Anita A. Shah
Pulmonary/Critical Care, Medical Director of Intensive Care Unit, 14th Combat Support Hospital, Bastion Hospital, Helmand Province, Afghanistan, 2012–2013
Alexander S. Niven
Theater Consultant, Pulmonary/Critical Care, Chief, Critical Care, 47th Combat Support Hospital, Mosul, Iraq, 2006
BLUF Box (Bottom Line Up Front)
- 1.
Lung injury and acute respiratory distress syndrome (ARDS) are common in battlefield casualties and are usually multifactorial in origin.
- 2.
Blast lung injury is a common contributing mechanism to respiratory failure.
- 3.
Management of blast lung injury is similar to other etiologies of ARDS, and the prognosis is excellent if patients survive their initial injuries.
- 4.
Endotracheal intubation and mechanical ventilation should be initiated early in casualties with altered mental status or respiratory insufficiency, especially prior to transport.
- 5.
Early application of positive end expiratory pressure (PEEP) is essential to maintain adequate lung recruitment and gas exchange.
- 6.
Mucus plugs, pneumothorax, and decreased lung compliance are common in combat casualties. A deliberate approach to mechanical ventilation troubleshooting is essential to accurately and rapidly address these problems.
- 7.
Low tidal volume ventilation (≤ 6 cc/kg) improves mortality in ARDS. Airway pressure release ventilation (APRV) is the primary mode employed in theater to manage refractory hypoxic respiratory failure.
- 8.
To minimize barotrauma and volutrauma, try to minimize the rate, tidal volume, and time on positive pressure ventilation.
- 9.
Permissive hypercapnia and moderate acidosis (pH > 7.2) are acceptable in the treatment of ARDS and should not prompt increases in rate or tidal volume.
- 10.
Routine access to high-level salvage modalities for hypoxemic respiratory failure (jet ventilation, inhaled nitrous oxide, etc.) is not available; thus, proper patient and ventilator management is critical.
- 11.
Veno-venous (VV) extracorporeal membrane oxygenation (ECMO ) to treat refractory hypoxemic respiratory failure may be available on a limited basis.
The survival of combat casualties from the point of injury to definitive medical care has significantly improved over the last decade. Survival is >95% for casualties who survive their initial injury and are evacuated to definitive care. This improvement can be credited to several factors, including advances in body armor, an improved skill set of prehospital personnel, the presence of forward surgical teams, the availability of surgical and critical care assets in austere environments, and deployment of an increased number of soldiers skilled in basic and advance trauma life support. Early and effective management of battlefield casualties can be successful when the basic principles of prehospital, trauma, and critical care are maintained throughout the entire medical evacuation process. A critical care-trained physician may not be available to treat casualties; thus, all deploying physicians should be familiar with principles of respiratory failure and standard ventilator management.
The most common mechanisms of battlefield injuries vary from blast injuries (due to improvised explosive devices [IED], rockets and mortar attacks) to gunshot wounds (GSW ). Prior studies have demonstrated that casualties of blast injuries have a higher prevalence of multiple injuries, specifically of the head and extremities. Due to the blast effects, the lungs are one of the most commonly injured organs. As a result, intubation for airway protection and mechanical ventilation to manage respiratory failure is often necessary. Even when the lungs are not directly injured, these patients may develop severe pulmonary failure due to their associated injuries, massive transfusion and resuscitation, thermal injuries, or even inhalational effects of various substances including weaponized chemical agents such as chlorine. The purpose of this chapter is to provide a practical overview to the management of respiratory failure in these patients and to discuss the logistics, management, and troubleshooting of the mechanical ventilator in this population. In addition to the traumatically injured patient, you may be frequently called upon to manage patients with a variety of nontraumatic illnesses or pathology that require intubation and mechanical ventilation, and having a good grasp of the principles of basic mechanical ventilation and ventilator management will serve you well in any deployed setting.
Which Combat Casualties Need Mechanical Ventilation ?
The indications for intubation and mechanical ventilation are the same for all patients, including battlefield casualties. Broadly, the indications for intubation include the inability to oxygenate or ventilate, the inability of a patient to protect their airway, increased work of breathing, a decreased level of consciousness (specifically a Glasgow Coma Scale [GCS ] < 8), and multiple injuries in which future surgical management or ongoing resuscitation is anticipated (Table 36.1). The combat environment frequently forces providers to rapidly evacuate patients to a higher echelon of care. Often this is required immediately upon initial stabilization which makes patient monitoring, identification of progressive clinical deterioration, and definitive airway management difficult. Given this, it is important to determine if patients with significant head, neck, or chest trauma would benefit from securing a definitive airway (endotracheal intubation or surgical airway) and initiating mechanical ventilation prior to transport.
