Introduction

Difficulty in airway management is the main cause of anesthesia-related death or permanent brain damage. In intensive care units and emergency departments, the incidence of life-threatening complications associated with airway management is even higher than in patients in the operating rooms [1–3]. To reduce the incidence of such serious complications, several major efforts have been made. In addition to the development of new reliable airway devices and routine use of oximetry and capnography, guidelines regarding difficult airway management have been formulated by several different societies [4–6]. Nevertheless, the current strategies for airway management are still not ideal [7–11] and, therefore, we need to update our knowledge to improve airway management further. This editorial describes some new findings which would reduce serious complications associated with airway management.

Adequate planning

One effective method of avoiding serious airway complications after induction of anesthesia is to predict the ease of airway management, and to make a clear preoperative plan for each patient. Although efforts have been made to find reliable predictive tests for difficult airways [12–14], these tests may frequently fail to predict the difficulty. Because of this, some authors consider that predictive tests are futile; however, prediction tests should be performed, as they frequently do identify difficult airways, and would reduce the incidence of serious airway complications after induction of anesthesia [13].

Sufficient pre-oxygenation of the patient is crucial, particularly when difficult airway management is predicted. The traditional method is to provide oxygen via a facemask for a minimum of three minutes. Recently, a high-flow nasal oxygen delivery system has been shown to be effective in reducing the risk of hypoxia during attempts at awake fiberoptic intubation [15].

Some authors consider that a neuromuscular blocking agent should not be given after induction of anesthesia until adequate ventilation via a facemask has been confirmed, but there is considerable evidence to support this practice being unsuitable. It is now clear that injection of a neuromuscular blocking agent immediately after induction of anesthesia facilitates mask ventilation and reduces the incidence of hypoxia [16]. During laryngoscopy, oxygen may be insufflated to the posterior pharynx to delay the time to become hypoxic [17].

Avoidance of repeated attempts at tracheal intubation

It is now clear that repeated attempts at tracheal intubation should be avoided, because such attempts may make mask ventilation difficult and increase the risk of pulmonary aspiration [1, 18, 19]. Videolaryngoscopes, which have potential roles in patients with difficult airways, may reduce repetitive attempts at intubation [20–22]. A large observational study has indicated that in patients in whom tracheal intubation using a conventional direct laryngoscope had failed, a videolaryngoscope was most frequently used as a second-line treatment, and was associated with a high success rate of intubation, compared with other intubation devices (e.g., supraglottic airways and fiberoptic bronchoscope) [23]. Another study has also shown that compared with the use of a supraglottic airway, the use of a videolaryngoscope may be able to prevent repeated attempts at tracheal intubation and reduce complications [24].

Suitable videolaryngoscopes are likely to differ in patients with different causes of difficult airways. For example, in a study of patients with restricted neck movement and limited mouth opening, the McGrath™ or C-MAC™ D-blade provided a higher success rate and a lower incidence of tissue injury, when compared with the A.P. Advance [21].

Videolaryngoscopes have roles in patients with difficult airways, but they may fail [21, 25, 26] and may not be able to reduce the incidence of anesthesia-related death [3]. Reported difficulties include limited mouth opening, a large tongue, a tumor in the oropharynx, laryngospasm, and blurred vision [22]. Recent studies [25, 26] have added several other risk factors—suboptimal head and neck position, cricoid pressure, inexperience, and patients undergoing otolaryngologic or cardiac surgery.

Therefore, we should know when videolaryngoscopes are more likely to fail, should avoid repeated attempts at the use of videolaryngoscopes, and should take the next steps (attempts at ventilation via a supraglottic airway or via an invasive airway) without delay. It is not clear whether tracheal intubation using a videolaryngoscope is less likely to traumatize the airway or to prolong apnea time, both of which may lead to serious airway complications [22]. Clarification of these would establish the true role of videolaryngoscopes in patients with difficult airways, particularly in patients receiving rapid-sequence induction of anesthesia and in those undergoing emergency Cesarean section [27, 28].

