Anesthesia Student Survival Guide.pdf - Index of

326 ● AnesthesiA student survivAl Guide
Table 20.1 Classification of obesity.
Obesity class BMI Health risk
Class i (overweight) 25–30 low
Class ii (obese) 30–35 Moderate
Class iii (severely obese) 35–40 high
Class iv (morbidly obese) >40 very high
BMI has its limitation and may not be an accurate way of assessing obesity in
body builders.
There are two types of obesity: “central-android” type, which is more
common in men and “peripheral-gynecoid” type more common in women.
The former is also known as apple-shape obesity and the latter is known
as pear-shape obesity. It is important to measure abdominal circumference in
addition to BMI. Central obesity (waist measurement more than 40 in. for men
and more than 35 in. for women) is associated with the respiratory and
cardiac co-morbidities. Waist-to-hip ratio (WHR) >0.95 for men and >0.8 for
women has been shown to confer higher risk of complications.
Physiologic Changes Associated with Obesity
Cardiovascular System
Obesity is an independent risk factor for cardiovascular disease. Since adipose
tissue needs perfusion, total blood volume and stroke volume will increase to
perfuse additional body fat. Cardiac output (C.O.) increases by 0.1 L/min for
each 1 kg addition in body weight.
Gradual accumulation of fat between fibers of heart muscle may cause
myocyte degeneration and cardiac dysfunction. Lipotoxicity of the myocardium
by free fatty acids may also cause apoptosis of lipid-laden cardiomyocytes
and contribute to cardiomyopathy. Increased C.O., left ventricular hypertrophy
(LVH), and LV diastolic dysfunction all predispose to heart failure. Diabetes
mellitus (DM), hypertension (HTN), and coronary artery disease (CAD) are
other factors that predispose these people to congestive heart failure.
Increased C.O. with normal peripheral resistance causes hypertension. For
every 10 kg increase in body weight, there is 3–4 mmHg increase in systolic
pressure and 2 mmHg increase in diastolic pressure. This increase is more
prominent with abdominal obesity. Peripheral vascular resistance may also
increase due to different substances released from adipocytes and sympathetic