Mass casualty events: The role of hospitals and trauma systems

Introduction

Large-scale events like the destruction of the Twin Towers in New York City, Hurricane Katrina in New Orleans, and the COVID-19 pandemic have focused the attention of surgeons on the challenges posed by mass casualty events (MCEs). Even though trauma surgeons play a key role in the medical response to such events, education and training for MCEs are still not included in the formal curriculum of surgical residency. The purpose of this chapter is to outline the principles governing the response of hospitals and trauma systems to an MCE. The goal is to rescue as many critically injured casualties as possible given the large surge and finite resources. We will focus on the role of the surgeon in the response to such incidents.

Definitions

Multiple Casualty Incident (MCI): An MCI occurs when a medical facility, confronted with a sudden large influx of casualties, continues to deliver a normal standard of care to the critically injured by mobilizing internal resources and prioritizing care. As a rough guide, a hospital is facing an MCI when the number of arriving casualties is less than the number of beds or gurneys available in the ED. A typical emergency department (ED) can process one severely injured patient per hour per 100 hospital beds during normal business hours (but much less during nights and weekends). This is often referred to as the surge capacity of the facility, the casualty arrival rate beyond which the quality of care begins to decline. Surge capacity is a central concept in disaster preparedness, since in an MCI the surge capacity of the facility is not exceeded, while in larger events it is progressively exceeded as more and more casualties arrive.

Mass Casualty Event (MCE): An MCE occurs when the arrival rate of severe casualties exceeds the surge capacity of the facility. This results in progressive delays or a declining level of care for critical casualties. Therefore, the term mass casualty implies some degree of failure to provide optimal timely trauma care to all severely injured patients. The appropriate initial response is to prioritize patients sustaining major injuries with the greatest chance of survival so that valuable resources are expended neither on patients with minor injuries nor those with little hope of survival. The process of sorting patients into immediate, delayed, and expectant care categories is called “triage” from the French word trier meaning to sort.

Disaster: A disaster is a large-scale catastrophe resulting in massive loss of life and collapse of the societal infrastructure in a given geographic area. This severely limits the ability to mount an organized medical response without outside assistance. External medical teams with appropriate logistic support can make a difference in the care of some survivors, but help typically arrives late and deals primarily with delayed complications. Examples of disasters in the first two decades of the 21st century include the tsunami that destroyed coastal areas of Southern Asia in 2004 and Hurricane Katrina, which devastated New Orleans in 2005. When a disaster strikes, the initial priorities are security, food, clothing, and shelter. Medical care is a secondary consideration.

The relevance of this classification to trauma care becomes obvious when we consider a critically injured casualty with intra-abdominal hemorrhage in each of the above scenarios. In an MCI, the patient will be triaged to a trauma resuscitation area, assessed by a trauma team, and taken to the operating room (OR) for an urgent laparotomy. In an MCE, effective triage may recognize the injury but a lifesaving laparotomy may be delayed, take place in an improvised OR, and/or be performed by a surgeon with limited trauma experience. In a disaster, a casualty with intra-abdominal hemorrhage is likely to either exsanguinate in the field or be transported to a severely damaged hospital lacking surgical capability.

Injury severity distribution

A key feature of every MCE is the injury severity distribution. Regardless of the cause or magnitude of the event, only about 10%–15% of survivors presenting to hospital will be severely wounded, of whom roughly one third will have immediate life-threatening injuries. Most others sustain relatively minor injuries. For example, during the London subway bombings in July 2005, the Royal London Hospital received 194 casualties within 3 hours, but only 27 (14%) were severely injured. Of these, only eight casualties (4% of the total) sustained immediately life-threatening injuries.

Although the death toll at the scene depends on the cause of the MCE and may be very high in the event of structural collapse (e.g., the Twin Towers during 9/11), the injury severity distribution remains roughly similar across a wide range of MCEs. This means that while the total number of casualties may be vast, the overwhelming majority will not require a high level of trauma care. These considerations form the rationale behind any effective medical response.