Obstruction of the natural airway occurs quite commonly in association with general anaesthesia. Laryngospasm and bronchospasm, although forms of airway obstruction, are regarded as distinct entities by most anaesthetists and are dealt with elsewhere in this set of articles.^1,2

Risk factors include a history of sleep apnoea or previous airway difficulties with anaesthesia, obesity, maxillary hypoplasia, mandibular retrusion, bulbar muscle weakness, cervicothoracic kyphosis, and specific obstructive lesions such as infected or oedematous structures or adenotonsillar and lingual hypertrophy.³ Effective manoeuvres for alleviating airway obstruction include head tilt, chin lift, jaw thrust, and oropharyngeal or nasopharyngeal airways, all of which can be combined with continuous positive airway pressure.^4–6

A number of additional factors may contribute to or cause obstruction of the natural airway (for example, a tumour mass or a granulomatous larynx) and/or make positive pressure ventilation of the lungs difficult by face mask (for example, a facial injury or deformity, a full beard), but difficulties also may be encountered in patients with no obvious predisposing factors. Some of those who obstruct during spontaneous ventilation under anaesthesia may also be difficult to ventilate by mask and, in a further subset, the larynx may be difficult or impossible to visualise. As these problems may occur unexpectedly and as the consequences for the patient may be serious, it is important that they are recognised immediately and handled promptly and effectively.

In 1993 a core crisis management algorithm, represented by the mnemonic COVER ABCD–A SWIFT CHECK, was proposed as the basis for a systematic approach to crisis management during anaesthesia (the AB precedes COVER for the non-intubated patient), where it is not immediately obvious what should be done or where actions taken have failed to remedy the situation.⁷ This was validated against the first 2000 incidents reported to the original Australian Incident Monitoring Study (AIMS). AIMS is an ongoing study which involves the voluntary anonymous reporting of any unintended incident which reduced or could have reduced the safety margin for a patient.⁸

It was concluded that, if this algorithm had been correctly applied, a functional diagnosis would have been reached within 40–60 seconds in 99% of applicable incidents, and that the learned sequence of actions recommended by the COVER portion would have led to appropriate steps being taken to handle the 60% of problems relevant to this portion of the algorithm.⁷ However, this study also showed that the 40% of problems represented by the remainder of the algorithm (ABCD–A SWIFT CHECK) were not always promptly diagnosed or appropriately managed.^7–9 It was decided that it would be useful, for these problems, to develop a set of specific sub-algorithms in an easy to use crisis management manual.¹⁰ This study reports on the place of the AB COVER CD–A SWIFT CHECK algorithm in the diagnosis and initial management of obstruction of the natural airway, provides an outline of a specific crisis management sub-algorithm for this problem during anaesthesia, and provides an indication of the potential value of using this structured approach.

METHODS

Of the first 4000 incidents reported to AIMS, those which made reference to airway and obstruction were extracted and analysed for relevance, presenting features, causes, diagnosis, management and outcome. Those due to laryngospasm were excluded, as were those in which the trachea had been intubated. The AB COVER CD–A SWIFT CHECK algorithm was applied, as presented elsewhere in this set of articles,¹⁰ to each relevant report to determine the stages at which the problem might have been diagnosed and to confirm that activating the COVER portion would have led to appropriate initial steps being taken. As management of obstruction to the natural airway is not dealt with by this algorithm, a specific sub-algorithm for airway obstruction was developed (see fig 1), and its putative effectiveness was tested against the relevant reports. The potential value of this structured approach—that is, the application of AB COVER CD–A SWIFT CHECK to the diagnosis and initial management of this problem, followed by the application of the sub-algorithm for obstruction of the natural airway (fig 1)—was assessed in the light of the AIMS reports by comparing its potential effectiveness for each incident with that of the actual management, as recorded in each report.

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Figure 1

 Obstruction of the natural airway.

RESULTS

Of the first 4000 AIMS reports, there were 62 cases of obstruction of the natural airway in which laryngospasm was thought not to be the cause. Most (87%) presented clearly as airway obstruction, but the remainder (13%) presented as desaturation. Major physiological change, morbidity, or mortality occurred in over half (55%) of all incidents (table 1). Desaturation occurred in 40 cases (65%), cardiac arrest in four patients (7%), one of whom died, and cardiac dysrhythmia in three (5%). There were two cases of post-obstructive pulmonary oedema and one case each of pulmonary aspiration, cerebral oedema, and pneumothorax. In only four cases (6.5%) were there no adverse sequelae.

In seven cases a foreign body (packs or swabs in five cases, a denture in one, and an oesophageal stent in one) and in 11 cases blood or secretions (infraglottic mucus or blood in four) contributed to the problem. Airway obstruction was unexpected in 17 of these 18 cases. Removal of the foreign body and suctioning (via a bronchoscope in one infraglottic case) solved the problem completely in seven cases; eight patients were intubated (intubation was reported as being difficult in one); two patients coughed up large mucous plugs, and one death followed bleeding into the lower respiratory tract from a “mini” tracheostomy.

In a further 12 patients anatomical problems contributed to the difficulty. In nine patients there was a tumour or polyp intruding into the airway, four of which were completely unexpected. Of the other three cases, one was due to unexpected laryngeal oedema, one due to facial oedema, and one to pre-existing facial deformity. Eight of these 12 cases were intubated (seven of which were described as difficult intubations) and two required cricothyrotomy or tracheostomy. Thus, overall, airway obstruction was completely unexpected in 22 of the 32 cases with identifiable predisposing or causative factors; 15 patients required intubation and two required surgical airways.

