**2. Definition of a difficult airway**

The definition of a difficult airway has been described multiple ways in the literature. There is no single definition of a difficult airway. According to the 2003 revised American Anesthesiology Task Force guidelines, a difficult airway is when a trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation, or both [2, 3]. Other definitions incorporate a broader definition whereby there is problematic ventilation using a facemask, incomplete laryngoscopic visualization, or as a difficult intubation with standard airway equipment [4]. Difficult ventilation is the inability to deliver the necessary tidal volume via the facemask even when using an oral or nasal airway and necessitating another device such as the laryngeal mask airway. Difficult laryngoscopy is impaired visualization of the true vocal cords despite elaborate external laryngeal repositioning. Difficult intubation requires external laryngeal manipulation, difficult laryngoscopy requiring greater than three attempts at intubation, intubation requiring nonstandard equipment or approaches, or the inability to intubate using all available methods [5].

Other important clinical considerations include obstructing upper airway disorders. Amongst these clinical diagnoses include a more progressive process like a glottis or supraglottic tumor, subglottic stenosis, history of longstanding vocal fold paralyzes either unilateral or bilateral [4]. The presentation of patients with significant obstructing airway disorders is variable depending on the cause of the obstruction as well as the acuity or long-term progression. With a gathered history in a stable patient, what is important is the decision to consider a fiberoptic laryngoscopy prior to intubation. Flexible laryngoscopy and bronchoscopy is advisable before airway management [10]. Flexible laryngoscopy is necessary to indicate the extent, location, and nature of the obstructing disorder, and can lead to a more informed and successful airway management communication and plan. Bronchoscopy is good for visualization distal to the vocal folds in cases of subglottic or tracheal stenosis that would impede

Intubation: Difficult Airway

117

http://dx.doi.org/10.5772/intechopen.75512

What is important in any difficult airway is the adoption of an algorithm that begins with tracheal intubation. When tracheal intubation is not successful, an algorithm can direct the next steps to securing the airway. The risk of repeated unsuccessful trachea intubations leads to increased morbidity and mortality [11]. As soon as one method is deemed impracticable, practitioners must quickly advance through the algorithm rather than persist in futile attempts.

The difficult airway algorithm is published annually by the American Society of Anesthesiologists (ASA) (**Figure 1**) to reinforce the guidelines and be utilized by anesthesiologists nationwide [2, 3]. It standardizes how to secure a difficult airway. The initiation of the airway algorithm is dependent upon assessing the likelihood and clinical impact of basic management problems such (1) difficult ventilation, (2) difficult intubation, (3) uncooperative patient, (4) difficult tracheotomy. It then proceeds to break down the algorithm into different basic management choices such as awake intubation, non-invasive techniques and spontaneous ventilation compared to intubation after general anesthesia delivery and invasive methods for intubation. Within the branched algorithm, each method is described in a step-wise fashion, and the algorithm offers steps depending on success or failure of each method. Conservative non-invasive methods only become invasive and/or require help and surgical expertise when ventilation is not successful. Caveats for invasive airway techniques are listed at the bottom of the diagram

The importance of a multidisciplinary team, the presence of an acting lead in securing the difficult airway, and the timing and number of intubation attempts are all critical components of

As described in the difficult airway algorithm, alternative approaches to intubation are only possible if the toolbox available has both the basic and the alternative instrumentation for securing the airway. The difficult airway 'cart' should be established and secure in an area in any hospital setting, whether it be in the operating room, the emergency room and/or a

intubation.

**2.2. Difficult airway algorithm**

in footnote fashion.

a difficult airway algorithm.

**2.3. Tools to secure the difficult airway**

The importance of identifying a difficult airway is not in a single definition—it is in the recognition by a team in charge of the airway to institute an algorithm to secure the airway appropriately, in order to prevent morbidity and mortality. The incidence of difficult intubation in the operating room ranges between 1.15 and 3.80% [6], with failed attempts in 0.05–0.35% of cases [7, 8]. In the emergency department, difficult intubation occurs in 3.0–5.3% [7, 8] of cases with failure rates ranging from 0.5 to 1.1% [7, 8]. The most common complication related to a difficult airway is mistakes in the algorithm, mainly caused by unpreparedness [4]. This chapter aims to describe ways to prepare and secure the difficult airway.

#### **2.1. Early clinical considerations of a difficult airway**

In order to prepare and implement a difficult airway algorithm, it is important to assess the clinical scenarios or patient factors that can help determine the airway plan. Both the environment and patient stability dictate the scope of evaluation and management. The pace at which the assessment, approach and intervention is made is vital to securing the airway.

The initial history and physical examination are crucial in the assessment of the airway. The history is most accessible in an elective scenario or controlled setting where the patient is stable. Patient's age, mental status and cooperativeness is also important [5]. Pertinent history includes prior history difficult intubation, obstructive sleep apnea (OSA), head and neck irradiation, obesity, congenital malformations, cervical spine disability, and thyroid goiters [4]. Each of these factors can be important when deciding electively to secure a potentially difficult airway. In an emergency situation when a patient is not stable, having a history of difficult intubations can be the most important. Lundstrom et al. found that 24% of the patients with a documented history of difficult prior intubation subsequently experienced a difficult tracheal intubation. Amongst the patients with no history of difficult intubation, 95% of them subsequently underwent an intubation with no difficulty [9].

