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NAPLEX Review > Calculations IV > Flashcards

Calculations IV Flashcards

1
Q

What is body mass index (BMI)?

A

Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women

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2
Q

What is BMI a useful measure of?

A

Body fat

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3
Q

What are the limitations of BMI?

A

BMI can over-estimate body fat in persons who are muscular, and can under-estimate body fat in frail elderly persons and others who have lost muscle mass

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4
Q

In terms of waist circumference, what waist size is associated with higher disease risk?

A

High risk is defined as a waist size > 35 inches for women or > 40 inches for men

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5
Q

What is the formula for BMI?

A

weight (kg)/[height (m)]^2 or weight (pounds)/[height (in)]^2 x 703

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6
Q

What BMI is considered underweight?

A

< 18.5 kg/m2

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7
Q

What BMI is considered normal weight?

A

18.5 - 24.9

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8
Q

What BMI is considered overweight?

A

25-29.9

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9
Q

What BMI is considered obese?

A

> 30

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10
Q

What are the three potential measures of body weight for a patient?

A

Actual (or total) body weight, ideal body weight and adjusted body weight

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11
Q

What is actual body weight or total body weight?

A

Actual body weight or total body weight is the weight of the patient when weighed on a scale

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12
Q

What is ideal body weight?

A

Ideal body weight is the healthy (ideal) weight for a person

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13
Q

How do you calculate IBW for males?

A

50 kg + (2.3 kg)(number of inches over 5 feet)

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14
Q

How do you calculate IBW for females?

A

IBW (females) = 45.5 kg + (2.3 kg)(number of inches over 5 feet)

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15
Q

What is adjusted body weight?

A

Adjusted body weight is calculated when patients are obese or overweight

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16
Q

What is the formula to calculate adjusted body weight?

A

IBW + 0.4(TBW - IBW)

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17
Q

If a person is underweight, what measure of body weight do you use?

A

Use total body weight for all medications

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18
Q

If a person is normal weight, what measure of body weight do you use?

A
  • Use total body weight for most medications

- Use ideal body weight for aminophylline, theophylline, acyclovir and levothyroxine

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19
Q

If a person is obese, what measure of body weight do you use?

A
  • Use ideal body weight for aminophylline, theophylline, acyclovir and levothyroxine
  • Use total body weight for LMWHs, UFH and vancomycin
  • Use adjusted body weight for aminoglycosides
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20
Q

What are flow rates?

A

Flow rates are used to specify the volume or amount of drug a patient will receive over a given period of time

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21
Q

What are examples of how flow rate can be expressed?

A

Milliters per hour, milligrams per hour, mcg/kg/min or as the total time to administer the entire volume of the infusion

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22
Q

What does flow rate depend on?

A

Flow rate depend on the dose of the medication and the concentration available

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23
Q

What is creatinine?

A

Creatinine is a breakdown product when muscle tissue makes energy

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24
Q

What is the normal range for serum creatinine?

A

The normal range for serum creatinine is approximately 0.6-1.3 mg/dL

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25
Q

What happens to creatinine when kidney function declines?

A

If kidney function declines and creatinine cannot be cleared, the creatinine levels will increase in the blood and the creatinine clearance with decrease

*Concentration of drugs that are renally cleared will also increase and a dose reduction may be required

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26
Q

What should be assessed when a patient is dehydrated?

A

Patients should be assessed for dehydration when the serum creatinine is elevated because dehydration can cause both the serum creatinine (SCr) and the blood urea nitrogen (BUN) to increase

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27
Q

What is the BUN:SCr ratio that indicates dehydration?

A

> 20:1

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28
Q

What are some signs of dehydration?

A

Signs of dehydration can include decreased urine output, tachycardia, tachypnea, dry skin/mouth/mucous membranes, skin tenting (skin does not bounce back when pinched into a fold) and possibly fever

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29
Q

What can usually cause dehydration?

A

Dehydration is usually caused by diarrhea, vomiting and/or a lack of adequate fluid intake

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30
Q

What is the Cockgroft-Gault equation?

A

CrCl (mL/min) = ([140 - (age of patient)]/[72 x SCr]) x weight in kg (x 0.85 if female)

*formula used to estimate renal function

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31
Q

When is the Cockcroft-Gault equation unreliable?

