DISCRETE EVENT SIMULATION MODELLING IN MASS CASUALTY EVENTS
The objective of this study (completed 2016) was to enhance the planning of blood management for emergency surgery systems under surge, approached through a worst-case mass casualty event (MCE) scenario. Simulation modelling is under-utilised in healthcare compared with other industry sectors despite the potential for rapid service improvements at minimal cost and logistical disruption compared to live simulation exercises.
Background
Surgical emergencies invariably require blood, especially in the case of traumatically injured patients, when haemorrhage accounts for almost 50% of deaths in the first 24 hours. Modern transfusion strategies have resulted in much greater volumes of components being transfused at an earlier stage of the resuscitation process. The blood system can therefore come under considerable stress with large volumes of blood and components required over a short time period. This burden on the system is further tested when the number of casualties requiring resuscitation increases to multiple patients and still further to mass casualty situations. The supply of blood eventually risks becoming outstripped by demand and the hospital is faced with the task of managing multiple severely injured casualties in quick succession within a resource-constrained environment.
Traumatic haemorrhage is a leading preventable cause of mortality following MCEs. MCEs include terrorist attacks of which there has been a nine-fold incidence globally since 2000.
Preparation for such events requires adequate planning before they occur to reduce service impact and minimise critical mortality. This three-year project aimed to improve planning for such events through the application of discrete event computer simulation modelling. This methodology allows:
- Improved understanding of the blood system under surge conditions.
- Appreciation of changes within the system that lead to the greatest effect on outcomes.
- The development of contingency plans for a range of defined scenarios and varied system constraints.
A discrete event simulation model was developed in the Arena Simulation software package giving an accurate representation of a generic trauma centre’s blood system.
This study had previously identified a statistically significant (p = 0.01) correlation between red cell use and number of severely (ISS>15) injured casualties from terror related MCEs, which has potential in guiding required on shelf blood stocks for future events.
Methodology
We wished to ascertain if blood requirements necessary to adequately manage a civilian MCE are predictable based on historical data and events.We performed a review of the adequacy of blood product use reporting across a full range of civilian MCEs. Improving MCE outcomes requires adequate in-hospital provision of high volume RBC transfusions (see the diagram below).
The relationship between the units of RBC held per casualty and the percentage of all bleeding casualties treated within 6 hours
Our research team used simulation modelling to investigate the best strategies for optimizing RBC provision to casualties in MCEs. We developed a computerized simulation model of a UK major trauma centre (MTC) transfusion system. The model used input data from past MCEs, civilian and military trauma registries. We simulated the effect of varying on-shelf RBC stock hold and the timing of externally restocking RBC supplies on MTC treatment capacity across increasing casualty loads from an event
We also considered whether a predictive relationship exists between blood use and available casualty profiles, and if these in turn are affected by the nature of the event itself (bombings, terrorist incidents of any kind, structural collapse, and non-terrorist MCEs). Finally, we investigated the potential effect that current trauma transfusion practices would have had on blood demands during previous events using a comprehensive review of literature from 1911 to 2011 and comparing findings with civilian blood use data from a major trauma center.
Findings
The surge in red blood cell (RBC) demand from casualties requiring a Massive Transfusion (MT) has the potential to decimate an individual hospital’s blood bank inventory, severely compromising a unit’s ability to treat bleeding casualties effectively. In-hospital event modelling has indicated the perceived capacity of hospitals to manage MCEs to be overly-optimistic. The majority of all trauma deaths that occur in the first hour and approximately 50% of deaths in the first 24 hours are due to bleeding. The result is two thirds of an event’s total RBC requirement on the first day is consumed within the first four hours.
We found that even limited sized MCEs threaten to overwhelm MTC transfusion systems. Whilst greater and greater stock volumes are able to maintain adequate rates of treatment, the logistical and financial implications of maintaining these volumes of RBCs at MTCs limits the feasibility of this solution long-term. Restocking RBCs early during an event can produce equivocal outcomes compared to an on-shelf stock hold, however, in order to achieve this, a ‘push over pull’ approach needs to be considered to prevent delay and maximise any potential benefits
The reporting of blood use in MCEs also needs to be improved if we are to better prepare for future events. Relationships clearly exist between casualty statistics and Red Blood Cell (RBC) requirements, which offer potential as future tools to guide required on-shelf stocks. Damage Control Resuscitation (DCR) and new transfusion strategies will put a major strain on plasma, platelet, and cryoprecipitate stocks. Clinical and transfusion services will need to develop new strategies to manage this demand for future events.
Publications
More detail about this project and its findings can be found in the article 'Mass casualty events: blood transfusion emergency preparedness across the continuum of care' (2016)'. An earlier article 'A comprehensive review of blood product use in civilian mass casualty events (2013)' provides more background to the study.
