Introduction

Tactical critical care (TCC) is the pre-hospital medical care rendered to a casualty in a tactical combat environment. Tactical neurocritical care (TNC) is TCC applied to casualties with brain or spine injury [1,2,3]. Both TCC and TNC differ significantly from their civilian critical care counterparts; civilian critical care relies heavily on evidence-based practices derived from randomized clinical trials, and TCC relies on military battlefield registries with some randomized trials [1,2,3]. Military casualties often suffer from blast injuries aggravated by the tactical environment [1,2,3]. While the civilian healthcare provider faces a clinical problem, the battlefield healthcare provider faces a clinical problem and a tactical challenge (good medicine can be bad tactics) [1,2,3]. Care in TCC is usually provided in a harsh, remote area with extreme temperatures, low visibility, and increased environmental noise from hostile/friendly fire, aircraft, or military vehicles [1, 2]. The medications and equipment available to the tactical provider are limited to those that can be carried in expeditionary medical bags. In TCC, priorities are altered due to the hostility of the environment. While in civilian medicine airway control takes priority, in the tactical environment hemorrhage control takes precedence because it is the leading cause of death [1,2,3,4,5,6].

This review will highlight the main differences between civilian critical care and TNC. Nuances of TNC that are specific to care under fire, care at the point of injury, tactical field care, and tactical evacuation care will be discussed. The care outlined here pertains mainly to role I (point of injury or battalion aid station) and to en route care while transporting casualties to a role II (field hospital with X-rays, laboratory, and possibly forward surgical team) or a role III (highest level of care in theater). Although many aspects of TNC apply to care in austere environments in general, this review will focus on the US military approach to battlefield TCC/TNC.

Tactical Critical Care Phases

The recognition that exsanguination was the main cause of death during the Vietnam and ensuing conflicts lead to the realization that the civilian approach to trauma was not applicable to battlefield injuries and gave rise to TCC [3,4,5,6]. In essence, TCC is a structured approach to combat injuries that balances tactical interests and the provision of field care in three phases—care under fire, TCC, and tactical evacuation care [1]. Care under fire, the initial phase, encompasses care provided at the point of injury while still under fire. During this phase, there is significant ongoing risk to the casualty and to the medic. Care is limited to what can be provided with the individual soldier’s Improved First Aid Kit (see Fig. 1) or the medic’s kit [1, 2]. Once hostile fire is suppressed or when an injury occurs on a battlefield without hostile fire, TCC can be initiated. In this phase, medical equipment is still limited. Depending on the location, weather, and tactical environment, this phase may last minutes to hours. Finally, tactical evacuation care occurs once the casualty has been loaded for transportation in any vehicle [1, 2]. The term “medevac” (medical evacuation) is used when the evacuation platform is a dedicated medical vehicle with specialized equipment and personnel, while “casevac” (casualty evacuation) is used when improvised platforms are used [1].

Fig. 1
figure 1

The Improved First Aid Kit (IFAK) contains combat dressing, chest seal, tourniquets, eye shields, an airway adjunct, and a tactical combat casualty care card

Full size image

Tactical Care under Fire

The main priorities during the care under fire phase are returning fire and moving the casualty to provide cover and concealment [1, 2]. Care is provided by a young fellow soldier or marine trained in combat life support or by the platoon medic; advanced care from a more skilled provider is available at later stages. Ideally a quick neurologic assessment should be done to determine whether the casualty can respond and can continue to engage fire. As the combat situation permits, the casualty should be assessed for signs of bleeding, and hemorrhage control should be attempted. Unlike in the civilian environment where airway, breathing, circulation, and stabilization of the cervical spine are immediate priorities, in TCC, hemorrhage control takes precedence [1,2,3,4,5]. Tourniquets and hemostatic dressings are applied to extremity wounds, the most common reversible injuries. Up to 69% of potentially reversible causes of death in recent conflicts have been the result of potentially compressible hemorrhage [1, 3,4,5]. Non-extremity wounds are treated with a hemostatic agent and are covered with a compressive dressing [1, 2]. Airway management is not attempted, and the casualty is allowed to place himself in a comfortable position [1, 2]. Airway trauma comprises only 1–2% of early combat deaths [2,3,4,5,6]. Cervical spine immobilization is not routinely attempted, as spine injury in this setting is rare and immobilization is time-consuming (median time 5.5 min) [1, 6,7,8,9]. However, if the tactical situation permits, spine immobilization may be considered in certain circumstances (see Table 1) [1, 2, 7, 8]. Leaving the body armor in place can help stabilize the thoracic spine (see Fig. 2). Standard litters may not be available, and the casualty may have to be dragged by his body armor, moved using a commercial drag device, or transported using a two-man carry while tanks, vehicles, smoke, or obscurants are used to conceal the move (Fig. 3).

