Department of Cardiothoracic Anaesthesia, Freeman Hospital, Newcastle upon Tyne NE7 7DN, UK *E-mail: i.d.conacher@btinternet.com
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Abstract
In the last decade, stents suitable for the management of tracheobronchial stenoses and obstruction have evolved from bulky prostheses requiring tracheal resection to small devices that are self-expanding and can be inserted using fibreoptic techniques. The experience base for this review is more than 100 patients between 1989 and 2001 who have been anaesthetized for stent insertion. Early cases required rigid bronchoscopy for the routine of insertion. Anaesthetic techniques have evolved from those that were designed and developed for laser surgery in the central airways. The advent of modern devices now extends the variety of anaesthetic management techniques that can be used. But the original one, based on the requirement for use of a rigid bronchoscope, is best for dealing with complications and extracting problem stents. The most frequent complication of the processes of stent insertion has been respiratory failure because of carbon dioxide retention, consequent on obstruction with secretions in the area of the carina. The nature of central airway problems suggests that anaesthesia induction, management and teaching should not be founded on the conventional model-base of upper airway obstruction.
Br J Anaesth 2003; 90: 36774
Keywords: complications, airway obstruction; equipment, stents
A common thoracic anaesthetic emergency to a tertiary referral centre is central airway obstruction. In the past, many sufferers would have been regarded either as inoperable or only manageable with surgery, with high morbidity and significant mortality.13 40 Developments in other fields, particularly vascular and oesophageal, have been copied, paralleled and applied so that nowadays insertion of a tracheobronchial stent is often the first-line management. Stents are not licensed for non-malignant lesions, but are being used increasingly for physical and functional stenoses of a benign nature in the trachea and major bronchi.18 30 32 38 39
For anaesthetists, challenges relate to the management of sick patients with major comorbidities, coping with central airway obstruction distal to a site suitable for rescue with a surgical airway, and sharing an airway that is easily and critically compromised. Total airway obstruction is a possibility that has to be faced occasionally. It is particularly important to learn to detect the almost characteristic signs of developing or advancing central airway obstruction in the anaesthetized patient who has had a stent inserted.
The number of difficulties in management has been reduced because of developments in technology, chiefly in stent size reduction and simplification of application. The nature of competition for the airway has also changed. The instrumentation occupies less of the common and shared conduits. Anaesthesia has been rendered less hazardous and has been simplified by developments in pharmacology, notably in total i.v. anaesthetic agents and non-depolarizing neuromuscular blocking drugs.8
Using vascular stents extends the range of indications: placement in segmental bronchi and use in paediatric practice are possible.4 12 16 However, procedures and processes are now within the ambit of practice of personnel, such as radiologists, not previously involved in the management of patients with acute airway problems. These personnel are inexperienced in the disciplines necessary to manage situations in which access has to be shared for vital functions to be maintained while therapy is undertaken.3 9 10 31 37
Stents
Early models were tubes of silicone based on a simplistic cylindrical concept of the trachea.23 An early development was the T tube (Montgomery), the limb of which is a tracheostomy tube and which, like the bifurcated stents that followed, was unlikely to become dislodged or migrate, but can be awkward and cumbersome to place and replace.11 14 16 17 36 46 Some later devices, based on a normal anatomical trachea, had stainless steel rings and a Silastic membranous portion. More recently, metal strut and self- and balloon-expanding devices, which are more stable and better anchored, have become available (Fig. 1).
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Stents are best regarded as permanent. Earlier versions were relatively easy to remove, but the modern ones tend to become embedded on expanding and invisible to the naked eye, with the potential to become difficult and traumatic to remove. Those with a nylon braid on either end are more visible, flexible and malleable, so that removal is possible, and they should be considered for use in predictably temporary situations, such as weaning off ventilators.7 32 There is a risk of these disintegrating (Fig. 3).
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The mechanics of inserting stents
Tracheal surgery, including resection, was required for the early prostheses.11 14 16 17 28 31 36 The next development was devices that could be inserted through a rigid bronchoscope. Anaesthetic techniques were those used for prolonged rigid bronchoscopy under general anaesthesia. Complex manipulations of applicators, bougies and guide wires were required within the confines of a rigid bronchoscope. Inevitably, there were significant periods of competition for the airway between operator and anaesthetist, notably on positioning of stents.11 39 There were periods when the stents and instrumentation, some of it sharp-pointed and rigid, were not visible to the operator, with the potential for the airway to become traumatized or totally obstructed. During such heady days, it was possible to experience a desperate scramble to abstract a kinked prosthesis that was preventing a patient from being ventilated or oxygenated.