Other important clinical considerations include obstructing upper airway disorders. Amongst these clinical diagnoses include a more progressive process like a glottis or supraglottic tumor, subglottic stenosis, history of longstanding vocal fold paralyzes either unilateral or bilateral [4]. The presentation of patients with significant obstructing airway disorders is variable depending on the cause of the obstruction as well as the acuity or long-term progression. With a gathered history in a stable patient, what is important is the decision to consider a fiberoptic laryngoscopy prior to intubation. Flexible laryngoscopy and bronchoscopy is advisable before airway management [10]. Flexible laryngoscopy is necessary to indicate the extent, location, and nature of the obstructing disorder, and can lead to a more informed and successful airway management communication and plan. Bronchoscopy is good for visualization distal to the vocal folds in cases of subglottic or tracheal stenosis that would impede intubation.

What is important in any difficult airway is the adoption of an algorithm that begins with tracheal intubation. When tracheal intubation is not successful, an algorithm can direct the next steps to securing the airway. The risk of repeated unsuccessful trachea intubations leads to increased morbidity and mortality [11]. As soon as one method is deemed impracticable, practitioners must quickly advance through the algorithm rather than persist in futile attempts.

#### **2.2. Difficult airway algorithm**

**2. Definition of a difficult airway**

116 Tracheal Intubation

or the inability to intubate using all available methods [5].

**2.1. Early clinical considerations of a difficult airway**

subsequently underwent an intubation with no difficulty [9].

airway.

The definition of a difficult airway has been described multiple ways in the literature. There is no single definition of a difficult airway. According to the 2003 revised American Anesthesiology Task Force guidelines, a difficult airway is when a trained anesthesiologist experiences difficulty with face mask ventilation of the upper airway, difficulty with tracheal intubation, or both [2, 3]. Other definitions incorporate a broader definition whereby there is problematic ventilation using a facemask, incomplete laryngoscopic visualization, or as a difficult intubation with standard airway equipment [4]. Difficult ventilation is the inability to deliver the necessary tidal volume via the facemask even when using an oral or nasal airway and necessitating another device such as the laryngeal mask airway. Difficult laryngoscopy is impaired visualization of the true vocal cords despite elaborate external laryngeal repositioning. Difficult intubation requires external laryngeal manipulation, difficult laryngoscopy requiring greater than three attempts at intubation, intubation requiring nonstandard equipment or approaches,

The importance of identifying a difficult airway is not in a single definition—it is in the recognition by a team in charge of the airway to institute an algorithm to secure the airway appropriately, in order to prevent morbidity and mortality. The incidence of difficult intubation in the operating room ranges between 1.15 and 3.80% [6], with failed attempts in 0.05–0.35% of cases [7, 8]. In the emergency department, difficult intubation occurs in 3.0–5.3% [7, 8] of cases with failure rates ranging from 0.5 to 1.1% [7, 8]. The most common complication related to a difficult airway is mistakes in the algorithm, mainly caused by unpreparedness [4]. This chapter aims to describe ways to prepare and secure the difficult

In order to prepare and implement a difficult airway algorithm, it is important to assess the clinical scenarios or patient factors that can help determine the airway plan. Both the environment and patient stability dictate the scope of evaluation and management. The pace at which

The initial history and physical examination are crucial in the assessment of the airway. The history is most accessible in an elective scenario or controlled setting where the patient is stable. Patient's age, mental status and cooperativeness is also important [5]. Pertinent history includes prior history difficult intubation, obstructive sleep apnea (OSA), head and neck irradiation, obesity, congenital malformations, cervical spine disability, and thyroid goiters [4]. Each of these factors can be important when deciding electively to secure a potentially difficult airway. In an emergency situation when a patient is not stable, having a history of difficult intubations can be the most important. Lundstrom et al. found that 24% of the patients with a documented history of difficult prior intubation subsequently experienced a difficult tracheal intubation. Amongst the patients with no history of difficult intubation, 95% of them

the assessment, approach and intervention is made is vital to securing the airway.

The difficult airway algorithm is published annually by the American Society of Anesthesiologists (ASA) (**Figure 1**) to reinforce the guidelines and be utilized by anesthesiologists nationwide [2, 3]. It standardizes how to secure a difficult airway. The initiation of the airway algorithm is dependent upon assessing the likelihood and clinical impact of basic management problems such (1) difficult ventilation, (2) difficult intubation, (3) uncooperative patient, (4) difficult tracheotomy. It then proceeds to break down the algorithm into different basic management choices such as awake intubation, non-invasive techniques and spontaneous ventilation compared to intubation after general anesthesia delivery and invasive methods for intubation. Within the branched algorithm, each method is described in a step-wise fashion, and the algorithm offers steps depending on success or failure of each method. Conservative non-invasive methods only become invasive and/or require help and surgical expertise when ventilation is not successful. Caveats for invasive airway techniques are listed at the bottom of the diagram in footnote fashion.

