Effect of Pre-hospital Blood Transfusion on Early Outcomes in Trauma Patients Transported by Physician-staffed HEMS (Helicopter Emergency Medical Service)

Background and rationale of the project Trauma is a leading cause of death among people younger than 44 years. Uncontrolled haemorrhage causing traumatic-haemorrhagic shock (THS) is the leading cause of potentially preventable deaths from severe trauma. Uncorrected hypervolaemia and prolonged shock cause severe tissue hypoperfusion, vital organ ischemia and subsequently acidosis. Shock, acidosis and hypothermia are recognized drivers of anti-coagulant and fibrinolytic pathways. In up to one third of trauma patients, laboratory findings suggest traumatic induced coagulopathy, which is further triggered by loss or dilution of coagulation factors. These patients have a significantly increased morbidity and mortality compared to patients with similar injury patterns without coagulopathy. Minimizing the time to surgical control of haemorrhage is key in order to improve outcome. However, immediate and goal directed volume and coagulation resuscitation including use of blood product transfusion is crucial to enable survival until definitive hospital care.

Role of HEMS in a trauma system. Helicopter Emergency Medical Services (HEMS) can rapidly deliver advanced medical care and speed up patient transport to designated trauma centres. In the Czech Republic, HEMS covers 76.5% of the area and 99.4% of the population of the Czech Republic within 20 minutes since the emergency call is received via Emergency Medical Dispatch Centre (EMDC). HEMS Hradec Kralove is one of the well-recognized systems in the country. Its catchment area is 1.1 million inhabitants living in the Hradec Kralove and Pardubice regions. Trauma patients include 100-120 multiple trauma injuries and 50-60 isolated traumatic brain injuries (TBI) annually. In 2017, there were 95.9% primary flights (to the scene of accident), of which 81.9% take-offs were decided by EMDC dispatchers immediately after receiving an emergency call. Management of patients in THS requires early identification of the bleeding source, use of effective techniques to stop compressible haemorrhage, support of clot formation and minimisation of on-going blood loss in non-compressible haemorrhage, judicious fluid resuscitation with monitoring of effect, and a pre-alert system for damage control resuscitation or surgery at the receiving hospital. HEMS teams must be skilled to recognise and treat massive bleeding and acute traumatic coagulopathy in the pre-hospital environment.

Diagnostics of THS. Haemorrhage leads to a fall in systemic filling pressure and venous return. The resulting decrease in cardiac minute volume, and therefore in oxygen and nutrient supply, sets off an endogenous stress response aiming to maintain perfusion pressure. Thus, blood pressure and heart rate must be interpreted with caution, and cardiac output might have dropped to some 60% until blood pressure will start to decrease. Although a systolic blood pressure <90 mmHg is the typically considered as the leading symptom of hypovolemic shock, clinical assessment of trauma patients comprises on-going and repeated evaluation of the mental status, capillary filling time, clinical appearance, changes in heart rate, and mechanism of injury. Current literature suggests that the combined evaluation of heart rate, SABP, Glasgow Coma Scale (GCS) and the ability to maintain a patent airway increases the predictability for advanced in-hospital interventions up to four times. This is of particular importance for an in-hospital blood transfusion request policy. Suitable triggers for preparation for massive transfusion are suspicion or evidence of active haemorrhage, incl. trauma triage criteria, systolic arterial blood pressure (SABP) < 90 mmHg, failure to respond to a fluid bolus, heart rate > 120/min, and penetrating injuries. Accordingly, physical examination on scene should focus on injury patterns known to cause haemorrhage such as penetrating trauma, pelvic or femoral fractures and blunt abdominal trauma.

Prehospital treatment of THS. The up-to-date concept of initial trauma care is called damage control resuscitation, which comprises hypotensive resuscitation, haemostatic resuscitation and damage control surgery. Control of haemorrhage is crucial in order to interrupt the vicious circle of blood loss, hypervolaemia, hypoperfusion, acidosis and coagulopathy, finally resulting in therapy refractory shock and death. Basic techniques like direct compression, pressure dressings, tourniquets, traction devices and pelvic splints are used routinely in obvious or suspicious bleeding. In life threatening haemorrhagic shock, fluid resuscitation is still the main stem therapy. The primary and ultimate goal of pre-hospital fluid resuscitation is to prevent hypovolemic cardiac arrest and to minimize organ damage caused by prolonged or uncorrected hypotension causing organ ischemia. For this reason permissive hypotension should only be applied in the first hour after the insult. There are extensive side effects of fluid resuscitation in uncontrolled bleeding patients. Inappropriate or over-infusion has been shown to harm and to worsen outcome. Hypotensive resuscitation is a temporary strategy for management of patients with uncontrolled blood loss until the source of bleeding is controlled. Fluid resuscitation should be spared or postponed in patients with uncontrolled haemorrhage, normal mental status and SABP > 90 mmHg. Fluids should be titrated in uncontrolled bleeding patients without head trauma to a target SABP around 90 mmHg. However, it is noteworthy that the concept of hypotensive resuscitation must be tailored and adjusted to the patients need. In patients with severe traumatic brain injury higher SABP must be achieved with higher amounts of fluids and very seldom use of vasopressor drugs when necessary. There is an on-going debate which fluids and what amounts should be considered optimal for haemorrhagic shock management. Colloids did not show to improve outcome when compared with crystalloids. The same is true for hyperosmolar solutions. Compared to the United Kingdom, Scandinavia and other highly developed countries, there are no prehospital blood products currently available in Central, Southern and Eastern Europe, partially because of high logistic and material demands, risk of wasting, high expenses, and unproven benefit of prehospital use of red blood cells without plasma.

Co-operation between HEMS and a trauma centre. The regional trauma system in the Hradec Kralove Region has been gradually developed during last couple of years. One of its main advantages is excellent long-term co-operation between EMDC, HEMS, and receiving trauma centre, incl. quality management. There are different triage tools used to help to outline patient routes to trauma centres. These latter can include immediate need for blood or life saving surgery. In Hradec Kralove, it was for the first time in the Czech Republic, when a new concept of trauma triage was implemented and improved on-scene triage. The triage criteria were adopted from the American College of Surgeons (ACS) and include: mechanism of injury (e.g. fall from height > 6 m, person trapped in a vehicle), anatomical and physiological criteria, and selected special considerations (e.g. age, comorbidities). Its specificity is 8-10% and sensitivity 95-97%. The same triage system was later implemented into all other prehospital systems, integrated into the nation-wide recommendations of the Ministry of Health (Trauma Care in the Czech Republic) and Guidelines of the Czech Society for Emergency and Disaster Medicine ČLS JEP. Use of pre-hospital triage can predict risk of THS and need for specialized trauma care.