KEY DEFINITIONS

A mass casualty event is defined as a situation in which the number of patients and the severity of their injuries exceed the capability of the facility to deliver care in a routine fashion. The appropriate initial response is to treat patients sustaining major injuries with the greatest chance of survival first so that valuable resources are not expended on patients with little hope of survival.

A multiple casualty event is defined as a situation in which the facility can mobilize additional resources in response to a large number of patients so as to continue to deliver care in a relatively routine fashion. The optimal field management of a mass casualty event is to convert it into a multiple casualty event for each receiving hospital. If appropriate distribution of victims to facilities occurs, the number of patients and the severity of their injuries will not exceed the ability of a facility to render care.

Triage refers to the medical sorting of patients according to their need for treatment and the available resources. In a mass casualty event, conventional standards of medical care cannot be delivered to all victims. The goal of triage is to optimize care for the maximum number of salvageable patients.

Patients are triaged into four categories at the scene: minor, delayed, immediate, and dead. In military triage systems, a fifth category, expectant care, is used for patients with a small chance of survival who would use scarce resources to such an extent as to adversely affect the chance of survival of other more salvageable patients. This category is rarely used in civilian situations as mobilization of additional personnel resources is usually possible. Numbers, colors, or symbols may be used to denote the categories (Table 1). “Undertriage” refers to assignment of patients to a level of care inadequate for their level of injury. An under-triage rate greater than 5% is unacceptable as it may lead to unnecessary morbidity and mortality in severely injured patients. “Overtriage” refers to assignment of patients to a level of care greater than required for their level of injury. An overtriage rate of 50% is considered acceptable to minimize undertriage. Excessive overtriage at the scene threatens the response of the entire system due to expenditure of limited resources on the wrong patients.

Table 1 The Four Colors of Triage

Adapted from Los Angeles Community Emergency Response Team.

PREHOSPITAL CARE IN MASS CASUALTY EVENT

The response to a mass casualty event requires the coordinated effort of many agencies with disparate cultures, command structures, and even communications equipment (Figure 1). Appropriate agencies should submit to the authority of the incident field commander at the scene. Prior joint training can break down these barriers and improve overall response to the event.

Figure 1 Components of disaster response.

Whether the event is caused by an accident, an intentional attack, or a natural disaster, the area of the event must be secured. In the event of a terrorist or military attack with conventional weapons, additional enemy operatives must be identified and neutralized. The area must be searched for additional unexploded ordinance and if found it must be either disarmed or exploded in a safe area. If these principles are not followed, the probability of a “second hit” is significantly increased.

Victims must be extracted, concentrated in a safe area, and triaged. Immediate care patients should be transported first, but often require management of airway, breathing, and circulation problems.

Transportation of victims from the scene to the hospital does not always occur in formal ambulances. Buses and private vehicles are sometimes used. Worried well persons and patients with minor injuries sometimes self-triage to hospitals without the knowledge of the incident field commander, leading to increased confusion and inundating the receiving hospitals.

Crowd control at the scene is a major problem. Multiple volunteers with various skills arrive to help and hinder. The triage area should optimally be secured and individuals inserted to help at the discretion of the triage commander.

HOSPITAL TRIAGE

If either a large number of casualties suddenly arrive without warning, or the hospital is informed of their impending arrival, the hospital should initiate its mass casualty plan. In a true mass casualty event, all area hospitals must participate in the care of victims to avoid exhaustion of the resources of any one facility. The common goal is salvaging as many lives as possible. A contingency plan for patients not involved in the mass casualty event must be in place as part of emergency preparedness. This plan permits the hospital to convert to mass casualty mode in a short period of time.

In preparation to receive and care for multiple victims, all elective surgery must be cancelled. Rapid disposition of pre-existing patients in the emergency department (ED) is required. Depending on the size of the event, hospitalized patients who are fit may be discharged and patients transferred within the hospital if required to maximize the availability of surgical beds.

The initial hospital triage (Figure 2) should occur outside the ED as patients arrive by ambulance. Ideally, ambulances should pass through a security checkpoint prior to entrance to the hospital grounds to identify terrorists or ordinance that may be on board. Initial triage need not be done by a surgeon, but should be done by a highly experienced clinician. If possible, the walking wounded should be escorted through a separate entrance.

Figure 2 Initial triage stations.

As soon as stretcher patients enter the ED, a senior surgeon should triage each patient to either immediate or delayed care (see Figure 2). The immediate treatment area should be reserved for salvageable patients with life-threatening problems. This area should have enough space for equipment and provide a one-way flow of traffic. The following personnel should be present at each bed in the immediate care area: a senior surgeon for decision making, an anesthesiologist to provide airway control, two ED or critical care nurses, and a junior surgeon for vascular access and tube thoracostomy as necessary.

