Calculations IV Flashcards
What is body mass index (BMI)?
Body mass index (BMI) is a measure of body fat based on height and weight that applies to adult men and women
What is BMI a useful measure of?
Body fat
What are the limitations of BMI?
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
In terms of waist circumference, what waist size is associated with higher disease risk?
High risk is defined as a waist size > 35 inches for women or > 40 inches for men
What is the formula for BMI?
weight (kg)/[height (m)]^2 or weight (pounds)/[height (in)]^2 x 703
What BMI is considered underweight?
< 18.5 kg/m2
What BMI is considered normal weight?
18.5 - 24.9
What BMI is considered overweight?
25-29.9
What BMI is considered obese?
> 30
What are the three potential measures of body weight for a patient?
Actual (or total) body weight, ideal body weight and adjusted body weight
What is actual body weight or total body weight?
Actual body weight or total body weight is the weight of the patient when weighed on a scale
What is ideal body weight?
Ideal body weight is the healthy (ideal) weight for a person
How do you calculate IBW for males?
50 kg + (2.3 kg)(number of inches over 5 feet)
How do you calculate IBW for females?
IBW (females) = 45.5 kg + (2.3 kg)(number of inches over 5 feet)
What is adjusted body weight?
Adjusted body weight is calculated when patients are obese or overweight
What is the formula to calculate adjusted body weight?
IBW + 0.4(TBW - IBW)
If a person is underweight, what measure of body weight do you use?
Use total body weight for all medications
If a person is normal weight, what measure of body weight do you use?
- Use total body weight for most medications
- Use ideal body weight for aminophylline, theophylline, acyclovir and levothyroxine
If a person is obese, what measure of body weight do you use?
- 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
What are flow rates?
Flow rates are used to specify the volume or amount of drug a patient will receive over a given period of time
What are examples of how flow rate can be expressed?
Milliters per hour, milligrams per hour, mcg/kg/min or as the total time to administer the entire volume of the infusion
What does flow rate depend on?
Flow rate depend on the dose of the medication and the concentration available
What is creatinine?
Creatinine is a breakdown product when muscle tissue makes energy
What is the normal range for serum creatinine?
The normal range for serum creatinine is approximately 0.6-1.3 mg/dL
What happens to creatinine when kidney function declines?
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
What should be assessed when a patient is dehydrated?
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
What is the BUN:SCr ratio that indicates dehydration?
> 20:1
What are some signs of dehydration?
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
What can usually cause dehydration?
Dehydration is usually caused by diarrhea, vomiting and/or a lack of adequate fluid intake
What is the Cockgroft-Gault equation?
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
When is the Cockcroft-Gault equation unreliable?
It is not reliable in very young children, ESRD patients or when renal function is fluctuating rapidly
If a patient underweight, what body weight measure should be used for calculating CrCL?
Total body weight
If a patient normal weight, what body weight measure should be used for calculating CrCL?
Ideal body weight
If a patient overweight or obese, what body weight measure should be used for calculating CrCL?
If BMI < 25, use ideal body weight. If BMI > 25, use adjusted body weight
What is pH?
The pH refers to the acidity or basicity of a solution
What does an increase or decrease in pH represent?
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
How can the acid-base status of. patient be determined?
The acid-base status of a patient can be determined with an arterial blood gas (ABG)
What is the primary buffering system of the body?
The bicarbonate/carbonic acid