, or ask the veterinarian to check your math. Very important. Another word about decimals, and this is an important point right here., you need to know where to put your decimal point and when to use zero, and when not to use a zero. If you're writing a value less than 1, so your writing .25 milligrams, you always want to have your place holder zero in front of your decimal point, okay? Otherwise it could potentially get washed away by a drop of water or it could end up being scribbled and you don't see it, because let's say all of a sudden the drop of water comes and just washes it away. Well, suddenly you have a very different drug dose. You started out with needing .25 milligrams, the decimal point got wiped away, and then suddenly you recording a dose that's a hundred times larger. That could have devastating consequences. Likewise, if you're writing a whole number, let's say you're writing a whole number 25 milligrams, you don't need to put your decimal and placeholder zero afterwards, that's not necessary. You could end up losing this decimal point somehow, maybe it's scribbled, maybe it's a pencil and it just got washed out, who knows? Or, it just doesn't show up that well and all the sudden you have something that's very different than what you need and what you started with. So, you need 25 milligrams of a drug and all of a sudden you're recording in an animal's medical record that you need 250 milligrams of a drug. Big difference. So be careful with your zeros and your decimals. Ok conversions: I have put a conversion table on Canvas, you can also find conversion tables, there's one in the Plumbs Veterinary Drug online in the Appendix, you can find them all over the internet too; if you have some kind of favorite jar or if you have an aap or something like that that's perfectly fine. But you should be able to convert between metric units, what we were just working on, and you also should be able to easily convert between different units of measurement. Here are some more common ones: converting between tablespoons and mls or teaspoons to mls or vice versa; between ounces and mls; grains to milligram, this is grains over here, grains to milligrams, milligrams to grains; pounds to kilograms- we do that all the time. Again, you're going to need a conversion chart. Some of these you'll eventually memorize. Alright, so let's practice the first one is asking 20 mls is how many teaspoons? I've given you the conversion here so you don't have to look it up. I'm going to do it this way: 20 mls, I know that I put mls on the bottom I can cancel out my units there it is right here five mls is equivalent to one teaspoon cancel, cancel, 20 / 5 equals 4 and our units are in teaspoons. Here are two practice problems for you. Pause the video, try them, I've given you the conversions. When you restart the video I'll go over the answers. ok let's go over the answers. First question asks - half a grain is equivalent to how many milligrams? I've given you the conversion - one grain equals 65 milligrams Easy to set up knowing what units you need to end up with, I'm going to put grain down here not here otherwise it'll look like gram. milligrams up on the top - 65 milligrams is equivalent to one grain. Cancel units, so the problem becomes 65 times a half or 65 / 2 which equals 32 . 5 milligrams. Second problem 45 milliliters is equivalent to how many ounces? Here's your conversion, same thing I can cancel, ounces on the top, 30 mils is equivalent to one ounce cancel units, so this problem becomes 45 x 1 / 30 which equals 1.5 ounces. Alright we're finished with part one of medical calculations, go ahead and take the calculations quiz number one that is in the calculations module on Canvas, make sure you have some sort of conversion chart that you have available while you're doing this. Okay, when you're finished with that, then go ahead and watch part 2 of medical calculations and then there is a quiz number two that's associated with that Thanks!

Transcript for:Review of Medical Calculations in Pharmacology

Transcript for:
Review of Medical Calculations in Pharmacology