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From the *Department of Anesthesiology, University Hospital Zurich, Zurich, Switzerland; and Department of Anesthesiology, University Hospital Freiburg, Freiburg, Germany.
Address correspondence and reprint requests to Hans-Joachim Priebe, MD, FRCA, FFARCSI, Professor of Anesthesiology, Department of Anesthesiology, University Hospital Freiburg, Hugstetter Str. 55, D-79106 Freiburg, Germany. Address e-mail to priebe{at}ana1.ukl.uni-freiburg.de.
Tracheal extubation is the logical consequence of tracheal intubation, and continued control of the airway after extubation constitutes part of the overall airway management. Thus, it appears logical that there would be a preformulated extubation algorithm. However, no such guideline is available for the period during and immediately after tracheal extubation. This is even more surprising as the incidence of complications associated with extubation may exceed those occurring during intubation (1). Eighteen of the 156 perioperative claims for difficult airway management between 1985 and 1999 included in the American Society of Anesthesiologists (ASA) Closed Claims database were associated with extubation in the operating room (2). Problems associated with tracheal extubation can be separated into those occurring during or after extubation (3). Upper airway obstruction after extubation with concurrent impairment of oxygenation is the most serious complication, mostly caused by dislocation of the arytenoid cartilages (4,5), tracheomalacia, laryngospasm (6), laryngopharyngeal edema, or bilateral vocal cord paralysis (7–9). Upper airway obstruction may, in turn, cause pulmonary edema (10). In most cases, supportive care will reestablish adequate oxygenation and ventilation, but sometimes reintubation becomes unavoidable.
In surgical intensive care unit (ICU) patients, reintubation rates of 5%–19% have been reported (11–16). Usually, tracheal reintubation will be more difficult than the initial intubation, because of the frequently emergent nature, the accompanying hypoxemia and cardiovascular instability, the lack of patient cooperation, insufficient time for adequate preparation, and limited access to the airway (as in cases of intermaxillary or cervical fixation, cervical instability, lingual, pharyngeal and laryngeal edema, neck swelling). Not surprisingly, then, an airway emergency and repeated intubation attempts have been associated with worse outcome, including death and brain damage (2,17). Although failure to tolerate extubation may be anticipated, it will often develop unexpectedly. There are no tests with acceptable positive and negative predictive value for extubation tolerance. Even patients with a statistically high risk of extubation failure mostly tolerate extubation.
An effective extubation strategy should have a low reintubation rate and not cause patient discomfort. It also should enable oxygenation and ventilation and facilitate reintubation if necessary. The ASA Task Force on Difficult Airway Management recommends a preformulated strategy for extubation of the difficult airway (18). Risk factors for failed extubation and difficult reintubation include difficult intubation and requirement for additional airway devices during induction of anesthesia, development of airway problems since intubation, obesity, and a history of obstructive sleep apnea (2,19). The extubation strategy of the difficult airway should be adjusted to the type of surgery, the medical condition of the patient, and the experience and preference of the anesthesiologist. It should include (a) consideration of the merits of extubation in the awake versus the unconscious state, (b) consideration of clinical factors that may impair respiration after extubation, (c) a preformulated airway management plan in case the patient is unable to tolerate extubation, and (d) consideration of the use of a device that can facilitate reintubation (18).
The airway exchange catheter (AEC) is such a device, designed to maintain access to the airway after extubation, and may, thus, facilitate reintubation. It is introduced through the endotracheal tube before extubation and is left in situ after removal of the tube until the likelihood of reintubation has become minimal (19–21).
