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Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

Drug Dosage Protocols – Insulin & Heparin Administration Introduction Some disease states demand very precise control over drug delivery. In these cases, drug dosage protocols are used to dictate and adjust the amount of medication required throughout drug therapy, in response to diagnostic tests. This is done to tailor drug delivery to a particular client, since usual doses are often inadequate for safe and effective treatment. This module will use insulin and heparin administration as illustrative examples, which will prepare you for similar protocols used in practice.

Overview x x x x x x

Regulation of Blood-glucose Types of Insulin Medication Insulin Administration Insulin Dosage Protocols Regulation of Blood Coagulation Heparin Protocol for Stroke

Module Outcomes x x x x x

Understand the physiological regulation of blood-glucose by pancreatic hormones. Recognize various types of insulin medication. Given a medication order, use a protocol to calculate the dosage of insulin required. Understand the role of heparin in blood coagulation and interpret the results of an aPTT test. Calculate initial rates for the infusion of heparin, and adjust these rates in response to aPTT values.

Regulation for Blood-glucose Blood-glucose concentration is typically expressed in millimoles (mmol) (In essence, this unit is a count of the number of molecules present.) of glucose per litre of blood. In healthy patients, blood-glucose ranges from 3.6 mmol/L to 5.8 mmol/L. This homeostatic (Homeostasis refers to the maintenance of variables, such as temperature, blood pressure and pH, within fixed (static) ranges.) range is tightly controlled by the pancreas, which constantly monitors blood-glucose, and secretes hormones in response to irregular concentrations. In particular, if blood-glucose is too high, then the pancreas secretes insulin into the bloodstream. This hormone causes the conversion of glucose into glycogen, a form of carbohydrate used for storage.

Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

On the other hand, if blood-glucose is below the homeostatic range, then the reverse process occurs. The pancreas secretes glucagon, a hormone that causes glycogen to convert into glucose.

Here, insulin and glycogen have opposing effects, but are complementary to one another. Together, they maintain a steady concentration of glucose in the blood. This is an example of a negative feedback loop. In such systems, there is a pre-determined range for the variable (3.6 mmol/L – 5.8 mmol/L for blood-glucose), a factor that increases the variable (glucagon), another factor that decreases the variable (insulin) and a monitoring mechanism (the pancreas). This is a very common theme in homeostasis. Everyday examples of negative feedback loops include thermostats and cruise control.

Insulin Concentrations Type 1 diabetes is characterized by the inability of the pancreas to secrete insulin. Left untreated, this would cause blood-glucose to increase to unsafe levels, a condition known as hyperglycaemia. To prevent this, the nurse or patient takes over the role of the pancreas by monitoring blood-glucose, and administering insulin by a parenteral route, usually subcutaneously. Insulin is most commonly available with a concentration of 100 units per mL, abbreviated as U-100. In addition, there are concentrated forms with U-500 concentration, and U-40 is typically reserved for veterinary use.

Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

Since the U-100 strength is so prevalent, syringes have been designed specifically for use with this insulin concentration. Rather than being labelled in millilitres, they use units to indicate the amount of medication drawn up. Here, each unit has a volume of 0.01 mL; however, it is not necessary to perform dosage calculations when preparing insulin for injection. Instead, U-100 insulin should only be administered using a U-100 syringe.

Concentrated, U-500 insulin is easily distinguishable from U-100 strengths. The term ‘U500’ is prominently displayed on the label, and the packaging includes “candy-cane” stripes to alert healthcare practitioners.

Types of Insulin Managing blood-glucose can be a challenging endeavour since glucose intake varies throughout the day. For this reason, several types of insulin have been developed, which vary in onset (Time between drug administration and beginning of therapeutic effect.), peak (Time period when drug is most effective.) and duration (Length of time that drug is effective.) of action. The rapid- and short-acting types of insulin are taken with or before meals. Rapid-acting insulin brands include NovoLog, Humalog and Apidra. Short-acting insulin brands, also known as regular insulin, are often labelled with a block letter R. Examples include Humulin R and Novolin R. x

x

Intermediate-acting insulin is designed to cover a 12-hour period, either during the day or overnight. This type of insulin can be recognized by the block letters N or NPH. Examples include Humulin N and Novolin NPH. Long-acting insulin types do not have an appreciable peak. They provide 24 hours of sustained effect. The most common brands of long-acting insulin are Lantus and Levemir.

Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

Rapid- and short-acting insulin types have a translucent appearance. They are often prescribed together with intermediate- and long-acting insulin, which have a cloudywhite colour. When administering two types of insulin from one syringe, the clear type should always be drawn first. This prevents contamination of the rapid- or short-acting insulin with the intermediate- or long-acting type. This is summarized as the “clear before cloudy” rule. Pre-mixed insulin is also available with commonly prescribed proportions. Examples: x x

Novolin 70/30 (70% NPH; 30% regular) Humulin 50/50 (50% NPH; 50% regular).

Insulin Administration Insulin Administration: Example Consider the following insulin order. Give 12 units Humalog U-100 subQ TID 30 min a.c. (Give 12 units of U-100 Humalog by subcutaneous injection three times per day, 30 minutes before meals.) Since a U-100 insulin concentration has been prescribed, a U-100 syringe should be used. These syringes indicate volume in units, rather than milliliters. Simply draw up 12 units of Humalog to give the prescribed dosage.

Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

Insulin Administration Activity Consider the following insulin order. Give 10 units Novolin NPH U-100 SC and 6 units Novolin R U-100 sc BID. Here, two types of insulin are to be combined into one syringe. 1) Which insulin should you draw up first? a) Novolin NPH; b) Novolin R Answer: b) Novolin R x

Remember, draw clear before cloudy. Rapid- and short-acting insulin types are clear in appearance.

2) What is the total number of units that you will administer? Answer: 16 units

Insulin Dosing Protocols A sliding scale may be used in conjunction with an insulin prescription for more precise dosing. Here, the patient’s blood-glucose concentration dictates the amount of insulin required. This is a simple example of a drug dosage protocol.

Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

BLOOD-GLUCOSE (MMOL/L)

ACTION TO TAKE

0 – 10

none

10.1 – 13

2 units Humalog subcut

13.1 – 16

4 units Humalog subcut

16.1 – 19

6 units Humalog subcut

> 19

8 units Humalog subcut and notify MD

Insulin Dosing Protocols Activity Consider the following insulin order. Administer 7 units Levemir U-100 subcut and Humalog U-100 subcut od per sliding scale. The patient’s blood-glucose reading is 11.8 mmol/L. 1) How many units of Humalog will you administer? Answer: 2 units 2) Which brand of insulin will you draw into the syringe first? a) Levemir b) Humalog Answer: b) Humalog 3) What is the total dosage of insulin that you will administer? Answer: 9 units

Regulation of Blood Coagulation Blood coagulation is regulated by a negative feedback loop, similar to blood-glucose maintenance. Heparin is one of several factors that influences blood clotting and is commonly prescribed as an anticoagulant. When administered parenterally, heparin prevents the formation of blood clots, and prevents existing blood clots from growing. Left untreated, blood clots can have severe effects on organs, and are particularly harmful in the lungs and the brain. As a clot travels through the circulatory system, it may clog narrow blood vessels, impeding the supply of oxygen to tissues.

Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

Note: Heparin does not dissolve existing blood clots. A different class of medications, called thrombolytic drugs, serves this purpose. These carry dangerous side effects and are only used in left-threatening situations.

Heparin Protocol for Stroke A stroke results when a blood clot significantly reduces oxygen flow to a portion of the brain. This can have permanent or lethal consequences. Heparin therapy is used to prevent further injury, but its effect must be closely monitored. Excess heparin could lead to haemorrhage; conversely, insufficient heparin could allow blood clots to cause subsequent strokes. Therefore, medical units use heparin protocols to adjust dosing based on patient diagnostics. A heparin protocol for stroke is used to dictate the specifics for IV infusion. It outlines: x x x x

directions to prepare an IV solution containing heparin; the initial infusion rate (units/kg/hr); the collection of diagnostics to monitor the patient’s response; and flow rate adjustments in response to diagnostics.