Treatment in the immediate care area is based upon the principles of advanced trauma life support. The goals of therapy in the immediate care area are airway control, ventilation, cessation of external hemorrhage, vascular access, and rapid transfer of the patient to the next appropriate treatment station, usually the intensive care unit (ICU) or the operating room (OR), for completion of the primary and secondary surveys and further diagnostic or therapeutic interventions. Factors affecting the decision as to where to perform the secondary survey and the patient’s ultimate disposition include the patient’s condition and the number of immediate care patients (Figure 3). This decision should be made by a senior surgeon.

Figure 3 Intra-hospital traffic flow.

Prior arrangements should be made to expand the ICU. The postanesthesia care unit is an ideal venue for expansion of ICU services. Since most victims do not require immediate access to the OR (unless they have penetrating trauma due to shrapnel, or traumatic amputations), even empty ORs could be used to temporarily manage critically ill patients in an unusual situation.

Patients with significant but non–life-threatening injuries are triaged to delayed care. A junior surgeon and nurse should be assigned to each of these delayed care patients. A senior surgeon, however, should be in charge of the delayed care area and the area designated for the walking wounded in order to provide advice and correct any errors in triage that may have been made.

Many of the walking wounded from a mass casualty event are not transported by emergency medical services. Civilian transport can make up as much as 80% of victims arriving at hospitals, often causing overtriage at the closest hospitals to the event. Most of the walking wounded patients can be discharged from the ED. Many of these patients require psychological counseling and support and should be screened for psychological trauma.

HOSPITAL EMERGENCY INCIDENT COMMAND SYSTEM

The Incident Command System in the United States was developed in the 1980s in order to improve command and control of firefighters in complex operations. An adaptation of that system, the Hospital Emergency Incident Command System (HEICS), is quickly becoming the standard for hospital disaster management. The goal of any disaster management scheme is to create an efficient system of care that will both save lives and return the hospital to routine function as soon as possible. The advantages of the HEICS include a predictable chain of command and a common language to facilitate communication among disparate agencies coordinating the response to the event.

The basic principle of HEICS is that one individual supervises no more than five people and reports to only one person. A senior surgeon is the ideal incident commander. This system allows for efficient and manageable lines of communication and easy accountability. There are four main section chiefs: planning, logistics, finance, and operations. The operations chief has overall responsibility for the triage of victims and their clinical care, and potential coordination with other area hospitals (Figure 4).

Figure 4 Simplified model of hospital emergency incident command system.

In order for HEICS to be effective, it must be incorporated into a hospital’s disaster plan and training exercises. Implementation of such a vast network plan requires that each individual be familiar with his or her role prior to the incident and have a working knowledge of the organizational chart.

CAUSES OF MASS CASUALTY EVENTS

Conventional Weapons/Blast Injury

The majority of terrorist attacks and unintentional mass casualty events involve “conventional” weapons. Bombings were responsible for almost 70% of terrorist attacks in the United States and its territories between 1980 and 2001. Many terrorist bombs contain intentionally placed fragments, such as nails, bolts, and tacks, in an effort to increase bodily harm. Some bombs, such as Molotov cocktails, cause burns.

Injury patterns from explosions are dependent on several factors: materials involved, surrounding environment (open versus closed space), distance of the victim from the explosion, and presence of protective barriers.

Physics of Blast Wave

Energy is transferred from the explosion to the atmosphere generating a supersonic blast wave that rapidly slows to the speed of sound (Figure 5). In an open space, the blast wave dissipates rapidly. In a closed space, however, the blast wave reverberates against a solid wall increasing the force of the wave. For this reason, the mortality rate and severity of injuries of the victims are significantly higher in closed-space as opposed to open-space explosions.

Figure 5 Physics of a blast wave.

A primary blast injury occurs when the pressure wave directly hits the body surface. Gas-filled organs are particularly susceptible to injury, such as the lungs, intestines, and ears. Damage to the eye and brain may also occur. Specific injuries are summarized in Table 2. A secondary blast injury occurs as a result of flying debris and bomb fragments. It can cause both blunt and penetrating injury and can affect any part of the body. Tertiary blast injury occurs as a result of blunt trauma as victims are thrown against solid objects by the blast impulse. A quaternary blast injury encompasses miscellaneous explosion-related injuries such as burns, crush injuries, and impalements. Illnesses directly related to the blast such as post-traumatic stress disorder, asthma exacerbations, angina, infection, or other complications secondary to inhalation of toxic fumes are also classified as quaternary blast injuries.

