A 60-year-old male with chronic obstructive lung disease, limited exercise tolerance, and new onset pneumonia required tracheal intubation because of hypoxemic respiratory failure. Optimal positioning for direct laryngoscopy (DL) performed by an experienced practitioner using a Macintosh 3 blade yielded a Cormack–Lehane (C/L) 3 view, despite external laryngeal pressure and head elevation. Intubation was achieved on the third laryngoscopy attempt with the aid of a tracheal tube introducer (commonly known as the bougie). After 6 days of assisted ventilation, the patient was weaned to a FiO₂ of 0.4, positive end expiratory pressure of 5 cm H₂O, and pressure support of 5 cm H₂O. The pulmonary infiltrates were much improved. His respiratory rate was 24 breaths per minute. A cuff-leak test was performed.

What Is a High-Risk Extubation?

Adverse respiratory events are more frequently associated with extubation than intubation yet until recently, extubation has received little attention.^1–6 A stratification of the risk associated with extubation has been proposed,^5,7 and although unsupported by randomized clinical trials, the need for an extubation strategy has been advocated by expert panels.^5,8,9 There are two dimensions to the risk of extubation: will the patient tolerate extubation and if not, how easily can the airway be managed. The extubation of patients with easily managed airways who are not physiologically compromised, can be regarded as low risk. At the opposite end of the risk continuum are those with difficult airways who are also physiologically challenged—these patients are higher risk.⁷ The space between is a zone of uncertainty but it behooves the practitioner to be mindful and anticipate potential difficulties. Many patients fall somewhere along an extubation risk continuum and the practitioner must exercise judgment and strategize how best to minimize complications.

Risk prediction is an inexact science. Regarding extubation failure, patients are at a greater risk if their work of breathing is increased, oxygenation or ventilation are marginal, dead space or CO₂ production are increased, airway obstruction is a possibility, or the ability to protect their airway is compromised. Even under controlled conditions, prediction of the difficult airway suffers from moderate¹⁰ to poor¹¹ sensitivity and specificity. When extubation fails and patients require emergency airway intervention, the additional difficulties include the lack of time, information, personnel, and equipment as well as the availability of and tolerance to medications that may facilitate ventilation and intubation. A previously easily managed airway may be quite difficult under such conditions. And one that had been difficult is very likely to be more difficult or worse. Examples include the patient in whom the larynx could not be seen (Cormack–Lehane view ≥3), who required multiple attempts, practitioners, or techniques, those with airways that have subsequently become more difficult (e.g., neck swelling, airway edema, macroglossia) or in whom access is limited (e.g., halo fixation, unstable neck, monitors, headboards, location).

For most patients, the risk of requiring re-intubation is low. The results of three studies involving nearly 50,000 patients presenting for a wide variety of surgical procedures indicated that only 0.09% to 0.19% required reintubation.^12–14 Studies from the United States,¹⁵ Thailand,¹⁶ and Taiwan¹⁷ yielded similar findings. Patients with systemic inflammatory response syndrome, ascites, chronic pulmonary disease, and pneumonia were at greatest risk of requiring reintubation.¹⁷ Certain surgical procedures such as panendoscopy and a variety of head and neck operations are associated with a risk of required reintubation approximately 10 times higher (1%–3%).^18–22 Patients in critical care units often have limited physiologic reserve, altered secretions, or an impaired capacity to protect their airways. In this group of patients, required reintubation is substantially higher still.^23–25 Furthermore, multiple intubation attempts in the intense care unit (ICU)²⁶ or emergency department (ED)²⁷ are associated with a higher incidence of serious adverse events.

What Strategies Can be Used for the High-Risk Extubation?

Intubation is a skill; extubation is an art. Timing and attention to detail are essential to ensure that airway control is not relinquished. For higher-risk extubations, it is especially important that every effort be taken to ensure that conditions are optimal. Extubation can be performed while the patient is deep or wide awake, though the former is rarely justified in the patient with a difficult airway. Optimal conditions include oxygenation, ventilation, the ability to clear secretions, and protect and maintain patency of the airway. Even when such conditions are optimal, reintubation may be required. Assessment of the airway prior to removing the endotracheal tube (ETT) might include:

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  Laryngoscopy with the ETT in situ—this is of limited value and unlikely to reveal the extent of periglottic edema or vocal cord movement. Direct visualization of the tube in situ does not ensure that laryngoscopy after extubation will afford the same view.²⁸ Such an examination may be appropriate when other airway injuries are of concern.

