**3.4 Predicting difficulty in airway instrumentation**

Assessment of the nasal passages should be done for nasopharyngeal airway insertion in case of nasal intubation, upper airway obstruction, or failing airway management as a rescue adjunct. Nasotracheal instrumentation can lead to trauma and epistaxis. So prior doing this, patency of nostrils, any presence of septal deviation, polyps, etc., should be looked for to avoid complications and increasing overall difficulty. Presence of clotting disorders or basal skull fractures should be warranted prior to nasal instrumentation.

## *Ultrasound (US) Imaging Use in the Management of the Difficult Tracheal Intubation DOI: http://dx.doi.org/10.5772/intechopen.108465*

Restricted mouth opening limits the insertion of almost all devices. So interincisor gap should be assessed so that appropriate oral devices can be used electively or in emergency situation. SADs and thin VL blades require mouth opening of < 3 cm, whereas Macintosh blade requires 3 cm inter-incisor gap. In patients with restricted mouth opening, the anesthesia team should have full knowledge of the pros and cons of the VL devices over the fiber optic technique. A high arched or narrow palate can reduce blade space in the oropharynx. Large breasts and barrel chests can pose difficult laryngoscope insertion; however, "ramp" position and appropriate device selection such as polio blade come as rescue. Indirect laryngoscopy can be fruitful in cases with relative or absolute retrognathia and restricted neck extension [10]. Cricoid pressure is an important part of rapid sequence induction; however, it can reduce optimal glottis visualization; however, in case of a difficult airway or difficult SAD insertion, cricoid pressure can be withdrawn under direct vision for improved glottis visualization or ease of SAD insertion, respectively.

Surgical airway such as cricothyrotomy or emergency tracheostomy are kept as a rescue in "can't intubate, can't ventilate" (CICV) situation. In patients with complex head and neck surgery or in anticipated emergency airway obstruction, the surgical airway is kept as rescue technique during the induction of anesthesia [8]. A difficult airway is anticipated in patients having history of neck radiation, obesity with fat deposited around anterior neck, thyroid mass or neck mass with or without deviation of trachea, previous tracheostomy, short neck, restricted neck flexion, and extension deformities. It is difficult to identify anatomical landmarks in young children and female patients. So in these patients with anticipated difficulty, anatomical landmarks should be marked with ultrasound assistance preoperatively.

## **3.5 Predictors of difficult laryngoscopy**

A traumatic laryngoscopy can result in failure to secure the airway or unanticipated difficulty. The first attempt should always be the best attempt, particularly in cases of difficult airway so that strategies can be formulated with best available facilities.

Anatomical factors such as prominent incisors, retrognathia, macroglossia, and small inter-incisor gap affect insertion of the laryngoscope and alter the final view achieved by line of sight approach [8]. Short TMD and SMD are the indicators of an anterior larynx relative to line of sight. Due to in proportionate tongue and oral cavity relationship, modified mallampati class 3 or 4 are the good predictors of DL. Limited neck extension because of increased pretracheal tissue, large occiput, or large neck circumference has been associated with a difficult airway as it causes difficulty to achieve sniffing positioning [10]. Diseases such as lingual tonsil hyperplasia, epiglottitis, and Ludwig's angina are the important predictors of difficult or impossible laryngoscopy.

There are several factors predicting compliance and volume of submandibular tissue such as TMD, temporomandibular joint dysfunction, difficulty in mandibular protrusion, relative tongue volume, and retrognathia. These factors alter tongue displacement into submandibular tissue during laryngoscopy influencing the glottis visualization. Disease affecting the airway such as tumor or pharyngeal adipose tissue deposits also makes the laryngoscopy difficult [10].

#### **3.6 Predictors of difficult intubation**

A reduced oropharyngeal space may lead to difficult endotracheal tube manipulation. Endotracheal tube (ETT) size and suitability for awake fiberoptic technique should be assessed for specific pathologies such as vocal cord palsy, laryngeal tumors, and subglottic stenosis [8]. Stridor with or without respiratory distress is an important symptom of these pathologies and should alert the anesthetist. Whether any further investigations are required depend on the onset of stridor and its progression and association with respiratory distress.

#### **3.7 Predicting a difficult extubation**

Extubation is extremely important in the airway management. In 2012, The Difficult Airway Society has published extubation guidelines highlighting extubation as an important step in patient management. Laryngeal edema causing airway obstruction is the most common cause of early postoperative reintubation. Many factors influence postoperative airway management and includes traumatic intubation, effects of residual general anesthetic drugs, opioids, inadequate reversal of muscle relaxants, or local anesthetized airway. The residual effect of these agents on respiratory drive and airway reflexes should be ruled out [11]. There are more chances of early desaturation and postoperative airway complications in patients having obesity. Patients undergoing head and neck surgery, airway surgery, having Trendelenburg or prone positions, and prolonged intubation should be assessed carefully prior to extubation.
