We read with interest the article by Choi et al., which examines the association between acute kidney injury in patients who have had their angiotensin-converting enzyme inhibitors or angiotensin receptor-blocking drugs withheld or continued, respectively, pre-operatively [1]. We commend them on a well-designed study that paid great attention to relevant propensity matching.

We want to comment on the difference between statistical significance and clinical relevance [2]. While we agree that an increase of 26.4 μmol.l^-1 in < 48 h is the definition of acute kidney injury as set out by the Acute Kidney Injury Network, both groups show increased serum creatinine values in the postoperative period [1, 3]. The actual difference in increased serum creatinine values is relatively small between the two groups, which would lead us to question the clinical significance. In contrast, the statistical significance of those who breach the threshold of 26.4 μmol.l^-1 is clear and undeniable. As discussed in the article, a recent meta-analysis by Hollmann et al. failed to show an association between peri-operative administration of angiotensin-converting enzyme inhibitors or angiotensin receptor-blocking drugs and mortality or major adverse cardiac events in patients undergoing non-cardiac surgery [3].

While we agree that the article by Choi et al. supports the routine withholding of angiotensin-converting enzyme inhibitors and angiotensin receptor-blocking drugs pre-operatively, we think the more interesting question is whether we can identify specific subsets of patients who are more significantly impacted by the continuation of these drugs in the peri-operative period. This is addressed in the supplementary material where we see that the odds ratio of developing an acute kidney injury appears to be much greater in those patients who present for surgery with an elevated baseline creatinine, low baseline haemoglobin, low BMI and those requiring pre-operative red blood cell transfusion. We are interested if the authors, knowing the data in detail, have any opinion on whether they see a need to cancel surgery in the higher-risk cohort of patients who erroneously continue these drugs peri-operatively.

The authors report that continuation of these drugs was associated with a mean reduction in intra-operative mean arterial pressure of 1.3 mmHg. While this has reached statistical significance, again, we question its clinical relevance. The patients who had these medications withheld also had a relatively large increase in baseline creatinine levels in the postoperative period. The difference in mean arterial pressure, fluid boluses and vasopressor administration between the groups was statistically significant but, again, we question the clinical significance.

The authors highlight that the type of maintenance of anaesthesia (volatile, total intravenous or even neuraxial techniques), sex of the patient and the type of surgery could potentially contribute to postoperative renal dysfunction. However, there were more male patients enrolled in the study (58%), more patients received volatile anaesthetic maintenance (75%) and there was no difference between the two groups. Oh et. al. performed a retrospective propensity score analysis showing no significant difference in postoperative acute kidney injuries between patients who received total intravenous anaesthesia and those who received sevoflurane-based inhalational anaesthesia [4]. This raises the question of whether these variables were clinically and statistically significant enough to be mentioned in this study.

While the primary outcome of the study by Choi et al. is relevant and an important addition to the literature, the supplementary material poses more interesting questions. Is the key to showing the actual effect of withholding these medications not seen because we are including cohorts of patients with greater renal functional reserve? If the data were further dissected to look at the impact of baseline values, we may find where the true clinical significance of this study lies.

我们饶有兴趣地阅读了 Choi 等人的文章，该文章研究了术前分别停用或继续使用血管紧张素转换酶抑制剂或血管紧张素受体阻断药物的患者急性肾损伤之间的关联 [1]。我们赞扬他们进行了一项精心设计的研究，该研究非常关注相关倾向匹配。

我们想评论统计显著性和临床相关性之间的差异 [2]。虽然我们同意急性肾损伤网络规定的急性肾损伤定义在 48 小时内 < 增加 26.4 μmol.l-1，但两组在术后均显示血清肌酐值升高 [1， 3]。两组之间血清肌酐值升高的实际差异相对较小，这将使我们质疑临床意义。相比之下，突破 26.4 μmol.l-1 阈值的人的统计意义是明显且不可否认的。正如文章中所讨论的，Hollmann 等人最近的一项荟萃分析未能显示血管紧张素转换酶抑制剂或血管紧张素受体阻断药物的围手术期给药与非心脏手术患者的死亡率或主要不良心脏事件之间存在关联 [3]。

虽然我们同意 Choi 等人的文章支持术前常规停用血管紧张素转换酶抑制剂和血管紧张素受体阻断药物，但我们认为更有趣的问题是，我们是否可以确定在围手术期受这些药物的持续使用影响更显着的特定患者亚群。这在补充材料中得到了解决，我们看到，在基线肌酐升高、基线血红蛋白低、BMI 低和需要术前输注红细胞的手术患者中，发生急性肾损伤的比值比似乎要高得多。我们感兴趣的是，作者在详细了解数据后，是否认为有必要取消围手术期错误继续使用这些药物的高风险患者队列的手术。

作者报告说，继续使用这些药物与术中平均动脉压平均降低 1.3 mmHg 相关。虽然这已经达到了统计学意义，但我们再次质疑其临床相关性。停用这些药物的患者在术后基线肌酐水平也有相对较大的增加。两组之间平均动脉压、液体推注和血管加压药给药的差异具有统计学意义，但我们再次质疑临床意义。

作者强调，麻醉的维持类型（挥发性麻醉、全静脉麻醉甚至椎管内技术）、患者的性别和手术类型都可能导致术后肾功能不全。然而，参加研究的男性患者更多 （58%），接受挥发性麻醉维持的患者更多 （75%），两组之间没有差异。哦，等等。等人进行了一项回顾性倾向评分分析，显示接受全静脉麻醉的患者和接受基于七氟烷的吸入麻醉的患者术后急性肾损伤无显著差异 [4]。这就提出了一个问题，即这些变量是否具有足够的临床和统计学意义，以至于在本研究中被提及。

虽然 Choi 等人的研究的主要结果是相关的，并且是对文献的重要补充，但补充材料提出了更有趣的问题。显示停用这些药物的实际效果的关键是否没有看到，因为我们纳入了肾功能储备更强的患者队列？如果进一步剖析数据以查看基线值的影响，我们可能会发现这项研究的真正临床意义所在。