  
  
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  Laryngeal examination adjacent to the ETT using a flexible bronchoscope (FB) has some of the same limitations as laryngoscopy.^29,30 Alternatively, an FB can be positioned within the ETT, and as the latter is withdrawn, an effort can be made to inspect the airway below and above the vocal folds. Unfortunately, this technique often fails. As the ETT is withdrawn, the patient may cough, swallow, or secretions may obscure the view. Even if a laryngeal view is achieved, it is likely to be too hurried to be of value. This technique is further limited by the need to withdraw the FB shortly after the examination.

  
  
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  If an extraglottic device (EGD, e.g., LMA) is inserted and the ETT is withdrawn, an FB can be passed through the EGD. This technique is compatible with either controlled or spontaneous ventilation, and it keeps extraglottic secretions from obscuring the view. It allows regulation of the FiO₂ and can facilitate reintubation should it be required. This technique does require a properly seated EGD and is hazardous if the airway is significantly compromised.

  
  
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  An Endotracheal Tube Introducer (ETTI, Portex Limited, Hythe, UK), METTRO Mizus airway obturator (Cook Critical Care, Bloomington, IN), or Eschmann Tracheal Introducer (i.e., bougie) can be introduced into the ETT. When the latter is withdrawn, the introducer can serve as a guide over which the ETT can be reintroduced if necessary. As in the case of intubating over an FB, ETT passage over one of the devices mentioned above is not without challenges. Because these devices are solid, they cannot be used to insufflate oxygen or provide ventilation.

  
  
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  A hollow tube exchanger can be introduced permitting airway access, a means of oxygen administration, and serving as an airway “stylet” should this prove necessary. Considerations regarding oxygen insufflation and jet ventilation will be discussed below.

  
  
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  If DL has or is likely to fail, reintubation using an alternative indirect technique such as video-laryngoscopy may be extremely helpful. This can be done in conjunction with a tube exchanger.³¹ Mort found that 47/51 (92%) of recently extubated patients with a difficult airway were successfully reintubated over a tube exchanger, 87% on the first attempt; this contrasts with a first-pass success rate using DL of 14% in patients requiring reintubation in whom the tube exchanger had already been removed. Oxygen saturations below 90% and 80%, the incidence of HR <40 accompanied by hypotension, multiple attempts, and esophageal intubation were also significantly higher in the group without tube exchangers.²³

What Types of Hollow Tube Exchangers Are Available?

There are several commercial tube exchangers including the Cook Airway Exchange Catheter (C-AEC, Cook Critical Care), the Endotracheal Ventilation Catheter* (ETVC, Cardiomed International), the Staged Extubation Set (Cook Critical Care), the Arndt Airway Exchange Catheter Set (Cook Critical Care), and the Sheridan Tracheal Tube Exchanger (Hudson Respiratory Care). The Staged Extubation Set and Arndt Airway Exchange Catheter leave Amplatz guidewires rather than hollow tube exchangers in the airway. In addition to aiding tube passage, the hollow devices can be used to insufflate oxygen or ventilate should it become necessary. Devices with a secure proximal connection and multiple distal end holes are preferred (C-AEC and ETVC). In contrast, the ETTI and the METTRO Mizus airway obturator are solid and cannot serve as an oxygen conduit. All of these devices are introduced through the existing ETT (or in the case of the Arndt device, through the working channel of a flexible endoscope), and the distance markings on the tube exchanger are aligned with those on the ETT to ensure the distal tip of the tube exchanger is located proximal to the carina. The tube exchanger or guidewire remains in the airway after the ETT is withdrawn.

How Long a Duration Should a Tube Exchanger Remain in the Airway?