Correctly siting an intraluminal stent was often difficult and attempts to do so were the usual reason for blind spots in the insertion process. The position for the stent was judged by placing the tip of a rigid bronchoscope first at one end and then at the other end of the stenosis, and using fluoroscopy to guide the placement of skin markers. The advent of metal components and radio-opaque markers has reduced the requirement for such manoeuvres. Much more can be done, including some adjustment if necessary, under direct vision with small-bore fibreoptic bronchoscopes, either rigid or flexible, inserted through the rigid conduit formed by a metal bronchoscope (Fig. 4).
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Indications
Indications for the use of stents are becoming legion but the bulk in the adult population are for palliation in various guises. Currently, stents are only licensed for malignant conditions, in part because the incidence of stent erosion or malfunction is probably a function of time. Unfortunately, for many of the more benign conditions alternative therapeutic options have been exhausted, sufficiently so for unlicensed stent use to be regarded as justifiable on clinical grounds (Table 1). All types of stent are limited functionally for use in abnormalities of the trachea and main bronchi, and will collapse if the circumferential pressure continues to build up with an expanding pathology.
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In the 10 yr up to the end of 2001, there were 115 patient episodes recorded locally for stent insertion (Table 2). Patients were most commonly graded ASA III or IV because of comorbidity, often related to central airway obstruction, that included pulmonary sepsis, obstructive airway disease, advanced neoplastic disease, superior vena cava obstruction and significant myocardial disease.
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It has proved of value to view the dilemmas these cases present from the perspective of the potential of the immediate consequences of treatment to alter ASA status, positively or negatively. For instance, if upstaging of ASA grading is considered achievable, say from ASA grade IV to III as a consequence of early recovery of functioning lung or an immediate increase in size of the airway, then the risks, including anaesthesia, are worth taking. The corollary is that, if this degree of confidence in improvement is not felt, there should be serious consideration about whether to proceed.
Preoperative investigation
Preoperative investigations beyond chest x-rays and tomography were usually unhelpful: the information gleaned was academic as it related to the degree of obstruction and the functional disability and rarely gave useful insight into the nature of the obstruction and its pathophysiology. Modern radiological techniques, however, can give very good representations of the pathological anatomy.4 5 45 But the mechanics of obtaining them, for instance by lying patients flat for a prolonged period, may increase the risk and, in our experience, is often an unjustified ordeal for the very sick.
First aid
The majority of our patients are only slightly distressed at rest on presentation and few have significant stridor, but all benefit from being in a sitting-up position and receiving supplementary inspired and humidified oxygen. These simple manoeuvres reduce the likelihood of precipitating severe coughing episodes, which in turn can lead to sudden and significant airway obstruction, particularly if other comorbidities, such as superior vena cava obstruction, are present. A few benefit from helium and oxygen (Heliox) before induction.20 Steroids continue to be advocated empirically, but we rarely administer them.40
Intubation
Most of our patients embody a category of airway problems for which there is no fail-safe procedure: the pathology is sufficiently central that transtracheal ventilation, tracheostomy or a similar surgical airway would not relieve the obstruction. Coughing is likely to set off a chain of events that can reduce the airway to a critical size and even total obstruction. For these two reasons, anaesthetic management plans for the airway are, in practice, not modelled on those traditionally advocated for upper airway obstruction.
The cant intubatecant ventilate scenario has occurred only once in this cohort of patients and in the significant body of those with similar conditions requiring anaesthetic intervention.8 On that solitary occasion, both a significant upper airway problem and subglottic stenosis were present in the same patient. Can intubate (with a bronchoscope)with potential for cant ventilate has been, virtually invariably, the worst-case scenario faced. Therefore, it has been concluded that local anaesthesia approaches for securing airways and gaseous inductions are usually contraindicated as, with either, the risk of precipitating a life-threatening coughing fit is very high. This advice could be qualified in the light of the introduction of sevoflurane into clinical practice.42 44 It is now possible to induce anaesthesia without sufficient irritation of the airways to provoke coughing but, in this patient population, the margin for error is small and there are no suitable surgical airways to deal with a consequent total airway obstruction.