The most common test used to monitor heparin therapy is the activated partial thromboplastin time (aPTT) test. Using a sample of blood, this test determines the time required for a blood clot to form. Normal values for this test range from 25 to 35 seconds. As heparin is administered, this value increases, prolonging the formation of blood clots. A heparin protocol may also indicate that the patient requires a loading dose (bolus) before infusion begins.

Mathematics for Medication Administration

Drug Dosage Protocols – Insulin & Heparin Administration

Heparin Protocol for Stroke: Example Data Consider the following heparin protocol for stroke: x

Prepare IV solution by adding 25 000 units of heparin to a 500 mL IV bag (This 25 000 units 50 units .) of D5W. results in a concentration of , which reduces to 500 mL

1 mL

x

Begin heparin infusion at 12 units/kg/hr. (The initial rate is based on the patient’s body weight. For each kilogram of mass, the patient is to receive 12 units of heparin 12 units each hour (think: per kg).) 1 hr

x

Goal of therapy is aPTT: 55 sec - 69.9 sec. Collect blood for aPTT analysis q6h and adjust infusion rate according to nomogram. aPTT (sec) < 35 35 – 44.9 45 – 54.9 55 – 69.9 70 – 84.9 85 – 100 > 100

Rate Change (mL/hr) ↑ by 3 mL/hr ↑ by 2 mL/hr ↑ by 1 mL/hr No change ↓ by 1 mL/hr Stop infusion for 30 min; ↓ by 2 mL/hr Stop infusion for 60 min; ↓ by 4 mL/hr

Heparin Protocol for Stroke: Example Mr. Harvey is being treated for stroke. He weighs 65.8 kg. a) What is the initial infusion rate (units/hr) for Mr. Harvey? Solution: The initial infusion rate is based on the prescription (12 units/kg/hr) and the patient’s body mass (65.8 kg). For each kg of body mass, the patient should receive 12 units/hr. 65.8 kg 12 units per hr = 789.6 units per hr × 1 kg 1 ≈ 790

units hr

.

b) What is the initial flow rate (mL/hr) for Mr. Harvey? Solution: The initial flow rate (mL/hr) is based on the initial infusion rate (units/hr) and the IV fluid concentration (50 units/mL).

Mathematics for Medication Administration 789.6 units 1 hr

×

Drug Dosage Protocols – Insulin & Heparin Administration

1 mL mL = 15.792 hr 50 units mL ≈ 16 . hr

After six hours, Mr. Harvey’s first lab result is reported. His aPTT value is 38.5 seconds. c) What will you do according to the nomogram? Solution: The nomogram is similar to a sliding scale used for insulin administration. The reported value is below the goal range, which means that the patient’s blood is clotting too quickly. This may result in additional tissue damage due to blood clots, so the flow rate should be increased in response. According to the nomogram, you are to increase the flow rate by 2 mL/hr. d) What is the new flow rate (mL/hr) and infusion rate (units/hr)? Solution: It has been established that the initial flow rate (16 mL/hr) is too slow to be therapeutically effective. Increasing this value by 2 mL/hr results in a new flow rate of 18 mL/hr. The associated infusion rate (units/hr) can be calculated by factoring in the heparin concentration. units 18 mL 50 units × = 900 hr 1 hr 1 mL This adjusted infusion rate should bring Mr. Harvey’s aPTT up into the goal range. Blood work continues every 6 hours to monitor the patient’s response. After an additional 6 hours, Mr. Harvey’s aPTT is reported as 71.3 seconds. e) What is your action for this value? Solution: This aPTT value is too high—the patient’s blood is clotting too slowly. Heparin infusion should be slowed down in response. According to the nomogram, the flow rate should be decreased by 1 mL/hr. f) What is the new flow rate and infusion rate? Solution: The new flow rate is calculated based on the most recent flow rate (18 mL/hr). Decreasing this value by 1 mL/hr yields a new flow rate of 17 mL/hr. The new infusion rate is

Mathematics for Medication Administration 17 mL 1 hr

×

50 units 1 mL

= 850

units hr

Drug Dosage Protocols – Insulin & Heparin Administration

.

Alternatively, this value can be calculated by subtracting 50 units/hr from the previous infusion rate. Remember that each millilitre of IV fluid contains 50 units of heparin. 900

units hr

− 50

units hr

= 850

units hr

.

