LAUSR

To the Editors, Thank you for the opportunity to reply to the letters by Ariffin as well as Wen et al. regarding the recently published article entitled ‘‘Elevated Lactate is Independently Associated with Adverse Outcomes Following Hepatectomy’’ [1]. We read the letters with interest. The aim of this study was to assess the association between early post-hepatectomy lactate (PHL) and shortterm post-operative outcomes. While interesting, many of the additional analyses suggested by the Ariffin and Wen fall beyond the scope of this study. Firstly, this study focused on early PHL (on the night of surgery). This timing can reliably be related to pre and intra-operative factors, rather than post-operative complications. Moreover, functional liver remnant issues are not relevant here as they would impact PHL later in the postoperative course. Secondly, this study sought to examine the ability of lactate to support identification of patients at risk poor postoperative outcomes early in the post-operative course, as part of a multi-factorial assessment encompassing. It was not meant to be examined as an isolated diagnostic test. Therefore, measures of sensitivity, specificity, positive and negative predictive values were not used. While it would be interesting to correlate the trends of PHL over the first post-operative night with outcomes, multiple lactate levels over that period were available for a minority of patients. Therefore, such an analysis would have been underpowered and not have yielded valid conclusions; it was not undertaken. This would be an interesting question to address, possibly with a prospective design. Finally, we acknowledge the selection bias inherent to the retrospective design of this study. This was accounted for as much as possible by (1) providing characteristics of the excluded patients for the reader to appreciate differences and enhance assessment applicability to one’s practice and (2) performing a detailed multivariable analysis. The multivariable analysis included variables associated with the outcomes on univariable analysis and determined to be potential confounders. We kept a final parsimonious set of covariates to ensure adequate fit and performance of the model. Comorbidities were adjusted for using the Charlson Comorbidity Index (CCI) which is a comprehensive and accurate measure known to provide a better assessment of comorbidity burden than a single comorbidity in isolation (such as diabetes) [2]. In addition, diabetes is included in the CCI and therefore was not added to the model to avoid collinearity issues. As a sensitivity analysis, we did replace the CCI with diabetes alone which did not alter the findings. Inflow occlusion was adjusted for in the model, with a practice of intermittent 15 min of clamp time followed up 5–10 unclamped. The extent of liver resection was included using consensus definition that is standard in research addressing hepatectomy [3]. Finally, post-operative complications being on the causal pathway to mortality, this variable was not included in the regression model as dictated by standard good statistical analysis methods, to avoid overadjustment [4]. This study provides an accurate assessment of the relationship between early PHL and short-term post-operative outcomes. It is based on a large contemporary cohort of & Julie Hallet [email protected]