Table 36.1
Combat injuries for which intubation and mechanical ventilation are indicated
Airway protection |
Decreased level of consciousness (GCS < 8) |
Significant head trauma, cognitive dysfunction following blast injury |
Airway trauma, obstruction |
Craniofacial, neck injury with risk for airway compromise (consider surgical airway) |
Significant secretions or blood in the airway |
Inability to oxygenate or ventilate |
Thoracic, lung injury |
Flail chest, pneumothorax (despite management with tube thoracostomy) |
Penetrating thoracic injuries |
Respiratory distress, oxygen requirements following blast injury |
Increased intracranial pressure (ICP), herniation syndrome |
Airway protection, hyperventilation to decrease ICP |
Multiple injuries with anticipated surgical management |
Injuries requiring massive transfusion |
Thoracic, abdominal, large soft tissue injuries |
>1 proximal amputation |
Hypotension, hypothermia on presentation |
Respiratory Failure in Combat Casualties: The Role of Blast Lung Injury
The lung is one of the most frequently injured internal organs when suffering a blast injury. ARDS and respiratory failure in severely injured combat casualties are common. ARDS was redefined in 2012 and is currently categorized using the “Berlin criteria,” which is primarily based on the degree of hypoxemia as measured by the ratio of the PaO2 to the FiO2. Using this system, mild ARDS is characterized by a P/F ratio of 200–300, moderate by a ratio of 100–200, and severe by a ratio of less than 100. Patients will also have bilateral opacities on chest x-ray (which are non-cardiogenic or atelectatic in etiology) or worsening respiratory symptoms within 1 week of the clinical insult. The etiology of ARDS in combat casualties is usually multifactorial and can be divided into early and late causes (Table 36.2).
Table 36.2
Causes of ARDS in combat casualties
Early |
Systemic inflammatory response following multi-organ trauma |
Aspiration, chemical pneumonitis |
Thermal, inhalation injury |
Transfusion-related acute lung injury (TRALI) |
Blast lung injury (BLI) |
Fat emboli (long bone fractures) |
Late |
Ventilator-associated pneumonia (VAP) |
Ventilator-associated lung injury (VALI) |
Of the common causes of ARDS listed in Table 36.2, blast lung injury (BLI) and its sequela are the least familiar to deploying providers. BLI has been reported to be present in 70% of civilian victims of terrorist violence and is likely even more prevalent in the combat environment. Because its onset can frequently be delayed and its radiographic presentation is variable, it is difficult to determine the true prevalence of BLI in the critically injured combat casualty or to differentiate its contribution from other potential etiologies.
Of the four categories of blast injury (primary, secondary, tertiary, and quaternary), the lung is most vulnerable to primary blast injury. Lung manifestations include barotrauma (pneumothorax, pneumomediastinum ) due to gross thoracic deformation, hemoptysis and pulmonary contusion due to alveolar disruption, and intraparenchymal hemorrhage within the lung. These injuries are caused from the blast wave traveling through the body armor and human tissue and releasing energy in any area where there is a gas-liquid interface. The released energy causes disruption of the epithelial cells and vascular structures in the thoracic cavity leading to both immediate and delayed effects (Table 36.3). The damage caused by the blast wave is related to the proximity of the victim to the blast site and is amplified in closed spaces. It is important to be aware that casualties from an indoor blast are more likely to have airway and/or lung injuries which may take up to 12–24 h to manifest.
Table 36.3
Sequela of blast lung injury
Immediate |
Respiratory disturbance (rapid, shallow breathing or transient apnea <30 s) |
Pulmonary hemorrhage and edema secondary to ruptured alveolar capillaries |
Hypoxemia |
Pneumothorax |
Pneumomediastinum |
Air embolism |
Delayed |
Progressive hypoxemia due to ventilation perfusion mismatch |
ARDS |
Persistent pneumothorax |
Alveolo-venous fistula |
Broncho-venous fistula |
The classic clinical presentation of BLI is the triad of respiratory distress, hypoxemia, and perihilar “bat wing” pulmonary infiltrates; however, this triad is infrequently seen. Hypoxia is the most common finding and may develop after the first few hours of injury. Other common manifestations of primary blast injury include tympanic membrane perforation, bowel contusion and perforation , brain axonal injury, and myocardial contusion.
Secondary blast injury, to the lungs, can be caused by weapon fragments and other debris scattered at high velocity by an explosion. While body armor generally protects victims from fragmentation injuries, it does not prevent primary blast injury. Tertiary blast injuries are caused by the blast wave throwing victims against a stationary object. Finally, quaternary injuries of the lung include inhalational burns from fires or heated gas or crush injuries that occur from structural collapse that follows an explosion.
Management of Lung Injuries and Respiratory Failure
Initiation of Mechanical Ventilation
Successful management of respiratory failure in a combat environment will largely depend on the level of expertise of the provider and available resources. Most deployed units will not have the depth or breadth of ventilator management experience as a stateside facility. The management of respiratory failure requires a multidisciplinary approach to include an experienced physician, respiratory therapist, and nurse. If your facility is not appropriately staffed with providers and does not have the appropriate resources, early evacuation to a higher level of care is the highest priority after initial stabilization. Initial ventilator settings will depend on the capability of the available ventilator. Advanced modes of ventilation can be utilized based on the ventilator’s capability, the patient’s lung mechanics, other associated clinical conditions, and the experience and comfort of the medical staff.
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