Background

Many of the studies of preventable deaths from trauma that highlight the importance of haemorrhage control also demonstrate that airway obstruction is a significant cause of preventable death in the pre-hospital setting [1, 2]. One extensive review of military battlefield trauma deaths concluded that airway obstruction represented the second most common category of death due to potentially survivable injury that occurred prior to arrival at a medical treatment facility (MTF) [3]. It is therefore imperative that providers of care in the pre-hospital environment have the necessary skills to recognise and manage airway compromise in the presence of life threatening haemorrhage.

Environment

For many patients with life threatening haemorrhage, damage control resuscitation will start in the pre-hospital environment (remote damage control resuscitation). This environment may be an urban setting with short transport times to sophisticated medical facilities. In many parts of the world, however, pre-hospital care is delivered in remote, austere and sometimes dangerous environments. There are many challenges associated with delivering remote damage control resuscitation, including safe and effective airway care, in such settings. There may be a lack of monitoring, equipment, communications, transport and medical supplies. Extended evacuation times may necessitate that providers undertake not only the time-critical, life-saving, airway interventions but also provide ongoing protection of the airway en-route to appropriate medical facilities.

Who Provides Care?

Initial airway care of the patient with life threatening haemorrhage is not the exclusive domain of any given medical provider but will fall to whoever has the necessary skills to recognise and manage airway compromise. In some health care systems, particularly civilian Emergency Medical Services (EMS) and Helicopter Emergency Services (HEMS), a small cadre of highly trained paramedical or medical staff can be deployed to supplement the basic airway skills of other providers on the few occasions when more sophisticated interventions are required. In more hostile, military environments, this may not be feasible and so basic healthcare providers may need to have a wider range of airway skills appropriate to the casualties they may encounter. Military initiatives such as the Tactical Combat Casualty Care (TCCC) training program and the Civilian Tactical Emergency Casualty Care (C-TECC) program seek to address these problems and emphasise the time-critical nature of not only haemorrhage control measures but also airway interventions. Such courses and an investment in the overall doctrine necessary to deliver these skills have been shown to have a significant impact upon outcomes from trauma. One study of military trauma outcomes following the introduction of a TCCC program demonstrated a dramatic reduction of preventable deaths on the battlefield [4].

Airway Care in Life Threatening Haemorrhage

Airway obstruction due to a reduced level of consciousness (due to reduced brain perfusion) is a significant risk for patients with life threatening haemorrhage. The priority of airway care for such patients is therefore to maintain a patent airway to facilitate adequate ventilation and tissue oxygen delivery whilst achieving haemorrhage control. Fick’s principle highlights that tissue delivery of oxygen (DO₂) is proportional to the haemoglobin concentration, oxygen saturation and cardiac output. (Fig. 14.1) A sustained fall in oxygen delivery below a critical point will precipitate accumulation of lactic acid and an “oxygen debt” which may lead to irreversible tissue ischaemia and coagulopathy [5]. Hence key damage control resuscitation strategies to ensure adequate tissue oxygen delivery for patients with life threatening haemorrhage are to maximise oxygen saturations, retain (and when possible, replace) haemoglobin, improve preload and cardiac output with plasma and minimise the detrimental effect upon cardiac output of any interventions undertaken.

Indications for Intervention

Many patients with life threatening haemorrhage need no immediate airway intervention, either in the pre-hospital setting or upon arrival at a medical treatment facility. Whilst basic airway skills can be delivered by providers with relatively limited training and experience, there are some patients who will need more sophisticated interventions. The proportion of patients requiring these advanced interventions varies by population studied. One review of 6875 combat casualties arriving at Combat Support Hospitals during Operation Iraqi Freedom found that 4.8% had undergone advanced airway interventions, delivered by a variety of providers, in the pre-hospital phase [6]. In another study of pre-hospital airway interventions in UK civilian practice, a significant proportion (57%) of trauma patients who had undergone initial airway intervention by EMS personnel still had airway compromise (partial airway obstruction or evidence of airway contamination) on arrival of an advanced care team and required advanced airway interventions [7]. Thus, providers of airway care in the pre-hospital environment must be trained not only in basic airway skills but also recognition of when more advanced interventions are required. Consideration needs to be given of which advanced airway skills and equipment will then be used and which providers will be required to deliver them.