Specimen philosophy and technique
Much experience of handling these cases has been learnt from using lasers in the airway.8 Standard local policy is that insertion of a rigid bronchoscope is the first line of management. This secures and maintains the airway while intelligence as to how to proceed is garnered at leisure from a well-protected, securely ventilated and oxygenated patient. The technique caters for the sicker cases as the single most stimulating effectthat of inserting rigid instrumentation and any subsequent pressor responseis ablated by using the modern agents in the way detailed. In principle, the technique has altered little over many years, except for the use of more specific pharmacological agents as and when they became available. Thus, propofol replaced etomidate; remifentanil infusions replaced alfentanil, which in turn had replaced fentanyl and phenoperidine; and mivacurium has ended the need for succinylcholine by bolus and infusion.8 Target-controlled total i.v. anaesthesia (TIVA) is recommended for those unfamiliar with the field, but current local procedures, based on simple infusion devices, empiricism, simple non-invasive monitoring, and experience, have proved more than adequate to safely manage cases of the kind illustrated in Figure 5.
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Once muscle paralysis has occurred, a rigid bronchoscope is inserted. A purpose-built jet ventilator, driven by oxygen 100% and developed on the principle of the Sanders technique, is attached to the ventilation port of the bronchoscope and set on automatic.29 The inspiratory and expiratory controls are set to provide visible and appropriate tidal ventilation. The airway having been secured and maintained, the conduit is then free for the introduction of equipment for end-tidal carbon dioxide monitoring, lasers, balloons, stents and jet ventilation, or for access for dealing with emergencies such as retention of foreign material, aspiration, haemoptysis and distal total obstruction. The ventilator is switched to be driven from an air source if lasers are to be used as part of the procedure.
Alternative techniques
Advances in anaesthesia and airway management and the revolution in fibreoptics have meant that almost any of the standard techniques can be used. Many of the dilemmas facing anaesthetists of past generations do not apply. The advent of self-expanding stents has made it possible for the procedure to be conducted on an awake patient with local anaesthesia, or with TIVA and a variety of other airway-securing devices and techniques, including intermittent tracheal intubation, a laryngeal mask airway (LMA) as a conduit for instrumentation, and ventilating bronchoscopes.6 9 12 19 20 21 43
LMAs have increased the number of options for safe anaesthesia and access to the upper airway, and for the insertion of ventilation conduits, such as small-bore catheters through stenoses. But limitations may be set by distal lesions and the type of instrumentation required to facilitate stent insertion or extraction. The patient can be self-ventilating with a volatile anaesthetic or given neuromuscular blocking agents and ventilated with positive-pressure ventilation of various modes, including jet ventilation and high-frequency ventilation, applied with various fine-bore conduits.6 19 21 43 At the other end of the spectrum of complexity is the use of cardiopulmonary bypass, realistically only sensible in those with benign lesions in whom the potential for total airway obstruction is significant, and which in emergency situations is reported as successful only rarely.14 21 35
Authors naturally advocate the technique of securing and servicing the airway with which they are most comfortable and experienced. However, the main disadvantage of the alternatives to the specimen method relates to the handling of complications, which are frequent, sudden and life-threatening. Although the diagnosis of a problem can be made with fibreoptic bronchoscopes and some suction clearance can be conducted, the presence of a rigid bronchoscope is the only sure way of ensuring distal oxygenation and access for the necessary instrumentation at the same time.
Reversing the anaesthetic
Usually, this is more difficult than induction. In our experience, 510% of patients require a lot of support through this phase. Stent insertion may not produce immediate relief, and the whole process may down-grade the patients fitness. However, the commonest problem experienced at this juncture has been the development of a type of acute central airway obstruction.
Acute postoperative central airway obstruction
Clinical presentation
Characteristically, the patient fails to re-establish effective spontaneous ventilation, and has a clinical appearance reminiscent of recurarization, for which the condition may well be mistaken. Respiratory effort is minimal and largely abdominal. Consciousness, initially lightening, becomes obtunded, so that there appears to be little distress and no ability to cough. Cardiovascular deterioration follows, with pallor, peripheral oxygen desaturation, hypotension and cardiac dysrhythmias.
