Dosage calculators

1. PO dosage calculator - solids   i.e. tablets, caplets, capsules, lozenges 2. PO dosage calculator - liquids     calculates liquid medications such as acetaminophen

elixir 3. IV dosage calculator     calculates IV medications such as furosemide and digoxin

Calculate IV rates

1. IV rate (gtt/min)     calculates IV rates without using an IV pump 2. IV rate (mL/hr)     calculates IV rates when given a time limit when IV must be infused 3. mcg/min as mL/hr     calculates IV medication rates such as norepinephrine and

nitroglycerine 4. mcg/kg/min as mL/hr     calculates IV medication rates such as nitroprusside and

dopamine

Calculate infusion time

1. IV time (hrs)     given an IV rate, calculates the duration of an IV

 

Calculate dosage given or infusing

There are times when the only way to figure out how much medication is being infused is by looking at the information on the IV bag and the rate of the infusion. 

1. mL/hr as dose/hr     calculates the dose of medications infusing such as heparin 2. mL/hr as mcg/min     calculates the dose of medications infusing such as nitroglycerine

and norepinephrine 3. mL/hr as mcg/kg/min     calculates the dose of medications infusing such as dobutamine

and nitroprusside

Clinical Calculators

1. pediatric dose calculator     converts an adult dosage into a pediatric using BSA 2. O2 remaining in e-cylinder     calculates how much O2 is left according to rate infusing 3. bsa calculator     calculates the BSA according to height and weight 4. drug absorption (Pka)     determines how well a medication will be absorbed into the

body  5. O.R. fluid requirements     calculates IV rate according to the type of surgery 6. N.P.O. fluid replacement     calculates fluid replacement for time NPO 7. allowable blood loss     calculates how much blood can be lost without needing a

transfusion 8. estimated blood volume     estimates how much blood is in a person's body 9. Ideal Body Weight (IBW)     compares an individuals weight against a statistical norm 10. Adjusted Body Weight (ABW)     calculates the ABW in obese persons for more accurate

drug dosing 11. ABG interpreter      interprets a respiratory or metabolic cause for pH disorders.

Conversion Calculators

1. °F,°C conversions     converts Fahrenheit and Celsius temperatures 2. pounds to kilograms     converts pound and kilogram weights 3. inches to centimeters     converts inch and centimeter lengths 4. foot, inch to centimeters     converts foot, inch and centimeter lengths (i.e 5'3" = 160 cm) 5. non-metric to metric     converts gr, tsp, tbs, oz, cup, min, dr to metric 6. metric units    converts between metric weights and volumes 7. % solutions to mg/mL     converts % solution into mg/mL concentration 8. epinephrine solutions to mg/mL     chart that converts a ratio into a mg/mL concentration

Drug  Calculators

1. Propofol bolus/infusion     calculates how many mL to push for intubation or rates for sedation and maintenance

2. Muscle relaxants     calculates how many mL to push for intubation

Example

You have received report on a patient with a heparin drip but the nurse forgot to say what dosage the drip was infusing at.  The heparin bag is labeled 25,000 units in 250 mL NS and the IV pump is infusing at 20 mL/hr.  In this example,

20 mL/hr = rate, an infusion.25,000 units = dosage available250 mL = volume available

So the dosage ordered, an infusion, = 2000 units/hour

See the example below.

Formula

          rate             mL available

x dose available

Using the formula on the example above looks like this:

20cc/hr250mL

x 25,000units

which = 2000 units/hr

Example

A patient is on a norepinephrine drip infusing at 56 cc/hr.  There is no titration table table at the bedside.  The IV bag is labeled 32 mg norepinephrine in 500cc Dextrose 5%.  How many

mcg/min is the patient receiving?  Use the example below to see how to solve this problem with the calculator.

rate = 56mL/hrdose available = 32mgmL available = 500mL

With the calculator, we see the patient is recieving 60 mcg/min of norepinephrine.  This is a higher than recommended dose!!!

