“The study refutes a key assumption that has limited the adoption of nephron-sparing surgery (NSS),” said Parekh, who is also the Dr. Victor Politano Endowed Chair in Clinical Urology, and Director of Robotic Surgery.
Sometimes known as a partial nephrectomy, NSS involves the removal of only the cancerous portion of a patient’s kidney when a cancer is at an early stage with small, localized tumors, when patients have already lost one kidney or when they are at risk of losing the other kidney.
“Until now, most urologists felt it was only safe to clamp the blood supply to the kidney – a process called ischemia – for up to 30 minutes,” said Parekh. “Now it is clear that clamps to the blood vessels can be applied safely for 45 to 60 minutes, opening the door for surgeons to save a portion of the kidney through NSS rather than settling for the rapid removal of the entire kidney.”
The study, “Tolerance of the Human Kidney to Isolated Controlled Ischemia,” was published recently in the Journal of the American Society of Nephrology.
The researchers performed renal (kidney) biopsies before, during, and after surgically induced renal clamp ischemia in 40 patients undergoing partial nephrectomy. In 82 percent of the patients, the ischemia lasted 30 minutes. The research team then analyzed changes in the subject’s biomarkers for acute kidney injury (AKI) and found elevations that did not correlate with renal functions.
“No other study has prospectively looked at biomarkers in the setting of renal ischemia and correlated them with renal ultrastructure and used real-time biopsies to see whether the concern about ischemia was justified,” Parekh said. “Our findings suggest that human kidneys can safely tolerate 30 to 60 minutes of controlled clamp ischemia with only mild structural changes and no acute functional loss.”
Parekh noted that NSS has grown in importance over the past decade with improvements in diagnostic imaging techniques. “Historically, surgeons had to remove a patient’s entire kidney since cancers were usually not detected until after substantial tumor growth,” he said. “Today, many cancers can be detected incidentally when tumors are small and can be excised without removing the entire kidney.”
In the U.S. there are about 65,000 new kidney cancer cases annually, Parekh said. “While NSS is suitable for about 80 percent of these patients, only about 25 percent undergo this kidney-sparing procedure,” he said. “The main reason is that NSS is perceived to be technically challenging with the added pressure of limiting renal ischemia to less than 20-30 minutes.”
The vascularity of the kidneys induces temporary occlusion of the renal vasculature for performing NSS in order to excise the tumor and close the ensuing defect in a relatively bloodless field. “The current belief that surgeons could not do that for more than 20 or 30 minutes inflicts time pressure to complete these surgeries quickly,” Parekh said. “By showing that the blood vessels can be safely clamped for longer periods, our study should make NSS procedures more attractive to other surgeons in their own practices.”
An expert in the prevention, diagnosis, and treatment of urologic malignancies, Parekh, who joined the Miller School faculty in August 2012, is among the world’s most experienced robotic surgeons for urologic oncology. He is the author of several scientific papers, abstracts and book chapters and an assistant editor for the preeminent Journal of Urology.
The study was conducted at the University of Texas Health Science Center at San Antonio, where Parekh was the Doctors Hospital at Renaissance Distinguished University Chair in Urology and Chief of Robotic Surgery and Urologic Oncology.
The study’s co-authors are Barbara Ercole, M.D., William Hilton, M.D., Manjeri A. Venkatachalam, M.D., and Joel M. Weinberg, M.D., University of Texas Health Science Center San Antonio; Kathleen C. Torkko, Ph.D., University of Colorado Denver; and Michael Bennett, Ph.D., and Prasad Devarajan, M.D., University of Cincinnati College of Medicine.