Table 2 Spectrum of Explosive Related Injuries

Organ System	Effect
Auditory	Ruptured tympanic membrane (almost always seen with blast lung), ossicular disruption, foreign body
Eye, orbit, face	Ruptured globe, foreign body, fracture, air embolus
Respiratory	Blast lung, pulmonary contusion, pneumothorax, left-sided air embolism, aspiration
Circulatory	Myocardial contusion, myocardial infarction (air embolism), hemorrhagic shock
Central nervous system	Closed or open head injury, stroke or spinal cord injury from air embolism, spinal cord injury from blunt trauma
Renal	Contusion, laceration, acute renal failure from hypotension or rhabdomyolysis
Gastrointestinal	Bowel perforation, hemorrhage, solid organ injury, mesenteric ischemia (air embolus)
Extremity	Amputation, crush, fracture, compartment syndrome, burns, vascular injury. Most common system needing operative intervention

Blast lung injury, the most serious common primary blast injury, is a direct result of injury to the pulmonary parenchyma due to barotrauma. Many victims of blast lung injury are dead at the scene. The clinical presentation is similar to pulmonary contusion. The most common symptoms and signs are hemoptysis and hypoxia leading to dyspnea, tachypnea, and poor compliance. Unlike pulmonary contusion, blast lung injury does not usually have associated rib fractures. Typical chest radiographic findings (Figure 6) include a “butterfly” pattern of infiltrates, pneumomediastinum, hemothorax, and pneumothorax.

Figure 6 Blast lung.

Intraparenchymal hemorrhage causes a V/Q mismatch that may be significant, requiring mechanical ventilation and judicious fluid resuscitation. For victims requiring mechanical ventilation, care includes avoidance of ventilator associated lung injury and further barotrauma by limiting tidal volumes and levels of PEEP. On occasion, a patient with blast lung injury can develop left-sided air embolism due to rupture of the alveolar capillary membrane. Neurologic symptoms are most common, but the patient can also develop coronary artery obstruction due to air embolism. Tidal volumes, peak inspiratory pressures, and PEEP levels should be kept as low as possible to decrease the risk of both left-sided air embolism and ventilator-associated barotrauma.

Chemical Agents

Four types of chemical weapons can potentially be used in a terrorist attack: nerve agents, cyanide, vesicants, and pulmonary agents. The most likely weapons to be employed are nerve agents and cyanide.

Nerve Agents

Nerve agents are organophosphate compounds that inhibit cholinesterase at the synaptic and neuromuscular junctions causing an excess of acetylcholine leading to a cholinergic crisis. Five nerve agents have been produced as weapons: tabun, sarin, soman, GF, and VX.

Acetylcholine binds to receptors on the post synaptic cell membrane, the smooth muscle end plates and secretory glands causing the muscarinic effects of acetylcholine. The muscarinic effects include bronchospasm, low pulmonary compliance, nausea, vomiting, diarrhea, miosis, blurred vision, bradycardia, and hypersecretions of the oropharynx, conjunctivae, tracheobronchial tree, and gastrointestinal tract.

Acetylcholine also binds to skeletal muscle end-plates and synaptic ganglia causing the nicotinic effects. The nicotinic effects of acetylcholine include fasciculations, flaccid paralysis, tachycardia, and hypertension. Heart rate during a cholinergic crisis is variable due to the opposing actions of the nicotinic and muscarinic effects. Patients may experience initial tachycardia progressing to bradycardia as the severity of the cholinergic crisis increases.

The severity of nerve agent poisoning is classified as mild, moderate, or severe. Patients who are comatose, seizing, or apneic are classified as severely injured, and will require admission to an intensive care environment with ventilatory support. Patients who are supine with wheezing, fasciculations, and incontinence are classified as moderately injured. The ambulatory patient with cholinergic symptoms is classified as having a mild injury.

There are two separate antidotes for a cholinergic crisis. Atropine is a very effective antidote for the muscarinic effects but has no influence on the nicotinic effects. Atropine competitively binds at the postsynaptic muscarinic receptor, thereby displacing acetylcholine. Atropine should be given until secretions abate and pulmonary compliance improves.

The antidote for the nicotinic effects of acetylcholine is a class of drugs called oximes. In the United States, pradiloxime chloride is the oxime of choice. Oximes act as a “molecular crowbar” separating the nerve agent from the cholinesterase, thereby allowing acetylcholine breakdown at the nicotinic receptors. Unfortunately, the oximes must be given before irreversible binding of the nerve agent and the cholinesterase occurs, a phenomenon known as aging. The aging half-life varies from 2 minutes for soman to several hours for sarin.

