As an incoming student, one of your first tasks will be memorizing the 'drug card'--a color-coded sheet of anesthetic drugs with the concentration of each drug; the volume syringe used to administer the drug; a range of the drug's effective dose in the typical adult patient, etc etc. The information on the drug card is vital, and you really do need to have it memorized by day 1.
I memorized the drug card using a special trick which will be discussed in the next entry. Had I taken the rote-memorization approach, as many of you probably will, there are a few pieces of additional information that I would have found helpful.
For one, any kind of visual aid would have been nice. For example, what do the syringes look like? What do the drug vials look like? Why is it so important to use a 3 mL syringe for one drug and a 5 mL for another?
Real-life Applications of the Drug Card
Having pictures of the drugs and syringes would have helped me form a tangible connection to the vague set of numbers on the card, and might have imparted a bit of logic to them, too. After all, it is much easier to memorize something to which you have at least *some* frame of reference . For example, if you saw the specific vial of Propofol (trade name Diprivan) referenced on the card, you would see that each vial contains 20 mL of Propofol, and, since we use the whole vial for every case, it would make sense that the 20 mL vial of Propofol is drawn up in a 20 mL syringe. No memorization required.
Pictured below are some of the drugs you need to memorize, drawn up for a case at Memorial Hermann TMC:
Foreground to background: Propofol (20 cc); Lidocaine (10 cc); Rocuronium (5 cc); Ondansetron (trade name Zofran) (3cc)...remember, 'mL' and 'cc' are interchangeable.
Left-to-right: Propofol (20 cc); Lidocaine (10 cc); Rocuronium (5 cc); Ondansetron (3 cc) ; Phenylephrine (above, purple label; 10 cc); Neostigmine (5 cc); Glycopyrrolate (green label; 5cc)
As far as your syringe selection goes, hospitals typically stock 1, 3, 5, 10 and 20 mL/cc syringes.
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| Packaging and contents of 3, 5, and 10 mL syringes |
Now, take a look at the picture below:
Let's look at the vial of Ondansetron (trade name Zofran), on the left. Notice the light pink strip running diagonally on the label: "4 mg per 2 mL." This means that the entire vial contains 2 mL of solution, and that solution contains 4 mg of the active ingredient, Ondansetron. Beneath that strip in parenthesis reads "(2 mg per mL)", which, if you didn't already do the math for yourself, tells you the concentration of Ondansetron is 2 mg for every 1 mL.
If you were to draw up the entire vial of Ondansetron in a syringe, which syringe would you use?
Remember, your syringe options are 1, 3, 5, 10 and 20 cc. In theory, you can use any syringe you like; but which size is most logical? Two 1 cc syringes would be a little wasteful and time-consuming. A 5 cc syringe would work, but it would be a less-efficient choice, as the majority of the syringe would be empty. Same goes for a 10 cc and a 20 cc syringe.
So, the answer is a 3 cc syringe--draw up all 2 cc's of Ondansetron in a 3 cc syringe. Makes sense, right?
Drawing up Propofol: The Deft-Handed Approach
A vial of Propofol (trade name: Diprivan) contains 200 mg of Propofol in 20 mL of solution. Therefore, the syringe choice is simple: Draw up all 20 mL in a 20 mL syringe
Propofol, drawn up and labeled (Right). Notice the deft gloved hand, with Casio watch (Left)
Now, on to a point of confusion on the drug card that needs a little clarification. You may have noticed some of the concentrations in the 'typical bolus' column do not agree with the drug's concentration
Why the Typical Bolus Numbers Don't Always Agree
The word 'bolus' has several meanings. The one we are interested in is: "the administration of a medication, drug or other compound that is given to raise its concentration in blood to an effective level".
Basically, 'typical bolus' is synonymous with 'the common single dose' of a medication. For example, if you have a headache or a fever, you might take 2 Ibuprofen. Each pill contains 200 mg, therefore we can call the 'typical bolus' of Ibuprofen 2 pills or 400 mg. If a patient's blood pressure begins to sag in the middle of the operation, but their heart rate remains the same, or is even elevated, we will often give a 1 cc bolus of phenylephrine, which is 100 mcg of phenylephrine. 100 mcg is a moderate and generally effective dose for any adult, regardless of their weight or age. If a patient shows signs of pain during the surgery, we give 1 cc or 50 mcg of Fentanyl. Again, this typically works for most adults. Some require more, others less; but generally speaking a single 'typical bolus' is a good place to start.