Table 1 Indications for spinal immobilization during tactical critical care
Full size table
Fig. 2
figure 2

Armor left in place to protect casualty and immobilize the thoracic spine. Tourniquet is placed in the right upper leg. Left leg has been immobilized with service weapon

Full size image
Fig. 3
figure 3

Casualty drag performed using commercial device. Vehicle used to obscure the movement to the battalion aid station

Full size image

Tactical Field Care

Tactical field care, initiated once hostile fire has ceased, is still limited by the equipment and expertise of the medics and by possible enemy contact [1, 2]. During this phase, the casualty will be moved to a casualty collection point and/or to a battalion aid station (if injury happened on a forward operating base as opposed to the battlefield) where more advanced care is available (Fig. 4). The duration of this phase varies depending on tactical and meteorological conditions. A more in-depth assessment of the patient can be performed to assess responsiveness, evidence of hemorrhage, pneumothorax, or airway compromise. Cardiopulmonary resuscitation is not attempted, as it is largely futile in this setting [1, 2]. Casualties with altered mental status should be disarmed of service weapons, grenades, explosives, and knifes, as they can become a hazard to themselves and others. Altered mental status suggests hemorrhagic shock, hypoxemia, and/or traumatic brain injury (TBI) [1, 2].

Fig. 4
figure 4

The battalion aid station allows for more advanced care to include placement of an advanced airway and intra-osseous access. Oxygen tanks, suction, and a crash cart with advanced cardiac life support medicines are available

Full size image

During this phase of care, treatment priorities continue to be hemorrhage control with hemostatic agents, tourniquets, or compressive dressings, treatment of pneumothorax, and sealing open chest wounds with occlusive dressings [1,2,3]. Airway compromise can result from head trauma, maxillofacial trauma, or inhalation burns. In an unconscious victim with signs of airway obstruction, a jaw-thrust or chin-lift maneuver is recommended. If needed, a nasopharyngeal airway can be placed. (Oropharyngeal airways dislodge during tactical movements.) Failure to obtain a patent airway should lead to consideration of an advanced airway or a cricothyroidotomy [1, 2]. In the field, the laryngoscope light poses a tactical risk, and a cricothyroidotomy or laryngeal mask airway may be necessary. If the casualty is at a battalion aid station, an advanced airway may be initially attempted (Fig. 4). Unresponsive casualties with flaccid tone or extensor response to pain or those who respond to pain with abnormal flexion and have abnormal pupils should be intubated if the resources are available.

Vascular access should be obtained using the intra-osseous (IO) or intravenous (IV) route; the IO route allows the administration of all medications needed to treat TBI or spinal cord injury [1, 2]. Environmental noise and vibration preclude field use of blood pressure cuffs and stethoscope; however, a palpable radial pulse and normal mentation indicate adequate hemodynamic status. If mentation is compromised, an attempt should be made to discern if it is caused by TBI or shock [1, 2]. In the case of hemorrhagic shock, tactical combat casualty critical care (TCCC) guidelines suggest using a 500-mL bolus of 6% Hetastarch while monitoring pulse and mentation, if improved, fluids should be stopped, if not, a second bolus should be administered while evaluating for ongoing bleeding [1, 2]. Although medics often prefer to carry Hetastarch as it is lighter than crystalloids, isotonic or hypertonic crystalloids are ideal fluids for resuscitating TBI casualties [10, 11]. If TBI is the cause, the patient should be resuscitated to a palpable radial pulse and promptly evacuated [1, 2]. Hypothermia should be treated with hypothermia kits, poncho liners, sleeping bags, or blankets while avoiding hyperthermia. Hearing loss due to tympanic rupture is common and can cause confusion and limit communication (blast injury, hearing loss, and TBI often coexist) [10,11,12]. Blast-related brain injury occurs in up to 50% of blast victims and is often undetected due to hearing loss and to the fact that hemorrhage control takes precedence [11,12,13]. Additionally, if the casualty is a host nation soldier, allied military, or an enemy prisoner, language barriers may limit neurologic assessment.

