Author's response to reviews

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1 Author's response to reviews Title: Trauma Registry Record Linkage: Methodological approach to benefit from complementary data using the example of the German Pelvic Injury Register and the TraumaRegister DGU Authors: Markus Burkhardt Ulrike Nienaber Joerg Holstein Ulf Culemann Bertil Bouillon Emin Aghayev Thomas Paffrath Marc Maegele Tim Pohlemann Rolf Lefering TraumaRegister DGU German Pelvic Injury Register DGU Version: 2 Date: 24 December 2012 Author's response to reviews: see over

2 Manuscript submission BMC Medical Research Methodology: Trauma Registry Record Linkage: Methodological approach to benefit from complementary data using the example of the German Pelvic Injury Register and the TraumaRegister DGU Markus Burkhardt, Ulrike Nienaber, Joerg Holstein, Ulf Culemann, Bertil Bouillon, Emin Aghayev, Thomas Paffrath, Marc Maegele, Tim Pohlemann, Rolf Lefering, TraumaRegister DGU and German Pelvic Injury Register DGU Reply to the comments of Reviewer #1 (Kate Curtis): We appreciated the fair and constructive comments of the reviewer. Please find in the following our point-by-point reply to the reviewer s comments. 1) The reviewer indicates that the language needs a general edit: The paper was now edited by a native speaker. 2) The reviewer argues that the authors state that pelvic fracture mortality rate remains unacceptably high and scientific explanations for this stagnation are still controversial but then go onto say that inconsistency between clinical data such as Hb and haemodynamics are not relevant. Finally, a statement that addresses this contradictory limitation and a statement regarding the future use of the date are needed. Looking for new information about this unacceptably high mortality rate of complex pelvic injuries was one of the main intentions of this record linkage. Being aware of the own limitations, the German Pelvic Injury Register (PIR) benefited from TraumaRegister DGU (TR) derived data from the preclinical setting as well as from the ICU stay, because both treatment periods are not recorded in the PIR. Undoubtedly, haemoglobin (Hb) and haemodynamics of trauma patients influence outcome and survival rate. Using solely PIR derived data, HOLSTEIN et al. investigated predictors of mortality in patients with pelvic fractures (Clin Orthop Relat Res (2012) 470: ). They found out that the median haemoglobin of the survivor group was 10 g/dl compared to 7 g/dl in the nonsurvivor group. Regarding the initial haemoglobin levels of our linkage groups, PIR data revealed means of 8.6 ± 2.9 g/dl and 9.6 ± 3.1 g/dl from TR data. Statistics showed significant differences reflecting inconsistency on the data entry level of both clinical parameters. Potential explanations for this inconsistency are numerous, e.g. data entry or coding errors, rounding up or down of numeric values, replicated values during the same treatment period and different error deviations of different haematology analysers or blood pressure measuring devices. Nevertheless, this limitation points out that efforts must be made to ensure high data quality of both registers in the future, e.g. by the integration of a pelvic fracture module into the TraumaRegister DGU with the goal that there would be no need for future record linkage with concomitant poor linkage rates. Finally, it is important to note that in the already published manuscript BURKHARDT et al. Acute management and outcome

3 of multiple trauma patients with pelvic disruptions. in Crit Care Aug 22;16(4):R163 we used the TR data with completion rates of 89%-95% for the investigated clinical parameters, respectively. The statement that the inconsistency between clinical data such as Hb and haemodynamics are not relevant in consequence was removed. 3) The reviewer asks for the AIS version that is used and if the same version was used across the whole study period: Across the whole study period ( ) the registries used the AIS98 and so in consequence no cross validation or conversion could occur in the pelvic scoring of the study population. 4) The reviewer argues the poor linkage rate and its consecutive conclusions about fluid management and clinical management research. Furthermore, the reviewer indicates that if BP and Hb are not mandatory it seems that until that is more complete there is little treatment research that could be performed as physiologic data are important: It is important to note that the poor linkage rate especially in the Pelvic Injury Register (PIR) must be a trigger for the responsible members of both trauma registries to think about a corporate venture in the future, likewise a modular system with individual modules, e.g. including a pelvic fracture module in the TraumaRegister DGU at least to improve data quality. On the other hand, in acetabular surgery, even more the operative procedure, e.g. anterior or posterior approach, reposition technique, used plates or screws etc., is more in focus than the initial haemoglobin in case of single injuries. Therefore, clinical emergency parameters such as haemodynamics or Hb on hospital arrival are not mandatory consequently in the PIR. In contrast, in complex pelvic injuries with a mortality of about 20% the abovementioned clinical parameters are mandatory. So in consequence the distinct emphasis of each registry must be kept in mind. Regarding the literature, the size of the study population of 420 multiple trauma patients with pelvic fractures is large scale dimensioned because of the small incidence of these injuries per se. The results of the investigation of the acute management of pelvic fractures from the abovementioned study population are already published in BURKHARDT et al. Critical Care 2012, 16:R163. For a better understanding we added a text passage that explains that the initial BP and Hb are only mandatory for complex pelvic injuries and not for benign pelvic ring or acetabular fractures without emergency fracture management.

