Patient BMI shows little impact on PCNL outcomes

November 1, 2006

Cleveland-There is a commonly held view that obese patients tend to present greater surgical challenges and have more complications after percutaneous nephrolithotomy. Researchers from Albert Einstein College of Medicine in New York have challenged that belief.

"In general, it is thought that the procedure will be cumbersome and less likely to result in a stone-free condition after the initial intervention. We showed that this is not true. We showed that obese people, overweight people, and average-weight people are equally likely to be stone-free after the initial procedure," Igor Sergeyev, MD, a former resident at Albert Einstein, told Urology Times at the 2006 World Congress of Endourology here.

The Albert Einstein team, led by David M. Hoenig, MD, conducted a study comparing PCNL outcomes by body mass index and stone size. The group's findings were presented by Dr. Sergeyev, now an attending physician in the department of urology at Long Island College Hospital, Brooklyn.

"When we initially did this study, we stratified by body mass index. There was criticism that body mass alone was not sufficient. Some patients have larger stones and some, smaller, and this can affect both OR time and outcomes, such as bleeding," Dr. Sergeyev said. "So we returned to the data and stratified by stone size. There are two CPT codes, one for stones <2 cm and one for stones >2 cm. It was not difficult; these were on the charts."

Minor differences

No differences were seen in hospitalization, postoperative fever, or hemoglobin among those with smaller stones regardless of BMI. However, hospitalization appeared to be a few days longer in the BMI <25 group with larger stones (±300 mm2 ) (p=.02).

Dr. Sergeyev said that, despite the overall size of the study (71 patients), stratifying these patients into six categories left each category small and sensitive to the status of individual patients. Seven patients were assigned to the cohort with BMI <25 and stones ±300 mm2 . One of these developed an embolism requiring anticoagulants and 17 days of hospitalization.

A journal reviewer asked what would happen if this patient were excluded from the data, Dr. Sergeyev said. He did so, and found that the difference noted in the length of hospital then was similar to those in the other cohorts.

"Of course, we cannot do that [drop a patient] without introducing bias," he said.

Dr. Sergeyev estimated the average operating time on these obese patients to be 2 to 2½ hours.

"At our institution, we place the patient prone, place a balloon [dilator] under fluoroscopy, and distend the system," he said. "Then the interventional radiologist places the guidewire. Since everything happens in the operating room, there is no need to transport the patient in and out of the interventional suite. It may be a little inconvenient for the radiologist, but it speeds everything up."

"There is no reason to fear doing percutaneous nephrolithotomy on obese people. Our study found no cases of pulmonary embolism, and there were no instances of other medical complications," he added. "There was one area in which the obese were separated from thin and normal patients. The study showed that people with a high body mass index were more likely to need a second-look procedure. Four of the obese were not stone-free after the initial procedure versus only one person with ideal weight and none who were only slightly overweight."