Formula

In this example, first determine how many milligrams/hour is being delivered by the IV pump.  The rate of the IV pump (mL/hr) is divided by the volume of the IV bag (mL available), then multiply this result by the total amount of medication (mg) in the IV bag.

          rate             mL available

x dose available

becomes

  56mL/hr  

500mL

x 32mg

which = 3.58 mg/hr

Next, after the milligrams/hour has been determined, use the next formula to convert from milligrams/hour to mcg/min.

  mg     60min

x 1000

becomes 

  3.58mg   60min

x 1000

which is 59.7 mcg/min (yikes!)

Example

You have received a patient from another hospital on a dopamine drip except no information was given about it.  The bag is labeled with the concentration of 800 mg in 500cc of D5W.  The IV pump is infusing at  53 cc/hr and the patient weighs 70kg.  How much dopamine is this patient receiving?  Use the example below to see how this problem was solved.

rate = 53mL/hrweight = 70kgdose available = 800ml available = 500

Using the calculator, we know the patient is receiving 20 mcg/kg/min of dopamine.

Formula

Using the example above, first determine how many milligrams/hour is being delivered by the IV pump.  The rate of the IV (cc/hr) is divided by the volume of the IV bag (mL available), then multiply this result by the total amount of medication (mg) in the IV bag.

          rate             mL available

x dose available

becomes

  53mL/hr  

500mL

x 800mg

which = 84.8 mg/hr

Next, after the milligrams/hour has been determined, use the next formula to convert from milligrams/hour to mcg/kg/min.

  mg     60min

x 1000 / kg

becomes

84.8mg60min

x 1000 / 70

which = 20.2 mcg/kg/min

Example

The doctor has ordered an antibiotic whose average adult dose is 250 mg per day.  What would the dosage for this medication be on a child who is 100 cm in length and weighs 25 kg?  See the example below.

In this example, 115 mg of medication would be given.

Formula

First, the body surface area (BSA) must be determined:

kg0.425 x cm0.725 x 0.007184 = BSA

The above formula is just one method for determining BSA.  Results with other formulas will vary.

Next, the following formula* is used:

BSA x adult dose = approx. child dose

1.73

You are transporting your patient, who has emphysema, from your unit to radiology for a CT scan.  Without oxygen at 6 L/min, your patient's O2 saturation on room air drops to 75%.  It will take you 10 minutes to get there and back.  The portable O2 tank you grabbed has 500 psi left in it.  Do you have enough oxygen left for the trip?  See the example below

At 500 psi with a flow rate of 6 liters per min, there are 28 minutes of oxygen left.  Yes, there is enough for the trip.

Formula

My text book uses the following formula and data:

capacity (in L) / service pressure (in psi) = remaining contents (in L) / gauge pressure (in psi)

1. The service capacity for an e-cylinder carrying oxygen is 1900 psi. 2. The volume of oxygen in an e-cylinder is 660 liters.

Now entering the values listed above:

660 L / 1900 psi = remaining contents (in L) / gauge pressure (in psi)

I find it easier to look at this formula this way:

  0.35 x psi on gauge     L/min to be delivered

The 0.35 comes from dividing 660 by 1900.

In the example above:

0.35 x 500 psi   6 L/min

 = 28 min

Reference:

Nagelhout, J. J., & Zaglaniczy, K., L. (2001). Nurse anesthesia (2nd ed.). Philadelphia: W.B. Saunders Co.

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I want to use a nomogram to determine BSA

Example

The doctor has ordered an antibiotic on 11 y/o Billy.   The average adult dose is 250 mg.  In order to calculate pediatric doses you must first determine Billy's body surface area (BSA).  Billy is 157.5 cm in height and weighs 45 kg.  Using the example below, plug in the numbers into the calculator to determine Billy's BSA.

Using the calculator, Billy's BSA is determined as 1.42 M2.

Formula

kg0.425 x cm0.725 x 0.007184 = BSA

Example

1)  The pH of the stomach is 2.5.  The pKa of sodium pentothal is 7.4 and it is acidic.  If a patient is given sodium pentothal orally instead of IV, will it put the patient to sleep?  See the example below:

None of the sodium pentothal is ionized in the stomach.  Therefore the patient would absorb 100% of this medication and it would put him to sleep.