4 5) The reviewer asks about the type of fluid management that is included in the TraumaRegister DGU : The participation in the TraumaRegister DGU (actually about 250 hospitals) is not associated with any obligatory type of fluid management such as limited amounts of fluids or permissive hypotension during the initial resuscitation period. Even when HUSSMANN et al. in 2011 showed that increasingly preclinical volume led to a slight elevation of lethality in multiply injured patients after severe abdominal and pelvic trauma with subsequent recommendation for a moderate prehospital volume replacement, our own study from 2012 revealed that massive fluid resuscitation in the initial resuscitation period still reflects the recent practice in multiple trauma patients with pelvic disruptions and low-volume resuscitation seems not yet accepted in practice in managing this special patient entity. Furthermore, we added the following paragraph: Concerning the fluid management, the TR records the infusion volume of crystalloids and colloids started in the preclinic as well as the transfused blood products later on until the first 24 hours in hospital. Literature: HUSSMANN et al.: Lethality and outcome in multiple injured patients after severe abdominal and pelvic trauma: influence of preclinical volume replacement, an analysis of 604 patients from the trauma registry of the DGU. Unfallchirurg 2011, 114: BURKHARDT et al.: Acute management and outcome of multiple trauma patients with pelvic disruptions. Critical Care : R163.

5 Manuscript submission BMC Medical Research Methodology: Trauma Registry Record Linkage: Methodological approach to benefit from complementary data using the example of the German Pelvic Injury Register and the TraumaRegister DGU Markus Burkhardt, Ulrike Nienaber, Joerg Holstein, Ulf Culemann, Bertil Bouillon, Emin Aghayev, Thomas Paffrath, Marc Maegele, Tim Pohlemann, Rolf Lefering, TraumaRegister DGU and German Pelvic Injury Register DGU Reply to the comments of Reviewer #2 (David Clark): We appreciated the fair and constructive comments of the reviewer. Please find in the following our point-by-point reply to the reviewer s comments. 1) At the beginning, the reviewer indicates that the authors do not describe any detailed investigation of the many cases in both registries that were not linked and that the study would be more interesting if we could say how many of these persons were mistakenly omitted from one registry, or how many were actually included in both registries but did not match using the linkage criteria: We did not intend to analyse all cases in both registries. The main goal of the study was to create an intersection set with medical records out of both anonymous trauma registries. We agree with the comment that also the analysis of not-linked cases would be interesting to show. However, such an analysis would considerably expand the paper, as we would have then to report about three patient groups 1) the linked ones, 2) the non-linked from PIR and 3) the non-linked from TR, and be not exactly within the scope of the analysis. On the other hand, as we don t have other identifier than those which we have used, we cannot say how many more cases were the same but not linkable using the applied criteria. This issue is now included in the limitation section of the paper. 2) The reviewer argues that the authors do not discuss whether they considered other approaches to record linkage. Furthermore, the reviewer indicates that we do not mention probabilistic methods, which have been studied extensively in many countries including Germany (for example numerous publications by Brenner and colleagues in Methods of Information in Medicine and elsewhere). An ad hoc deterministic method such as we describe might or might not have sufficed for the relatively small patient population, but it is difficult to generalize the scientific value of this experience to other registry combinations: The kind of creation of the match code itself could explain the large number of drop-outs either because there was no tolerance given e.g. in admission and discharge date, reflecting an ad hoc deterministic linkage. In contrast to the recently published use of linkage

6 procedures on basis of encrypted personal identifiers (KAJÜTER et al.) or use of a probabilistic record linkage (BRENNER et al.), for us only an extensive hand search of both anonymous data sets might have offered the possibility to isolate the persons that where mistakenly omitted from one registry or to answer the question how many persons were missed by our linkage criteria. Because of the huge efforts in time and resources we waived a thoroughly hand search like that. 3) The reviewer indicates that there are several improvements of the written English that should be made during the editing process for an English-language journal: The paper was now edited by a native speaker. Furthermore, the subtitle was changed and the term accordance was replaced by concordance throughout the manuscript.