The critical airway in adults: The facts.

An algorithm on the indications and timing for a surgical airway in emergency as such cannot be drawn due to the multiplicity of variables and the inapplicability in the context of life-threatening critical emergency, where human brain elaborates decisions better in cluster rather than in binary fashion. In particular, in emergency or urgent scenarios, there is no clear or established consensus as to specifically who should receive a tracheostomy as a life-saving procedure; and more importantly, when. The two classical indications for emergency tracheostomy (laryngeal injury and failure to secure airway with endotracheal intubation or cricothyroidotomy) are too generic and encompass a broad spectrum of possibilities. In literature, specific indications for emergency tracheostomy are scattered and are biased, partially comprehensive, not clearly described or not homogeneously gathered. The review highlights the indications and timing for an emergency surgical airway and gives recommendations on which surgical airway method to use in critical airway.

INTRODUCTION

Critical airway is a life-threatening scenario of hypoxemia about to become hypoxia, following failed or inadequate ventilation. In such scenarios, esophageal intubation compounds the criticality of the situation as, besides the loss of oxygenation, the risk of stomach contents being aspirated into the airways is enhanced by ventilating into the stomach.[12] Cervical spine injury or non-exclusion is not an issue, as almost always endotracheal intubation (ETI) can be done with little head manipulation and without neck manipulation; the problem would lie, in the end, on whether the patient can be ventilated or not.[3-6] In the last two decades, a new philosophy of airway control has shifted emphasis from mask ventilation to supraglottic ventilation with the introduction of supraglottic ventilatory devices (SGVDs). SGVDs obviate the need for cervical manipulations and can be used as a bridge during the attempts at ETI, even by untrained or inexperienced personnel in outdoor settings. Protection from stomach contents being aspirated is not guaranteed, but the risk is reduced with the introduction of extra channels for nasogastric tube (NGT) and endotracheal tube (ETT). Other drawbacks are the effects of decubitus on oral and pharyngeal structures, the decrease of lung compliance with increase of airway resistance and the need to be inserted in an unconscious patient. SGVDs are optimally placed for airway control outdoors in suspected or not excluded cervical spine injuries (CSIs) or in the small percentage of cases of severe maxillofacial traumas difficult to intubate,[7] for obviating the need for neck manipulation or for the protective tamponade effect on intra-pharyngeal bleeding, respectively.[89]

Indications for surgical airway in elective scenario, specifically for tracheostomy, are well established: in intensive care unit (ICU). It is required for medium-to long-term ventilation and advised as an early procedure in head injury with coma expected not to recover in the short term; in patients with any cancer in the neck compressing the trachea, and it is often the only practicable procedure for inoperable cancer or as an airway control procedure before or during surgery; after thyroid surgery in patients with longstanding goiter and tracheomalacia, as a tracheostomy prevents postoperative airway obstruction; before surgery in some neck abscesses, as it protects the lower airways from accidental or spontaneous pus release into the lungs during the procedure.[10]

In emergency or urgent scenarios, on the other hand, there is no clear or established consensus, for example, as to specifically who should receive a tracheostomy as a life-saving procedure; and more importantly, when. This is partly due to a biased, specialist, incomplete perspective, partly as a result of generic recommendations that do not keep an account of logistics, timing and the specific situations/scenarios in which to use one.

The two classical indications for emergency tracheostomy, viz., laryngeal injury and failure to intubate and/or ventilate the patient, are too generic and encompass a broad spectrum of possibilities. In literature, specific indications for emergency tracheostomy are scattered and are biased, partially comprehensive, not clearly described or not homogeneously gathered.[11] As a matter of fact, the two groups of indications are not sensitive, specific or accurate. In principle, they are unquestioned; in practice, they are of difficult application and not helpful in deciding who exactly should have an emergency tracheostomy as a life-saving bedside procedure; and most importantly, when. Their application, therefore, depends often on the operator's experience and skills. A universal algorithm on the indications and timing for a surgical airway in emergency, as such, cannot be drawn, due to the multiplicity of variables and the inapplicability in the context of life-threatening critical emergency, where human brain elaborates decisions better in cluster rather than in binary fashion.[12]

PATIENT SELECTION AND SCENARIOS

Some categories of patients in specific scenarios are to be considered as candidates for an emergency surgical airway (ESA) [Table 1].