Six hours later, his aPTT reading is 56.2 sec. g) What is your action for this value? Solution: This aPTT value falls within the goal range. Infusion should be maintained at 17 mL/hr with continual aPTT monitoring at 6-hour intervals. For this value, the nomogram indicates that no change is required in the flow rate.

Heparin Protocol for Stroke: Activity Heparin Protocol for Stroke: Activity Data Consider the following heparin protocol for stroke: x x x

Prepare IV solution by adding 100 000 units of heparin to a 1000 mL IV bag of D5W. Begin heparin infusion at 19 units/kg/hr. Goal of therapy is aPTT: 55 sec - 69.9 sec. Collect blood for aPTT analysis q6h and adjust infusion rate according to nomogram. aPTT (sec) < 35 35 – 44.9 45 – 54.9 55 – 69.9 70 – 84.9 85 – 100 > 100

Rate Change (mL/hr) ↑ by 3 mL/hr ↑ by 2 mL/hr ↑ by 1 mL/hr No change ↓ by 1 mL/hr Stop infusion for 30 min; ↓ by 2 mL/hr Stop infusion for 60 min; ↓ by 4 mL/hr

Heparin Protocol for Stroke: Activity Mrs. Wzorek is being treated for stroke. She weighs 204.3 lbs. a) What is the initial infusion rate (units/hr) for Mrs. Wzorek? Solution:

Mathematics for Medication Administration 204.3 lbs 1

×

Drug Dosage Protocols – Insulin & Heparin Administration

1 kg 19 units units × per hr ≈ 1 764 hr 2.2 lbs 1 kg

b) What is the concentration of heparin in the IV bag? Solution: 100 000 units units = 100 1 000 mL mL c) What is the initial flow rate (mL/hr) for Mrs. Wzorek? Solution:  units 1 764.40909 1 mL mL × ≈ 18 hr 1 hr 100 units After six hours, Mrs. Wzorek’s first lab result is reported. Her aPTT value is 56.1 seconds. d) What will you do according to the nomogram? a. ↑ by 3 mL/hr b. ↑ by 2 mL/hr c. ↑ by 1 mL/hr d. No change e. ↓ by 1 mL/hr f. Stop infusion for 30 min; ↓ by 2 mL/hr g. Stop infusion for 60 min; ↓ by 4 mL/hr Answer: d. No change After an additional six hours, her aPTT reading is 87.8 sec. e) What is your action for this value? a. No change b. ↑ by 2 mL/hr c. ↑ by 1 mL/hr d. No change e. ↓ by 1 mL/hr f. Stop infusion for 30 min; ↓ by 2 mL/hr g. Stop infusion for 60 min; ↓ by 4 mL/hr Answer: f. Stop infusion for 30 min; ↓ by 2 mL/hr f) What is the new flow rate (mL/hr) and infusion rate (units/hr)? Solution:

Mathematics for Medication Administration 18

mL hr

−2

mL hr

= 16

Drug Dosage Protocols – Insulin & Heparin Administration

mL hr

16 mL 100 units units × = 1 600 hr 1 hr 1 mL Six hours later, Mrs. Wzorek’s aPTT is reported as 77.3 sec. g) What is your action for this value? a. ↑ by 3 mL/hr b. ↑ by 2 mL/hr c. ↑ by 1 mL/hr d. No change e. ↓ by 1 mL/hr f. Stop infusion for 30 min; ↓ by 2 mL/hr g. Stop infusion for 60 min; ↓ by 4 mL/hr Answer: e. ↓ by 1 mL/hr h) What is the new flow rate and infusion rate? Solution: 16

mL mL mL −1 = 15 hr hr hr

15 mL 1 hr

×

1 600

100 units 1 mL

= 1 500

units hr

Or

units units units − 100 = 1 500 hr hr hr

After an addition six hours, her aPTT value is 59.2 sec. i) What is your action for this value? a. ↑ by 3 mL/hr b. ↑ by 2 mL/hr c. ↑ by 1 mL/hr d. No change e. ↓ by 1 mL/hr f. Stop infusion for 30 min; ↓ by 2 mL/hr g. Stop infusion for 60 min; ↓ by 4 mL/hr Answer: d. No change...