If reintubation is anticipated, one should use a tube exchanger with the outer diameter (OD) that closely matches the internal diameter (ID) of the ETT. However, smaller diameter tube exchangers are generally better tolerated.²³ Although guidewires are presumed to be more comfortable than exchange catheters, to date this has not been tested. Most patients tolerate the tube exchanger surprisingly well. With a properly positioned and well secured tube exchanger, it is generally possible for patients to speak, swallow, and cough with the device in situ.³² Although most often used orally, tube exchangers are more easily secured (and better tolerated) when inserted nasally. It is this author’s experience that the longer the patient had been intubated, the more tolerant they are of the tube exchanger. If the patient has been intubated for several hours, coughing may indicate that the distal tip of the tube exchanger is near or beyond the carina. The distance marking should be checked and a chest x-ray performed to confirm correct placement. If the patient remains intolerant of the tube exchanger despite proper placement, it may be appropriate to remove the device, although the need for reintubation may not declare itself for several hours.²³ As patients with known or suspected difficult airways are more likely to be successfully reintubated with fewer complications if performed over a tube exchanger,²³ a more cautious approach would be to promote tolerance by instilling topical anesthesia through the tube exchanger. A specific or arbitrary time period to leave a tube exchanger in situ is not rational. It is this author’s practice to leave the device in place until the concern about the airway is resolved. Any patient requiring a tube exchanger would require the vigilance and expertise of a post anesthetic care unit (PACU), ICU, or ED. It is essential that all those involved in the care of the patient appreciate that the tube exchanger is not a feeding tube.

How Is a Tube Exchanger Used to Support Oxygenation or Ventilation?

There have been reports of patients suffering disastrous outcomes when tube exchangers were used to deliver oxygen. This may be a consequence of misusing the device.³³ However there is a report of a tube exchanger being used with low-flow oxygen insufflation that nonetheless produced fatal barotrauma.³⁴ An explanation of how this occurred is lacking but Duggan et al. advocated the administration of oxygen by face mask, cautioning against the use tube exchangers for this purpose. Generally, such advice seems prudent, however if the facemask oxygenation or ventilation proves inadequate and oxygen saturation falls during efforts to reintubate, this author would recommend low-flow oxygen insufflation or cautious jet ventilation. Alternatively, a Bousiggnac CPAP valve (VYGON, Lansdale, PA) can be used with a tube exchanger to improve oxygenation.³⁵

If face-mask oxygen supplementation, CPAP administration, or low-flow oxygen insufflation (1–2 LPM) fails to correct hypoxemia, reintubation may be necessary. Low-flow oxygen insufflation can continue, if deemed necessary, even while intubation is being attempted. If reintubation is delayed or prolonged and hypoxemia is persistent or worsening in spite of oxygen insufflation, jet ventilation should be considered. To avoid the morbidity associated with jet ventilation, the following points should be addressed:

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  Confirm that the distal tip of the tube exchanger is appropriately positioned above the carina, since jet ventilation into the bronchus or oropharynx can produce barotrauma.

  
  
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  Delegate an assistant to hold the tube exchanger close to the lips or nose to ensure that the device does not get ejected during ventilation.

  
  
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  Administer a muscle relaxant with appropriate sedation (if tolerated) to ensure vocal cord relaxation and facilitate both laryngoscopy and jet ventilation. This will lessen the risks of barotrauma.

  
  
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  Attach the tube exchanger to the jet ventilator by means of a Luer-Lok adapter (the C-AEC, ETVC, and Sheridan JETTX have these).

  
  
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  Using a pressure-reducing valve, select the lowest driving pressure that results in chest expansion. “Wall pressure” of 50 psi is equivalent to 3500 cm H₂O and can produce dramatic, life-threatening barotrauma very quickly.^33,34,36

  
  
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  Correct hypoxemia—this should be the primary objective. One breath causing adequate chest expansion may correct hypoxemia even though it may take a short while for this to become apparent.

  
  
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  To avoid “breath stacking,” the chest must be carefully observed. Subsequent breaths should not be delivered until it is clear that the chest has recoiled to a “resting volume.”

  
  
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  Facilitate exhalation by minimizing airway obstruction (vocal cord relaxation, optimal positioning, tongue displacement, suctioning, etc.).³⁶

  
  
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  Jet ventilation may prove lifesaving, but it requires fastidious attention to detail to ensure that life-threatening complications do not develop.³⁷ This should be performed by an experienced practitioner, ideally someone who is dedicated to the task of ventilation while the airway is managed by someone else.

What Factors Lead to Airway Edema?

Airway edema is not restricted to the vocal folds. In children subglottic swelling is the greatest concern, whereas in adults glottic and supraglottic edema are the focus of concern. Patients may have airway swelling due to prone or Trendelenburg positioning, allergic or hereditary angioedema, thermal injuries, superior vena cava syndrome, or generalized swelling as in anaphylaxis, anasarca, and massive volume overload. They may have sustained injury to their tongue, uvula, or epiglottis during tracheal intubation or as a result of subsequent trauma, such as suctioning or seizures.

