Pathophysiological and Perioperative Features of Morbidly Obese Parturients

Yigal Leykin; Tommaso Pellis

Disclosures

Expert Rev of Obstet Gynecol. 2009;4(3):313-319. 

In This Article

Definition

The BMI (bodyweight [kg]/height2 [m]) is widely used to grade obesity. A patient with a BMI of 20-25 kg/m2 is considered normal weight; 26-29 kg/m2: overweight; 30-34 kg/m2: class I obesity; 35-39 kg/m2: class II obesity; and over 40 kg/m2: class III obesity (formerly considered morbidly obese). A patient with a BMI greater than 50 kg/m2 is considered to be super morbidly obese, and super-super-morbidly obese if greater than 60 kg/m2.[13]

Since most anesthetic drugs are administered on the basis of ideal bodyweight, lean bodyweight or total bodyweight, the anesthesiologist must be familiar with these terms as they pertain to the management of obese patients.

Ideal bodyweight is a definition initially introduced by life-insurance companies to describe the weight statistically associated with maximum life expectancy. In the absence of weight in vitro, ideal bodyweight can easily be estimated by the simple formula: ideal bodyweight = (22)(m2), with normal weight within 10% of ideal bodyweight.[11] Super morbidly obese is a term that was proposed by Mason in 1987 to describe patients with a weight equal to or greater than 225% of ideal bodyweight.[14]

Lean bodyweight is total bodyweight minus the weight of body fat. Lean bodyweight includes muscles, bones, tendons, ligaments and body water, while body fat is only adipose tissue. In normal patients, lean bodyweight should be approximately 80% of the total bodyweight for males and 75% for females. In nonobese patients, total bodyweight approximates ideal bodyweight. In morbid obesity, lean bodyweight is estimated by increasing ideal bodyweight by 20-30%.

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