Table 1

Scenarios potentially requiring an ESA

Patients with anticipated[13-14] [Table 2] or unanticipated [Table 3] difficult airway[15-24] who cannot be intubated and/or ventilated with an SGVD fall in the ‘critical airway’ category. Percutaneous/Transtracheal jet ventilation (PTJV/TTJV) cannot be relied upon for long in patients who are unconscious or have inadequate ventilation, due to unpredictable effect on ventilation and the predisposition to barotrauma with high or prolonged exposures; so readiness to follow with cricothyroidotomy or tracheostomy is mandatory.[17-20]

Table 2

Anticipated difficult airway in adults[13–14]

Table 3

Standard ETI drill, management of unanticipated difficult airway, deviation from the drill

High-frequency jet ventilation (HFJV) is used for tracheo-bronchial surgery or procedures,[21-23] but occasionally it can be used as an emergency oxygenation method through the trachea too.[2425]

Trismus. Critical airway scenarios are best managed by cricothyroidotomy (CTY); where trismus is expected to last for some time and secretions are a problem, like in tetanus, an urgent tracheostomy is practically always necessary from the start.

Foreign body in the upper airways. Patients with foreign bodies in the upper airways (from oropharynx to vocal cords) with impending or actual airway obstruction where Heimlich maneuver (if patient standing and not fainted yet) or abdominal thrust (if patient on the floor or fainted), and direct laryngoscopy have failed to relieve the obstruction, should also have emergency surgical airway, specifically CTY. A coughing patient with foreign body in the airways should be encouraged to continue coughing more strongly. In upper airways obstruction, the acute and dramatic picture of inspiratory stridor, central cyanosis and extra-respiratory muscles recruitment should prompt the mental gear into fulminous action. Upper airways obstruction kills by hypoxia and/or reflex hyperacute vagal-mediated cardiac arrest. In less emergent cases, bronchoscopy is usually resolutive.

Tumor in the upper airways. Any tumor rapidly expanding within the upper airways following internal hemorrhage and narrowing of the passage, or bleeding into the airways and making difficult the visualization of the vocal cords, can require ESA if ETI fails and an SGVD cannot ventilate the patient or prevent blood from tracking down in the lower airways.

Neck abscess. Some patients with Ludwig angina, retropharyngeal abscess and some with para-pharyngeal abscesses deemed to be at risk of spontaneous rupture or actually having narrowing of the upper airways, require ESA as standard preoperative management to prevent the catastrophic consequences of rupture of the abscess with release of pus into the lungs. The problem often faced is the sudden and unpredictable onset of the stenotic effect. A surgical airway remains a rare indication in not complicated or stable abscesses when techniques such as awake fiberoptic intubation are available.

Edema of the larynx. Patients with acute allergic, inflammatory or infective edema, whose stridor and hypoxemia do not improve satisfactorily with adrenaline, or less emergent cases of patients who do not show improvement with intravenous anti-inflammatory drugs or antibiotics and continue to exhibit stridor, overuse their accessory respiratory muscles, have respiration-related tachycardia, and are not able to maintain acceptable PaO2, PaCO2 and SaO2 levels, should receive a tracheostomy under GA if they can still ventilate satisfactorily or be induced under PTJV followed by tracheostomy if they cannot.

Face/Neck burn. Patients with burns involving face and neck in presence of soft tissue swelling or signs of inhalation injury in the nasopharynx (carbonaceous discoloration of naso-oropharynx, inflammatory edema or mucosal damage) must be intubated soon. A delayed intubation leads almost invariably in the great majority of cases to the requirement of a surgical airway even if the epiglottis entry is visible to direct laryngoscopy (DL), due to the impossibility to negotiate the entry of an endotracheal tube of suitable size in an edematous hypopharynx. A delay in ETI also increases the damage to the vocal cords as the ETT has to negotiate an already involved swollen larynx.

Penetrating face/neck trauma. Penetrating injuries to the face and neck are better served with ETT except in one circumstance, viz., when a tracheal wound is already in communication with a skin wound and it is straightforward, quicker and easier to introduce a tracheostomy cannula, or even an ETT, than to attempt endotracheal intubation, which must anyway follow as more secure and convenient route. Rarely, however, these wounds are central or near central and the tracks are suitable for direct device insertion. In these cases if ETT cannot be inserted from above and the track is too distal and straight for a tracheostomy cannula, a smaller size than standard ETT through allows for 100% oxygenation and protected ventilation support until surgical control of the leak is achieved. A loss of airway pressure, besides prevention of blood/debris aspiration, is the reason why airway control is an emergency and should be done as soon as possible.