Back to the original point: Look up Ephedrine on your drug card. The concentration is 50 mg, which means every 1 mL of drug contains 50 mg of Ephedrine. So, one would expect the typical bolus, 1 mL, to be 50 mg. However, the card says 1 mL=5 mg, or '5 mg = 1 mL; to be exact. You see the same discrepancy with Dilaudid, Morphine, Epinephrine, Norepinephrine, and Vecuronium.
These discrepancies are not typos; they are a result of dilution. Drugs like Ephedrine and Epinephrine are manufactured at high concentrations; concentrations that are way too potent for our purposes. So, we dilute the manufacturer's concentration down to a more therapeutic level, making our doses safer and more reasonable. For example, we dilute the concentration of Ephedrine from 50 mg/mL to 5 mg/mL. A 1 mL bolus of 5 mg/mL Ephedrine--the typical bolus--will gently bump up heart rate and blood pressure by roughly 10 or 20%. A 1 mL bolus of
50 mg/mL--the concentration it originally comes in--will send the heart rate and blood pressure through the roof, and could possibly cause a heart attack or stroke.
Dilution Math
So, how do we dilute 50 mg of Ephedrine to 5 mg/mL? Remember, Ephedrine comes in solution, meaning that, in a sense, it is already 'diluted': each vial contains a liquid solution of 50 mg solute (Ephedrine) dissolved in 1 mL of solvent (distilled water, preservatives, etc), and that 1 mL of solvent isn't going anywhere, unless you do something crazy like boil your vial of ephedrine, which....just don't do that.
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| Ephedrine Sulfate, (50 mg/mL) contains 50 mg of solid Ephedrine dissolved in 1 mL of a solvent, such as distilled water |
So to dilute the concentration of Ephedrine down to 5 mg/mL, you add not 10, but 9 additional mL of solvent. Your solvent of choice is going to be IV fluid: either Lactated Ringer's (LR) or Normal Saline (NS).
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| 1L of Lactated Ringer's, aka 'LR'. A great choice for dilution |
Think of the dilution like this:
We use exactly the same quantity of LR or NS (9 mL) to dilute Hydromorphone (Dilaudid), and Morphine--though double check your drug card on Morphine. It may have the typical bolus concentration at .1 mg/1 mL, which I have never seen in practice.
Compared to Ephedrine and Hydromorphone, vials and/or ampules of Phenylephrine, Norepinephrine and Epinephrine are much more potent, and must be diluted into a larger volume of solution to achieve the desired concentration.
Diluting Epinephrine
Supplies: 1 bag of 100 mL 'Sodium Chloride Injection' or Normal Saline (NS) and 1 mL ampule of 1:1000 EPINEPHRINE (1 mg/mL), not to be confused with Ephedrine.
(Left) Break off the top of the ampule. (Right) Draw the entire mL of Epinephrine into an empty syringe
(5 cc syringe shown here...3 or 1 cc work fine as well). The syringe now contains 1 mL or 1 mg of Epinephrine.
(Left) Inject the whole mL--1 mg--of Epinephrine into the 100 mL bag of NS, (Right) appr. diluting the Epinephrine by a factor of 100, from 1 mg/mL--which is equivalent to 1000 mcg/mL--down to 10 mcg/mL.
Finally, from the bag of 10 mcg/mL Epinephrine, draw 10 mL in to a 10 mL syringe (not shown above).
You may notice that, technically-speaking, the Epinephrine has been diluted to 9.9 mcg/mL:
However, as you dilute 1 mL of anything into larger and larger volumes of solvent, that extra 1 mL of original solvent becomes increasingly negligible. It is a veritable drop in the bucket. Now, if you are a *really* OCD, you can remove 1 mL from the 100 mL bag of NS--leaving 99 mL--and then add the 1 mL of Epinephrine. That would mean you have added 1 mL of 1 mg/mL Epi to 99 mL of NS, giving you 1 mg of Epi/100 mL solvent: An even 10 mcg/mL of Epinephrine. But most everybody will make fun of you for being so anal, so I wouldn't recommend it.
So that's it for this installment. Hopefully it helped. If you have the time, I encourage you to look up pictures of the drugs that were not shown here, and look for any tutorials or videos that give a real-world meaning to all those random numbers on the card. Good luck!
