shutterstock_60800920There is no one-size-fits-all rule for lipoaspirate volume thresholds, according to a report in the September issue of Plastic and Reconstructive Surgery®. Turns out that complications are not wholly dependent on the absolute volume of lipoaspirate, but rather include the synergistic effects of other relevant patient factors—namely, body mass index (BMI).

To help surgeons get a better handle on “relative liposuction volume threshold,” the study authors have created a risk assessment tool.

 “Our results instead suggest that complications are not wholly dependent on the absolute volume of lipoaspirate, but rather include the synergistic effects of other relevant patient factors, namely, body mass index.”

There’s a long history of debate over the safe volume of fat tissue that can be removed via liposuction. Current American Society of Plastic Surgeons (ASPS) guidelines define 5,000 milliliters (5 liters) as “large-volume liposuction” potentially associated with a higher risk of complications. But the guidelines acknowledge there is no scientific data to support an absolute cutoff point.

In the new study, John Y.S. Kim, MD, a plastic surgeon at Northwestern University’s Feinberg School of Medicine in Chicago, and colleagues analyzed data on more than 4,500 liposuction patients, drawn from the ASPS’s “Tracking Operations and Outcomes for Plastic Surgeons” (TOPS) database. They evaluated the relationship between liposuction volume and complication risk—including interactions with the patient’s BMI.

“Our study shows that liposuction is associated with a very low complication rate, with major complications occurring in less than 1 in 1,000 patients,” Kim says in a news release. “It also calls into question the concept of simple absolute thresholds for lipoaspirate volume—the amount of liposuction that can be performed safely seems to depend in part on how much fat content a person begins with.”

The overall complication rate was 1.5%, with few serious complications and no deaths. By far, the most common complication was a fluid collection (seroma) requiring drainage. The average liposuction volume was about 2 liters.

Patients with complications had larger liposuction volumes—average 3.4 liters—and higher BMIs. Patients undergoing “large-volume” liposuction of more than 5 liters had a higher overall complication rate: 3.7% versus 1.1%. This resulted almost entirely from an increase in seromas.

There was also a significant interaction between liposuction volume and BMI: when patients with higher BMIs had a greater liposuction volume, the complication rate was actually somewhat lower.

“In other words, obese patients may tolerate larger lipoaspirate volumes without an increased risk of complications,” the researchers write. In contrast, patients with lower BMIs experience a “more exponential increase in risk” at higher liposuction volumes. This relationship between a patient’s pre-existing fat content and “safe” liposuction volumes had not been previously shown.

The “relative liposuction volume threshold” provides a relative threshold where complications start to increase, but does not imply an absolute limit on liposuction volumes. Other considerations such as length of surgery, adjunct procedures, and the patient’s overall health status are also important to consider when evaluating liposuction risk, they write.

 Relative Liposuction Volume Threshold: Do the Math

A new odds ratio calculator demonstrates this effect. “In a patient with a body mass index of 30, increasing the lipoaspirate volume from 2 liters to 6 liters results in a nearly 25-fold increase in the likelihood of a complication, reflected by an increase in the adjusted odds ratio of any complication from 20.3 to 500.7,” they write. “Conversely, in the patient with a body mass index of 50, the same increase in lipoaspirate volume results in a modest increase in the risk of an overall complication from 32.9 to 49.2.”

These hypothetical patients demonstrate the important nonlinear nature of the relationship between BMI and liposuction volume, they write. “Instead, the two variables serve as buffers whereby an increase in liposuction volume in a patient with a lower body mass index results in a far greater magnitude of increased risk than in a patient with a higher body mass index.”