The importance of a multidisciplinary team, the presence of an acting lead in securing the difficult airway, and the timing and number of intubation attempts are all critical components of a difficult airway algorithm.

#### **2.3. Tools to secure the difficult airway**

As described in the difficult airway algorithm, alternative approaches to intubation are only possible if the toolbox available has both the basic and the alternative instrumentation for securing the airway. The difficult airway 'cart' should be established and secure in an area in any hospital setting, whether it be in the operating room, the emergency room and/or a

designated area where it can be accessed by anyone who needs it [6, 12]. The tools for a dif-

Intubation: Difficult Airway

119

http://dx.doi.org/10.5772/intechopen.75512

One of the most pertinent tools in any intubation is the laryngoscope. Direct laryngoscopy is the paradigm of tracheal intubation, and has been a part of the armatarium of any provider securing the airway. The role of videolaryngoscopy over direct laryngoscopy has been a topic of discussion and published research, in regards to providing improved benefit over the traditional direct laryngoscopic approach. The authors of a large meta-analysis of five randomized controlled studies with 1301 patients found no difference in first time success in endotracheal intubation between using videolaryngoscopy over direct laryngoscopy [13]. The caveat to this meta-analysis was that most endotracheal intubations were done in an ICU setting. Other reviews and case series demonstrate an improvement in first time intubations in an emergency room setting using videolaryngoscopy over direct laryngoscopy, although

In the predicted difficult airway, when a patient is able to maintain spontaneous breathing, an awake intubation is an option. The tools for an awake intubation can be either non-invasive or invasive. LMA, supraglottic airways, and nasal-rays are examples of non-invasive tools. Fiberoptic laryngoscopy allowing for placement of a nasal-ray can be done awake. Invasive techniques include a surgical airway under local sedation- open versus percutaneous trache-

Other tools that can be used for awake intubation include a fiberoptic bronchoscope. Apfelbaum et al. described bronchoscope success in 88–100% of these patients, although other tools such as intubation through supraglottic devices, glidescope, and other tools are also successful [3]. The fiberoptic bronchoscope is successful if someone with proficiency is able

Other tools are also important in placement of endotracheal intubation. Intubating stylets or tube changers are also an option and can be used successfully for difficult intubations.  This is a blind

Supraglottic airways such as the LMA have shown to be rescue devices in patients who cannot be intubated or mask ventilated. The LMA can be used with a fiberoptic bronchoscope for intubation, and can maintain or restore ventilation in the difficult airway patient [5, 6, 18].

In the algorithm of the difficulty airway, the surgical airway is the definitive step in securing the airway. The placement of a surgical airway does not necessitate it being the last step in the algorithm, when non-invasive methods are unsuccessful. It may be the first step in securing the airway dependent upon the clinical context and stability of the patient. A surgical airway may be planned such as an awake tracheostomy in a patient where intubation through the glottis is not possible, or it may be an emergency when a trauma patient initial assessment

there is no large randomized control study that verifies this [14–17].

ficult airway can be multiple.

ostomy, or retrograde intubation [1].

to perform it [3].

technique.

**2.4.  Difficult airway algorithm by the American Society of Anesthesiologist Task Force (2003).

designated area where it can be accessed by anyone who needs it [6, 12]. The tools for a difficult airway can be multiple.

One of the most pertinent tools in any intubation is the laryngoscope. Direct laryngoscopy is the paradigm of tracheal intubation, and has been a part of the armatarium of any provider securing the airway. The role of videolaryngoscopy over direct laryngoscopy has been a topic of discussion and published research, in regards to providing improved benefit over the traditional direct laryngoscopic approach. The authors of a large meta-analysis of five randomized controlled studies with 1301 patients found no difference in first time success in endotracheal intubation between using videolaryngoscopy over direct laryngoscopy [13]. The caveat to this meta-analysis was that most endotracheal intubations were done in an ICU setting. Other reviews and case series demonstrate an improvement in first time intubations in an emergency room setting using videolaryngoscopy over direct laryngoscopy, although there is no large randomized control study that verifies this [14–17].

In the predicted difficult airway, when a patient is able to maintain spontaneous breathing, an awake intubation is an option. The tools for an awake intubation can be either non-invasive or invasive. LMA, supraglottic airways, and nasal-rays are examples of non-invasive tools. Fiberoptic laryngoscopy allowing for placement of a nasal-ray can be done awake. Invasive techniques include a surgical airway under local sedation- open versus percutaneous tracheostomy, or retrograde intubation [1].

Other tools that can be used for awake intubation include a fiberoptic bronchoscope. Apfelbaum et al. described bronchoscope success in 88–100% of these patients, although other tools such as intubation through supraglottic devices, glidescope, and other tools are also successful [3]. The fiberoptic bronchoscope is successful if someone with proficiency is able to perform it [3].

Other tools are also important in placement of endotracheal intubation. Intubating stylets or tube changers are also an option and can be used successfully for difficult intubations.  This is a blind technique.