Insertion of a round tube through a triangular glottis results in contact and pressure at the posteromedial aspect of the larynx.³⁰ Injury can occur very early but this is usually of little consequence. Excessive or prolonged pressure can result in arytenoid perichondritis or chondritis, which heals poorly. Healing may result in fibrosis, producing subacute or chronic laryngeal or tracheal stenosis or an exuberant growth of granulation tissue. Early post-extubation obstruction is likely to be a consequence of edema, bleeding, and occasionally granulation tissue or arytenoid dislocation.

Much has been written about the duration of intubation and resultant airway injuries. However, the association between duration and incidence of airway injuries remains controversial. Most would maintain that the longer the duration of intubation, the greater the likelihood of airway edema. Significant airway injury may, however, occur early as a result of inadequate ETT securement, persistent attempts to phonate or cough, gastroesophageal reflux, larger diameter ETT, excessive cuff inflation pressure, traumatic laryngoscopy or intubation, and vocal fold granulomas. Some authorities recommend laryngoscopy at approximately day 7 under general anesthesia, using telescopes and image magnification to assess the severity of injury. Only then can a judgment be made regarding the feasibility of extubation, prolonging translaryngeal intubation, or the need for a tracheotomy.³⁸

What Techniques Are Useful to Assess Airway Edema?

We have discussed the limited value of DL with the ETT in situ in contrast to extubation under general anesthesia with DL and image magnification. An alternative approach consists of controlled visualization using a flexible bronchoscope through an EGD. DL with image magnification provides the best anatomical evaluation; the EGD/FB examination with spontaneous ventilation provides a good assessment of both form and function. This is achieved by substituting an EGD for the ETT.

If tissue swelling is sufficiently severe, it may encroach on the ETT at any point along the length of the ETT. Prior to extubation, a “cuff-leak test” can be used to assess this. The oropharynx is suctioned and the cuff is slowly deflated. The patient is asked to inhale and exhale slowly as the ETT is occluded.³⁹ An audible leak indicates the flow of air around the ETT. This has been found to be a useful predictor of successful extubation in pediatric trauma and burn victims as well as children with croup⁴⁰ and was sensitive but not specific in predicting post-extubation stridor and the need for reintubation in adults.⁴¹ The cuff-leak test can be enhanced by quantifying the leak during controlled ventilation. Lower cuff-leak volumes are predictive of post-extubation stridor, a need for reintubation, or both.^42,43 Engoren did not find this to be predictive in postoperative cardiothoracic surgical patients⁴⁴ although others have suggested that the cuff leak, expressed as a proportion of the delivered tidal volume, may have greater utility.^45–47

Recently, ultrasonography has been proposed as a method of predicting laryngeal edema⁴⁸ but others have found it no more sensitive than a cuff-leak test.⁴⁹

Are There Methods of Reducing Airway Edema?

It is unlikely that laryngeal edema can be eliminated but it may be possible to reduce it by intubating atraumatically under visual guidance when possible, selecting appropriately sized ETTs, inflating the cuff with no more air than is required to achieve a seal, minimizing tube movement with proper securement and ETT support, head-up positioning when possible and possibly the prophylactic administration of corticosteroids. The benefits of steroids in preventing post-extubation stridor have been variable and probably depend on the patients selected, the specific steroid, the doses and the timing of initial and subsequent doses.^50–53 If the patient manifests signs or symptoms suggestive of airway obstruction, laryngospasm and upper airway obstruction should be considered. If these are excluded, epinephrine (5 mL of 1:1000 solution) by inhalation often results in rapid improvement of airway edema by means of temporary local vasoconstriction. Epinephrine can be administered as tolerated, although caution must be exercised in patients with hypertension, tachycardia, or conditions in which these are poorly tolerated. Rebound vasodilation can also occur. Additional management measures might include fluid restriction or diuretic therapy.

Helium is less dense than nitrogen and can be used, in lieu of nitrogen as a transport medium for oxygen when turbulent airflow is present. This mixture consists of a blend of oxygen and helium, typically 30:70, although the oxygen concentration can be enriched if required. The benefits are proportional to the concentration of helium and the extent to which turbulent flow is present. Helium–oxygen (Heliox) can be used concurrently with head elevation, corticosteroids, and epinephrine. The benefits from Heliox and epinephrine should be apparent within minutes. Deteriorating conditions should prompt reintubation.