Monitoring should involve the continual assessment of mental status, radial pulse, and pulse oximetry (available in medic bag). Pulse oximetry readings need to be interpreted cautiously at high altitude. If appropriate, pain should be controlled with oral acetaminophen or meloxicam or with IM/IV/IO ketamine, IM/IV/IO morphine, or transbuccal fentanyl [1, 2]. Ketamine can be repeated every 30 min until pain relief or until nystagmus develops [1]. Being injured in combat is a frightening experience, and efforts should be made to comfort the patient and to explain the situation to him/her. Eye protection, ear protection, and blankets should be used in preparation for transport [1, 2]. If care is being provided at the battalion aid station, some of the interventions mentioned in the tactical evacuation phase (below) may actually be initiated during the tactical field care phase.

Tactical Evacuation Phase

The tactical evacuation phase starts once the casevac or medevac platform arrives and allows for more advanced TCC/TNC. Personnel will arrive in a ground or air platform and bring additional equipment and medications. The flight medical crew is variably comprised of critical care paramedics, critical care nurses, and flight surgeons. If the tactical situation permits, preventable causes of death should be addressed pre-transfer (compressible hemorrhage, tension pneumothorax, airway obstruction) [1, 2]. The arriving personnel will have received a Mechanism of Injury, Signs, Treatment (also known as MIST) report from the ground force and have prepared equipment/supplies accordingly. Typically, a rotary wing aircraft will be used for tactical evacuation (Blackhawks in the US Army), and cruising altitude will vary between 6000 and 10,000 feet depending on the terrain. The usual goal is to have wheels up within 5 min of landing; therefore, the time available for preparation is limited [14]. Aeromedical transportation can pose risks to the TBI casualty, and the crew needs to anticipate them. Decreases in the arterial content of oxygen are rare in typical rotary wing operations, but coexisting pulmonary injury or smoking can result in hypoxia aggravating TBI [14,15,16]. Pneumocephalus expansion during ascent can increase intracranial pressure (ICP) [17]. Similarly, gas dysbarism resulting from the expansion of air within fractured sinuses can result in severe facial or head pain. The nine stressors of flight (see Table 2) can all negatively affect neurologic function, and the medical team needs to be aware of them [11]. If chemical contamination is suspected, a hasty decontamination is done pre-flight.

Table 2 Nine stressors of flight
Full size table

If circumstances permit, a brief pre-flight neurologic exam should be performed, as once air-bound the assessment will be very limited, communication may be impossible, and pupillary examination may not be feasible either because light poses a tactical risk or because eye shields have been placed for eye trauma. Looking for purposeful repetitive movements, the ability to follow commands (by mimicking) and the presence of smooth, regular respirations may constitute the extent of the in-transport exam [1]. Transient decreases in the level of consciousness that gradually improve are common after blast injury due to the primary injury (blast). However, the secondary (flying debris), tertiary (body displacement), and quaternary injury (burns, displaced structures) can also inflict neurologic injury [13]. The patient is loaded head toward aft of the aircraft if increased ICP is suspected. Once on board, the casualty will undergo standard cardiac monitoring using a military airworthy monitor, blood pressure monitoring using an automated cuff, and continuous pulse oximetry. However, these monitors tend to function poorly in the air. Pulse oximetry readings are typically 3% off at normal cruising altitudes, and the treating clinician needs to account for that. Oxygen saturation decreases with altitudes above 8000 ft [15]. All casualties who are unconscious, have signs of TBI, have torso trauma, or have low oxygen saturation should receive supplemental oxygen [1, 2, 14]. If the patient has been intubated or a cricothyroidotomy has been performed, the possibility of balloon air expansion during ascent needs to be considered and may require cuff deflation or the use of saline instead of air. Acceleration of the aircraft can also increase ICP, and the head should be placed so the vector of greatest anticipated acceleration is perpendicular to the long axis [16, 17].

