Mechanical Ventilation

Since the SARS epidemic of 2002–2003, and the threat of an influenza pandemic, specific attention has been focused on how to plan for and implement a large-scale bioevent approach that requires triage management of large numbers of survivable and nonsurvivable respiratory failure cases where evacuation is not an option (32). The demand for positive pressure ventilation will likely far exceed conventional ICU capabilities, and without careful predisaster planning, hundreds or thousands of victims may have to forgo potentially life-saving critical care. Whereas most of these MCIs will likely occur in chemical inhalation disasters, radiation exposures, and tsunamis causing aspiration pneumonia and septic shock, it is bioevent public health emergencies that many believe have the greatest likelihood of causing mass respiratory failure.

Thousands of ventilators will be required for a mass illness response event such as an influenza pandemic. To support such a disaster, the number of full-feature ventilators currently available for use in the United States approximates 62,000, with another 83,000 less sophisticated ventilators also available (33). The US Centers for Disease Control’s Strategic National Stockpile (SNS) maintains an unpublished number of ventilators for deployment to disaster areas.

The stockpiling of full-feature ventilators by hospitals, hospital systems, or states is cost-prohibitive according to Rubinson et al. (34,35), suggesting that the stockpiling of portable ventilators, which provide only a basic mode of ventilation and are easy and safe to use for both adult and pediatric patients is the right thing to do, especially if large numbers of patients are monitored by single respiratory providers or small teams that may include health care providers with EOC-directed just-in-time training. Because pulse oximetry devices may also be in short supply, this training would also include frequent checking of vital signs with attention to respiratory rate and use of accessory muscles (32).

Medical Oxygen

Patient management will be limited by the availability of medical-grade oxygen, which is not supplied through the Strategic National Stockpile (32). Bulk liquid is the main source of oxygen for hospitals and remains the best option for supporting mass mechanical ventilation. The large majority of nonventilated patients will be maintained outside the hospital setting with oxygen supplies using reservoir cannulas or pulsed-dose technology.

Personnel

Workforce shortages, where staffing is a critical triage issue for most hospitals, are already prevalent on a daily basis, and 12% of ICUs have been forced to close beds due to nursing shortages (32). Critical shortages also exist in trained respiratory care specialists, pharmacists, and physicians. This will be the major barrier to the provision of critical care should an MCI occur. A two-tiered staffing model, using the care team approach, calls for non–critical-care trained personnel to work collaboratively with specialized health care professionals (28). This model is also supported by the Society of Critical Care Medicine’s Fundamental Disaster Management course, which imparts core critical care knowledge and skills to non–critical-care, hospital-based personnel. For example, teams of dentists, a profession comfortable with the airway and who, in the past, have been trained by the military to be anesthetists during all-out war, can be trained in intubation and manual ventilation while being supervised by a respiratory therapist who assumes the role of team respiratory supervisor.

Infection Control

The goal of all care management in a large-scale bioevent is to prevent secondary infections (2,15). The risk of secondary infections may be higher in the critical care setting in part due to the number of interventions (e.g., endotracheal intubation, suctioning, manual ventilation) causing aerosolization of infectious material (36,37). Studies support the efficacy of personal protective equipment (PPE). Unfortunately, compliance among health care providers is low, ranging between 56% and 67%. Thus, infection control is a key component of any MCI involving an infectious bioagent. As mentioned earlier, the SARS pandemic showed that HCWs and patients in the critical care environment are particularly vulnerable to nosocomial transmission of infectious agents, due to invasive procedures such as intubation, suctioning, and central line insertion (36–39). This highlights the need for infection control to be incorporated into all disaster planning (40). The basic approach to infection control in critical care units should utilize administrative controls, environmental engineering, protective equipment, and quality control (36). The primary goal is to prevent transmission of infection to HCWs and other patients. Cohorting of patients based upon likelihood of infection is an important first step in containing the spread of illness, and is facilitated through use of the SEIRV protocol discussed in the Triage section below.

