Mass casualty respiratory failure

Mechanical Ventilation with Room Air is Feasible in a Moderate Acute Respiratory Distress Syndrome Pig Model - Implications for Disaster Situations and Low-Income Nations

INTRODUCTION

Patients with respiratory failure are usually mechanically ventilated, mostly with fraction of inspired oxygen (FiO2) > 0.21. Minimizing FiO2 is increasingly an accepted standard. In underserved nations and disasters, salvageable patients requiring mechanical ventilation may outstrip oxygen supplies.

STUDY OBJECTIVE

The hypothesis of the present study was that mechanical ventilation with FiO2 = 0.21 is feasible. This assumption was tested in an Acute Respiratory Distress Syndrome (ARDS) model in pigs.

METHODS

Seventeen pigs were anesthetized, intubated, and mechanically ventilated with FiO2 = 0.4 and Positive End Expiratory Pressure (PEEP) of 5cmH2O. Acute Respiratory Distress Syndrome was induced by intravenous (IV) oleic acid (OA) infusion, and FiO2 was reduced to 0.21 after 45 minutes of stable moderate ARDS. If peripheral capillary oxygen saturation (SpO2) decreased below 80%, PEEP was increased gradually until maximum 20cmH2O, then inspiratory time elevated from one second to 1.4 seconds.

RESULTS

Animals developed moderate ARDS (mean partial pressure of oxygen [PaO2]/FiO2 = 162.8, peak and mean inspiratory pressures doubled, and lung compliance decreased). The SpO2 decreased to <80% rapidly after FiO2 was decreased to 0.21. In 14/17 animals, increasing PEEP sufficed to maintain SpO2 > 80%. Only in 3/17 animals, elevation of FiO2 to 0.25 after PEEP reached 20cmH2O was needed to maintain SpO2 > 80%. Animals remained hemodynamically stable until euthanasia one hour later.

CONCLUSIONS

In a pig model of moderate ARDS, mechanical ventilation with room air was feasible in 14/17 animals by elevating PEEP. These results in animal model support the potential feasibility of lowering FiO2 to 0.21 in some ARDS patients. The present study was conceived to address the ethical and practical paradigm of mechanical ventilation in disasters and underserved areas, which assumes that oxygen is mandatory in respiratory failure and is therefore a rate-limiting factor in care capacity allocation. Further studies are needed before paradigm changes are considered.

The Critical Care Society of Southern Africa Consensus Statement on ICU Triage and Rationing (ConICTri)

Background

In South Africa (SA), intensive care is faced with the challenge of resource scarcity as well as an increasing demand for intensive care unit (ICU) services. ICU services are expensive, and practitioners in low- to middle-income countries experience daily the consequences of limited resources. Critically limited resources necessitate that rationing and triage (prioritisation) decisions are frequently necessary in SA, particularly in the publicly funded health sector.

Purpose

The purpose of this consensus statement is to examine key questions that arise when considering the status of ICU resources in SA, and more specifically ICU admission, rationing and triage decisions. The accompanying guideline in this issue is intended to guide frontline triage policy and ensure the best utilisation of intensive care in SA, while maintaining a fair distribution of available resources. Fair and efficient triage is important to ensure the ongoing provision of high-quality care to adult patients referred for intensive care.

Recommendations

In response to 14 key questions developed using a modified Delphi technique, 29 recommendations were formulated and graded using an adapted GRADE score. The 14 key questions addressed the status of the provision of ICU services in SA, the degree of resource restriction, the efficiency of resource management, the need for triage, and how triage could be most justly implemented. Important recommendations included the need to formally recognise and accurately quantify the provision of ICU services in SA by national audit; actively seek additional resources from governmental bodies; consider methods to maximise the efficiency of ICU care; evaluate lower level of care alternatives; develop a triage guideline to assist policy-makers and frontline practitioners to implement triage decisions in an efficient and fair way; measure and audit the consequence of triage; and promote research to improve the accuracy and consistency of triage decisions. The consensus document and guideline should be reviewed and revised appropriately within 5 years.