2)  A basic drug with a pKa of 7.8 is a known teratogen.  If given IV to a pregnant woman whose blood pH is 7.4, will this drug cross the placenta and effect the baby?  See the example below:

In this example, 72% of the drug is ionized which means 28% of the drug is unionized and will pass through the placenta to effect the baby.

Basics on Ionization

Ionized = water soluble = poor absorption through stomach, BBB, and placenta.

Non-ionized = lipid soluble = absorbed well (cell membranes are composed of lipids)

For example, sodium (Na+) and chloride (Cl-) are both ionized.  Cells must provide a channel for these ions to enter an otherwise impenetrable lipid membrane.

 

Formula

Percent Ionized Formula

 where x = -1 if acid drug or 1 if basic drug

 

Basic Rules

pKa is defined as the pH were a drug exists as 50% ionized and 50% unionized

 

If pKa - pH = 0, then 50% of drug is ionized and 50% is unionized

 

An acid in an acid solution will not ionizeAn acid in a basic solution will ionize

A base in a basic solution will not ionizeA base in an acid solution will ionize

 

If pKa - pH = 0.5, then the solution is 75% ionized/ 25% unionized or75% unionized/ 25% ionized

 

If pKa - pH > 1 then the solution is 99-100% ionized or 99-100% unionized*

Slight discrepancy between this statement and formula used for calculator.  Formula used indicates solutions would be 90-100% ionized or unionized.  These rules were taken from my Nursing 605 course.  My chemistry background is weak and I'm unable to verify the formula used.  Other than this, the formula

follows the basic rules.

Example

What is the NPO deficit for a patient who weighs 50 kg who has been NPO for 10 hours prior to surgery?  The answer is 1 liter (500 mL 1st hour, 250 mL 2nd hour, and 250 mL 3rd hour).  See how the numbers were used on the calculator below.

Formula

IV fluid replacement for NPO  deficit = 2mL/kg for each hour NPO prior to surgery. 

50% of this deficit is replaced within the first hour of surgery with the remaining 50% being replaced over the next 2 hours.  If the patient stayed in the hospital overnight with an IV infusing while NPO, subtract this amount from the NPO deficit.

In the example above:

2 mL/kg/hr = 2 x 50 x 10 = 1000@1st hr, 500 mL will be replaced2nd hr, 250 mL will be replaced

3rd hr, 2hr 250 mL will be replaced

If in this example, the patient stayed in the hospital overnight with an IV infusion at 100 mL/hr while NPO, all their NPO deficit (1 liter) would already be replaced.

Formulas

Allowable Blood Loss (ABL)*

EBV x (Hi - Hf)Hi

 = ABL

Hi = initial HctHf = final lowest acceptable Hct

 

Estimated Blood Volume (EBV)

EBV = weight (kg) x average blood volume

 

Average blood volumes**

Age Blood volume

Premature Neonates 95 mL/kg

Full Term Neonates 85 mL/kg

Infants 80 mL/kg

Adult Men 75 mL/kg

Adult Women 65 mL/kg

 

Normal Hct Values***Men 42-52%

Women 37-47%

 

If the patient is obese, using the IBW or ABW will give more accuracy than an actual weight.

 

Example

Question:  Before surgery is to take place, what is the estimated blood volume (EBV) of a female patient weighing 50 kg?  Also, what is the allowable blood loss (ABL) of this patient if her Hct is

45?

In the example above, EBV = 50kg x 65 (adult woman's blood volume) = 3250The initial Hct (Hi) = 45%, her current HctThe final lowest acceptable Hct (Hf) = 30% (What ever cut off is used clinically to decide how low the individual's Hct will be allowed to drop.  Thirty percent is used in this calculator but in reality this will vary from case to case.)So the example would look like this:

3250 x (45 - 30)45

 = 1083

Using this rough estimate, the patient in this example could loose 1083 mL of blood without needing a transfusion.