Supraglottic airways such as the LMA have shown to be rescue devices in patients who cannot be intubated or mask ventilated. The LMA can be used with a fiberoptic bronchoscope for intubation, and can maintain or restore ventilation in the difficult airway patient [5, 6, 18].

#### **2.4. Surgical airway**

**Figure 1.** Difficult airway algorithm by the American Society of Anesthesiologist Task Force (2003).

118 Tracheal Intubation

In the algorithm of the difficulty airway, the surgical airway is the definitive step in securing the airway. The placement of a surgical airway does not necessitate it being the last step in the algorithm, when non-invasive methods are unsuccessful. It may be the first step in securing the airway dependent upon the clinical context and stability of the patient. A surgical airway may be planned such as an awake tracheostomy in a patient where intubation through the glottis is not possible, or it may be an emergency when a trauma patient initial assessment is bypassed by airway compromise and a surgical airway is the most appropriate next step for airway security. An awake tracheostomy tube is performed with no sedation and local anesthesia is used. The patient maintains spontaneous ventilation while the tracheostomy is being performed. Plain lidocaine (1%) is injected into the trachea before entering the airway to minimize coughing. After return of CO<sup>2</sup> is confirmed, generalized anesthesia is immediately administered [4]. Difficulties with awake tracheostomy start with inability for the patient to be fully cooperative. Physical factors include fixed cervical spine flexion deformity, obesity and increased neck circumference that decreases ability to palpate laryngeal landmarks. Large thyroid goiters can also be a limitation. History of head and neck radiation also results in distorted anatomy and loss of palpable laryngeal structures that make it hard to complete an awake tracheostomy [4].

Furthermore, a needle cricothyroidotomy compared to a surgical cricothyroidotomy limits the time for ventilation before a more secure airway is designated [22]. A cricothyroidotomy

Intubation: Difficult Airway

121

http://dx.doi.org/10.5772/intechopen.75512

In a retrospective chart review conducted by Dillon et al. over a 6-year period at a level-one trauma center, there were 34 surgical airways, of which 10 were cricothyrotomies, whereas the remaining were emergent tracheotomies [24]. The authors concluded that the paucity of cricothyrotomies could not be accounted for and only that at their institution, tracheostomy was preferred in an emergent situation. Other studies have also found that the use of tracheotomy in the setting when intubation is not possible is considered a safe alternative [21, 25]. These studies suggested that although cricothyrotomies are the surgical airway of choice in an emergent setting, emergent tracheotomies are safe and maybe more commonly performed.

There are a few limitations for cricothyrotomy as demonstrated below in the table (**Figure 2**). Cricothyrotomy should not be performed in children less than 12 years of age, as the cricothyroid membrane is quite narrow resulting in an increased risk of permanent laryngeal injury [24]. Furthermore, patients with suspected laryngotracheal trauma should not undergo

Tracheostomy is a secure, permanent surgical airway. The indications and timing of placement has been reviewed extensively [26]. The complications associated with tracheostomy placement can be divided into early and late complications. Hemorrhage is the most common early complication. Any major bleeding, especially from an arterial source, may require operative exploration. Pneumothorax and/or subcutaneous emphysema are less common. Mucous plugging or obstruction due to blood clots can occur postoperatively and can be

The part of a tracheostomy tube is important in patient teaching, for long-term use. Most tracheotomy tubes used commonly have an inner cannula which can be removed and cleaned on a routine basis, thus minimizing obstruction. In the early postoperative course, inadvertent displacement of the tracheotomy tube may result in a false passage, as the tract is not mature. Most of the later complications are secondary to constant pressure/irritation applied to the surrounding tracheal mucosa. This includes formation of granulomas, tracheal stenosis, and formation of fistulas in either the esophagus or the innominate artery [25]. An uncommon but

**Figure 2.** Indications and contraindications for cricothyroidotomy according to the American College of Surgeons (2008).

managed with the use of humidified air and regular gentle suctioning [25].

should eventually be converted to tracheostomy as it is a more secure airway [23].

Both can be performed on the field or an in hospital setting.

cricothyroidotomy [25].

In the case of an airway emergency or acute destabilization of a patient requiring immediate airway protection, a surgical airway can take place in two forms: a cricothyroidotomy or a tracheostomy. The pros and cons of each approach are discussed in the next section.

The steps of the emergent surgical airway are:

#### **2.5. Pros and cons of tracheotomy versus cricothyroidotomy**

The American Society of Anesthesiologists difficult airway algorithm identifies two acceptable emergency surgical airways in the 'cannot intubate, cannot ventilate' scenario: cricothyrotomy and tracheotomy [2].