During a biologic disaster involving an infectious agent, separate ICUs should be developed to deal with infectious and noninfectious patients. For example, a hospital with a single medical-surgical ICU and a coronary care unit (CCU) could designate its medical-surgical ICU as the infectious ICU, and then use its postanesthetic care unit (PACU) to manage noninfectious surgical patients and the CCU for all noninfectious medical patients requiring critical care. When planning alternative critical care locations during a surge, infection control issues must also be considered. One option includes the use of portable high-efficiency particulate air (HEPA) filters to create negative pressure units (41). As discussed earlier, some procedures in the ICU require higher levels of personal protection, given they have the potential to generate aerosols, thus increasing the risk of airborne transmission even for infectious agents that would otherwise typically be transmitted only via droplets. Additional precautions, and possibly the use of special procedure rooms, should be considered for high-risk procedures. A full discussion of infection control practices in critical care is beyond the scope of this chapter, and interested readers should refer to comprehensive articles discussing the transmission of respiratory pathogens (42,43).

A common theme that has been revisited throughout this chapter is the need for real-time data to guide decision making and responses. This is also true for infection control, as was demonstrated during the Ebola virus disease events of 2014–2015 (44) as well as the SARS epidemic. In Toronto, we learned that during a biologic disaster, even more important than the initiation of the response, was the transition from response to recovery. Simply put, how to detect and respond to an outbreak was well understood, but how to end an outbreak was not. The failure to detect an ongoing chain of SARS transmission in a hospital led to a second large wave of infections and deaths after infection control precautions were discontinued. Appropriate surveillance data could have detected and prevented this second wave of illness (45,46).

Critical Care Beds

Guidelines suggest that 20% of general hospital beds are available within 24 hours during conventional disasters, and a several-fold increase can be realized if acute care patients are admitted preferentially (32). Theoretically, if personnel and equipment are available, most of a general hospital can be modified to deliver critical care services. This may require repurposing PACUs, endoscopy suites, and other monitored bed settings. Further capability may arise with expeditious discharge of low acuity patients to home, skilled nursing facility, or even alternate care setting established in the community. This increased availability of normal hospital beds, therefore, will allow movement of “step-down” patients from much needed critical care settings to normal wards (30).

Conventional Mass Casualty Incident Triage

The vast majority of MCIs involve patients with traumatic injuries, most of whom are not critically injured. These MCIs do not generate large numbers of casualties with respiratory failure, septic shock, or coma, and those that do present usually receive rescue, transportation, stabilization, and definitive critical care using existing local or regional capabilities (32,53–55). The National Disaster Medical System (NDMS) designates the simple triage and rapid treatment (START) as the uniform method for initial field triage in conventional MCIs and disasters (56). START evaluates respiratory, circulatory, and neurologic function and provides four care categories (unsalvageable or dead, major injury, minor injury, and walking wounded). Field emergency care is restricted to the ABCs (airway, breathing, and circulation procedures) (56). A second-phase triage process, termed secondary assessment of victim end point (SAVE), further assesses injuries on the basis of trauma survival statistics to direct limited resources, triage tags, and tracking to victims expected to derive the most benefit from treatment (57). Both methodologies remain the basis for point-of-care (i.e., prehospital or the emergency department) initial evaluation for all-hazards disaster planning documents, and in basic and advanced disaster life-support training aimed primarily at managing traumatic MCIs (2,56).

Restrictive resource limitations and a worsening case definition in a conventional MCI, or an explosive or nuclear event, may require further EOC triage decisions based on inclusion and exclusion criteria and minimal qualifications for survival (MQS) (2,15,58–60).

1. Inclusion criteria are the expected management standards that health care providers are trained to meet based on a resource-complete environment. Examples of inclusion criteria are the universally accepted standards for the use of resources for resuscitation and management that are traditionally found in courses for advanced cardiac, trauma, and pediatric life support.
   
2. Exclusion criteria conversely refer to situations where expected resources are limited or lacking and care must proceed without all standards of care and equipment being met.
   
3. Minimum qualifications for survival represents a ceiling on the amount of resource expenditures that will be allocated to any one case, ensuring that maximum benefit of available resources is realized to ensure a population-based best opportunity for survival. Examples are the EOC determining that resource limitations would dictate that high resource maintenance cardiac or respiratory arrest interventions might be limited, as would restrictions on transfusions for traumatic injuries, or in the implementation of criteria protocols for ventilator use in those with a low likelihood of survival. Each MQS diagnosis is subject to change on arrival of surge capacity resources.

The operational level EOC must balance available resources against the best opportunity to survive. The impact of this triage management practice and decisions may not be fully known until the end of the MCI when outcome analyses are performed.

