Does Body Mass Index Affect Mortality in Coronary Surgery?

The Body Mass Index (BMI) quantifies nutritional status and classifies humans as underweight, of normal weight, overweight, mildly obese, moderately obese or morbidly obese. Obesity is the excessive accumulation of fat, defined as BMI higher than 30 kg/m². Obesity is widely accepted to complicate anaesthesia and surgery, being a risk factor for mediastinitis after coronary artery bypass grafting (CABG). We sought the evidence on operative mortality of CABG between standard BMI groups.

A simple literature review of papers presenting the mortality of CABG by BMI group: Underweight (BMI ≤ 18.49 kg/m²), normal weight (BMI 18.5–24.9 kg/m²), overweight (BMI 25.0–29.9 kg/m²), mild obesity (BMI 30.0–34.9 kg/m²), moderate obesity (BMI 35.0–39.9 kg/m²), or morbid obesity (BMI ≥ 40.0 kg/m²).

We identified 18 relevant studies with 1,027,711 patients in total. Their variability in size of samples and choice of BMI groups precluded us from attempting inferential statistics. The overall cumulative mortality was 2.7%. Underweight patients had by far the highest mortality (6.6%). Overweight patients had the lowest group mortality (2.1%). The group mortality for morbidly obese patients was 3.44%.

Patients with extreme BMI’s undergoing CABG (underweight ones more than morbidly obese) suffer increased crude mortality. This simple observation indicates that under nutrition and morbid obesity need be further explored as risk factors for coronary surgery.