Airway Assessment and Basic Care

All patients with haemorrhagic shock are at risk of developing airway compromise and therefore require rapid initial assessment and ongoing observation for impending airway compromise. The starting point of all airway care are the traditional methods of visual inspection of the airway and associated ventilatory efforts, listening for typical noises of airway obstruction and when necessary feeling for the movement of air. These methods may be more time consuming and inaccurate than generally realised, particularly in austere or hostile environments [8]. Monitoring with continuous wave-form capnography will help assess the net results of airway patency and ventilatory effort and is essential if advanced airway interventions are subsequently performed [9]. Pulse oximetry will provide information about oxygenation and circulation of blood although is often unreliable in the low flow states found in life threatening haemorrhage. Providers should avoid overreliance upon such adjunctive monitoring and be prepared to make repeated clinical assessments of airway patency, ventilatory effort and mentation. A stepwise approach to airway care should be used to ensure that simple strategies are the starting point after which an escalation of intervention can be employed to achieve a patent airway. Positioning of patients plays a vital role in initial airway care. In many settings, providers will want to position the patient in the supine position to facilitate airway care, interventions to address life threatening haemorrhage and casualty transport, but for many patients this represents a suboptimal position. Patients with life threatening obstetric haemorrhage may suffer aorto-caval obstruction when placed in the supine position and so should be managed in a tilted position. Patients with life threatening haemoptysis or haematemesis may aspirate blood if placed in the supine position. Similarly, patients with soiling of the airway or inability to maintain an airway in a supine position may be best managed in the lateral position to allow gravity to assist with postural drainage and opening of the airway. Many providers are naturally concerned about the potential risk of the lateral position for patients with suspected spinal injury, but a systematic review identified no evidence to suggest that placing patients with spinal injury into a lateral position carries a risk of neurological deterioration provided appropriate precautions are taken [10]. Simple airway opening manoeuvres such as jaw thrust, chin lift or head tilt may be required in the presence of airway obstruction but only jaw thrust is suitable for trauma patients with suspected cervical spine injury. Numerous studies have shown that cervical spine injury is rare in the presence of penetrating neck injury or gunshot wounds to the head and that in such settings airway management should take priority over cervical spine immobilisation [11, 12].

Airway Adjuncts

In some patients, a patent airway can only be maintained by the use of simple airway adjuncts, either a nasopharyngeal (NPA ) or an oropharyngeal airway (OPA) . Nasopharyngeal airways have the advantage of being relatively easy to insert, are better tolerated in patients who are not completely obtunded (hence less likely to cause gagging or vomiting) and can be inserted when a patient has trismus. Conversely, there is some evidence that incorrectly sized NPAs are ineffective or can actually precipitate airway obstruction [13]. Furthermore, there are case reports of intracranial passage of NPAs in patients with associated major head injury and of significant epistaxis with incautious insertion of the device [14, 15]. The relatively low risks of insertion must be balanced with the perceived benefits in each setting. OPAs are widely used as airway adjuncts but are usually only tolerated by deeply unconscious patients. In the event that these basic strategies fail then providers will need to escalate to more invasive methods of airway care.

Surgical Airways and Extraglottic Airway Devices (EADs)

Airway care in remote or austere settings often falls to relatively inexperienced providers with limited training or equipment and hence strategies to manage airway problems must take their level of training and experience into account. For this reason, many military organisations have chosen to train their pre-hospital medical providers in the skills required to perform surgical airway insertion (cricothyrotomy) when there are direct airway injuries or providers are unable to perform alternative advanced techniques such as the use of extraglottic airway devices (EAD) or drug-assisted endotracheal tube placement. There are many advantages of cricothyrotomy as an advanced airway intervention in an RDCR setting. It is a relatively easily learned and remembered technique that in its simplest form requires little equipment or post-procedural care [16]. There are a variety of techniques from simple dissection and insertion of a cuffed tracheal tube (“scalpel, finger, bougie”) to Seldinger devices and techniques that require more equipment and training. There would currently appear to be no clear advantages of any given technique or equipment [17]. Military studies have shown success rates of up to 93% [18–20]. A potentially compelling advantage is that this procedure can also be performed under local anaesthetic or with appropriate sedation (using agents least likely to cause hypotension or respiratory depression). When an airway has been secured, patients can be allowed to breathe spontaneously as muscle paralysis is not required to facilitate this procedure. There are clear haemodynamic benefits of spontaneous negative pressure ventilation over positive pressure ventilation for patients with life threatening haemorrhage. Cricothyrotomy is less widely used in civilian pre-hospital care settings due to lower rates of ballistic facial injury, concerns about potential harm of the procedure, increasing use of extraglottic airway devices and wider availability of drug- assisted intubation skills.