Bioevent Triage Management

Bioevents include both naturally occurring and the deliberate release of a biologic agent in a population resulting in a mass illness incident (epidemic or pandemic). Whereas these bioevents have similarities with other MCIs, there are also major differences, especially in the approach to triage management of surge capacity resources (2). Bioevents are characterized by massive numbers of individuals seeking health care (2). Unique to the planning for bioevents is that only 40% to 50% of health care providers are expected to respond or be available, in contrast to conventional MCIs where HCFs are often inundated with health care volunteers (61). A population-based approach requires a shift from the individual care role of clinicians to a population-based decision-making approach of patients. This does not minimize the importance of clinical tasks, but rather adds the dimension of new public health and surge capacity interventions that improve access and availability of limited health resources for the entire population. Individuals within a population experiencing a bioevent share the following (2,62).

• Most have either the same condition or are susceptible to it.
  
• All have shared health care needs.
  
• Everyone in the population requires some intervention, which ranges from education to critical care.
  
• Large-scale bioevents may require a sustained operational response, lasting 12 to 24 months.
  
• Especially with long-term bioevents, operational continuity of the health care system to manage medical issues other than those related to the involved biologic agent must remain a focus.

Severity, as indicated by rising case fatality rates, occurs dramatically as disease transmission increases and resources become limited. What at first appears to be a static, well-controlled local event can quickly become a regional, national, or international disaster of paralytic proportions (2,15,63).

The central jurisdictional EOC will determine surge capacity requirements for five population categories: those susceptible but not exposed (Susceptible category), those exposed but not yet infectious (Exposed category), the infectious (Infectious category), those removed by death or recovery (Removed category), and those protected by vaccination or prophylactic medication (Vaccinated category), termed the SEIRV methodology (2,64,65). The unique requirements and demands of each triage category may mandate that professionals with specific category expertise be assigned to the medical component of the ICS or centralized EOC (26). In turn, the EOC:

• Determines surge capacity requirements for each SEIRV category
  
• Determines triage criteria, including MQS and exclusion criteria
  
• Enforces compliance measures
  
• Ensures data collection, analysis, and measures of effectiveness using this information as the basis of daily reports and determination of effectiveness of triage management

Conventional triage methodologies, such as START and SAVE, risk impeding control of transmission by not recognizing those most in need of care in a bioevent MCI. The START and SAVE triage methodologies are based on severity of presentation and have limited application in bioevents in which point-of-contact decisions must be based on exposure, duration, or infectiousness (2,15). Decisions at every level are influenced by bioagent lethality, dose-dependent onset and duration, illness severity profiles, time to death or recovery, and surge capacity requirements and resources (2).

Within the community, the initial point of contact (POC) for potential victims comes through established hotlines and 911 calls. A simple series of questions can determine whether the caller is probably exposed or infectious versus probably not exposed or infectious. A series of questions concerning transport capacity and self-assisted care would follow, pointing the caller to one of three options: ambulatory clinic, designated influenza hospital, or home (self or assisted) care. A similar hotline approach was successfully used by the City of Toronto during SARS and has become the first level of triage in future outbreaks (2). Current CDC guidelines recommend phone triage with pre-established criteria for emergency transport and plans for coordination with other transport organizations for delivery of large numbers of victims at the height of the pandemic, the transport of multiple patients on a single run, and use of vehicles other than those designed for medical transport (e.g., buses) (66). The EOC may consider system wide exclusion criteria that would limit EMS transport to only noninfectious cases. EMS providers in Hong Kong experienced a higher attack rate for SARS, a risk dependent on the use of PPE, type of transfer, and decision to intubate (67). Such population-based triage decisions underscore the importance for a central EOC management authority.

In contrast to the availability of trauma capacity to implement interventions in conventional MCIs, resource implementation for bioevents varies considerably from jurisdiction to jurisdiction; this is especially evident in critical care. The developing situational awareness process within the EOC will identify gaps, limitations, and the surge capacity requirements gained from disaster managers, HCFs, volunteer agencies and organizations, and others with specific roles and responsibilities for each triage category. Because it is possible that fewer health care providers than expected will report to work during a major bioevent, the EOC must provide means to include provisions for just-in-time training, personal and family support, immunization or prophylactic antibiotics and antivirals, and bioagent-specific protective equipment to these workers and potential volunteers (2,61,68).

