BANFF, Alberta—Percutaneous nephrolithotomy (PCNL) is relatively safe in patients with a higher body mass index (BMI), but is associated with a longer operative time, more minor and major complications, and a higher retreatment rate than in thinner individuals, according to the findings of a large international study.

The results were presented at the Canadian Urological Association’s annual meeting and published in the Journal of Urology (2012;188:138-144).

The Global PCNL Study involved data collected from 2007 to 2009 from 3,709 patients treated at 96 centers around the world. The rates of intraoperative complications—failed access, perforation, and hydrothorax—were similar in the those with a BMI greater than 40 kg/m2 and those with a BMI of 18.5-25 kg/m2. However, the respective average lengths of the procedure in these two groups were 112.2 minutes and 86 minutes. Furthermore, the rates of 30-day complications were 22.1% and 6.5%, respectively, and the retreatment rates were 28.1% and 12.4%, respectively.

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The investigators suggest that in light of the increasing number of obese individuals, whenever possible, urologists should use—among other measures to minimize complications and need for retreatment—a long-access needle, sheath and nephroscope, and flexible ureteroscopy.

“Flexible ureteroscopy is a procedure that can be used when the stone is less than two cm in diameter; it is a potentially less morbid procedure than PNCL,” said lead investigator Hassan Razvi, MD.

Dr. Razvi, Professor of Urology and Chair of the Division of Urology at the Schulich School of Medicine and Dentistry, University of Western Ontario, London, is part of the Clinical Research Office of the Endourological Society, which administers the database from which the information for the study was obtained. The investigators found 97 ‘super-obese’ individuals among the cohort of 3,709 patients.

Morbidly obese patients were more likely to be female and had a higher American Society of Anesthesiologists classification than the 1,394 normal-weight individuals. They also were significantly more likely to have staghorn stones. Intraoperatively, in the morbidly obese, percutaneous access was more likely to be performed by an interventional radiologist than a urologist compared with normal-weight subjects. Larger individuals were also less likely to be placed in a supine position, to have  multiple  access tracts, telescopic dilation, or postoperative stenting.

Matching of the 97 morbidly obese patients with 97 normal-weight patients confirmed the higher operating time in the heavier patients. It also showed they were more likely to experience a reduction in hemoglobin intraoperatively.

While both the average length of hospital stay and the stone-free rate were similar in the two matched groups, the rates of minor complications within 30 days were 11.6% and 5.4% in the morbidly obese and normal-weight individuals, respectively. The 30-day major complication rates were 10.5% and 1.1%, respectively.

The heavier group also had a higher retreatment rate and was more likely to undergo retreatment with PCNL or ureteroscopy than SWL.

The investigators did not have enough data to perform sub-analyses according to country, center volume, and community versus academic center. If such analyses had been performed, this may have explained differences between this study and previous American studies. For example, a study performed at the University of Texas Southwestern Medical Center in Dallas (Urology 2008;72:756-760), found no significant differences in complication rates, operative time, or need for multiple accesses between normal-weight or obese individuals.