For the longest time it was LBs, but now BMI is the unit of measure surgical facilities use to determine whether an overweight patient is a safe and suitable candidate for same-day surgery. "It's not What do you weigh? but rather What is your body mass index? that we ask," says anesthesiologist Steven Gayer, MD, MBA, chief of surgery and anesthesia at Bascom Palmer Eye Institute in Miami, Fla., and chair of the American Society of Anesthesiologists' Ambulatory Surgical Care Committee.

But how heavily should you weigh a patient's weight-to-height ratio (BMI = kg/m2) when considering whether he's safe for outpatient surgery? Just as there are varying degrees of obesity — a BMI of 25 to 29.9 is considered overweight, over 30 is obese, over 40 is morbidly obese and over 50 is super obese — BMI alone can't predict operative risk.

"Many ASCs will default on doing morbidly or super-obese patients and refer those patients to a hospital," says Dr. Gayer. "But as with all things, it's advantageous to set a consensus guideline for your facility that makes the decision binary: yes or no — that's it. If a surgeon is aware that the center has these fairly hard stops, then he'll book the patient in a hospital setting."

Fairly hard stops suggests there's a little leeway. Some see a high BMI as a red flag that danger could lie ahead. Others view it as more of a sliding scale than a hard-and-fast limit. For example, one facility might have an absolute BMI cutoff of 50 — "I will do patients on occasion that are above 50, but in general we don't," says Dr. Gayer — and then consider those patients with a BMI of 40 to 49 on a case-by-case basis depending on anesthesia's risk assessment.

For others, it's a game of tug-of-war, the surgeons wanting to push the BMI limit up, the anesthesia providers wanting to pull it down a notch. Some have raised their BMI cutoff for an unlikely reason: too many of their patients exceeded it. OSM