Methodology for Measuring Intraoperative Blood Loss: Protocol for a Scoping Review.

Background: At present, there is no standardized method for measuring intraoperative blood loss. Rather, the current data on existing methods is very broad and opaque. In many cases, blood loss during surgery is estimated visually by the surgeon. However, it is known that this type of method is very prone to error. Therefore, better standardized methods are needed.

Objective: This study aims to conduct a scoping review to present the currently available methods for measuring intraoperative blood loss. This should help to capture the current status and map and summarize the available evidence for measuring blood loss to identify any gaps.

Methods: We will use a state-of-the-art methodological framework. The databases PubMed (MEDLINE) and Cochrane Library will be searched using a search strategy based on the PICO (Population, Intervention, Comparator, and Outcome) scheme. The search period will be limited to January 01, 2012, to December 31, 2023, and our search will be restricted to clinical trials or clinical studies, randomized controlled trials, and observational studies (in line with PubMed definition of study types). Only publications in English and German will be considered. The intention is to identify clinical studies that define "blood loss" as a target criterion or as a primary or secondary end point. EndNote (version 20.6; Clarivate) will be used for the screening process. The data will be collected and analyzed using Microsoft Excel (version 16.77.1).

Results: The included studies will be listed in a database, and the following basic data will be extracted: title, year of publication, country, language, study type, surgical specialty, and type of procedure. The number of participants will be listed and the distribution of the participants will be documented in terms of gender and age. The following results are extracted: the type of measurement method used to measure blood loss in this study and whether the parameter "blood loss" was recorded as a primary or secondary outcome.

Conclusions: Currently, there is no comparable review, resulting in ambiguous data regarding the prevailing measurement methods for intraoperative blood loss. The aim of this study is to provide a comprehensive overview-from methods of measurement to various formulae for calculating blood loss-and to establish a status quo. This could then serve as a foundation for further studies.

International registered report identifier (irrid): DERR1-10.2196/58022.