During flight, the crew will continue to assess for ongoing hemorrhage and reassess airway, breathing, and neurologic condition. If indicated, c-spine immobilization may be performed. If an advanced airway is in place, the patient may need analgosedation with a Sedation Agitation Scale goal of 1–2 (very sedated to unarousable) [14]. Sedation can be accomplished with ketamine 0.5–1 mg/kg q10–20 min, fentanyl 1 mcg/kg q30–60 min, or propofol 10–50 mcg/kg/min (IV/IO). Neuromuscular blocking agents can be used if skeletal muscle paralysis is desired. This can be achieved with vecuronium 0.1 mg/kg q30–60 min or rocuronium 1 mg/kg q30–45 min (IV/IO). Much like their civilian counterparts, Army flight paramedic guidelines rely on the Glasgow Coma Scale (GCS) and the presence of a gag reflex to determine the need for an advanced airway; GCS below 8 with an absent gag reflex requires an advanced airway [14]. Civilian studies suggest that pre-hospital intubation is associated with poor outcome; battlefield intubation should take into account the GCS, the ability to protect the airway, the oxygen saturation, the presence of thoracic injury, the transport time, and the tactical environment and resources [18]. In a combat environment, the tactical situation always takes priority and may limit assessment or interventions. In such cases, proper documentation in the patient care record is necessary. During rotary wing operations, temperature will decrease with increasing altitude dropping by approximately 3.5° Fahrenheit for every 1000 feet (aggravated in Blackhawk helicopters by rotor wash and forward speed). This can result in hypothermia and shivering, which can increase ICP and metabolic oxygen demand [14, 18, 19].

Avoiding secondary injuries (hypoxia, hypotension, hypercarbia, hypo/hyperthermia) and treating new complications (seizures, fever) are the main goals during the tactical evacuation phase [18, 19]. Hypoxia, hypercarbia, and hypotension significantly increase morbidity and mortality [19,20,21,22,23]. In a prospective study of US and allied personnel with TBI presenting to role III facilities in Iraq and Afghanistan, the incidence of hypoxia was 52.5%, the incidence of hypocarbia was 20.3%, the incidence of hypercarbia was 50%, and the incidence of hypotension was 21.1% [21]. In a separate study looking at in-flight complications during rotor-wing transfers during Operation Iraqi freedom, 53% of patients required in-flight mechanical ventilation, and 20% required vasopressors [16]. Aircraft have low cabin humidity and insensible losses are increased in-flight often, leading to hypovolemia. Such findings underscore the importance of obtaining an advanced airway when appropriate and of ensuring adequate oxygenation, ventilation, and hemodynamic resuscitation.

During transfer, the medical crew will continue neurologic monitoring, looking for unilateral/bilateral dilated, sluggish, or fixed pupils; vomiting, Cushing’s reflex, decorticate or decerebrate posturing, an abnormal breathing pattern, and an overall change in responsiveness. As previously stated, the examination will be very limited due to poor illumination, noise, vibration, and other tactical elements. In this phase of care, the US Army guidelines recommend using crystalloids to achieve the goal systolic blood pressure of 100–110 mm Hg (hypotonic fluids should be avoided) [11]. If available, blood should be used to resuscitate patients with hemorrhagic shock [1,2,3]. Diligent efforts to look for ongoing hemorrhage are necessary in the hypotensive TBI casualty [1,2,3, 11, 14]. Associated unrecognized spinal cord injury can be an overlooked cause of hypotension in the tactical environment. If hemorrhagic shock is suspected, bleeding control should be attempted and blood products and tranexamic acid (TXA) administered if available and authorized by command policy [1]. Hypothermia prevention is imperative in cases of hemorrhagic shock [24]. In non-traumatic shock, the recommendation is to use a norepinephrine infusion (2–12 mcg/min) or dopamine (2–20 mcg/kg/min) [1, 2, 11, 14]. If spinal cord injury is suspected, a MAP goal of 80–90 mm Hg is recommended.

Seizures, if present, are treated with lorazepam 1–2 mg or midazolam 2–2.5 mg (IV/IM/IO) [14]. If available, finger-stick glucose should be checked to rule out hypoglycemia. Clinical signs of increasing ICP/herniation merit using 3% saline bolus (250 cc) or IV mannitol 1 g/kg; both can be administered IO, but mannitol requires a filter. In cases of impending herniation, transient hyperventilation to a PaCO2 of 30–35 mm Hg is recommended [14]. If capnography is not available, hyperventilation is defined as 20 respirations per minute in an adult casualty [14]. Table 3 outlines the management of suspected increased ICP in the battlefield. Of note, blast injury and chemical agents can cause transient iridoplegia—not to be confused with uncal herniation [12]. If expansion of a pneumocephalus is suspected, communication with the pilot in command is needed to explore, if permissible, altitude descent. Pain should be treated cautiously, and small doses of the above-mentioned analgesics in small increments should be used, bearing in mind that opiates and ketamine can increase ICP [14]. If neuromuscular paralysis is required, vecuronium (bolus dosing) is preferred because it does not require refrigeration [11].

