Recent Advances in Anesthesiology

Diagnostic imaging tests play an increasingly important role in diagnosing a difficult airway. The variety of tests and their relatively easy availability provide anaesthesiologists with valuable information regarding the challenge of potential difficulty in managing airways. In this chapter, the radiological parameters proven most useful in the various imaging techniques commonly employed in clinical practice will be reviewed: conventional radiology, computed tomography, and ultrasonography.

Because inadequate airway management continues to be an important contributor to serious complications, ultrasound is an emerging tool that has many obvious advantages (safe, fast, repeatable, portable, widely available, and gives dynamic images in real time) that we can use for patient safety. In the upper airway, there are many uses for the ultrasound, for example, oesophageal intubation, adequate placement of the endotracheal tube, selection of the appropriate size of conventional tube and double-lumen tube, adequate placement of supraglottic devices, predictors of difficult airway, predictors of post-extubation stridor risk, prandial status, nerve blocks, or percutaneous tracheostomy.

General anaesthesia induction leads to an apneic period which may be longer in case of a difficult airway. Apnea interrupts oxygen supply and may lead to hypoxemia. Desaturation is associated with several serious complications, like brain injuries, rhythm disturbances or cardiac arrest. Preoxygenation and apneic oxygenation help to prevent desaturation.

Difficult Airway Devices (DAD) are instruments used in difficult airway management, with or without intubation. The characteristics of an “ideal” airway device are adequate contact with the upper airway that allows an adequate ventilation, easy insertion for beginners, with short learning curve, minimum risk of aspiration, effective sealing of the upper airway which allows ventilation with positive pressure, no distortion of the pharyngeal anatomy by the pressure cuff or the shape of the device, low morbidity, and good quality. Supraglottic Airway Devices (SAD) are those devices that are placed above the glottis with the objective of ventilating patients, transporting anesthetic gases and oxygen. However, some of these devices can also be located below the glottis, so that some groups now call them Extraglottic Devices (DE). In the last years of the 20th century, many SADs were introduced, and currently, there are at least 20 types of non-disposable and disposable laryngeal masks.

Difficult orotracheal intubation (OTI) represents the main cause of anaesthetic morbidity and mortality. A third of all anaesthesia-related deaths are secondary to the inability to maintain a clear airway to guarantee a correct oxygenation, and nearly two-thirds of problems related to the management of the airway occur during anaesthetic induction.

Introducers and stylets are two very useful devices for overcoming difficulties in airway management. In fact, they are the first option in many difficult airway algorithms. The design and use of these tools have evolved over the years, and several introducers and stylets are currently available on the market, with different indications and applications in daily clinical practice. Anaesthetists should be familiar with the different devices, characteristics and indications in order to ensure correct application in each situation [1].

A difficult airway is defined as the clinical situation in which a conventionally trained anaesthesiologist experiences difficulty with facemask ventilation of the upper airway, difficulty with tracheal intubation, or both.

In 1954, the first coherent fiberoptic bundle capable of transmitting an image was built, and in 1958, the first flexible fibergastroscope prototype. In 1967, Murphy introduced the technique of tracheal intubation by a coledoscope, through which he slid a 7.5 mm endotracheal tube (ETT) into the nasopharynx, visualizing only the entrance to the larynx because it was too short to guide the ETT. In 1968, the first fiberoptic bronchoscope (FBO) was constructed and, later, 60 cm. insertion cords appeared. In 1972, a series of 100 intubations with FBO was published with 96% success. Following the publication of the ASA airway management guidelines of 1993, the use of FBO increased considerably, becoming the gold standard for Difficult Airway (DA).

Local anesthesia in airway management allows orotracheal or nasotracheal intubation in awake patients with anticipated or known difficult airway predictors. Until a few years ago, the device that was used for awake intubation was the Fiberscope (FBO) but currently, in addition, you can use any airway device, as long as you effectively anesthetize the structures through which the device is inserted [1]. This requires adequate local anesthesia during the necessary time, waiting long enough for the local anesthetic to work in order to achieve quick and easy intubation with minimal or nil sedation, although other working groups use sedation during this procedure [2].