The efficacy of the AEC as part of a "staged" extubation strategy is addressed in the study by Mort in this issue of Anesthesia & Analgesia (22). The author reviewed a prospectively collected difficult airway quality-improvement database for patients with known or suspected difficult airway, who had been extubated over an AEC in the operating room, the postanesthesia care unit, or the ICU during a 9-yr period. Careful review of the text reveals that a relatively large database of 329 patients was analyzed. A total of 87 patients (26.4%) required reintubation. At the time of reintubation, an indwelling AEC was in place in 51 (59%) and absent in 36 (41%) of the 87 patients. Twenty-one of the 51 patients (41%) with an indwelling AEC in place required reintubation within 2 h of extubation, and the remaining 30 patients within 24 h, but mostly between 2 and 10 h after extubation. Forty-seven of the 51 patients (92%) with an indwelling AEC in place were successfully reintubated, with a first-pass success rate of 87%. Four patients (7.8%) could not be reintubated via the AEC; the AEC became dislodged during attempted reintubation in three patients, and the endotracheal tube could not be advanced over the AEC in another patient. Severe hypoxemia (Spo2 <70%) developed in 4 patients, and bradycardia and hypotension in 3. However, compared with patients without an indwelling AEC in place at the time of reintubation, the first-pass success rate for reintubation was significantly higher (87% vs 17%), episodes of severe hypoxemia (6% vs 19%) and multiple intubation attempts were fewer (10% vs 77%), esophageal intubation was less frequent (0% vs 18%), and there was less need for additional rescue airway devices and techniques and surgical airways (6% vs 90%).
What is the significance of Mort's findings? First and foremost, they confirm the effectiveness and safety of AEC-facilitated reintubation in patients with known or suspected difficult airway (14,15). To avoid the complications of reintubation, patients with a suspected difficult airway may be kept intubated longer than necessary. In agreement with this assumption, up to half of patients with unplanned extubation did not require reintubation (23). An indwelling AEC may justify an earlier trial of extubation without taking unnecessary risk. As prolonged intubation increases morbidity and costs, more frequent use of an AEC may be cost effective by allowing earlier assessment of extubation tolerance.
In patients with suspected or documented previous difficult reintubation, elective tracheotomy constitutes an alternative approach for maintaining airway access. However, tracheotomy is highly invasive and associated with serious complications. Furthermore, even after maxillofacial or major neck surgery, only about 10% of patients required reintubation (14). Thus, "prophylactic" tracheotomy will unnecessarily expose most of patients to considerable risk. Use of an AEC may be an acceptable compromise between liberal indication for prophylactic tracheotomy and liberal indication for a trial of extubation without maintained airway access. However, AEC-facilitated reintubation is not perfect: in Mort's study the incidence of reintubation failure and severe complications, and the need for additional airway devices, was low but real.
Additionally, Mort's findings suggest that an AEC-based extubation strategy does not necessarily reduce the reintubation rate. Considering the frequently serious problems and complications associated with reintubation (with or without an AEC in place), the reported overall reintubation rate of 26.4% is worrisome. Of particular concern is the finding that 36 of 278 patients (13%) required reintubation after the AEC had been removed. Thus, the assumption of extubation tolerance after removal of the AEC had been wrong in 36 of 87 (41%) patients.
The high reintubation rate in Mort's study is in contrast to the findings of two previous studies using an AEC in a comparable manner in a comparable patient population (14,15). In 40 sequential postoperative surgical ICU patients with at least one risk factor for difficult tracheal reintubation, an AEC had been inserted prior to tracheal extubation (15). The AEC remained in situ for a mean duration of 9.4 h (range, 15 min to 52 h). Patients were extubated when standard extubation criteria were met, when the patient was conscious, hemodynamically stable, and expected to protect and clear the airway. Only 3 of 40 patients (8%) required reintubation. In the other study, all 36 adult patients who had undergone maxillofacial or major neck surgery and had risk factors for difficult reintubation were extubated after a pediatric AEC had first been inserted through the endotracheal tube (14). Criteria for extubation were consciousness, normothermia, normal blood gas analysis at an inspired oxygen concentration of 0.4, a positive end-expiratory pressure of <5 cm H2O, and pressure support <8 cm H2O. Four of the 36 patients (11%) required reintubation between 2 and 18 h after extubation.
It is difficult to explain the considerably higher reintubation rate (26%) reported by Mort (22). It may reflect a more aggressive approach to extubation, with possibly lesser adherence to conservative extubation criteria and reliance on the AEC in case of intolerance to extubation. Details regarding the decision for removal of the endotracheal tube are not provided, and objective criteria for removal of the AEC were not applied.