 

Replacing Blood Loss

    "Ideally, blood loss should be replaced with crystalloid or colloid solutions to maintain intravascular volume (normovolemia) until the danger of anemia outweighs the risks of transfusion.  At that point, further blood loss is replaced with transfusions of red blood cells to maintain hemoglobin concentration (or hematocrit) at that level.  For most patients, that point corresponds to a hemoglobin between 7 and 10 g/dL (or a hematocrit of 21-30%).  Below a hemoglobin concentration of 7 g/dL, the resting cardiac output has to increase greatly to maintain normal oxygen delivery" (Morgan & Mikhail, 1996).

 

Estimating blood loss***

Dry sponges

4x4 hold ~ 10 mL bloodRay-techs ~ 10-20 mL bloodLap sponges ~ 100 mL blood

Pediatric cases should have sponges & gauze weighed for blood loss**

 

Blood loss replacement***

Replace 1 mL blood with:

3 mL crystalloid (i.e. NS, Dextrose, LR)1 mL colloid (i.e. albumin**, Hespan®, Dextran®)1 mL whole blood1 mL PRBC

Formulas

Allowable Blood Loss (ABL)*

EBV x (Hi - Hf)Hi

 = ABL

Hi = initial HctHf = final lowest acceptable Hct

 

Estimated Blood Volume (EBV)

EBV = weight (kg) x average blood volume

 

Average blood volumes**

Age Blood volume

Premature Neonates 95 mL/kg

Full Term Neonates 85 mL/kg

Infants 80 mL/kg

Adult Men 75 mL/kg

Adult Women 65 mL/kg

 

Normal Hct Values***Men 42-52%

Women 37-47%

 

If the patient is obese, using the IBW or ABW will give more accuracy than an actual weight.

 

Example

Question:  Before surgery is to take place, what is the estimated blood volume (EBV) of a female patient weighing 50 kg?  Also, what is the allowable blood loss (ABL) of this patient if her Hct is

45?

In the example above, EBV = 50kg x 65 (adult woman's blood volume) = 3250The initial Hct (Hi) = 45%, her current HctThe final lowest acceptable Hct (Hf) = 30% (What ever cut off is used clinically to decide how low the individual's Hct will be allowed to drop.  Thirty percent is used in this calculator but in reality this will vary from case to case.)So the example would look like this:

3250 x (45 - 30)45

 = 1083

Using this rough estimate, the patient in this example could loose 1083 mL of blood without needing a transfusion.

 

Replacing Blood Loss

    "Ideally, blood loss should be replaced with crystalloid or colloid solutions to maintain intravascular volume (normovolemia) until the danger of anemia outweighs the risks of transfusion.  At that point, further blood loss is replaced with transfusions of red blood cells to maintain hemoglobin concentration (or hematocrit) at that level.  For most patients, that point corresponds to a hemoglobin between 7 and 10 g/dL (or a hematocrit of 21-30%).  Below a hemoglobin concentration of 7 g/dL, the resting cardiac output has to increase greatly to maintain normal oxygen delivery" (Morgan & Mikhail, 1996).

 

Estimating blood loss***

Dry sponges

4x4 hold ~ 10 mL bloodRay-techs ~ 10-20 mL bloodLap sponges ~ 100 mL blood

Pediatric cases should have sponges & gauze weighed for blood loss**

 

Blood loss replacement***

Replace 1 mL blood with:

3 mL crystalloid (i.e. NS, Dextrose, LR)1 mL colloid (i.e. albumin**, Hespan®, Dextran®)1 mL whole blood1 mL PRBC

 

Formulas

Allowable Blood Loss (ABL)*

EBV x (Hi - Hf)Hi

 = ABL

Hi = initial HctHf = final lowest acceptable Hct

 

Estimated Blood Volume (EBV)

EBV = weight (kg) x average blood volume

 

Average blood volumes**

Age Blood volume

Premature Neonates 95 mL/kg

Full Term Neonates 85 mL/kg

Infants 80 mL/kg

Adult Men 75 mL/kg

Adult Women 65 mL/kg

 

Normal Hct Values***Men 42-52%

Women 37-47%

 

If the patient is obese, using the IBW or ABW will give more accuracy than an actual weight.

 

Example

Question:  Before surgery is to take place, what is the estimated blood volume (EBV) of a female patient weighing 50 kg?  Also, what is the allowable blood loss (ABL) of this patient if her Hct is

45?