Conclusion

In recognition of the absolute need to limit patient access to ICU because of the lack of sufficient intensive care resources in public hospitals, recommendations and a guideline have been developed to guide policy-making and assist frontline triage decision-making in SA. These documents are not a complete plan for quality practice but rather the beginning of a long-term initiative to engage clinicians, the public and administrators in appropriate triage decision-making, and promote systems that will ultimately maximise the efficient and fair use of available ICU resources.

Preparing your intensive care unit to respond in crisis: considerations for critical care clinicians

OBJECTIVE

In recent years, healthcare disaster planning has grown from its early place as an occasional consideration within the manuals of emergency medical services and emergency department managers to a rapidly growing field, which considers continuity of function, surge capability, and process changes across the spectrum of healthcare delivery. A detailed examination of critical care disaster planning was undertaken in 2007 by the Task Force for Mass Critical Care of the American College of Chest Physicians Critical Care Collaborative Initiative. We summarize the Task Force recommendations and available updated information to answer a fundamental question for critical care disaster planners: What is a prepared intensive care unit and how do I ensure my unit's readiness?

DATA SOURCES

Database searches and review of relevant published literature.

DATA SYNTHESIS

Preparedness is essential for successful response, but because intensive care units face many competing priorities, without defining "preparedness for what," the task can seem overwhelming. Intensive care unit disaster planners should, therefore, along with the entire hospital, participate in a hospital or regionwide planning process to 1) identify critical care response vulnerabilities; and 2) clarify the hazards for which their community is most at risk. The process should inform a comprehensive written preparedness plan targeting the most worrisome scenarios and including specific guidance on 1) optimal use of space, equipment, and staffing for delivery of critical care to significantly increased patient volumes; 2) allocation of resources for provision of essential critical care services under conditions of absolute scarcity; 3) intensive care unit evacuation; and 4) redundant internal communication systems and means for timely data collection.

CONCLUSION

Critical care disaster planners have a complex, challenging task. Experienced planners will agree that no disaster response is perfect, but careful planning will enable the prepared intensive care unit to respond effectively in times of crisis.

A porcine model for initial surge mechanical ventilator assessment and evaluation of two limited-function ventilators

OBJECTIVES

To adapt an animal model of acute lung injury for use as a standard protocol for a screening initial evaluation of limited function, or "surge," ventilators for use in mass casualty scenarios.

DESIGN

Prospective, experimental animal study.

SETTING

University research laboratory.

SUBJECTS

Twelve adult pigs.

INTERVENTIONS

Twelve spontaneously breathing pigs (six in each group) were subjected to acute lung injury/acute respiratory distress syndrome via pulmonary artery infusion of oleic acid. After development of respiratory failure, animals were mechanically ventilated with a limited-function ventilator (simplified automatic ventilator [SAVe] I or II; Automedx, Germantown, MD) for 1 hr or until the ventilator could not support the animal. The limited-function ventilator was then exchanged for a full-function ventilator (Servo 900C; Siemens-Elema, Solna, Sweden).

MEASUREMENTS AND MAIN RESULTS

Reliable and reproducible levels of acute lung injury/acute respiratory distress syndrome were induced. The SAVe I was unable to adequately oxygenate five animals with Pao2 (52.0±11.1 torr) compared to the Servo (106.0±25.6 torr; p=.002). The SAVe II was able to oxygenate and ventilate all six animals for 1 hr with no difference in Pao2 (141.8±169.3 torr) compared to the Servo (158.3±167.7 torr).

CONCLUSIONS

We describe a novel in vivo model of acute lung injury/acute respiratory distress syndrome that can be used to initially screen limited-function ventilators considered for mass respiratory failure stockpiles and that is intended to be combined with additional studies to definitively assess appropriateness for mass respiratory failure. Specifically, during this study we demonstrate that the SAVe I ventilator is unable to provide sufficient gas exchange, whereas the SAVe II, with several more functions, was able to support the same level of hypoxemic respiratory failure secondary to acute lung injury/acute respiratory distress syndrome for 1 hr.