The recommended initial treatment for mild to moderate nerve agent injury is atropine, 2 mg IM; and pradiloxime chloride, 600 mg IM. For severe injury, atropine, 6 mg IM; and pradiloxime chloride, 1200 mg IM, are recommended.

Cyanide

Cyanide is a highly effective chemical weapon when employed in closed spaces as demonstrated by the criminal efficiency of the gas chambers in Nazi concentration camps during World War II. The high volatility of cyanide makes it an ineffective weapon when employed in open spaces because of rapid dissemination. The explosive device used in the first World Trade Center bombing in New York in 1993 contained enough cyanide to contaminate the entire building, but fortunately it was destroyed by the force of the blast.

Moderate exposure causes a bright red appearance to the skin and venous blood, metabolic acidosis, and the odor of bitter almonds. Severe exposure causes coma, apnea, and cardiac arrest.

Patients with cyanide poisoning should be treated by inhalation of a 0.3-ml ampule of amyl nitrite or 10 ml of 3% sodium nitrite (300 mg) IV over 3 minutes to produce methemoglobin. Methemoglobin has a high affinity for the cyanide ion. Subsequently, 50 ml of 25% sodium thiosulfate (12.5 g) should be given IV over a 10-minute period to convert the cyanomethemoglobin complex to the metabolically inactive thiocyanate ion, which is excreted in the urine.

Vesicants

The mustards are liquid chemical weapons that cause burns to the skin and mucous membranes and induce bone marrow suppression. Treatment involves decontamination, management of the burn wounds, and treatment of hematologic abnormalities. At least 40,000 Iranian casualties sustained vesicant injuries when Iraq employed mustard agents during the Iran–Iraq War in the 1980s. Terrorist use of a vesicant chemical weapon is less likely than a nerve agent or cyanide because of the large volumes required.

Pulmonary Agents

Chlorine and later phosgene were employed as chemical weapons causing pulmonary edema and respiratory insufficiency during World War I. Patients exposed to these agents developed chest tightness progressing to cough, hoarseness, stridor, and hypoxia over a period of 2–4 hours depending on the degree of exposure. The pulmonary parenchymal injury resembles an inhalation injury resulting from exposure to smoke and burning plastic.

Implications of Chemical Weapon Attack for Scene Management and Hospital Disaster Plan

If a chemical agent is suspected, individuals providing care at the scene should don protective clothing. Ideally, victims should be decontaminated at the scene before leaving the “hot zone” (Figure 7).

Figure 7 Algorithm for chemical decontamination at the scene.

Experience from the Aum Shinrikyo Japanese sarin attacks demonstrates that nerve agents are more of a “mass hysteria” weapon than a “mass destruction” weapon. Most of the severe cases will be dead in the field. A large number of worried well or mildly exposed patients will flood the hospital. Hospital security and early lockdown is essential to prevent contamination of the facilities and staff, as happened in the Tokyo sarin attack. There most likely will not be time to employ a decontamination facility prior to arrival of the first patient. At San Francisco General Hospital, it takes a minimum of 1 hour to deploy the decontamination tent during prearranged drills occurring in daylight with all key personnel assembled in advance.

Decontamination is a critical part of the treatment. Early decontamination protects the patient from further exposure. Late decontamination protects the medical team. Simple removal of clothing results in decontamination of approximately 80% of a liquid nerve agent. Decontamination showers should be part of a hospital mass casualty event plan in case of a terrorist nerve agent attack. The problem of hypothermia during decontamination in cold climates has yet to be solved.

Patients in severe cholinergic crisis will require resuscitation by health care personnel in the decontamination zone wearing personal protective equipment. The idea that efficient resuscitation of large numbers of patients with cholinergic crisis due to nerve agent poisoning by staff unpracticed in this procedure wearing bulky unwieldy protective clothing is naïve. Surgeons and anesthesiologists should be aware of the potentiating effect of nerve agents on neuromuscular blockade as well as the effect of hypersecretions and bronchospasm on general anesthesia in the event that surgery is required to treat a trauma patient exposed to nerve agents.

CONCLUSION

Surgeons should take an active role in preparation for disasters and mass casualty events. A well–thought out plan with elements of efficient triage and resource allocation is critical in order to maximize the number of lives saved and provide protection to personnel. Mass casualty events secondary to terrorist attacks most likely involve conventional explosive devices. However, hospital disaster plans should be prepared in the event that chemical, biologic, or radioactive agents are components of the attack.