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## Body Surface Area Calculator (BSA)

#### BSA and Dosage Calculator

Height: Weight:
Drug dosage/ M2 :

## Equation Used:

Program uses the following equation:
(Weight) kg0.425 x (Height) cm0.725 x 0.007184 = BSA in M2

Reference:
DuBois D, DuBois DF. A formula to estimate the approximate surface area if height and weight be known. Arch Int Med 1916;17:863-71.

## Background

How is BSA used?:

BSA has the following uses:

1. It determines the dose of chemotherapy for a patient.

2. In order to calculate the maintenance doses or to compare the high dose use with the maintenance need, the glucocorticoid dosing is stated in terms of the BSA.

3. For gaining the appreciation of true glomerular filtration rate (GFR), the renal clearance needs to be divided by the BSA, i.e 1.73 m².

4. A modified version of the BSA is the Quetelet index.

5. When we divide the cardiac output by the BSA, the cardiac index is obtained. This indicates an effective cardiac output.

5.  For the hemodynamic parameters, in case of extreme height and weight, it can be seen that BSA is not as reliable as the Body Mass Index.

6. This parameter is used for adjusting the creatinine clearance while making a comparison between the BSA and normal values for assessment of the presence as well as the intensity of kidney issues.

What are the main BSA formulas?:

There are a number of formulas for calculating the BSA, as already stated. We will look into each one of them in detail here:

1. Mosteller Formula:

It is calculated by multiplying the person's height in cm with his/her weight in kilograms and dividing the value by 3600. Then take the square root of the resulting value to get the BSA as stated below:

BSA = [(W x H)/ 3600] 0.5

A simpler version of this formula is stated below:

BSA  = 0.016667 × W0.5 × H0.5

Let us consider an example to be more clear:

Suppose the weight of a random person is 95.45 kg and his height is 190.5 cm, then multiplying these values and diving the resulting value with 3600, we get 5 and the square root of 5 is 2.24 m².

2. Du Bois formula:

It is the product of the weight of the person raised to the power 0.425, height raised to the power 0.725 and 0.007184, i.e:

BSA = 0.007184 × W0.425 × H0.725

3. Haycock formula:

It is the product of the weight of the person raised to the power 0.5378, height raised to the power 0.3964 and 0.024265, i.e:

BSA = 0.024265 × W0.5378 × H0.3964

4. Gehan and George formula:

It is the product of the weight of the person raised to the power 0.51456, height raised to the power 0.42246 and 0.0235, i.e:

BSA = 0.0235 × W0.51456 × H0.42246

5. Boyd formula:

It is calculated as follows:

BSA = 0.03330 × W(0.6157 - 0.0188 × log10(W) × H0.3

6. Fujimoto formula:

It is the product of the weight of the person raised to the power 0.444, height raised to the power 0.663 and 0.008883, i.e:

BSA = 0.008883 × W0.444 × H0.663

7. Takahira formula:

Calculation:

BSA = 0.007241 × W0.425 × H0.725

8. Schlich formula:

Here, the BSA for men and women use alternative equations:

Women:

BSA = 0.000975482 × W0.46 × H1.08

Men:

BSA = 0.000579479 × W0.38 × H1.24

What  parameters require BSA for calculation?:

BSA is helpful for calculating the following parameters:

1. Cardiac index(CI):

We calculate by dividing the cardiac output by BSA. The normal range of the cardiac index is  2.5 – 4.0 L/min/m². In case it is below the normal range, the underlying cause has to be identified. After this, the treatment modalities have to be planned. The person may need a fluid bolus for dehydration and tachycardia. For heart failure, an inotropic agent might also be required.

2. Stroke volume index(SVI):

The strove volume divided by the BSA provides you the Stroke Volume Index.

3.Systemic vascular resistance index (SVRI):

Divide the systemic vascular resistance by BSA to get the SVRI.

4. Pulmonary vascular resistance index(PVRI):

It is obtained by dividing the vascular resistance by BSA.

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