According to the guidelines of the American Trauma Life Support developed by the American College of Surgeons, cricothyrotomy is recommended in an emergent setting [19]. Cricothyroidotomy is perceived to be easier to perform as it is safer theoretically, has less bleeding, and requires less surgical time [20, 21]. The difference between a cricothyroidotomy and a tracheostomy is that a cricothyroidotomy is a temporizing measure only [20]. Furthermore, a needle cricothyroidotomy compared to a surgical cricothyroidotomy limits the time for ventilation before a more secure airway is designated [22]. A cricothyroidotomy should eventually be converted to tracheostomy as it is a more secure airway [23].

is bypassed by airway compromise and a surgical airway is the most appropriate next step for airway security. An awake tracheostomy tube is performed with no sedation and local anesthesia is used. The patient maintains spontaneous ventilation while the tracheostomy is being performed. Plain lidocaine (1%) is injected into the trachea before entering the airway to

administered [4]. Difficulties with awake tracheostomy start with inability for the patient to be fully cooperative. Physical factors include fixed cervical spine flexion deformity, obesity and increased neck circumference that decreases ability to palpate laryngeal landmarks. Large thyroid goiters can also be a limitation. History of head and neck radiation also results in distorted anatomy and loss of palpable laryngeal structures that make it hard to complete

In the case of an airway emergency or acute destabilization of a patient requiring immediate airway protection, a surgical airway can take place in two forms: a cricothyroidotomy or a

tracheostomy. The pros and cons of each approach are discussed in the next section.

**1.** Identifying surgical landmarks, including the laryngeal skeleton and midline trachea

airway (such as obesity, enlarged thyroid goiter, neck irradiation)

**2.** Assessment of the patient's body habitus and any potential obstructions to entering the

**3.** Topical anesthetic to the skin for local anesthetic and less patient discomfort (if there is

**4.** Taking a large gauge needle and syringe and placing it directly into the airway, with con-

**5.** Vertical incision with a 15 blade into the overlying soft tissue and through the trachea or a vertical stab incision into the cricothyroid membrane. Placement of an endotracheal tube

**6.** Securing the airway is important which may require transportation to an operating room setting if in the emergency department, with revision to a traditional tracheostomy, neck-

The American Society of Anesthesiologists difficult airway algorithm identifies two acceptable emergency surgical airways in the 'cannot intubate, cannot ventilate' scenario: cricothy-

According to the guidelines of the American Trauma Life Support developed by the American College of Surgeons, cricothyrotomy is recommended in an emergent setting [19]. Cricothyroidotomy is perceived to be easier to perform as it is safer theoretically, has less bleeding, and requires less surgical time [20, 21]. The difference between a cricothyroidotomy and a tracheostomy is that a cricothyroidotomy is a temporizing measure only [20].

confirmation.

is confirmed, generalized anesthesia is immediately

minimize coughing. After return of CO<sup>2</sup>

The steps of the emergent surgical airway are:

firmation of aspirated air back

ties and achievement of hemostasis.

rotomy and tracheotomy [2].

into the lumen is important with end tidal CO<sup>2</sup>

**2.5. Pros and cons of tracheotomy versus cricothyroidotomy**

an awake tracheostomy [4].

time)

120 Tracheal Intubation

In a retrospective chart review conducted by Dillon et al. over a 6-year period at a level-one trauma center, there were 34 surgical airways, of which 10 were cricothyrotomies, whereas the remaining were emergent tracheotomies [24]. The authors concluded that the paucity of cricothyrotomies could not be accounted for and only that at their institution, tracheostomy was preferred in an emergent situation. Other studies have also found that the use of tracheotomy in the setting when intubation is not possible is considered a safe alternative [21, 25]. These studies suggested that although cricothyrotomies are the surgical airway of choice in an emergent setting, emergent tracheotomies are safe and maybe more commonly performed. Both can be performed on the field or an in hospital setting.

There are a few limitations for cricothyrotomy as demonstrated below in the table (**Figure 2**). Cricothyrotomy should not be performed in children less than 12 years of age, as the cricothyroid membrane is quite narrow resulting in an increased risk of permanent laryngeal injury [24]. Furthermore, patients with suspected laryngotracheal trauma should not undergo cricothyroidotomy [25].

Tracheostomy is a secure, permanent surgical airway. The indications and timing of placement has been reviewed extensively [26]. The complications associated with tracheostomy placement can be divided into early and late complications. Hemorrhage is the most common early complication. Any major bleeding, especially from an arterial source, may require operative exploration. Pneumothorax and/or subcutaneous emphysema are less common. Mucous plugging or obstruction due to blood clots can occur postoperatively and can be managed with the use of humidified air and regular gentle suctioning [25].

The part of a tracheostomy tube is important in patient teaching, for long-term use. Most tracheotomy tubes used commonly have an inner cannula which can be removed and cleaned on a routine basis, thus minimizing obstruction. In the early postoperative course, inadvertent displacement of the tracheotomy tube may result in a false passage, as the tract is not mature. Most of the later complications are secondary to constant pressure/irritation applied to the surrounding tracheal mucosa. This includes formation of granulomas, tracheal stenosis, and formation of fistulas in either the esophagus or the innominate artery [25]. An uncommon but

**Figure 2.** Indications and contraindications for cricothyroidotomy according to the American College of Surgeons (2008).

life-threatening complication is a tracheo-innominate fistula. These are linked to low-placed tubes and patients with excessive movement of the head. This complication has a 25% mortality rate [27]. If it does occur, manual pressure over the tract or over inflation of the cuff when it is seated in this tract can help tamponade the bleed until the patient can be taken back to the operating room for further exploration.