Mort's findings further demonstrate that the optimal timing for removal of the AEC remains to be determined. Based merely on the attending physicians' subjective assumption of extubation tolerance, the AEC was kept in situ for a mean of 3.9 h (range, 5 min to 72 h). Eighteen of the 36 patients (50%) required reintubation within 2 h of removal of the AEC, 4 between 2 and 4 h, and the remaining 14 patients beyond 4 h. If the likely cause for possible subsequent extubation failure is edema of the upper airway, maintaining access to the airway for 1–2 h may be reasonable. In patients with cardiopulmonary problems or unstable clinical condition, or in whom an extubation trial had previously failed, it would seem advisable to extend the duration of maintained access to the airway. For how long? The author recommends 12–24 h or even longer. However, this recommendation is not evidence-based.
The main findings of Mort's study can be summarized as follows: 1) In experienced hands, AEC-facilitated reintubation has a considerable, but not a 100%, success rate; 2) the incidence of complications during AEC-facilitated reintubation is low, but the nature of the complication can be severe; 3) an AEC-based extubation strategy does not necessarily reduce the reintubation rate; 4) premature removal of the AEC may lead to life-threatening hypoxemia and require an advanced airway technique to reestablish a secure airway; and 5) a smaller sized AEC is usually better tolerated than a large one.
The study has several limitations. It was not randomized, nor did it compare different methods of maintaining airway access. We do not know the incidence of patients with a known or suspected difficult airway. Therefore, the question of whether this extubation strategy reduces the reintubation rate and improves overall outcome remains to be answered. The decision for insertion and removal of the indwelling AEC was based on individual judgment rather than on predetermined criteria.
Concern has been raised that prolonged use of an AEC may cause airway trauma, aspiration due to glottal functional incompetence, and retention of tracheal secretions due to impaired coughing. In the relatively small number of patients prospectively studied thus far, these concerns have not been substantiated. With the use of a pediatric-size AEC, patient tolerance seems to be excellent, vocalization is preserved, and the risks of airway trauma and pulmonary aspiration are minimal (14,15,22). As with the use of a fiberoptic bronchoscope, the tip of the endotracheal tube may impact on the epiglottis or other laryngeal soft tissue structures during advancement over the AEC. Inappropriate use of a tracheal tube exchanger during tracheal extubation can result in lung laceration, followed by pneumothorax and lung abscess (24,25).
The analysis of a prospectively collected database by Mort (22) supports the concept of an AEC-facilitated "staged" extubation strategy. This concept is an attractive one on a theoretical basis as well as on the basis of demonstrated benefit in selected patients. Furthermore, it is in agreement with the recommendation of the ASA Task Force on Difficult Airway Management for a preformulated strategy for extubation of the difficult airway (18). Since tolerance of extubation cannot reliably be predicted, it is reassuring to know that an AEC facilitates reintubation in the vast majority of patients with difficult airway. Even if the initial attempt at reintubation fails in the presence of severe respiratory insufficiency, a jet-stylet-type AEC allows capnography, oxygen insufflation, and jet ventilation, thereby "bridging" the time required to obtain additional airway equipment and qualified help.
However, AEC-facilitated extubation is not a fool-proof method. It does not automatically reduce the incidence of reintubation, it has the potential for serious complications, and it is not always successful. Thus, even when using an AEC, conventional extubation criteria should be strictly observed, and the options for direct laryngoscopy, cricothyroidotomy, fiberoptic or retrograde intubation, and jet ventilation or other techniques for resecuring the airway should be preserved. Although AEC-facilitated extubation is a method with a satisfactory success rate and patient acceptance, and does not require overly sophisticated equipment and skills, well-designed, controlled, prospective trials are necessary to ultimately determine the most effective extubation strategy.
Independent of the results of future trials and the chosen extubation strategy, strict avoidance of a cavalier approach to extubation, optimizing the medical condition of the patient at the time of extubation, availability of appropriate know-how and equipment at the time of, and immediately after, extubation, and preparedness for the possibility of extubation failure will remain the mainstays of any safe extubation strategy.
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