Videolaryngoscopes are theoretically useful for non-experienced persons who may need to perform tracheal intubation outside the operating room. One study, however, has shown that, compared with novice paramedics who had no experience with the use of a Macintosh laryngoscope, those with previous training of tracheal intubation using a Macintosh laryngoscope had a lower success rate of tracheal intubation using a videolaryngoscope [29]. This report indicates that training with a videolaryngoscope is necessary, and we need to find an appropriate training method [30].

‘Rescue device’

Although the supraglottic airway is regarded as a ‘rescue device’ in the ‘cannot intubate, cannot ventilate’ scenario [4–6], it may fail in some patients, particularly in those in whom repeated attempts at intubation have been made [3]. A validation study of a new clinical score to predict difficult ventilation through a supraglottic airway (based on the risk factors of male, age >45 years, short thyromental distance, and limited neck movements) [31] indicated that a high score is associated with a six- to seven-fold increased risk of failure. When a supraglottic airway has been inserted, its cuff should not be overinflated as it would increase the risk of pulmonary aspiration [32].

Invasive access to the infraglottic airway (such as cricothyrotomy or tracheostomy) is regarded as the last resort [4–6], but recent large-scale studies have shown that the success rate may be low [1, 33]. Therefore, it is necessary to find which method is most effective [34–36]. There is growing evidence that percutaneous cricothyrotomy using a narrow-bore cannula (once advocated for use for its simplicity) may frequently be ineffective [1, 37]. A systematic review [37] has shown that the use of jet ventilation is associated with a high incidence of serious complications (e.g., device failure or barotrauma), particularly when it is used during ‘cannot intubate, cannot oxygenate’ emergency situations.

Studies using cadavers and animal models have shown that, compared with percutaneous cricothyrotomy (with Seldinger or Trocar method), surgical cricothyrotomy was associated with a higher success rate and a lower incidence of complications [38, 39]. Because of these reasons, it is now recommended that surgical cricothyrotomy should be regarded as the most reliable method, and should be learned and regularly rehearsed by all anesthesiologists [4, 40]. One major reason of failed cricothyrotomy is difficulty in identifying the cricothyroid membrane [35, 38, 41], and the use of ultrasonography will minimize the incidence of failed identification [42] (Fig. 1).

Fig. 1
figure 1

Identification of the cricothyroid membrane with ultrasonography (longitudinal view). The ultrasound transducer placing longitudinally in the midline, indicating the puncture site of cricothyroid membrane (arrow) between the thyroid cartilage (Thy) and cricoid cartilage (Cr), together with tracheal cartilages (Tr)

Full size image

Training

It has repeatedly been pointed out that airway complications are commonly associated with poor standards of care [1, 33]. Therefore, regular training for routine and emergency airway management (including cognitive, psychomotor, and behavioral areas) has been stressed [43–45].

The fiberoptic bronchoscope is regarded as the most reliable tool in patients with difficult airways, but considerable skill and knowledge are required to achieve smooth tracheal intubation [46, 47]. A bronchoscopy simulator (ORSIM® bronchoscopy simulator) [47] allows training and assessing subjects on both normal and abnormal airway simulations. As the use of a fiberoptic bronchoscope for tracheal intubation has been reduced (due partly to use of alternative devices such as videolaryngoscopes), training using this kind of a simulator may be necessary. A simple procedure (traction of the tongue) may facilitate fiberoptic intubation [48].

One reliable method of training is to use a suitable model and setting. Compared with a manikin model, a cadaver with lifelike conditions (Thiel embalming technique) [49, 50] or a porcine model of an obese neck or a neck with a burn [43] has been shown to be a better model for training. A new visually based cognitive aid (‘Vortex’) [51], which is designed to be used in real-time during emergency airway management, has been devised to support team function and target recognized failings in airway crisis management.

Conclusions

This brief summary of recently published articles indicates that there has been a considerable progress in difficult airway management. By updating our knowledge and skills, we should keep attempting to achieve trouble-free airway management.