McCormick BJ, Horns JJ, Das R et al: Nephrectomy is not associated with increased risk of mortality or acute kidney injury after high-grade renal trauma: a propensity score analysis of the Trauma Quality Improvement Program (TQIP). J Urol 2021; 207: 400.

The kidney is the most commonly injured genitourinary organ, with 1%–4% of all trauma patients sustaining some degree of renal injury. Around 55% of renal injuries are low grade, ie AAST (American Association for the Surgery of Trauma) grade 1–2, in nature and are nearly universally managed with observation.¹ High-grade injuries (AAST grade 3–5) are still common, however, and their management is less uniform. Over the past several decades, selective renal artery angioembolization has emerged as safe and effective in treating patients with high-grade renal trauma (HGRT), but the rate of nephrectomy in HGRT patients remains high–up to 1% in grade 3 injuries, 24% in grade 4 and 62% in grade 5.²

The rate of mortality in patients undergoing trauma nephrectomy is as high as 34% in the acute setting.³ While early mortality is largely driven by hemorrhagic shock and unsurvivable injuries, late mortality is primarily due to multisystem organ failure and sepsis. We hypothesized that performing nephrectomy would decrease renal reserve, leading to an increased risk of acute kidney injury (AKI) and inhibiting the body’s ability to overcome the initial trauma and resultant multisystem organ failure.

To investigate the potential relationship between nephrectomy and mortality, we first examined HGRT data from 21 level 1 trauma centers through MiGUTS (Multi-institutional Genitourinary Trauma Study). We analyzed the association between nephrectomy and mortality, controlling for multiple demographic and injury severity markers, including shock. Our results showed that HGRT patients undergoing nephrectomy had an associated 2.1 times higher risk of mortality compared to those who did not undergo nephrectomy (see figure).⁴ While we were intrigued by this strong relationship, the primary limitations of this study were low mortality numbers and significant missingness of blood transfusion data, allowing for the possibility of unaccounted confounders.

Figure. The evolution of our efforts to evaluate the link between nephrectomy and mortality in patients with high-grade renal trauma.

In order to better characterize the relationship between nephrectomy and death, we utilized the National Trauma Data Bank^® (NTDB^®), a long-standing U.S. trauma registry maintained by the American College of Surgeons. In the NTDB we identified nearly 49,000 patients with HGRT. We adjusted for physiological indicators of injury severity, shock and whether or not the patient had a blood transfusion. We found that performing nephrectomy was independently associated with an 82% increase in mortality (see figure).⁵ We published our findings in The Journal of Urology^®, where we concluded that nephrectomy should be avoided if at all possible. However, while the NTDB does contain some data regarding blood transfusions, one of the limitations of the NTDB study was lack of detailed blood transfusion data. In the NTDB, we were able to ascertain whether or not a patient had had a blood transfusion, but we were unable to determine the number of transfusions. This limitation invited the possibility that we were not adequately adjusting for the degree of hemorrhagic shock, and that this could be the primary driver of mortality rather than nephrectomy.

In an effort to better account for degree of hemorrhagic shock as a possible confounder in mortality after nephrectomy, we used the American College of Surgeons TQIP^® (Trauma Quality Improvement Program), which is a large national trauma database containing very granular blood transfusion data, including the exact number and timing of transfusions. In TQIP, we identified 12,780 patients with HGRT between 2013 and 2017.⁶ To eliminate as much bias as possible, we performed propensity scoring. Propensity scoring essentially calculates a probability for each patient according to their likelihood of receiving a nephrectomy based on injury severity, concomitant intra-abdominal organ injuries and other factors. In order to develop 2 similar cohorts for comparison, we matched nephrectomy patients and nonnephrectomy patients with similar propensity scores and created a pseudo-randomization to receiving nephrectomy. Once patients had been matched, we used a similar adjusted analysis to our previous work analyzing the risk of death after nephrectomy, but this time including the volume of blood transfused in the first 24 hours after injury. In addition, we added AKI as a secondary outcome given our hypothesis that nephrectomy would increase risk of AKI, which would in turn increase mortality. The results of this study showed that performing nephrectomy was not associated with higher mortality or incidence of AKI. Rather, increasing blood transfusions, increasing age, nonCaucasian race, addiction and decreasing Glasgow Coma Score were found to be associated with increased risk of mortality.⁶

Given our most recent results, which we believe represent a more accurate picture of the the relationship between nephrectomy and mortality, we concluded that while nephron-sparing treatments should be first line for all stable HGRT patients, urologists and trauma surgeons should not hesitate to perform nephrectomy in patients who are unstable and requiring ongoing blood transfusions, as the degree of hemorrhage appears to be the primary driver of mortality in this population (see figure).

There are 2 findings that illustrate current knowledge gaps about management of renal trauma, which were highlighted in these studies. First, only 2% of the HGRT patient cohort underwent selective renal artery angioembolization for management of hemorrhage. This is less than the expected 6% rate in other studies, and it would be important to investigate if centers with higher utilization of angioembolization demonstrate lower nephrectomy rates; if so, angioembolization could be encouraged as a means of avoiding nephrectomy and the potential long-term consequences. Second, we found that nonCaucasian race was associated with substantially increased mortality in HGRT patients. Disparities in trauma outcomes based on race is not a new finding, but this research into HGRT offers a new opportunity for us as urologists to make health care more equitable for all.