PCNL outcome may be unrelated to BMI, stone burden

October 1, 2007

A recent retrospective study suggests that PCNL outcome is independent of body mass index, at least in terms of successful stone removal, operative blood loss, length of hospital stay, and postoperative pyrexia.

Typical concerns associated with PCNL in overweight patients include such complications as pulmonary embolism, acute myocardial infarction, greater hemoglobin loss, longer hospitalization times, elevated fever, and difficulties in stone removal, said lead study author Igor Sergeyev, MD, attending physician at Long Island College Hospital, Brooklyn, NY. Most of those concerns are unwarranted, he said.

"We saw that BMI does not affect the overall outcome for PCNL," Dr. Sergeyev told a moderated poster session at the AUA annual meeting. "The stone-free outcome and morbidity associated with PCNL were largely independent of patient BMI and the stone burden. The one exception was in thinner patients with large stone burden, who stayed in the hospital longer."

Kidney stone burden was measured by surface area in square millimeters, based on preoperative computed tomography scans. Scans were available for 85 patients.

Of these 85 patients, 37 (43.5%) were obese or morbidly obese, 33 (38.8%) were overweight, and 15 (17.7%) were within normal weight parameters. Patients were also stratified on the basis of stone burden >300 mm2 or <300 mm2 . Of the total group, 54 patients (63.6%) had stone burdens <300 mm2 and 31 (36.4%) had a stone burden >300 mm2 .

Similar stone-free rates

No statistically significant differences were noted between patients in the three BMI groups for stone burden, stone-free rate, postoperative fever, or changes in hemoglobin when stratified either by BMI alone or BMI plus kidney stone burden. The majority of patients studied were either obese or morbidly obese, and these patients were more likely to undergo a second-look procedure, Dr. Sergeyev said.

The only statistically significant difference among the three groups was length of stay. When stratified by both BMI and stone burden, patients with normal BMI and a higher stone burden were more likely to spend more time in the hospital than other patients were. Average length of stay for normal BMI, high-stone-burden patients was 7 days, compared to 3.5 days for overweight patients and 4.3 days for obese and morbidly obese patients. Statistical significance of differences in length of hospital stay was more pronounced when patients were stratified by BMI alone (p=.01) compared to BMI plus stone burden >300 mm2 (p=.03).

Two patients accounted for the increased length of stay in the normal BMI group, Dr. Sergeyev pointed out. One patient was diagnosed with pulmonary embolism and stayed in the hospital for proper anticoagulation; the second became septic following PCNL and remained hospitalized for intravenous antibiotic treatment. Two morbidly obese patients in the study group had BMI >50, he added.

"They did not end up having any complications, but a larger sample would give us more statistically significant results," Dr. Sergeyev said. "We may go to four BMI groups in the next study."