In 30 cases the airway obstruction was unexpected and no predisposing factor could be identified; 17 required intubation, two of which were described as difficult intubations. In the remaining two cases muscle relaxants were inadvertently given to awake patients and airway obstruction was the presenting sign. Both of these patients required intubation. Thus, overall, of the 62 cases of airway obstruction, 52 were completely unexpected, 34 required intubation (of which nine were difficult intubations), 32 had identifiable predisposing or causative factors, and two required a surgical airway.

When the AB COVER CD–A SWIFT CHECK algorithm was applied to each report, it was considered that the majority of cases would have been detected at the A (Airway) stage of the AB preceding COVER, at either the SCAN or CHECK level.⁹ However, eight patients (13%) presented as desaturation and hence would have been detected at the C2 (“Colour”) stage of COVER. It was considered that the nature of the problem would nearly always have been detected at the A stage of the AB preceding COVER at the CHECK level, but that it would still be worthwhile going through the full algorithm in order to identify the occasional rare cause such as inadvertent administration of a sedative drug or a muscle relaxant. The actions recommended by the COVER algorithm (100% oxygen, turning off the vaporiser and, if necessary, removing the patient from the anaesthetic machine and circuit) were all considered reasonable immediate steps. It was also considered that carrying out the recommendations of the sub-algorithm outlined in fig 1 would have constituted an acceptable course of action in all cases. When the potential effectiveness of the structured approach, represented by the AB COVER CD–A SWIFT CHECK algorithm and the sub-algorithm for airway obstruction (fig 1) was compared with that of the actual management as documented in each of the 62 incident reports, it was considered that, properly applied, the structured approach would have led to a quicker and/or better resolution of the problem in seven cases (11%). These were cases in which problems arose because of persistent attempts at intubation when ventilation was not attempted (one case) or was not possible, or in which prolonged attempts at non-invasive airway management were made when intubation or cricothyrotomy appear to have been indicated (six cases).

DISCUSSION

Management of the airway is one of the fundamental skills of anaesthetic practice. It would appear, however, that this management may occasionally lack direction or be poorly organised, and this may lead to morbidity and possible mortality. Analysis of the 62 relevant AIMS reports has confirmed, not surprisingly, that airway obstruction may have many presentations, degrees of severity, and methods of resolution. This is reflected in the range of suggested algorithms and management plans for dealing with problem airways.^11–13 Some of these involve complex decision trees and/or flow diagrams when what is needed in a dire emergency is a simple set of instructions. Such instructions will not handle every conceivable situation as these problems are frequently multifactorial. However, it is suggested that the advantages of following a structured sequence of actions would outweigh the disadvantages. Most anaesthetists are very familiar with the management of airway problems. However, in 11% of the incidents reported the problem was not well managed. In these cases it was felt that the outcome would have been improved if the algorithm in fig 1 had been followed.

Most of the major morbidity and mortality associated with airway obstruction is due to hypoxaemia. Desaturation was documented in two-thirds of the cases in this series and four patients went on to suffer a cardiac arrest. One patient had cerebral oedema following an hypoxic episode and one died. In one patient high positive airway pressures led to pulmonary barotrauma and a pneumothorax on the contralateral side to the obstructed lung, and there were two cases of post-obstructive pulmonary oedema following relief of obstruction of the non-intubated airway. Also, the difficulty of maintaining a patent airway may expose patients to excessive force from airway instrumentation which leads to an increased risk of direct trauma to all parts of the airway, from lips to tracheobronchial tree.

Speed in resolving airway problems is essential and is central to the management algorithm. Analysis of the reports supported the steps recommended in the airway obstruction sub-algorithm shown in fig 1. As hypoxia poses the most severe and immediate threat, the administration of 100% oxygen is mandatory in all cases of airway obstruction.

The algorithm recommends early clearance of the airway. In 18 cases the obstruction was simply due to a foreign body, blood, or secretions and in six cases clearance of the upper airway completely resolved the problem. It is important to ensure that the pharynx and airway are clear to prevent problems arising due to mask ventilation, including laryngospasm or aspiration.¹⁴

The other options in the left panel of fig 1 should be cycled through rapidly. These are usefully supplemented by the information in the right panel of fig 1 that, together, form part of a Crisis Management Manual for anaesthesia.¹⁵ Ensuring availability of the necessary help and equipment preoperatively is important. Whenever possible, anaesthesia should be undertaken with skilled assistance available.

It is possible that this sequence may expose certain patients to interventions that might not be necessary. However, when anaesthetists persisted with airway manoeuvres that were ineffective without progression to other techniques, one death, three cardiac arrests, and one case of post-obstructive pulmonary oedema ensued. In another patient, persistent attempts at intubation led to hypoxia when insertion of an airway or laryngeal mask may have alleviated the problem sooner. Cricothyrotomy and/or tracheostomy must be considered early and instituted without hesitation if both intubation and ventilation are not possible. Fortunately, this situation arises in only 0.01–2 cases per 10 000 anaesthetics.¹¹

After the obstruction has been relieved it is important to consider possible sequelae. These include aspiration pneumonitis, post-obstructive pulmonary oedema, cerebral hypoxia or oedema, and trauma to any part of the airway, trachea, or bronchial tree. In all cases consideration should be given to maintaining an artificial airway until these conditions have either been excluded or managed in an appropriate manner.

Finally, it is important that a full explanation of events be given to the patient, that the problem be clearly documented in the anaesthetic record, and that the patient be given a letter to warn future anaesthetists. If a particular precipitating event was significant or a particular action was useful in resolving the crisis, this should be clearly explained and documented.