In the example above, EBV = 50kg x 65 (adult woman's blood volume) = 3250The initial Hct (Hi) = 45%, her current HctThe final lowest acceptable Hct (Hf) = 30% (What ever cut off is used clinically to decide how low the individual's Hct will be allowed to drop.  Thirty percent is used in this calculator but in reality this will vary from case to case.)So the example would look like this:

3250 x (45 - 30)45

 = 1083

Using this rough estimate, the patient in this example could loose 1083 mL of blood without needing a transfusion.

 

Replacing Blood Loss

    "Ideally, blood loss should be replaced with crystalloid or colloid solutions to maintain intravascular volume (normovolemia) until the danger of anemia outweighs the risks of transfusion.  At that point, further blood loss is replaced with transfusions of red blood cells to maintain hemoglobin concentration (or hematocrit) at that level.  For most patients, that point corresponds to a hemoglobin between 7 and 10 g/dL (or a hematocrit of 21-30%).  Below a hemoglobin concentration of 7 g/dL, the resting cardiac output has to increase greatly to maintain normal oxygen delivery" (Morgan & Mikhail, 1996).

 

Estimating blood loss***

Dry sponges

4x4 hold ~ 10 mL bloodRay-techs ~ 10-20 mL bloodLap sponges ~ 100 mL blood

Pediatric cases should have sponges & gauze weighed for blood loss**

 

Blood loss replacement***

Replace 1 mL blood with:

3 mL crystalloid (i.e. NS, Dextrose, LR)1 mL colloid (i.e. albumin**, Hespan®, Dextran®)1 mL whole blood1 mL PRBC

 

Formulas

Allowable Blood Loss (ABL)*

EBV x (Hi - Hf)Hi

 = ABL

Hi = initial HctHf = final lowest acceptable Hct

 

Estimated Blood Volume (EBV)

EBV = weight (kg) x average blood volume

 

Average blood volumes**

Age Blood volume

Premature Neonates 95 mL/kg

Full Term Neonates 85 mL/kg

Infants 80 mL/kg

Adult Men 75 mL/kg

Adult Women 65 mL/kg

 

Normal Hct Values***Men 42-52%

Women 37-47%

 

If the patient is obese, using the IBW or ABW will give more accuracy than an actual weight.

 

Example

Question:  Before surgery is to take place, what is the estimated blood volume (EBV) of a female patient weighing 50 kg?  Also, what is the allowable blood loss (ABL) of this patient if her Hct is

45?

In the example above, EBV = 50kg x 65 (adult woman's blood volume) = 3250The initial Hct (Hi) = 45%, her current HctThe final lowest acceptable Hct (Hf) = 30% (What ever cut off is used clinically to decide how low the individual's Hct will be allowed to drop.  Thirty percent is used in this calculator but in reality this will vary from case to case.)So the example would look like this:

3250 x (45 - 30)45

 = 1083

Using this rough estimate, the patient in this example could loose 1083 mL of blood without needing a transfusion.

 

Replacing Blood Loss

    "Ideally, blood loss should be replaced with crystalloid or colloid solutions to maintain intravascular volume (normovolemia) until the danger of anemia outweighs the risks of transfusion.  At that point, further blood loss is replaced with transfusions of red blood cells to maintain hemoglobin concentration (or hematocrit) at that level.  For most patients, that point corresponds to a hemoglobin between 7 and 10 g/dL (or a hematocrit of 21-30%).  Below a hemoglobin concentration of 7 g/dL, the resting cardiac output has to increase greatly to maintain normal oxygen delivery" (Morgan & Mikhail, 1996).

 

Estimating blood loss***

Dry sponges

4x4 hold ~ 10 mL bloodRay-techs ~ 10-20 mL bloodLap sponges ~ 100 mL blood

Pediatric cases should have sponges & gauze weighed for blood loss**

 

Blood loss replacement***

Replace 1 mL blood with:

3 mL crystalloid (i.e. NS, Dextrose, LR)1 mL colloid (i.e. albumin**, Hespan®, Dextran®)1 mL whole blood1 mL PRBC