28.2.1 What Is a High-Risk Extubation?
In anesthesia, and most likely in critical and emergency care, adverse respiratory events are more frequently associated with extubation than intubation.1,2 Nonetheless, much less attention has been paid to the management of extubation. A stratification of risk associated with extubation has been proposed,3 and although unsupported by controlled, randomized clinical trials, the need for an extubation strategy has been advocated by expert panels.4,5 The extubation of patients, who were easily intubated and in whom no intervening event has occurred to jeopardize their airways, can be regarded as "low-risk extubations." Those who were easily intubated but who are at greater risk of requiring reintubation (due to hypoxemia, hypercapnia, inadequate clearance of secretions, inability to protect their airway, or airway obstruction) are "intermediate-risk extubations. " Those in whom airway management is likely to be challenging or complex if reintubation is required represent "high-risk extubations." The last group includes:
Patients with a difficult tracheal intubation (failure to visualize their glottis —C/L ≥ 3—requiring multiple attempts or alternative techniques).
Those with interval complications (airway edema, extrinsic compression, glottic injuries).
Those with clinical conditions associated with difficult ventilation and/or intubation. This latter group would include, for example, patients with paradoxical vocal cord motion, morbid obesity, obstructive sleep apnea, airway surgery, maxillofacial surgery (particularly when it involves inter-maxillary fixation), deep-neck infections, cervical surgery, angioedema, or prolonged intubation.3
For most patients, the risk of requiring reintubation 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.6-8 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%).9-13 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.14-16
When patients require emergency reintubation, the airway practitioner may have limited clinical information, equipment, supportive personnel, or preparation time. Furthermore, the patient may be hemodynamically unstable with associated airway obstruction, hypoxemia, or acidosis. There may be a reluctance to administer paralytics when there is uncertainty about the probability of securing the airway. Topical anesthesia may be ineffective due to time constraints or the presence of secretions or edema. Thus a struggle could ensue between the practitioner and an agitated and possibly hypoxemic patient. Generally, any urgent reintubation is likely to be more challenging than the original intubation procedure. If the original intubation had been difficult, the reintubation could be life threatening.
28.2.2 What Strategies Can Be Used for the High-Risk Extubation?
For high-risk extubations, it is especially important that every effort be taken to ensure that conditions are optimal. 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:
- Laryngoscopy with the ETT in situ, although this is of limited value and is unlikely to reveal the extent of periglottic edema or vocal cord movement. Direct visualization of the tube in situ does not ensure that reintubation by this technique will be successful.17
- Laryngeal examination adjacent to the ETT using a flexible bronchoscope (FB) has some of the same limitations as laryngoscopy.18,19 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.
- If an extraglottic airway device (EGD, eg, 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.
- An ETTI (Portex Limited, Hythe, UK) or METTRO Mizus obturator (Cook Critical Care, Bloomington, IN) 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 the FB is not without challenges. Because these devices are solid, they cannot be used to insufflate oxygen or provide ventilation.
- 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.
- 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.20 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 exchange catheter had already been removed. Oxygen saturations below 90% and 80%, the incidence of HR less than 40 accompanied by hypotension, multiple attempts, and esophageal intubation were also significantly higher in the group without exchange catheters.14