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Body Surface Area (BSA)

Body Surface Area (BSA)

Body Surface Area (BSA) is the total surface of the human body.  This measurement is used in the medical field to help determine the appropriate dosages of medicine and the amount of IV fluids that need to be administered.

Body Surface Area has many different formulas for calculating the number, each with slightly different results.  The most commonly used formula now is that of Mosteller, published in 1987 in The New England Journal of Medicine.  Mosteller’s derived a simplified calculation in metric terms.  The body surface area = the square root of product of the weight in kg times the height in cm divided by 3600.

Mosteller Body Surface Area Formula

Mosteller Body Surface Area Formula

Here are a few other formulas for determining Body Surface Area

Body Surface Area Formulas

Body Surface Area Formulas

When trying to calculate what the normal Body Surface Area other considerations than just height and weight need to be taken into account.  Other factors include age and gender.  Here are some examples for Body Surface Area:

  • Average BSA for adult men: 1.9 m2
  • Average BSA for adult women: 1.6 m2
  • Average BSA for children (9 years): 1.07 m2
  • Average BSA for children (10 years): 1.14 m2
  • Average BSA for children (12-13 years): 1.33 m2

Other Medical Purposes

There are other medical purposes that require the aid of the Body Surface Area measurement.  A few examples include:

  • The glomerular filtration rate, which is calculated in regard to the body surface area; is used for renal function patients.
  • The cardiac index is a measure of cardiac output divided by the body surface area, giving a better approximation of the required cardiac output.
  • Chemotherapy and pharmacotherapies are often dosed according to the patient’s body surface area.
  • Glucocorticoid dosing is also expressed in terms of body surface area for calculating maintenance doses or to compare high dose use with maintenance requirement.

Reference: Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098.

Burn Patients

In emergency situations (such as burn victims) there is little time to determine the body surface area.  In these an accurate estimation of body surface area burn is important.  For the purpose of a fast approximate clinical estimation, the total palmar surface of palm plus five digits of the patient’s hand be assumed to be approximately equivalent to 1%.  You can think of this area as the “hand print” and just for calcification, the area is slightly less than 1% of the body surface area.

Rule of Nines

The Rule of Nines is another fast method to determine body surface area.  This method divides the body’s surface area into percentages as is also used in burn patients.

  • The front and back of the head and neck equal 9% of the body’s surface area.
  • The front and back of each arm and hand equal 9% of the body’s surface area.
  • The chest equals 9% and the stomach equals 9% of the body’s surface area.
  • The upper back equals 9% and the lower back equals 9% of the body’s surface area.
  • The front and back of each leg and foot equal 18% of the body’s surface area.
  • The groin area equals 1% of the body’s surface area.
Rule of Nine Chart for Determining Body Surface Area

Rule of Nine Chart for Determining Body Surface Area

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