Overall, the role of an otolaryngologist is both a consultant, and a surgeon. Ultimately, in any difficult airway scenario, the otolaryngologist is a member of a multi-disciplinary team that is involved in securement of the airway with an interdependent and algorithmic approach [2, 4, 5].

Intubation: Difficult Airway

123

http://dx.doi.org/10.5772/intechopen.75512

In conclusion, the definition of a difficult airway is not rigid, nor is it an over-arching diagnosis. A difficult airway can come in all shapes and sizes, keeping in mind that an airway is never stable without ability to oxygenate or ventilate. The importance of a difficult airway algorithm is crucial in organization of steps involved in securing the airway. A difficult airway does not necessarily have to be an emergency, but it does take require a team approach to initiate the appropriate steps in saving a life. Resources such as equipment available to secure a difficult airway, the steps involved in performing a surgical airway, and the pros and cons of a tracheostomy over a cricothyroidotomy, were summarized in this chapter. The goal of this chapter is to allow readers to identify the difficult airway and have a broad understanding of how to provide the appropriate care for these patients. For the otolaryngologist, this chapter aims to serve as a guideline by which to address the airway with the tools and resources avail-

Vaninder K. Dhillon declares no conflict of interest in the publication of this manuscript.

Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University,

[1] Artime C, Hagberg C. Is there a gold standard for management of the difficult airway?

[2] Caplan RA, Benumof JL, Berry FA, Blitt CD, Bode RH, Cheney FW, Connis RT, Guidry OF, Nickinovich DG, Ovassapian A. Practice guidelines for management of the difficult airway.

**3. Conclusion**

**Conflict of interest**

**Author details**

Vaninder K. Dhillon

Baltimore, MD, USA

**References**

able, both in a controlled and emergency situation.

Address all correspondence to<EMAIL_ADDRESS>
Anesthesiology Clinics. 2015;**33**:233-240

Tracheostomy placement in the form of an open versus percutaneous approach has been evaluated in many studies, to see if there is an advantage of one approach over the other. A Cochrane analysis of all randomized control and quasi-randomized control studies, evaluated approximately 20 trials that compared percutaneous to open technique [28]. The goal was to evaluate whether there was a higher complication profile amongst one technique over the other. The review looked at studies completed in an ICU over an emergency room setting. Overall, the systematic showed some benefits in terms of effectiveness and safety of the use of percutaneous techniques for tracheostomy, especially in regards to rates of late non-life threatening complications. However there is overall low quality evidence to suggest a difference in postoperative mortality or total mortality from life threatening complications like bleeding, between the two techniques. Generalizability of one technique over the other was not possible according to the Cochrane review [28].

The review concluded that open tracheostomy may still be indicated for selected patients, despite the continuing broader indications for use of percutaneous technique [28]. Again, this review did not evaluate studies that looked at the use of percutaneous tracheostomy in an emergent, difficult airway setting.

#### **2.6. The role of the otolaryngologist-head and neck surgeon**

The role of the otolaryngologist-head and neck surgeon is to be an important counterpart to the team involved in a difficult airway. O'dell describes the role of the otolaryngologist as involved in the preoperative evaluation of a difficult airway and the comprehensive algorithm in identifying and evaluating the airway prior or during induction of general anesthesia [4]. The fiberoptic laryngoscopy, used in evaluating the airway, is the trademark tool of the otolaryngologist. The technical expertise and familiarity with the upper airway and larynx allows an otolaryngologist to screen a difficult airway [5], as well as provide therapeutic means to fiberoptically intubate at the same time if needed. Nasotracheal intubations done with the use of a fiberoptic laryngoscope is a common practice, and can be done with the patient spontaneously breathing. The availability and expertise with certain equipment allows the otolaryngologist a more invasive approach to the airway, with determination of what branch of the difficult airway algorithm should be taken next based upon findings.

An otolaryngologist is also equipped to handle the placement of a surgical airway whether it is an awake tracheostomy in a controlled setting for a patient with known upper airway obstruction and difficult intubation [4, 26]. An otolaryngologist is also able to assist in placement of an emergency surgical airway, with most otolaryngologists placing an emergent tracheostomy over a cricothyroidotomy [23, 26].

Overall, the role of an otolaryngologist is both a consultant, and a surgeon. Ultimately, in any difficult airway scenario, the otolaryngologist is a member of a multi-disciplinary team that is involved in securement of the airway with an interdependent and algorithmic approach [2, 4, 5].