Critical care management of major disasters: a practical guide to disaster preparation in the intensive care unit

Recent events and regulatory mandates have underlined the importance of medical planning and preparedness for catastrophic events. The purpose of this review is to provide a brief summary of current commonly identified threats, an overview of mass critical care management, and a discussion of resource allocation to provide the intensive care unit (ICU) director with a practical guide to help prepare and coordinate the activities of the multidisciplinary critical care team in the event of a disaster.

Preparing your intensive care unit for the second wave of H1N1 and future surges

Faced with increased demands for critical care services as a result of the novel H1N1 pandemic, hospitals must prepare a surge response in an attempt to manage these needs. In preparing for a surge response, factors to consider are staff, stuff (supplies and equipment), space, and systems necessary to respond to the event. This article uses this general framework to discuss surge issues in the context of H1N1 challenges that we are facing currently and to provide specific advice for hospitals. Particular attention is given to how hospitals can estimate the potential impact of H1N1 and pharmaceutical stockpiling.

Protective mechanical ventilation does not exacerbate lung function impairment or lung inflammation following influenza A infection

The degree to which mechanical ventilation induces ventilator-associated lung injury is dependent on the initial acute lung injury (ALI). Viral-induced ALI is poorly studied, and this study aimed to determine whether ALI induced by a clinically relevant infection is exacerbated by protective mechanical ventilation. Adult female BALB/c mice were inoculated with 104.5 plaque-forming units of influenza A/Mem/1/71 in 50 μl of medium or medium alone. This study used a protective ventilation strategy, whereby mice were anesthetized, tracheostomized, and mechanically ventilated for 2 h. Lung mechanics were measured periodically throughout the ventilation period using a modification of the forced oscillation technique to obtain measures of airway resistance and coefficients of tissue damping and tissue elastance. Thoracic gas volume was measured and used to obtain specific airway resistance, tissue damping, and tissue elastance. At the end of the ventilation period, a bronchoalveolar lavage sample was collected to measure inflammatory cells, macrophage inflammatory protein-2, IL-6, TNF-α, and protein leak. Influenza infection caused significant increases in inflammatory cells, protein leak, and deterioration in lung mechanics that were not exacerbated by mechanical ventilation, in contrast to previous studies using bacterial and mouse-specific viral infection. This study highlighted the importance of type and severity of lung injury in determining outcome following mechanical ventilation.

An improvised oxygen supply system for pandemic and disaster use

BACKGROUND

Current disaster planning for pandemic influenza anticipates overwhelming numbers of patients in need of hospitalization. The anticipated use of extra, or "surge," beds is common in both hospital and community disaster response planning. In a pandemic of respiratory illness, supplemental oxygen will be a life-saving intervention. There are currently few options to provide these proposed surge beds with the necessary oxygen.

OBJECTIVES

A method of providing an improvised oxygen delivery system for use in a disaster was developed and tested. This system was designed to use readily available commercial materials to assemble an oxygen delivery system.

METHODS

The study consisted of a laboratory design, assembly, and testing of an improvised oxygen system.

RESULTS

A liquid oxygen (LOX) Dewar container was used to supply oxygen systems built from inexpensive commercially available plastic tubing and fittings. The system will drive ventilators without significant pressure drop or ventilator malfunction. The final developed system will supply 30 patients with up to 6 L/min (l pm) oxygen each by nasal cannula from a single oxygen Dewar.

CONCLUSIONS

An improvised system to deliver oxygen for patient beds or ventilator use can be easily assembled in the event of a disaster. This could be life-saving in the event of a pandemic of respiratory illness.