Another advanced strategy of airway care is the use of an extraglottic airway device (EAD) . Such devices are relatively easy to use and can be rapidly inserted with little risk of harm in deeply unconscious patients. They can be used for either spontaneous or assisted ventilation. They may require little or no ancillary equipment , particularly when a version is used that does not require cuff inflation after insertion. Although they all feature some sort of cuff or seal to limit the risk of aspiration of gastric contents or airway contaminants, they cannot be considered to offer a secure airway. Furthermore, to allow insertion, patients must either be deeply unconscious or drugs must be administered to obtund airway reflexes otherwise vomiting may occur. This can make them complex to employ in patients with dynamic airway compromise. Some providers suggest the use of pharmacologically assisted laryngeal mask (PALM) placement although this does expose the patient to all the risks of sedation or even paralysis without the advantages of achieving a secure, cuffed endotracheal tube [21]. The safety and efficacy of this technique remain unclear. There is no doubt, however, that as rapidly inserted airway interventions for unconscious patients or as “rescue” devices in the case of failed endotracheal intubation, EADs have a role to play in the advanced airway care of patients with life threatening haemorrhage [22].

When Should Patients with Life Threatening Haemorrhage Be Intubated?

Patients with life threatening haemorrhage who are unable to be oxygenated by use of any of the basic airway manoeuvres or adjuncts described above, or whose airway cannot be protected from contamination of blood, debris or gastric contents will need placement of an endotracheal tube to maintain oxygenation. This is usually facilitated by a process of drug-assisted sedation and paralysis to achieve rapid sequence intubation (RSI) . Paralysed patients must then be ventilated by positive pressure ventilation. In the presence of haemorrhagic shock, any induction agent can exacerbate the hypotensive state and positive pressure ventilation will further reduce cardiac output. Given these risks, controversy exists about the efficacy of pre-hospital intubation, with some retrospective studies seeming to show that it confers no survival advantage whilst other prospective studies have suggested improved outcomes [23–25]. Furthermore, some studies have even suggested that a strategy of rapid transport to hospital by police or private transport rather than Emergency Medical Services is associated with lower mortality for trauma patients, perhaps highlighting the time-critical need to achieve haemorrhage control as the greatest priority [26, 27]. On arrival at a medical treatment facility, patients who have not already been intubated are likely to need rapid sequence intubation to allow invasive haemorrhage control procedures as part of a coordinated damage control resuscitation strategy. The significant risk of haemodynamic compromise of this procedure should be mitigated whenever possible by a policy of aggressive blood product resuscitation in the peri-intubation phase.

When Should Patients with Life Threatening Haemorrhage Not Be Intubated?

Life threatening haemorrhage is not in itself an indication for intubation and positive pressure ventilation despite the perception that this brings order to a sometimes chaotic and challenging situation. When undertaken in awake hypotensive trauma patients in the field, pre-hospital intubation and positive pressure ventilation have been shown to be associated with increased in-hospital mortality [28]. Whilst many such patients will eventually require intubation to facilitate haemorrhage control procedures, this should be deferred, whenever safely possible, until the patient can be adequately resuscitated. Providers of airway care, particularly in remote settings where blood products may be less widely available, must therefore be trained in a range of appropriate airway strategies to manage the airway without resorting to intubation. Reduced level of consciousness due to life threatening haemorrhage should also not in itself mandate intubation in the pre-hospital setting as this does not necessarily correlate with ability to maintain an airway. If adequate oxygenation can be maintained and the airway protected from contamination using appropriate measures (e.g. postural drainage or suction) in a patient who is self-ventilating, then consideration should be given to transporting the patient to an appropriate medical treatment facility as rapidly as possible without performing intubation. When advanced airway practitioners are deployed into the pre-hospital environment, it must be recognised that they possess the vital skills and experience not only to perform intubation but also to identify when patients with life threatening haemorrhage can safely be managed without intubation. Providers must weigh the potential benefits of intubation and positive pressure ventilation against the significant risks of these procedures, particularly critical organ hypo-perfusion and cardiac arrest, in the presence of life threatening haemorrhage and consider whether alternative, lower risk, airway management strategies (including EAD placement or cricothyrotomy) can be employed pending the availability of more definitive resuscitation facilities.

Rapid Sequence Intubation in the Presence of Life Threatening Haemorrhage

If intubation must be performed in the presence of life threatening haemorrhage, there are specific considerations that minimise risk and optimise outcomes: