CHICAGO — For decades, after opening up a patient to remove part of a kidney with cancer, urologic surgeons have dumped slushy ice on top of the organ before proceeding with the partial nephrectomy.
Despite being a bit crude, this practice has seemed sensible: by chilling the kidney, the surgeon could slow metabolism and help prevent or minimize tissue injury caused by diminished blood flow after clamps are placed on blood vessels to enable the kidney surgery to proceed. The goal has always been to preserve renal function.
Now, researchers from Canada, led by Rodney Breau, MD, University of Ottawa, Ontario, say that this practice of icing the kidney, or renal hypothermia, does not benefit patients.
In a first-of-its-kind randomized clinical trial at six academic tertiary care hospitals, the team found that 1 year after undergoing open partial nephrectomy, renal function was not significantly better among 79 patients who received icing for 10 minutes during surgery than among 82 patients who did not.
Breau and colleagues concluded that hypothermia is no longer necessary. Their new study was presented here at the American Urological Association (AUA) 2019 Annual Meeting.
"These findings suggest that intraoperative hypothermia should be abandoned as a method for long-term renal function preservation," the Canadian team writes in their meeting abstract.
Breau told Medscape Medical News that "bottom line, the trial is very compelling — we don't know if anyone benefits from hypothermia."
The kidney is "quite resilient to ischemia," he summarized. At the same time, Breau said it is acceptable to continue the practice of icing, because most study patients "did not do worse with hypothermia." In short, use of icing had the same effect as not using it.
However, the word "abandoned" in the abstract disturbed Jihad Kaouk, MD, Glickman Urologic and Kidney Institute at the Cleveland Clinic, who was not involved with the study and attended the meeting.
True, the great majority patients can forgo renal hypothermia, he agreed.
But not all patients, he told Medscape Medical News.
Icing should be used selectively for three subgroups of patients who are more vulnerable to the potential deleterious effects of ischemia, he argued.
The first group comprises patients with compromised baseline kidney function, such as those with stage 3 or 4 chronic kidney disease. The second group consists of patients with only one kidney. The third group consists of patients whose condition requires significant reconstruction during partial nephrectomy and who are thus at risk for excessively warm ischemia, owing to longer surgery time.
These three groups account for 5% to 10% of all patients who undergo partial neprectomies, Kaouk told Medscape Medical News.
But Breau countered that these three subgroups were analyzed in the study. "We did not see significant benefit" with hypothermia in the groups, he said flatly.
Primary Outcome: Criticism and Rebuttal
The primary outcome for the study was glomerular filtration rate (GFR) 1 year post surgery.
Beau reported that for the patients who underwent hypothermia and for those who did not, 1-year GFRs were similar (89.0 vs 80.5 mL/min/1.73m2; mean difference, 8.5; 95% confidence interval [CI], ‒0.4 to 17.4).
Additionally, the overall decreases in GFR were similar: ‒9.0 mL/min/1.73m2 in the hypothermia group compared to ‒8.8 mL/min/1.73m2 in the no-hypothermia group (mean difference, 0.2 mL/min/1.73m2; 95% CI, ‒5.4 to 5.7).
"The commonly held belief about hypothermia being beneficial may not be true. Our trial suggests that it's probably not true," asserted Breau.
But Kaouk said the study has important limitations.
For starters, the primary outcome was not a good measure because the period of 1 year is too great, said Kaouk. "We do not expect to see a hypothermia effect at 1 year," he commented.
Instead, acute tubular necrosis, a short-term outcome that occurs between 3 to 6 weeks postoperatively, is a much better measure, he said. This outcome looks at filtration units of the kidney, which are very sensitive and slough off and die in the absence of oxygen (once blood flow stops from surgical clamps).
"That is a belief, which everyone is entitled to, but there is no evidence to support it," countered Breau about Kaouck's claim that acute tubular necrosis is a superior outcome measure.
Patients who have severe acute tubular necrosis will typically need temporary dialysis, Kaouk also said. "That's a bad thing," he summarized.
But Breau said that there is no proof that hypothermia will reduce the need for dialysis, nor is there evidence that acute tubular necrosis is clinically meaningful for most patients.
The 1-year outcome on GFR/kidney function is well suited to learning whether or not hypothermia is valuable, Breau asserted.
Cleveland Clinic's Kaouk also said that patients such as those in the three above-mentioned subgroups would also benefit from icing during robotic partial nephrectomy (as opposed to open surgery, which was evaluated in the clinical trial).
The Ohio urologist led a study that showed that renal hypothermia using ice slush is "technically feasible" in the minimally invasive approach ( Urology . 2014;84:712-8). His team also employed real-time parenchymal temperature monitoring to demonstrate that the cooling did in fact occur, which was something Breau and colleagues did not show, he said.
More Detail From New Study
The study authors used broad inclusion criteria; patients were only excluded if they were younger than 18 years or pregnant or if it was planned that they were to undergo surgery on the contralateral kidney within 12 months. The GFR was assessed by plasma clearance of 99mTc-DTPA and differential renal function by renal scintigraphy
Kidney-specific decreases in GFR were similar between the hypothermia and no-hypothermia treatment groups (‒7.0 vs ‒6.8 mL/min/1.73m2; mean difference, 0.2 mL/min/1.73m2; 95% CI, ‒3.6 to 4.0).
No difference in renal function was observed when patients were stratified by median age, baseline renal function (>45 vs <45 mL/min/1.73m2), or duration of ischemia (<20 vs >20 min; <30 vs >30 min). There was no difference in surgical complications or quality of life between the groups.
The study was funded by the Canadian Institute of Health Research. The study authors and Kaouk have disclosed no relevant financial relationships.
American Urological Association (AUA) 2019 Annual Meeting: Abstract LBA15. Presented May 5, 2019.
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Cite this: Icing Kidneys Unnecessary in Cancer Surgery - Medscape - May 06, 2019.
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