Table 3 Management of suspected increased intracranial pressure during tactical evacuation
Full size table

The role of TXA in the treatment of traumatic intracranial hemorrhage has not been clearly elucidated. There is firm evidence that TXA is beneficial in battlefield hemorrhagic shock. The MATTERS study found that in this population TXA reduced incidence of shock, coagulopathy, and need for ventilator support [25]. A small prospective case–control study suggested that TXA may reduce hematoma expansion and improve the outcome in patients with non-surgical TBI [26]. It stands to reason that if TXA can help decrease systemic bleeding, it can improve cerebral perfusion pressure, and it may be of indirect benefit in the TBI casualty with systemic trauma. However, the role of TXA in isolated battlefield TBI in the absence of systemic bleeding is still unclear.

Patients with penetrating injuries to the head or spine or with sinus fractures that communicate with the cranial vault are at risk for neurologic infections. Initial field care should include wound coverage with sterile dressings that do not restrict decompression but protect from infection followed by administration of prophylactic antibiotics [1, 2, 27]. The US Army recommends using moxifloxacin in patients able to take PO and Ertapenem in patients unable to take PO [1, 2, 27]. Moxifloxacin is no longer available in the medical kit that soldiers carry but is available to field medics. Ertapenem (available to combat medics) provides broad spectrum coverage, does not require refrigeration, and can be given IV/IM/IO. Both medications have good vitreous penetration, which is important given the frequent occurrence of penetrating eye trauma [2]. Ertapenem can increase the risk of seizures, and this can be of concern in the patient with TBI. The incidence of cerebrospinal fluid leak in combat TBI is 8.6%, but otorrhea or rhinorrhea may not become evident until higher cruise altitude is achieved [7]. Treatment includes elevating the head, covering the nose/ear canal with clean gauze, and administering antibiotics. Cefazolin 2 gm IV q6-8 and consideration of metronidazole 500 mg IV every 8–12 h should be administered at the first level of surgical care.

Point-of-care ultrasound use in austere environments is gaining interest. It has been used successfully to diagnose pericardial effusions, high-altitude pulmonary edema, and pneumothorax [28]. Point-of-care ultrasound has also been used for the diagnosis of high-altitude mountain sickness through the examination of optic nerve diameter [28]. In the future, it is conceivable that point-of-care ultrasound may be used to evaluate battlefield TBI. Clinical decisions could then be made based on the optic nerve diameter. Optic nerve diameters exceeding 5 mm are associated with increased ICP [28]. Previous studies have demonstrated that flight crews can perform point-of-care ultrasound with good sensitivity and specificity for the detection of pneumothorax, hemothorax, and free abdominal fluid [29]. Conceivably, flight personnel can be trained to perform point-of-care ultrasound of the optic nerve. Extreme caution must be exercised when using optic nerve ultrasound when there is coexisting ocular trauma due to risk of enucleation or ocular trauma.

Promising future technologies for the battlefield include EEG, near-infrared spectroscopy, and transcranial Doppler [30,31,32]. Wireless EEG technology using a 6-channel recording can be performed in the pre-hospital setting. The EEG leads are easy to apply, and the EEG tracings are of adequate diagnostic quality allowing seizure detection, sedation titration, and prognosis determination [30]. Near-infra red spectroscopy uses the reflection of light in a hand-held device to detect hemoglobin in the brain; asymmetric readings can indicate the presence of subdural, epidural, or extracranial bleeding with adequate sensitivity [31]. Transcranial Doppler has been utilized in the pre-hospital evaluation of severe TBI to indirectly estimate cerebral blood flow (by measuring diastolic velocity)and intracranial pressure (by measuring pulsatility index) [32]. Use of this type of technologies requires portable, rugged, airworthy equipment that can easily be applied and interpreted by novice users.

Conclusions

Tactical neurocritical care concludes once the aircraft has arrived at the higher care facility. At this point, there is a quick handoff to the receiving physicians, typically including a neurosurgeon at a capable role III hospital. Emphasis is placed on the initial GCS, the presence/absence of in-flight complications, the in-flight interventions, and the last time sedation/paralytics were used. The patient care record will be reviewed by the unit flight surgeon who will provide feedback to the air crew. Of particular concern is ensuring that flight personnel adhere to established in-flight management guidelines. Civilian studies suggest that adherence to Brain Trauma Foundation Guidelines during air transportation is associated with improved outcome [22]. Although it is easy to be nihilistic about the application of TNC in austere environments, there are many interventions the tactical provider can perform that can significantly impact outcome. The significant improvements in morbidity and mortality achieved in recent conflicts attest to the impact that organized medical field care can have.