Although other indices of adiposity have gained momentum in terms of their ability to diagnose children who may develop perioperative respiratory complications, a study from the University of Michigan has found that body mass index (BMI) actually outperforms its competitors. This finding is buoyed by the fact that BMI is easier to calculate than the other indices, making it a much more attractive option for anesthesiologists, particularly those pressed for time.
“It’s well known that childhood obesity is an increasing problem,” said Olubukola O. Nafiu, MD, assistant professor of pediatrics and anesthesiology at the University of Michigan Medical School, in Ann Arbor. “We’ve also shown that childhood obesity is associated with perioperative complications, predominantly airway-related adverse events [AEs].” Although obesity in children is typically defined using BMI, other measures of adiposity, such as neck and abdominal circumference, may show better diagnostic ability for identifying potential problems.
“The theory behind these other measures is that central adiposity is dangerous: If you distribute fat more centrally, you have more problems,” Dr. Nafiu said. “So, given that most institutions measure BMI in children, we wanted to compare the various measures of adiposity in terms of how well they identify who will develop acute perioperative complications.”
To that end, the researchers enrolled 756 children, all undergoing elective, noncardiac surgery, into the trial. The BMI was calculated as weight in kilograms divided by the square of height in meters (kg/m2). Other measures included waist circumference, neck circumference and waist-to-height ratio. Using age- and sex-specific reference growth charts, children were classified as being normal weight (BMI <85th percentile), overweight (85th-95th percentile) or obese (>95th percentile). Perioperative respiratory events were defined as the occurrence of laryngospasm, bronchospasm and post-induction desaturation.
As Dr. Nafiu reported at Pediatric Anesthesiology 2015 (abstract GA2-60), 10.9% of patients experienced respiratory AEs. All of the indices of adiposity were significantly positively correlated with these events. Although receiver operating characteristic (ROC) curve analysis indicated that all measures of adiposity performed well in identifying children with respiratory AEs, the ROC performance of BMI showed the highest discriminant accuracy among the measured indices of adiposity in predicting respiratory AEs.
“Indeed, with each successive analysis, BMI performed better than the other indices of adiposity, which is slightly different from what is described in the literature with respect to predicting complications,” Dr. Nafiu told Anesthesiology News. “On the other hand, weight alone was not very good. It did not have any significant diagnostic capacity.”
These findings were surprising, he said. “I thought measures of central adiposity would perform better than BMI, because they tend to be more associated with things like obstructive sleep apnea and difficulty breathing, which tend to be associated with adverse events.”
Both BMI and neck circumference were positively and significantly associated with the highest odds of respiratory AEs; in contrast, weight and waist circumference were not.
“Essentially, our message to our colleagues is this: If we say we’re concerned about the growing childhood obesity epidemic, then we need to be measuring BMI, not only for the epidemiologic documentation of children coming for surgery, but also for the fact that BMI has the most capacity to catch kids who will suffer adverse perioperative respiratory events.
“From a practical standpoint, it’s a much easier metric to measure.”
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