Copyright © 2020 The Authors. Transfusion Medicine published by John Wiley & Sons Ltd on behalf of British Blood Transfusion Society.
This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
The primary aim of this scoping review is to describe the current use of pre‐hospital transfusion of red blood cells (PHTRBC) and to evaluate criteria used to initiate PHTRBC. The effects on patients' outcomes will be reviewed in Part 2.
Haemorrhage is a preventable cause of death in trauma patients, and transfusion of red blood cells is increasingly used by Emergency Medical Services (EMS) for damage control resuscitation. However, there are no guidelines and little consensus on when to initiate PHTRBC.
PubMed and Web of Science were searched through January 2019; 71 articles were included.
Transfusion triggers vary widely and involve vital signs, clinical signs of poor tissue perfusion, point of care measurements and pre‐hospital ultrasound imaging. In particular, hypotension (most often defined as systolic blood pressure ≤ 90 mmHg), tachycardia (most often defined as heart rate ≥ 120/min), clinical signs of poor perfusion (eg, prolonged capillary refill time or changes in mental status) and injury type (ie, penetrating wounds) are common pre‐hospital transfusion triggers.
PHTRBC is increasingly used by Emergency Medical Services, but guidelines on when to initiate transfusion are lacking. We identified the most commonly used transfusion criteria, and these findings may provide the basis for consensus‐based pre‐hospital transfusion protocols.
Keywords: damage control resuscitation, emergency medical service, major haemorrhage, pre‐hospital transfusion, red blood cells, transfusion criteria
Trauma is a major cause of death and disability.1, 2 In injured patients, death within 24 hours is primarily attributable to haemorrhage,3, 4, 5 and many of these deaths are potentially preventable.6, 7, 8 To optimise bleeding patients' odds of survival, pre‐hospital treatment focuses on early haemorrhage control to avoid hypovolaemic shock and the lethal triad of acidosis, hypothermia and coagulopathy. This is commonly attempted with topical treatment,9 such as haemostatic dressings, tourniquets and/or pelvic binders. However, haemorrhage is often non‐compressible and cannot be controlled by topical treatment alone.7, 10, 11 Moreover, patients may already be in haemorrhagic shock when pre‐hospital healthcare providers arrive at a scene. Therefore, to replace (ongoing) blood loss, liberal volume replacement, typically with readily available crystalloid fluids, has been long advocated.12 However, this practice is associated with adverse effects including dilutional coagulopathy, acidosis, hypothermia and accelerated blood loss.13 In contrast, damage control resuscitation (DCR) involves restrictive fluid resuscitation, which avoids crystalloids while accepting some degree of hypotension, and is increasingly preferred until bleeding can be surgically controlled.13, 14, 15, 16, 17, 18
Red blood cells (RBCs) provide a more effective volume expansion than crystalloids; the infusion of large volumes of crystalloids or colloids can thus be avoided. The RBCs benefit haemostasis and thrombosis19 and restore oxygen‐carrying capacity,20 thereby potentially reducing acidosis through tissue hypoxia. Military medical teams have long been transfusing blood products prior to patients' arrival at a surgical unit.4, 21 As proposed by Jansen et al,22 differences in survival between civilian casualties who require massive transfusion (60%)23 and military casualties (93%)22 may be partly explained by this practice.
In recent years, civilian Emergency Medical Services (EMS) are increasingly transfusing RBCs before hospital arrival.24, 25 However, logistic and operational challenges are hampering the widespread implementation of blood transfusions in the pre‐hospital setting. Moreover, consensus regarding pre‐hospital indications for blood transfusions is lacking, and evidence regarding the efficacy of this practice is scarce. Therefore, this systematic review consists of two parts. Part 1 is a scoping review in which we systematically gathered the research done in the area of pre‐hospital transfusion of red blood cells (PHTRBC), aiming to describe the current challenges of pre‐hospital transfusion and, in particular, to evaluate which criteria are currently used to initiate PHTRBC. This review may serve as guide to derive consensus based pre‐hospital transfusion protocols and informed practice guidelines. In Part 2, the effect on patient outcomes will be systematically appraised.
The review was registered at Prospero (website: https://www.crd.york.ac.uk/prospero, identification number: CRD42018084658) and was conducted in accordance with PRISMA‐Scr (Preferred Reporting Items for Systematic Reviews and Meta‐Analyses—Extension for Scoping Reviews) guidelines.26
PubMed and Web of Science were searched through January 2019 using the following terms: PUBMED: (“emergency medical services”[MeSH Terms] OR (“emergency”[All Fields] AND “medical”[All Fields] AND “services”[All Fields]) OR “emergency medical services”[All Fields] OR “Warfare”[Mesh] OR “Warfare”[All Fields] OR combat[All Fields]) AND (“blood transfusion”[MeSH Terms] OR (“blood”[All Fields] AND “transfusion”[All Fields]) OR “blood transfusion”[All Fields]). WEB OF SCIENCE: TOPIC: (((emergency medical services) OR (emergency AND medical AND services) OR (emergency medical services) OR (Warfare) OR (combat)) AND ((blood transfusion) OR (blood AND transfusion))). Titles and abstracts were screened by two reviewers, and the full texts of all potentially eligible articles were retrieved.
All manuscripts discussing PHTRBC were eligible for inclusion, provided they were written in English, German, French or Dutch. Since we sought to describe typical practice and identify commonly used indications and transfusion triggers, we did not limit the inclusion to studies allowing comparisons between PHTRBC patients and controls. Reviews and editorials were excluded. Eligibility was assessed independently in a blinded manner by two reviewers (ET & SB). Disagreements about manuscript eligibility were resolved by discussion within the investigator group. Reference lists of suitable articles were screened for additional relevant content.
We developed a standardised data‐extraction sheet, which was refined after testing with the first 20 articles. In one case, further information was obtained after contacting the authors.27 The setting and type of transport the EMS used (civilian or military, scene or interfacility), as well as the availability, frequency and volume of PHTRBC transfusions were extracted. Descriptions of problems that arose during PHTRBC are summarised in the text.
Transfusion criteria were recorded and classified as “major criteria” or “minor criteria,” depending on whether only one criterion needed to be met to initiate PHTRBC or whether a combination of several criteria was required. Some groups published studies regarding pre‐hospital transfusion with the same EMS more than once. In this case, only the most recent and best specified description of transfusion criteria was considered. Criteria are summarised in diagrams (Figures (Figures2 2 and and3 3 ).
Criteria for pre‐hospital transfusion of red blood cells (PHTRBC) most commonly used in civilian emergency medical services, and injury characteristics used as criteria for PHTRBC in civilian emergency medical services
Criteria for pre‐hospital transfusion of red blood cells (PHTRBC) most commonly used in military emergency medical services, and injury characteristics used as criteria for PHTRBC in military emergency medical services
The search in PubMed and Web of Science yielded 2172 hits after removal of duplicates. Of which, 2024 articles were excluded based on the title and/or abstract, because they did not discuss PHTRBC or were not original research (eg, editorials, reviews). Ninety articles were excluded after screening their full texts because they did not meet the inclusion criteria. For this review, 71 articles were included (Figure (Figure1 1 ).
PRISMA flow diagram
In total, 57 articles discussed PHTRBC in civilian medical services. Notably, five articles primarily dealt with a different study topic, but were included as they additionally provided valuable information regarding PHTRBC.28, 29, 30, 31, 32 Table Table1 1 describes studies' characteristics, listing study design, region and period in which the study took place, the primary goal, study group and control group, whether matching occurred, the number of subjects, the type of transport and, in the case of trauma patients, the mechanism of injury and Injury Severity Score.