**2. Background**

that advocate energy conservation for green buildings have been promoted, wherein the building energy efficiency upgrade program for reducing power consumption in buildings is one of the crucial contents outlined in the policy. Green building's three main pillars are environmental, economic, and social in aspect. Considered a paramount method to maintain quality of life, designed to replace use of environmentally harmful products, we could say that sustainable design is an important process involving science and arts from all fields [1]. In China, estimates indicate that more than 80% of annual new buildings and over 95% of existing buildings have high-energy consumption designs [2]. Low energy-efficiency buildings

of "green legislation" together with increased green building construction is forcing architects, planners, and builders to consider the environmental impact of buildings they design and construct [4]. Aside from the moderate amount of sunlight required for the health and comfort of occupants, solar radiation is particularly useful as an energy resource [5]. Apart from this, sunlight provides light more efficiently than electric light sources, while producing less heat for the same amount of light. With the development of sustainable design, researchers are attaching much more importance to energy savings related to sun exposure on buildings, an important component of sustainable development. One of the performance analyses done by architects is to predict how buildings are performing in terms of their luminous environment as a result of daylighting [6]. If energy savings from harvesting sunshine on buildings are considered in the building design stage, an optimal energy design can be selected. Demand for solar power has expanded in recent years for domestic and industrial needs. Solar power is produced by collecting sunlight and converting it into electricity, which is normally done by use of large, flat solar panels composed of many individual solar cells. Solar arrays are most often located remotely, although urban sitting is becoming more popular as well. As the cost of solar energy falls, more and more buildings are being outfitted with photovoltaic systems and some even generate more electricity than they use, which structures are called "energy positive," an impressive feat. In some areas, solar-enabled buildings actually turn a profit from surplus energy, which is sold to local utility companies and fed it onto the grid. In practice, photovoltaic materials (like solar panels) are normally used to replace conventional building materials in parts of the building envelope such as roofs, skylights, and facades. As a principle or ancillary source of electrical power, solar panels are increasingly incorporated into the construction of new buildings, although existing buildings may be retrofitted with similar technology. However, current analysis of solar energy extraction in comparison with the complexity of sunlight models needed for energy calculations clearly reflects the limited use of building information modeling, as well as the lack of effective visualization techniques. Sunlight analysis is performed by hand calculations or by computer simulation tools. In the process of hand calculation, the preparation of initial data can be a very lengthy and laborious, consisting as it does mostly of manual or semimanual translation from architectural model data to simulation data, which often results in numerous coding errors [7]. To solve the problem, graphic user interfaces have been created in simulation tools for defining model geometry. In addition, 3D digital technology, such as building information modeling (BIM), has been applied to sunlight simulation. BIM integrates all kinds of relevant information from construction projects, while related software enables energy consumption to be predicted and adjusted during the design

of urban buildings in China [3]. As well, the advent

account for 98% of more than 4 × 1010 m2

108 Emerging Solar Energy Materials

stage, thus providing great convenience for sustainable design.

#### **2.1. BIM and sustainable design**

With the importance of BIM becoming increasingly appreciated, BIM and sustainable design strategies in the building industry have drawn more and more attention. A number of published papers on BIM-related sustainable design have focused mostly on energy usage analysis alone [8]. Wang and Xuan [9] suggest a BIM-based parametric design method to establish the BKE (Bio-inspired Kinetic Envelop) system combined with utilization of solar radiation to make buildings acclimate to temperature swings, thus minimizing the energy needs. Wong and Fan [8] find two most significant benefits of BIM for sustainable building design: integrated project delivery (IPD) and design optimization. Hardin [10] established three main areas of sustainable design with a direct relationship to BIM, which are "material selection and use," "site selection and management," and "systems analysis." In addition, Azhar and Brown [11] investigate the development of a conceptual framework to illustrate the use of BIM for sustainability analyses throughout the project life-cycle.

In previous study on the integration BIM and building performance, it has been indicated that BIM can aid in the sunlight analysis [12]. BIM technologies offer new insights into the dynamic relationship and specificities of sunlight conditions and the individual building's use and properties, helping us identify the balancing points of solar gains and daylight conditions resulting from urban geometry [13]. Welle et al. [14] designed an automated product model decomposition and re-composition methodology for BIM-centric climate-based daylighting simulation called the BIM-Centric Daylight Profiler for Simulation (BDP4SIM). Joo et al. [15] developed a tool capable of analyzing various design schemes during the early stages of design by building a reasonable BIM data system for sustainability analysis and using the architectural BIM model to carry out sunshine and energy analysis in a Web environment. Generally, two main methods are used for sunlight analysis in building design. One method is the graphing method, which includes normal shadow-graph, pole shadow-graph, instantaneous shadow-graph, and hours shadow overlay. The other method is the modeling test, which performs analysis based on a scale-model of buildings and a sundial. Though the sun spacing coefficient table was widely used in China during the late 1990s, table's usefulness is restricted by some limitations that require compliance during early building layout design, where the sun spacing factor is applied in parallel with layer settings for the building. Shadow graphs created for software applications offer a new detailed representation of shadow constraints. Overall, the solar analysis model using BIM has advantage of being importable to related software, generating shadow animations for target periods and simulation results that can be saved on BIM database for property management and quality control.

technology's market penetration, while the current direct cost of photovoltaic solar panels is widely acknowledged to be much greater than fossil fuel generation or many other renewable energy sources. The initial cost of the solar panels may be expensive, but it is the only cost plus their installation provides potential complete relief from electric utility costs. Maintenance can be perceived as an added cost, but in reality, all the panels need is dusting and/or washing. Therefore, the cost analysis of solar panels is an important factor to be considered when making

