Researchers call for new standard to measure obesity risks in surgery

“The most important factor is not how much
body fat you have but where it is”. Central
obesity, or the 'apple belly' creates high risk.

by Anne Crawford

Monash University and Alfred Hospital researchers are conducting research that challenges the popular way of measuring obesity – using Body Mass Index (BMI) – as a perioperative risk.

Professor Paul Myles, Director of Anaesthesia and Perioperative Medicine at Alfred Health and Monash University, recently co-wrote an editorial in the leading British Journal of Anaesthesia that questions the use of BMI as a measurement indicating risk and which calls for a better approach. BMI is body weight in kilograms, divided by the square of height in metres.

The paper says that although it is generally believed that overweight and obese people are at greater risk of complications after surgery that studies using BMI have found otherwise – the so-called ‘obesity paradox’.  

However, BMI does not distinguish lean muscle from fat mass, meaning that a fit, highly muscular rugby player, for example, could be labelled obese. Muscular people could be therefore be classified as having high BMI yet be healthy, skewing the results in such studies.

“The most important factor is not how much body fat you have but where it is,” Professor Myles said. “People with central obesity – the typical ‘apple belly’ most often seen in men – are the group that do very badly in cardiovascular disease, diabetes and so on. It’s this central obesity that actually puts them at higher risk of these diseases,” he said.

Waist circumference is strongly associated with metabolic risk factors (such as high blood pressure), increased morbidity and mortality from type 2 diabetes and cardiovascular disease.

“Putting a tape measure around the abdomen is likely to be more predictive and reliable as a measure of risk in surgery, anaesthetic complications and surgical complications – and probably in terms of public health generally,” Professor Myles said.

The authors argue that waist circumference should be used as the standard obesity measure in the perioperative setting. The paper has attracted keen interest around the world.

A large international study, led by Monash and the Alfred, is now testing the assertion. Professor Myles said the NHMRC-funded study, nearing completion, has reviewed the cases of 3000 people having major surgery in 70 hospitals across seven countries, using waist circumference as a measure of risk.

Obesity is becoming more prevalent throughout the world – and so too are the health problems associated with it. Almost two in three Australian adults are obese or overweight.

Obese people undergoing operations are at greater risk of wound infection, respiratory complications, post-operative pneumonia, deep vein thrombosis and are more likely to end up in the intensive care unit, spend longer in hospital and need antibiotics. In the longer term they are more likely to be at risk of diabetes, sleep apnoea and cardiovascular disease.

Obesity also poses practical problems for hospitals and health professionals. New, larger operating tables have to be purchased because ‘super super obese’ people are becoming too big to fit on existing ones, and handling and moving patients requires more staff.       

Professor Myles said correctly diagnosing and treating obese people gives medical professionals a ‘golden opportunity’ to help them develop healthier lifestyle habits that could help reduce complications perioperatively and in the longer term.

Watch this space for the results of the study . . .

Gurunathan U, Myles PS. Limitations of body mass index as an obesity measure of perioperative risk. Br J Anaesth. 2016 Mar;116(3):319-21. doi: 10.1093/bja/aev541.