Due Today

The Chemical and Biological Response Team (CBRT): Making a Case for Being Better

Prepared for the Worst

Certain chemical and biological weapons are surprisingly accessible, and should one be

released, it could pose an enormous public health threat. To prepare for such an event and

minimize the damage it could cause, local government officials have assembled a team of

doctors, nurses, and scientists called the Chemical and Biological Response Team (CBRT). The

CBRT has been charged with medically responding to local and state threats involving known or

suspected chemical or biological agents. In order to prepare the members of the CBRT for this

responsibility, they have been undergoing extensive training; part of this training has included

exercises in which they respond to mock threats.

The CBRT exercise we will follow involves a class of known chemical weapons called

the lung-damaging agents. Many of these agents are easy to obtain or manufacture, and are

therefore agents of concern for any counterterrorism efforts. We follow the victims of exposure

to this gas for the first 6–24 hours after the simulated incident.

Unknown persons have released an unknown gas into a subway station. Victims reported

detecting the scent of mown grass, after which they state they began to suffer from “watering”

eyes and “runny” noses; a burning sensation in their nasal cavities, mouths, and throats; and

difficulty speaking. The symptoms resolved about 30 minutes after the victims were removed

from the subway station and taken to the street above. None of the victims reported any difficulty

breathing during the incident.

Many of the victims who experienced symptoms immediately following the release of the

gas agreed to be taken to the hospital to be monitored for several hours. However, several of the

victims who did not experience severe symptoms declined to be taken to the hospital.

In order to provide the healthcare workers at the hospital with the information they

needed to treat the victims, the members of the CBRT were trying to identify the lung-damaging

agent. The first clue in this scenario was the scent of “mown grass,” which is characteristic of the

lung-damaging agent phosgene. Phosgene, also called carbonyl chloride (COCl2), has many

legitimate uses, such as in the manufacturing of plastics and pharmaceuticals, but it has also been

used during warfare and acts of terrorism. A second clue that points to phosgene gas was found

in the victims’ initial symptoms—irritation of the mucous membranes of the eyes, nose, mouth,

pharynx, and larynx. Phosgene reacts with the water in mucus to produce the highly irritating

chemical hydrochloric acid, which causes inflammation of the mucous membranes lining these

parts of the body.

A final clue is the fact that the victims did not report any dyspnea, or difficulty breathing.

Phosgene tends to spare the conducting zone of the respiratory tract below the level of the

larynx, and instead impacts the airways of the respiratory zone. As a result, people who have

been exposed to phosgene gas tend to have no dyspnea initially, but they then develop it 4–6

hours after exposure. Thus, the victims who lacked initial symptoms and declined to be taken to

the hospital were still very much at risk for developing respiratory problems.

Since the members of the CBRT had good reason to believe that the agent released in part

one of the scenario was phosgene gas, they anticipated an influx of patients to hospitals and

clinics with respiratory symptoms over the next several hours. The CBRT opted to increase the

availability of medical staff, especially emergency personnel and respiratory therapists, as well

as increasing the number of available mechanical ventilators. The team also issued a mandate

that exposed patients presenting with any shortness of breath were to be given supplemental

oxygen as soon as possible.

In the second part of the scenario, from 2–6 hours after the incident, the witnesses

exposed to the gas began arriving at the hospital’s emergency department. Many patients

complained of dyspnea, especially on exertion, a cough, and chest pain. On physical exam and

chest x-ray, some of the patients were showing early symptoms of respiratory disease; however,

some of the patients who presented were merely worried that they might experience symptoms

but were currently asymptomatic.

The CBRT correctly anticipated that after the initial symptom-free lag time, or latent

period, many victims exposed to phosgene would begin to seek medical attention for respiratory

complaints. The preparations the team made were in anticipation of the most dangerous

consequence of phosgene exposure: damage to the respiratory membrane. When the respiratory

membrane is damaged, the permeability of the pulmonary capillaries increases, resulting in large

volumes of fluid leaking from the capillaries into the space surrounding the alveoli. This

condition of having fluid in the lungs is called pulmonary edema, and it results in increased

alveolar surface tension and decreased pulmonary compliance. One of the first treatments for

pulmonary edema is the delivery of supplemental oxygen to counter the hypoxemia that these

patients experience.

Phosgene’s extended latent period, the time from gas exposure to onset of symptoms, makes the

task of deciding which patients will need extensive care and those who will not very difficult. To

ensure that each patient received appropriate care, the CBRT put a system into place whereby

presenting patients were classified as either: 1) asymptomatic, 2) serious (patients experiencing

dyspnea without signs of pulmonary edema), or 3) critical (patients with signs of pulmonary

edema).

As pulmonary edema worsens, the alveoli can actually fill with fluid, which prevents gas

exchange from taking place altogether, causing hypoxemia and hypercapnia. The severity of the

hypoxemia and hypercapnia can be determined by measuring the arterial blood gases, which is

a test that evaluates arterial blood for its PO2 and PCO2. The patients in our scenario had decreased

PO2 and increased PCO2, which was not surprising considering that their alveoli were filled with

fluid.

In severe pulmonary edema, supplemental oxygen is often inadequate to maintain the PO2

within a normal range, and mechanical ventilation is required to restore oxygenation. Patients

exposed to phosgene require a type of mechanical ventilation called high positive end–expiratory

pressure (high PEEP). High PEEP maintains a high pressure inside the alveoli during expiration

so that intrapulmonary pressure remains higher than atmospheric pressure. This prevents collapse

of the alveoli during expiration and facilitates gas exchange. High PEEP is typically effective,

but if it is prolonged, it can lead to further complications. The CBRT determined that patients

who were asymptomatic after the first 24 hours were not likely to develop symptoms, and thus

could be released from the hospital. However, those still in the “serious” or “critical” categories

would remain in a critical care unit until their measured level of oxygenation was adequate. The

team recommended follow-up with a pulmonologist for all patients requiring high PEEP

mechanical ventilation.

In this final part of the exercise, the asymptomatic patients were released from the

hospital, and none returned with symptoms. Most patients in the “serious” category who did not

require mechanical ventilation showed signs of improvement after 3–4 days, and most in the

“critical” category that required high PEEP mechanical ventilation showed signs of

improvements after 5–7 days. In the months that followed, several patients developed asthma-

like symptoms and reported frequent dyspnea, for which they sought medical attention. The

members of the CBRT anticipated that victims might need follow-up care after release from the

hospital. Many victims exposed to phosgene are likely to develop asthma-like symptoms from

irritation of the airways. Others would be expected to report dyspnea on exertion for a year or

more following exposure. However, some of the lasting effects from phosgene exposure might

not come from the gas itself, but rather from the treatment. High PEEP greatly enhances survival

from severe pulmonary edema, but it is not without complications. One of the most frequent

complications of PEEP is barotrauma—damage to the airways of the respiratory zone from

high pressures. If the degree of barotrauma is significant, the alveoli may be damaged, leading to

emphysema. However, even with these possible complications, most patients without underlying

diseases will fully recover from phosgene inhalation, as long as the situation is recognized and

treated aggressively from the start. The CBRT team concluded that the exercise showed that their

recommendations could be used to write protocols for managing a disaster involving exposure to

lung-damaging agents.