A BIM-Based Study on the Sunlight Simulation in Order to Calculate Solar Energy…

http://dx.doi.org/10.5772/intechopen.74161

111

The importance of developing an integrated approach for potential solar energy analysis of buildings using BIM technology has been established above. Integration of quantitative results for energy consumption by building objects and 3D visualization of spatial modeling requires a well-managed framework that combines sunlight simulation and the calculation of solar energy. Such a framework should be designed to transmit data in the basic steps used for developing an effective building sunshine model. Our research aims to estimate the solar energy consumption and cost analysis of photovoltaic solar energy systems that could be installed on the rooftops and vertical walls of buildings with the use of BIM for building performance simulation and sunlight analysis. In order to estimate total harvestable solar energy and to analyze cost of photovoltaic systems, the following four-level research framework was

Level 0: CAD drawing. The building object selected in this study was described according to construction drawings made on AutoCAD Architecture. Original 2D image information is

Level 1: 3D modeling. In the course of preparing 3D building models, the virtual data are exported from the CAD system to a suitable CAD exchange format (e.g., DWG), then processed to re-build the plan in a 3D environment with the aid of BIM software system (e.g., Revit). The BIM 3D model is used to generate traditional building abstractions: plans, sections, details, and elevations. 3D models produced using BIM also possess interactive viewing properties.

Level 2: Sunlight simulation. Building environment analysis (like energy analysis and sunhour analysis) is normally carried out as part of BIM based design. In this step, the representative rooftop and surface area of the sample building are selected. Sunlight simulation is made by input of the Industrial Foundation Classes (IFC) model into the sunlight analysis program, followed by additional related analysis on occlusion relationship, sunshine duration sheet,

Level 3: Solar energy analysis. The main objective of Level 3 is to assess the geometric characteristics under sunlight models in solar energy analysis. This step obtains dimensions of the useful rooftop and vertical surfaces, where photovoltaic solar panels could be installed, from which the solar energy generation potential and the energy costs are calculated for the sample building.

decisions about solar systems in building design.

provided in regard to points, lines, surfaces, text, etc.

**3. Methodology**

**3.1. Analysis method**

executed (see **Figure 1**):

isohel map, shadow outlines, etc.

#### **2.2. Solar energy and buildings**

Solar energy is the portion of the sun's energy available at the earth's surface for useful applications, such as exciting electrons in a photovoltaic cell and indoor illumination. Solar energy system is currently the most widely installed renewable energy system in the building sector in an effort to reduce the energy consumption of buildings [16]. Developing the calculation model for solar energy in buildings is helpful to describe the mathematical relations between the solar energy and building attributes such as orientation, location, height, area, etc. An important aspect in calculating solar energy is the accuracy of the developed model, which is evaluated using initial data input [17]. The large volume of residential building construction in recent years and the deficit of conventional energy sources justify any initiatives conducive to the construction of self-sustainable residential buildings that are capable of producing their own energy for illumination, HVAC, electrical appliances, etc. [18].

The design of alternative energy devices is a predictable way to develop a wide range of new technologies for a more sustainable future. To achieve energy sustainability, the installation of building-integrated solar panels is a viable option. Solar panels are a type of semiconductor device that converts the energy from sunlight into electric energy. Solar panels do not use chemical reactions to produce electric power, and they have no moving parts. Rooftop and vertical surfaces on buildings are convenient installation position to supply solar energy to meet growing energy demands. Depending on material, solar panels can be classified into different kinds: silicon solar cell, compound solar cells, polymer solar cell, nanocrystal solar cell, organic solar cell, and plastic solar cell. Many of factors play part in determining the practicality of a given solar installation and the selection of solar panels. One major factor is the available sunlight. Considering the sun is what combines with the photovoltaic panels to produce the energy, an area rich in sunlight is highly desirable [19]. Glasnovic and Margeta [19] performed an analysis of photovoltaic pumps versus diesel pumps and concluded that photovoltaic pumps were more efficient than diesel pump. Photovoltaic solar cells are thin silicon disks that convert sunlight into electricity. These disks act as energy sources for a wide variety of uses, such as rooftop panels on buildings. The past decade has seen a remarkable evolution in mainstream silicon solar cell technology, documented by greatly increased production volumes and greatly reduced costs.

By using solar panels, electricity costs from outside sources are negated by the electricity produced by the building's surface installations. Additionally, emissions that are the environmental cost of burning coal to produce electricity are significantly reduced. Although solar energy is renewable, more efficient than fossil fuel and environmentally friendly, it is costly. According to Borenstein [20], the high cost of power from solar panels has been a major deterrent to the technology's market penetration, while the current direct cost of photovoltaic solar panels is widely acknowledged to be much greater than fossil fuel generation or many other renewable energy sources. The initial cost of the solar panels may be expensive, but it is the only cost plus their installation provides potential complete relief from electric utility costs. Maintenance can be perceived as an added cost, but in reality, all the panels need is dusting and/or washing. Therefore, the cost analysis of solar panels is an important factor to be considered when making decisions about solar systems in building design.