The success of awake intubation depends on the ability of the anaesthesiologist and adequate sedation which promotes safe intubation in a cooperative patient. In order to achieve this, it is advisable to know the pharmacokinetics of the different drugs and choose those which you are more familiarised with.

The condition of “cannot intubate cannot ventilate” is very rare and stressful scenario in paediatric patients, requiring a deep knowledge about anatomic and physiologic features as well as their congenital anomalies. Their anatomical differences as compared to adults imply different laryngoscopy techniques and, for this reason, the endotracheal tube placement is more difficult than in adults. Moreover, paediatric patients have increased oxygen consumption and a reduced functional residual capacity, so the apnea time decreases considerably. In healthy infants under the age of 6 months, with the previous preoxygenation, the saturation pulse oximetry reaches 90% in 90 seconds, while in adults, it happens at 6 minutes [1]. The respiratory events are very common in the paediatric population during general anaesthesia induction. There are some risk factors such as age of under 12 months and the experience and skills of the anaesthesiologist [2]. The hypoxemia (airway management) is one of the causes of cardiac arrest in the operating-room (27%), while failed endotracheal intubation appears in 7% of the cases [3]. All paediatric anaesthesiologists should be warned about the anatomical and physiological characteristics of the paediatric airway [4].

Airway management in the obstetric patient is a challenge for anaesthesiologists, not only because of the anatomical and physiological changes during pregnancy, but also because of the surgery´s urgency, the location of the procedure, which sometimes takes place even outside the operation theatre, and also due to conflicts emerging between the needs of mother and foetus. The arising incidence in maternal comorbidities such as obesity, contributes to complications in airway management in this population.

Obesity, associated with a greater chance of difficult/failed intubation, as well as bag-mask ventilation is also known to be troublesome. Obese patients present a different set of challenges and require specific peri-operative care and a robust airway strategy must be planned and discussed, as desaturation occurs quickly and airway management can be difficult.

Tracheal intubation is a frequent and dangerous procedure in the intensive care units (ICU), and is usually performed in more difficult conditions than in the operating room. Intubation failure can occur unexpectedly, and is the second most common event reflected in the ICU in the NAP4. Complications that cause damage to the patient (severe hypoxemia, arrhythmia, hypotension, cardiovascular collapse, etc.). Videolaryngoscopes present theoretical benefits, as proper and correct use, offering the potential to reduce the difficulty of intubation in the ICU. Videolaryngoscopes allow a view of the entrance of glottis independent of the line of sight, and have also been shown to improve glottis and intubation success rates, specifically in patients with known predictors of the difficult airway (DA).

Physicians of emergency department should be trained in airway management and be familiar with the algorithms and devices at their hospitals. Whenever possible, a rapid evaluation should be carried out in order to attempt to manage a possible difficult airway. Limiting the number of attempts (maximum of three attempts) to achieve a timely nontraumatic endotracheal intubation is the main goal in airway management. Therefore, it is important to make the first attempt in the best conditions and with a device with the highest likelihood of success in order to prevent airway trauma and progression to a “cannot intubate, cannot oxygenate” situation.

The ability to guarantee adequate and quick access to the airway in lifethreatening situations poses a challenge for clinicians who attend critically ill patients. Surgical or percutaneous techniques have an important role in stabilizing patients in such emergency scenarios. Patients who need prolonged mechanical ventilation may benefit from a tracheostomy to avoid complications related to the orotracheal tube. In these cases, tracheostomy must be achieved in the safest conditions to minimize risks for patients. As an alternative to surgical techniques, the use and indications of percutaneous management of the airway are rapidly increasing.