The Ebola outbreak in West Africa in 2014–2015 posed significant challenges to the affected countries’ governments, economy, health care infrastructure, and providers themselves. Triage in this resource poor setting was practiced, but not consistently between nations, or even clinical settings within a country (69).

A partial list of resources commonly triaged includes the following.

• Antivirals/antibiotics
  
• Vaccines
  
• Mechanical ventilators and ancillary equipment
  
• Pulse oximeters
  
• Medical oxygen
  
• Protective masks and equipment
  
• Nursing staff
  
• Laboratory support
  
• Acute care/ICU beds
  
• Housekeeping staff
  
• Morgue services
  
• Trained volunteers

Critical Care Triage

Normally critical care is offered only to those whose condition is potentially reversible and who have a good chance of surviving with intensive care support (70–72). Since the critically ill are often near death, the outcome of this intervention is difficult, if not impossible, to predict. Many patients still die in the ICU. A prime requisite for admission is that the underlying condition is reversible. Therefore, treatment is merely meant to support the patient, during which time treatments or the natural history of the acute affliction will lead to resolution. Rubinson and Toole suggest that a major challenge of MCIs is “to determine when, and on what basis, traditional standards of critical care are modified to accommodate emergency conditions, and when modified standards to focus on key interventions” (73). This model of care is referred to as mass critical care (34). In an MCI, mass critical care is implemented when usual surge protocols such as canceling elective surgery, discharging or transferring patients as soon as possible, and opening up alternative care areas will be insufficient to meet the demands placed on the health care system. Coordination of affected hospitals to facilitate implementation of similar measures in triage management is required (2,73). Furthermore, Farmer and Carlton suggest that shortfalls in critical care that will impact services are as follows (74).

• Insufficient coordination between hospitals and civil/government response agencies (e.g., the NIMS/ICS)
  
• Insufficient on-site critical care capability
  
• A lack of portability of acute care processes (e.g., patient transport)
  
• Education and training shortfalls
  
• The inability of hospitals to align disaster requirements with other competing priorities

Mechanical ventilator availability most likely serves as the limiting critical care capability in an overwhelm MCI, especially a bioevent. Hick and O’Laughlin (75) provide an operational model for the development of triage criteria for restriction of mechanical ventilation in these situations. Christian et al. (76) and Melnychuk and Kenny (77) provide an expanded critical care pandemic triage protocol for assessment of admission to critical care units during an influenza pandemic. This triage protocol uses the Sequential Organ Failure Assessment score (SOFA), and specifically addresses the importance of a centrally placed province or state EOC-level triage committee to implement critical inclusion, exclusion, and MQS criteria. Also stressed is the central jurisdictional EOC’s “absolute command and control over critical care resources in order to ensure accountability” (76). The EOC must support the critical care triage issues by authoritatively implementing the protocols in all hospitals when appropriate, and then monitoring its effectiveness through maintaining and analyzing outcome indicators. Both studies emphasize ethical principles and potential pitfalls of their approaches (75,76). Triage for critical care begins in the prehospital setting and extends to the emergency department. Given the complexity of triage for critical care, this coordinated triage process should be performed under the guidance of a trained critical care triage officer and/or critical care leadership of a multidisciplinary triage team. Knowing that many victims will require a critical care admission, a critical care triage officer may be called upon to join the emergency department triage officer or team at the entry site to implement the best means to supply crucial services, whether they be in existing critical care units, in resource expanded ward settings, or at another health care facility, thereby necessitate a transfer. The team approach may prove more efficient and effective, given the many resource variables come into play during the triage decision-making process; no one professional will possibly know the full impact of or what other innovative opportunities for survival are available within the larger response system. These triage decisions are thus only as accurate as the knowledge concerning what is operationally current and the resources available in each triage category. Ultimately, each triage level decision will have a direct effect on clinical decisions at the critical care level (2).

Since the recommended use of SOFA scores in critical care triage was published, its predictability across populations has varied and thus it remains an untested, unvalidated prognostic score. With this caveat, Christian et al. (78) focused recent recommendations on considering thresholds for providing care and resources. As well, implementation requires a defined set of pre-event protocol development and team-based employment during the event.