Emergency Mass Critical Care

At any moment regular television programming could be interrupted with news of the emergence of a new strain of infective agent, a major industrial accident, or a terrorist event. Many devastating events are widespread and naturally occurring, like hurricanes, in which we have ample warning time to enact preparation plans; while others, like earthquakes, volcanoes, or tsunamis may kill or injure thousands before the news reports hit the airwaves. Industrial accidents and terrorist events are usually sudden and occur without any warning. Any of these events may have a local or regional effect; some may even have a global impact [1]. Regardless of the cause, after such an event, large amounts of the populace will be seeking medical care, whether from their primary care providers, public health departments, or local hospitals.

Mechanical ventilation in an airborne epidemic

With the increasing threat of pandemic influenza and catastrophic bioterrorism, it is important for intensive care providers to be prepared to meet the challenge of large-scale airborne epidemics causing mass casualty respiratory failure. The severe acute respiratory syndrome outbreak exposed the vulnerability of health care workers and highlighted the importance of establishing stringent infection control and crisis management protocols. Patients who have acute lung injury and acute respiratory distress syndrome who require mechanical ventilation should receive a lung protective, low tidal volume strategy. Controversy remains regarding the use of high-frequency oscillatory ventilation and noninvasive positive pressure ventilation. Standard, contact, and airborne precautions should be instituted in intensive care units, with special care taken when aerosol-generating procedures are performed.

Definitive care for the critically ill during a disaster: current capabilities and limitations: from a Task Force for Mass Critical Care summit meeting, January 26-27, 2007, Chicago, IL

In the twentieth century, rarely have mass casualty events yielded hundreds or thousands of critically ill patients requiring definitive critical care. However, future catastrophic natural disasters, epidemics or pandemics, nuclear device detonations, or large chemical exposures may change usual disaster epidemiology and require a large critical care response. This article reviews the existing state of emergency preparedness for mass critical illness and presents an analysis of limitations to support the suggestions of the Task Force on Mass Casualty Critical Care, which are presented in subsequent articles. Baseline shortages of specialized resources such as critical care staff, medical supplies, and treatment spaces are likely to limit the number of critically ill victims who can receive life-sustaining interventions. The deficiency in critical care surge capacity is exacerbated by lack of a sufficient framework to integrate critical care within the overall institutional response and coordination of critical care across local institutions and broader geographic areas.

Clinical review: allocating ventilators during large-scale disasters--problems, planning, and process

Catastrophic disasters, particularly a pandemic of influenza, may force difficult allocation decisions when demand for mechanical ventilation greatly exceeds available resources. These situations demand integrated incident management responses on the part of the health care facility and community, including resource management, provider liability protection, community education and information, and health care facility decision-making processes designed to allocate resources as justly as possible. If inadequate resources are available despite optimal incident management, a process that is evidence-based and as objective as possible should be used to allocate ventilators. The process and decision tools should be codified pre-event by the local and regional healthcare entities, public health agencies, and the community. A proposed decision tool uses predictive scoring systems, disease-specific prognostic factors, response to current mechanical ventilation, duration of current and expected therapies, and underlying disease states to guide decisions about which patients will receive mechanical ventilation. Although research in the specifics of the decision tools remains nascent, critical care physicians are urged to work with their health care facilities, public health agencies, and communities to ensure that a just and clinically sound systematic approach to these situations is in place prior to their occurrence.

Pandemic preparedness

PURPOSE OF REVIEW

Pandemic influenza remains a threat to world health and will probably result in an overwhelming number of critically ill patients. Preparations should be made now to meet this threat.

RECENT FINDINGS

Limited data are available on which to base preparations. Adequate staffing is crucial to the functioning of an ICU and therefore occupational safety is of central concern. In the absence of knowledge of the method of spread of a pandemic disease, it would seem appropriate to take airborne and contact precautions, and the literature related to this area is reviewed. Methods of recruiting and training additional staff and the issues of bed capacity, stockpiling, triage and ethics are discussed.

SUMMARY

Extensive preparation is needed in advance of an epidemic. This should include occupational safety measures, stockpiling of equipment and drugs, staff training, development of triage policies, and discussion of the limits of duty of care to patients. These preparations take considerable time and therefore these issues should be tackled urgently.