The airway management in the operating room has received a lot of attention during the last years from the anaesthesiologists. However, in recent years there has been a significant increase in the demand for anesthetic care in diagnostic and therapeutic procedures performed outside the operating room. Metzner et al. investigated the main mechanisms of injuries of 87 cases in the United States [1] compared with cases outside the operating room. The most frequent procedure was monitored anaesthetic care, and the most frequent mechanism was adverse respiratory events. The results highlighted inadequate ventilation/oxygenation in 18 cases, difficult intubation in 6 cases, oesophageal intubation in 8 cases and stomach contents aspiration in 3 cases. The majority of the adverse effects were due to excessive sedation manifested by severe respiratory depression. Therefore, it could be concluded that general anesthesia with endotracheal intubation management may be safer than the monitored anesthesia care (MAC) for these procedures.

The high complication rate following inadequate airway management and its fatal consequences sometimes call for a cross-national comparison to understand different approaches in different settings. Anaesthesiologists have long been considered experts in Airway Management (AM), notwithstanding other medical professionals are frequently solicited to perform such procedures outside Operating Rooms (OR), in some cases without adequate training.

Emergency Management of the Airway (EMA) may become a major challenge in the prehospital setting, in part because of differential and specific characteristics of Patient, Pathology and Environment. Sometimes, these procedures will be part of the initial resuscitation efforts, even in respiratory or cardiac arrest scenarios. Historical and preliminary articles show an increased incidence in airwayrelated complications in the prehospital. Most of this variability depends on the distinct comparison between different Prehospital Emergency Medical Services (EMS) and sources, different personnel origin, educational programs, level of skills, etc. The idea is to reduce these important differences to promote safety as the main goal.

Emergency management of the critical patient in some specific scenarios is a difficult job, not only related to the patient's condition but also to austere and hostile environments. Working as a medical provider in this arena, specific procedures, techniques and treatments must be reconsidered as per the most important factor, i.e. the presence and characteristics of a major threat over you.

Although extubation is often considered a mere intubation reversal, it is actually a potentially dangerous process where there is a transition from a controlled to an uncontrolled situation. Anatomical and/or physiological airway changes secondary to airway manipulation or related to the surgical procedure, as well as other factors as hemodynamic instability and time pressure, contribute to a situation that can become more challenging than intubation for the anaesthesiologist. Management of the airway during this phase of anaesthesia may be more complex than induction and requires careful planning that is frequently overlooked.

Until recently, the anaesthesiology and resuscitation resident training in difficult airway (DA) consisted solely of learning the techniques to maintain a patent airway, ventilation with face mask and direct laryngoscopy. In addition, it was believed that their acquisition was possible only with the repetition of such techniques during training, assuming that enough cases were exposed to meet this objective. There are several reasons that make it necessary to review this training system. such as the known data of avoidable morbidity related to DA, the development of a large number of new techniques for the management of DA in the last decade, the lower exposure of the resident to tracheal intubation, derived from the great thrust of regional anaesthesia, use of supraglottic elements or greater dedication to rotations outside the operating room. Besides, there have been advances in research on airway learning that deserve attention.

After an unexpected difficult intubation, management, documentation and sharing of relevant clinical information in the perioperative period may be useful to enhance the safety of the patient. The inclusion of these patients in a computerized hospital database, together with the creation of a visible information sheet, was proposed in 1992. Digital coded recognition, distribution and access to the digital data of the patient by different providers of health, and the registration of the patient in a medical alert base with a 24-hour access were also proposed as procedures to reduce the anesthetic morbidity and mortality related to the unexpected difficult intubation.

Bibliometrics or citation analysis, the statistical analysis of written publications, is an increasingly popular approach for the assessment of scientific activity. Using databases, a search of published manuscripts on the difficult airway from January, 1981 to December, 2013 was conducted. 2,412 articles were identified and analyzed as a group to assess the indicators of productivity, collaboration, and impact over this time period. There has been an increase in the productivity over the study period, with 37 manuscripts published between 1981 and 1990, and 1,268 between 2001 and 2010 (P <.001). The number of scientific papers on difficult airway was higher than that of anesthesiology research in general.