Blunt face/neck trauma. In the category of patients with blunt trauma to face and neck, no precise guidelines have been standardized for the requirement of an emergency surgical airway.[26] Blunt trauma to the airways is less common but has higher injury severity score (ISS) and mortality than the penetrating one, with injury to the lower airways having a higher mortality than injury to the upper ones.[27]

A great deal of intuition and experience are required in decision-making. In a blunt trauma to face and neck, only four scenarios, each occurring singularly or in combination, will benefit from, or necessitate, an ESA, specifically an open standard tracheostomy [Table 4].[28] Severe and complex facial injuries with disruption of the mid-face or of the lower face (mandible and mouth floor/tongue complex) warrant emergency tracheostomy under three different rationales: the risk of airway loss that can occur at any time unpredictably as a consequence of the mechanical derangements and the posttraumatic hemorrhage/edema;[29] the inability to intubate the patient or fix safely the ETT; the inefficacy or contraindication of facemask and the inability to open the mouth fully. Face-mask ventilation in facial trauma worsens hypoxemia by pushing blood, debris and tissues into the lower airways, and compounds the damage to facial structures. SGVDs are particularly suitable outdoors as a temporary method of airway control and safe ventilation, to avoid blood and debris going down the airways, when ETI fails; and as a bridge to definitive tracheostomy. Tracheostomy for these patients represents also the most convenient and definitive way to secure the acute airway, and it obviates technical difficulties and disadvantages of doing delayed emergency/elective surgery in an area with an ETT in situ.

Table 4

Indications for ESA in blunt trauma to face and neck[ref28]

Retropharyngeal hematoma following cervical spine injury[30-31] and posterior cerebellar fossa hematoma following head injury,[32] results of associated concomitant injuries to head and cervical spine often involved in severe facial trauma, are very rare causes of posttraumatic respiratory obstruction, requiring ESA, that need to be kept in mind. Hyoid bone (HB) fractures after blunt injuries are also rare due to the strategically well-protected position of the bone, but potentially lethal; the bone, in fact, gives posterior attachment to the tongue/mouth floor complex, and its breakage is ominous of unpredictable onset of sudden airway obstruction.[33] Furthermore, a hyoid bone fracture with hematoma tracking down its inferior musculo-facial attachments, as well as a direct injury to the larynx complex, can obscure the thyroid cartilage (TC) and cricoid cartilage (CC) landmarks. Extravasations of blood from blunt vascular injury in the carotid sheath instead, though pushing or compressing the trachea,[34] remain usually confined within its facial compartments and do not obscure the anterior neck landmarks.

Indications for ESA after blunt trauma to face and neck have been delineated and can be regarded as a paradigm for universal indications for ESA [Table 4].

TIMING OF INTERVENTION

In a life-threatening situation such as a critical airway, the time window for useful decision-making is often very narrow, and any delay in recognizing the need for the most demanding of ESAs, i.e., a tracheostomy, affects patients’ outcome in terms of exitus and severe neurological or cardiac damage. While definitions of emergency and urgent are clear in case of hemorrhage or hemorrhagic shock, in airway compromise such definitions cannot be used due to the impossibility to predict how many minutes to hours of fatigue endurance a patient can tolerate in hypoxemia from incomplete airway obstruction [Table 5]. Actual (complete) airway obstruction causes cardiac arrest by acute severe vagal reflex or respiratory arrest soon followed by cardiac arrest (respiratory-cardiac arrest), depending on functional residual capacity (FRC) and cardiac physiological reserve. Impending (incomplete or partial) airway obstruction kills by exhaustion from hypoxemia or by the damages from relative hypoxia to organs like heart and brain. Signs suggesting an impending airway obstruction warranting ESA must therefore be recognized in a clear and unmistakable manner [Table 6].

Table 5

Cluster indications for ESA in critical airway in adults

Table 6

Signs indicating the need of an ESA for impending airway obstruction and impending respiratory-cardiac arrest

Deformity may be the only hard sign of significant laryngeal injury elicited in an unconscious or not ventilating patient, whereas inspiratory stridor is the most important sign in a conscious, spontaneously ventilating patient; tenderness, hoarseness, voice change and subcutaneous emphysema are soft signs of laryngeal injury and per se not indicators of significant damage. Blunt trauma to the neck is almost always associated with facial trauma, different degrees of head injury, and posttraumatic edema with loss of anterior neck landmarks. The loss of those landmarks has two important clinical implications: a cricothyroidotomy cannot be performed safely, and deformity cannot be confirmed or excluded. In such a scenario, gurgling noises or stridor in presence of clinical (central cyanosis) and objective (low SaO2 and PaO2) hypoxemia, or hypoventilation and hypercapnia (visible slow respiratory rate or apnea, high PCO2) are cardinal signs of impending (incomplete) airway obstruction demanding ESA.

Other nonspecific signs of impending airway obstruction that invariably present in different scenarios are use of accessory respiratory muscles, tachypnea, tachycardia, systolic hypertension, diaphoresis, restlessness, agitation, confusion.

The presence of such specific and nonspecific signs also demands an ESA in presence of edema of the glottis not relieved medically by intravenous cortisone within 6 to 8 hours, even in presence of a borderline scenario.