Laboratory findings
In those cases in which blood gases have been done, the invariable finding, besides hypoxaemia, has been hypercapnia [PaCO210 kPa (1218 kPa, local findings)], almost certainly secondary and responsible for the clinical picture of consciousness deterioration and areactivity.
Diagnosis
This clinical picture is acute central airway obstruction until proved otherwise: the only other condition that has ever appeared similar, albeit much rarer, is tension pneumothorax after a traumatic stent insertion. This is the end result of obstruction in the lower third of the trachea or, more usually, at the level of the carina, in which case the major bronchi may also be obstructed. The most common cause is glutinous secretions, but it can be because of secretions released from previously obstructed bronchi, a malfunctioning stent, blood clot, tissue slough (if laser treatment preceded stent insertion) or stent blockage.
Treatment
Tracheal intubation, positive-pressure ventilation and suction may be life-saving but are not curative. Rigid bronchoscopy is required urgently. Consciousness is so obtunded that these various manoeuvres can be conducted without the use of induction agents and neuromuscular blocking agents, but usually a small dose of induction agent, etomidate or propofol, is administered first. Suction clearance of material in the trachea and adherent to the carina or stents, and some hyperventilation, usually results in a rapid and dramatic improvement in the quality of tidal spontaneous ventilation.
Prophylaxis
Such a scenario was so commonly experienced that now it is local practice and teaching to leave the rigid bronchoscope in situ until the patient virtually coughs it out. A useful end-point to signal suitability for discharge to a recovery unit is the presence of all parts of the cough reflex: that is, deep non-stridulous inspiration, active closure of the glottis and an explosive expiration that is free of sounds of laryngeal spasm and that clears secretions.
Complications of stents
Stent malposition is not uncommon and is usually treated by insertion of a second or even third stent: some patients have a mixture of types within large parts of the airway. Occasionally, balloon dilatation of the stent may be attempted. Extraction of a broken stent or a badly positioned one can be a long and tense procedure. Under such circumstances, the anaesthetic technique recommended above is often shown to its best advantage.
Apart from the occasional loss of control of the airway as a result of the stent malfunctioning, being malpositioned or disintegrating, and which has produced short-lived but total obstruction, there has only been the tension pneumothorax mentioned earlier and one major perioperative surgical incident in this series. Unlike earlier laser series, there are no immediate perioperative deaths.8 26
Airway laceration, total airway obstruction, tracheobronchial wall perforation, stent breakage and erosion into the mediastinum or great vessels are all reported as sequelae to the placement of stents, and are often catastrophic. Many of these have required either interventional radiology or major surgery for cure.1 15 21 24 26 30 35
A recent local audit of one type of stent and one surgeons experience (M. Blacking, S. Barnard, personal communication) reflects the palliative nature of the stenting process. Two-thirds of deaths occurred within 10 weeks of the procedure, and in a subgroup of patients in the terminal stages of cancer. All patients within the benign subgroups were alive.
Conclusions
It is evident that stent insertion is an increasing workload, and locally is fast approaching a weekly exercise. Patients need a lifetime of follow-up and much servicing of the airway. In providing a stenting service and in order to deal with complications, it is necessary to be able to proceed to balloon dilatation and thoracotomy and, on occasion, to have access to cardiopulmonary bypass facilities, even though these have rarely had a successful outcome.
Although it is the period after anaesthesia that has proved the most problematical, it is induction of anaesthesia where practical experience has shown that the models of upper airway obstruction (e.g. epiglottitis, lingual tonsils, supralaryngeal tumours) are not usually appropriate as anaesthetic management templates for central airways obstruction. I.V. induction and tracheal intubation after full neuromuscular block has proved most efficient and safe for central airway obstructive conditions.
Locally, three patients with central airway lesions have now been attending for more than 15 yr, requiring between them more than 50 interventions under general anaesthesia. Perhaps it is a tribute to the advocated techniques that anaesthesia has not been the worst part of their ordeals and has proved adequate and safe for cases of the kind illustrated in Figure 5.
Acknowledgement
I am grateful to Dr M. L. Paes and Dr B. G. Watson (retired), consultant cardiothoracic anaesthetists, who, over the years, have shared the burden of setting up an anaesthetic service for central airway stenting, and to Mr S. Barnard, consultant thoracic surgeon, and Ms M. Blacking, stage 4 medical student, for some data.
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