A

It is not reliable in very young children, ESRD patients or when renal function is fluctuating rapidly

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32
Q

If a patient underweight, what body weight measure should be used for calculating CrCL?

A

Total body weight

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33
Q

If a patient normal weight, what body weight measure should be used for calculating CrCL?

A

Ideal body weight

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34
Q

If a patient overweight or obese, what body weight measure should be used for calculating CrCL?

A

If BMI < 25, use ideal body weight. If BMI > 25, use adjusted body weight

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35
Q

What is pH?

A

The pH refers to the acidity or basicity of a solution

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36
Q

What does an increase or decrease in pH represent?

A

As a solution becomes more acidic (the concentration of proton increases), the pH decreases. When the concentration of protons decrease, the pH increases and the solution is more basic, or alkaline

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37
Q

How can the acid-base status of. patient be determined?

A

The acid-base status of a patient can be determined with an arterial blood gas (ABG)

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38
Q

What is the primary buffering system of the body?

A

The bicarbonate/carbonic acid

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39
Q

What organ helps maintain neutral pH?

A

The kidneys help to maintain a neutral pH by controlling bicarbonate reabsorption and elimination

40
Q

What is the role of bicarbonate in the body?

A

Bicarbonate acts as a buffer and a base

41
Q

How does the lungs help maintain a neutral pH?

A

The lungs help maintain a neutral pH by controlling carbonic acid (which is directly proportional to the partial pressure of carbon dioxide or pCO2) retain or released from the body

42
Q

What is the role of carbon dioxide in the body?

A

Carbon dioxide acts as a buffer and an acid

43
Q

What is acidosis?

A

An acid-base disorder that leads to a pH < 7.35

44
Q

What is alkalosis?

A

If the disorder leads to a pH > 7.45

45
Q

What is the primary disturbance in a metabolic acid-based disorder?

A

The primary disturbance in a metabolic acid-base disorder is the plasma HCO3 concentration

46
Q

How is metabolic acidosis categorized?

A

A metabolic acidosis is characterized primarily by a decrease in plasma HCO3 concentration

47
Q

How is metabolic alkalosis characterized?

A

In a metabolic alkalosis, the plasma HCO3 concentration is increased

48
Q

What is metabolic acidosis associated with?

A

Metabolic acidosis may be associated with an increase in the anion gap

49
Q

What is the primary disturbance in a respiratory acid-base disorder?

A

The primary disturbance in a respiratory acid-base disorder is pCO2

50
Q

How is respiratory acidosis characterized?

A

In respiratory acidosis, the pCO2 is elevated

51
Q

How is respiratory alkalosis characterized?

A

In respiratory alkalosis, the pCO2 is decreased

52
Q

What is the reference range of pH?

A

7.35 - 7.45

53
Q

What is the reference range for pCO2?

A

35 - 45 mmHg

54
Q

What is the reference range for pO2?

A

80 - 100 mmHg

55
Q

What is the reference range for HCO3?

A

22 - 26 mEq/L

56
Q

What is the reference range for O2 sat?

A

> 95%

57
Q

How are ABGs presented in a written chart note?

A

ABG: pH/pCO2/pO2/HCO3/O2 sat

58
Q

What is the anion gap?

A

The anion gap is the difference in the measured cations and the measured anions in the blood

59
Q

What are the possible causes of metabolic acidosis?

A

Cyanide, uremia, toluene, ethanol (alcoholic ketoacidosis), diabetic ketoacidosis, isoniazid, methanol, propylene glycol, lactic acidosis, ethylene glycol, salicylates

60
Q

When is the anion gap considered high?

A

> 12 mEq/L

61
Q

How is the anion gap calculated?

A

Anion gap (AG) = Na - Cl - HCO3

62
Q

What is the role of buffer systems?

A

Buffer systems help to reduce the impact of too few or too many hydrogen ions in body fluids. Buffers minimize fluctuations in the pH so that harm is avoided

63
Q

What could the under or overproduction of hydrogen ions do?

A

These hydrogen ions could cause harm, including degrading some drugs, destabilizing proteins, inhibiting proteins, inhibiting cellular functions and, with too much of a change outside of the narrow change, cells die and death can occur

64
Q

What are buffer systems composed of?

A

Buffer systems are composed of either a weak acid and salt of the acid or a weak base and a salt of the base

65
Q

What is an acid?

A

An acid is a compound that dissociates, releasing (donating) protons into solution

*Once the proton is released, the compound is now a conjugate base, or its salt form

66
Q

What is a base?

A

A base picks up, or binds, the proton

67
Q

How are acid-base reactions equilibrium reactions?

A

There is drug moving back and forth between the acid and base state

68
Q

What can be used to determine if the drug is acting as an acid or base?

A

The pH and pKa

69
Q

What does it mean when pH = pKa?

A

When the pH = pKa, the molar concentration of the salt form and 50% in acid form. When the pH = pKa, this is the point at which half of the compound is not protonated (ionized), and half is protonated (un-ionized)

70
Q

What does it mean when there is a strong acid or base?

A

A strong acid or base means 100% dissociation

71
Q

What does it mean when there is a weak acid or base?

A

A weak acid or base means very limited dissociation

72
Q

What does it mean when pH > pKa?

A

If the pH > pKa, more of the acid is ionized, and more of the conjugate base is un-ionized

73
Q

What does it mean when pH = pKa?

A

If the pH = pKa, the ionized and un-ionized forms are equal

74
Q

What does it mean when pH < pKa?

A

If the pH < pKa, more of the acid is un-ionized, and more of the conjugate base is ionized

75
Q

Why is the percentage of drug in the ionized vs. un-ionized state important?

A

An ionized drug is soluble but cannot easily cross lipid membranes. An un-ionized drug is not soluble but can cross the membranes and reach the proper receptor site. Most drugs are weak acids so they are soluble and can pick up a proton to cross the lipid bilayer

76
Q

What is the purpose of Henderson-Hasselbalch equation?

A

It is used to solve for the pH

77
Q

What is the weak acid formula?

A
78
Q

What is the weak acid formula?

A

pH = pKa + log [salt/acid]

79
Q

What is the weak base formulas?

A

pH = (14 - pKb) + log [base/salt] = pKa + log [base/salt]

80
Q

How do you calculate the percent ionization of a weak acid?

A

% ionization = 100 / [1 + 10^(pKa - pH)]

81
Q

How do you calculate the percent ionization of a weak base?

A

% ionization = 100 / [1 + 10^(pH - pKa)]

82
Q

Describe calcium carbonate

A

Calcium carbonate has acid-dependent absorption and should be taken with meals. It is a dense form of calcium and contains 40% elemental calcium

83
Q

Describe calcium citrate.

A

Calcium citrate has acid-independent absorption and can be taken with or without food. It is less dense and contains 21% elemental calcium

84
Q

What is calcium acetate used for?

A

Calcium acetate is used as a phosphate binder and not for calcium replacement

*Though the capsules contain 25% elemental calcium, absorption from this formulation is poor

85
Q

How is aminophylline and theophylline dosed?

A

They are dosed using IBW in normal weight and obese patients for safety

86
Q

How do you convert from aminophylline to theophylline?

A

Multiply by 0.8

87
Q

How do you convert from theophylline to aminophylline?

A

Divide by 0.8

88
Q

What happens when a patient’s neutrophil count is low?

A

The lower a neutrophil’s count, the more susceptible that patient is to infection

89
Q

What is the Clozapine REMS programs designed for?

A

The Clozapine REMS Program is designed to reduce the risk of severe clozapine-induced neutropenia; clozapine cannot be refilled if the ANC is < 1000 cells/mm^3

90
Q

If a patient is neutropenic, what are some monitoring parameters?

A

A neutropenic patient should be monitored for signs of infections, including fever, shaking, general weakness or flu-like symptoms. Precautions to reduce infection risk, such as proper hand-washing and avoiding others with infection, should be followed

91
Q

What is normal ANC levels?

A

2200 - 8000

92
Q

What is neutropenia levels?

A

< 1000 (at risk for infection)

93
Q

What is severe neutropenia levels?

A

< 500

94
Q

What is profound neutropenia levels?

A

< 100

95
Q

How do you calculate ANC?

A

Multiply the WBC by the percentage of neutrophils (the segs plus the bands) and divide by 100

ANC (cells/mm^3) = WBC x [(% segs + % bands)/100]

96
Q

How can neutrophils be labeled on a lab report?

A

Neutrophils can be labeled polymorphonuclear cells (PMNs or polys) or segmented neutrophils (segs) on a lab report

NAPLEX Review (45 decks)

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