RECOMMENDATIONS ON WHICH ESA TO USE IN CRITICAL AIRWAY SCENARIOS

Comparative studies among the various methods of ESA would be unethical. Furthermore, operator's training and experience are relevant for indications and performance. Guidelines for specific indications, timing and type of ESA can therefore only be given according to axioms and corollaries; personal experience; reliable comparative studies of the techniques in election done by teams of ENT and maxillofacial or cardiothoracic surgeons experienced in both procedures, and their meta-analyses.

Advantages, scenario indications, contraindications and disadvantages of the different methods are outlined in Table 7.

Table 7

Pros and cons of surgical airways

Despite the wave of enthusiasm accompanying percutaneous tracheostomy (PCT) in the last two decades,[35-39] there is no evidence that the closed technique is superior to, or more convenient than, the open standard tracheostomy (OST). Far too many comparative studies between PCT and OST done in election in the last 20 years have stated PCT has less complications and mortality rates, is less costly and faster than OST. These conclusions, in fact, cannot be accepted, for different reasons such as small sample size, lack of randomization of the patients, lack of randomization for the procedure, biased patient selection criteria, uneven operators-to-procedures ratio within the same team, lack of a single-team performance of both the procedures, no direct comparison between the techniques but indirect comparison with other studies.[40-45] The evidence brought on elective patients by teams experienced in both techniques with sound prospective randomized controlled trials (PRCTs) has however proved, as a matter of fact, a superiority of OST over PCT in elective scenarios (ICU, operating theater and bedside) in terms of overall safety and cost-effectiveness and in terms of perioperative and postoperative complications;[46] and an increased risk of delayed airway loss (more difficult cannula changes or inability to replace the cannula) in the PCT groups.[47] Indeed a major meta-analysis of elective studies had found much higher perioperative complications rate and mortality with PCT than with OST, which appeared to have more minor problems related to postoperative wounds.[41] The same conclusions were confirmed in a meta-analysis of studies on elective tracheostomies on cardiothoracic patients.[48] Late complications, i.e., airway structural damages in the form of stenosis, seem not to differ among the techniques, suggesting a direct correlation between length of tracheostomy and damage to the trachea.[49] PCT, though, is reported to give an earlier and more serious subglottic stenosis compared to open tracheostomy;[50] burns are an indication particularly prone to this complication. An association between ETT and tracheal stenosis has also been found. The problem of late stenosis in patients receiving ETT or tracheostomy for burns is a difficult one to solve. It can be speculated that apart from duration, a direct damage to tracheal mucosa from the burns or from smoke inhalation must have occurred.[5152] Consideration should be given to low-dose steroids as adjuvant prophylactic therapy in patients with burns to face and neck or those with smoke inhalation requiring airway control. (Pers Obs)

The decision with regard to which ESA to use in critical airway, in the end, depends essentially on three factors, namely, i) setting and logistics, i.e., whether outdoors or indoors and which equipment is available; ii) underlying pathology, i.e., whether temporary and reversible or a medium- to long-term one; and iii) presence or the absence of palpable anterior neck landmarks (HB, TC, CC, trachea of sufficiently palpable length and circumference).[285354] The author's personal recommendations for ESA in critical airway are outlined in Table 8.

Table 8

Recommendations on which ESA to use in critical airway

The non-exclusion or presence of CSI — by palpation of the posterior neck landmarks (spine processes, intervertebral gaps) for tenderness, deformity and swelling; and/or by suggestive history and neurological examination — is not a discriminating criterion in the choice of an ESA as long as there is a palpable trachea with sufficient length and diameter. (Pers Obs) If this is not the case, any attempt to position the neck in deep impalpable tracheas has to be resisted and an open or semi-open technique should be utilized.

PERSPECTIVES

In the short term, what is needed would be the capacity to know beforehand who with certainty cannot be intubated. This can be achieved only with (magnetic resonance imaging) MRI studies of the structure and dynamics of oropharynx and larynx on those patients who present with objective risk factors for both difficult-to-impossible intubation and SGVD insertion.

Other very useful information to obtain possibly with certainty and beyond doubt is before the administration of a general anesthesia is whether the stomach is empty or not. This can only be achieved with advances in sonar technology, which is at the moment not reliable, especially in emergencies without ileus or obstruction.

The medium- to long-term future of ESA is an instrument like a mechanical nail-shooter or a pistol, which by aided incorporated sonar and video guidance under blue tooth technology and by a trachea-clasping or partially encircling mechanism while oxygenating via a separate channel during trephine, makes a hole in one go from skin to anterior wall of the trachea.[5556]

The long-term future of ETI is in a heat-laser-guided blind ETI insertion with the ETT cuff stopping above tracheal bifurcation as directed by a percutaneous landmark identified with external sonar on the anterior aspect of the neck at a level above the carina.