Airway Management in Special Situations

Special situations in cancer airway management, including unexpected difficult tracheal intubation, airway bleeding, and extubating a difficult airway, are major challenges in cancer airway management. Although the majority of airway events are managed uneventfully, failure of airway management occurs despite the application of various techniques and leads to fatal outcomes, emphasizing the importance of situation awareness, preparing for unexpected difficulties, appropriate working environment, and team collaboration.

Management of Unanticipated Difficult Airway

Due to rapid progress and local invasion of the cancerous disease in the upper aerodigestive tract, the complex changes in airway anatomy from previous surgery, the tissue changes resulting from head and neck radiotherapy, and so on, management of unexpected situations occurs more often in patients undergoing head and neck cancer resection than in those with gross normal anatomy in the airway. These cases often present unique challenges. However, the obstruction of airflow and/or the intubation path are primary issues in management of the cancer airway regardless of the underlying pathologic change; therefore the principle of airway management in these cases is not different from any other airway management. A systemic approach with appropriate strategies for various unexpected situations ahead of time and abundant clinical experiences plays key roles in these scenarios.

Cancer Airway Assessment

Understanding the baseline condition and underlying airway mechanism is essential for formulating a practical strategy. A comprehensive perioperative assessment of a patient undergoing head and neck cancer surgery should include a focused history related to respiratory symptoms, issues of intolerance of hypoxia, history of anticancer therapy, including surgery and radiotherapy, and records of previous airway management. Conventional airway assessment tools focus on the patients’ characteristics to evaluate the potential issues of (1) patient cooperation or consent, (2) difficult mask ventilation, (3) difficult supraglottic airway placement, (4) difficult laryngoscopy, (5) difficult intubation, and (6) difficult surgical airway access. In general, bedside airway assessment tools have low sensitivity and high variability. For a cancer airway, the following information is also carefully inquired and assessed:

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Primary versus recurring disease: For a primary neoplasm, the mass effect and corresponding anatomic change due to the tumor growth are the primary assessing points. For a recurring disease, the impacts of tissue change to the airway management from previous cancer therapies, including surgery and radiotherapy, must also be included in the airway assessment.
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Cancer stage and location: The staging system (TNM) for cancer in the upper aerodigestive tract is the tumor (T), node (N), and metastasis (M). The stage and location of cancer pathology exert significant influence on airway management. The “T” is the primary consideration in managing the airway. Oral cavity or oropharyngeal cancer rarely causes significant obstruction of the intubation path, whereas a cancer located in the hypopharynx or larynx will be more likely to cause obstruction of not only the airflow, but also of the intubation path. Invasion of cancer into cartilage at an advanced cancer (stage 3–4) will markedly restrict the intubation pathway and curb the insertion of an endotracheal tube (ETT) through the tumor site. It is worth mentioning that forcing an ETT though a critical stenosis site may result in immediate airway obstruction and a fatal outcome.
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Head and neck radiation: Radiation toxicity induces significant tissue changes and organ dysfunction. The issues that affect the airway management include acute airway edema (early stage change), lymph edema and/or diffused tissue thickness, and tissue fibrosis (later stage change). Crucial laryngeal edema is rare but may require tracheostomy to maintain the airway. A study showed that more than 50% of patients who received a full dose of head and neck radiotherapy develop acute laryngeal edema. Tissue fibrosis, lymphedema, and/or diffused tissue thickening are common late issues. One study (n = 81) showed that 75% of patients developed lymphedema and 30% had edema only in the aerodigestive tract. Therefore facial edema is not always correlated to the internal change in the airway and should not be used as a predictor of airway edema. Lymphedema lasts many years and imposes remarkable adverse impacts to airway management in these patients. Loss of tissue compliance after tissue fibrosis challenges the exposure of the glottis and increases the failure of laryngoscopy. Coexisting restriction in neck range of motion and trismus resulting from tissue fibrosis further curb the intubation efforts. One must understand that these problems cannot be solved by administration of a neuromuscular relaxant.
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Anatomic changes from previous surgery: Although previous surgery in the upper aerodigestive tract may raise the concern of local anatomic changes, clinical experiences have indicated that a well-healed surgical site rarely curbs face mask ventilation and the performance of tracheal intubation. One study of 472 oral cavity and oropharyngeal cancer airways showed that only 7.4% of these airways managed with an advanced technique were due to the concern of distorted airway anatomy from previous surgery, and failure of airway management in this population is low.
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Inability to support the airway immediately after surgery: Inability to support the airway immediately after surgery is not uncommon in cases of free tissue transfer (free flap) reconstruction surgery. The airway manipulation and pressure added to the flap during rescue of the airway may result in severe flap damage or failure. The potential risks of extubating the airway in these cases must be carefully assessed ahead of time.

Limits of Diagnostic Imaging Studies for Cancer Airway Evaluation

The primary goal of various cancer imaging studies is to facilitate cancer evaluation, rather than airway assessment. The limits of imaging findings in airway assessment should be fully appreciated. The commonly used imaging studies for cancer evaluation include magnetic resonance imaging (MRI), contrast enhanced computed tomography (CECT), and ultrasound study. Diagnostic imaging studies depict the tumor margin and the anatomic location of the tumor. However, the caliber of the airway varies depending on the respiratory circle. Deep inspiration increases the caliber of the airway and expiration reduces it. MRI or CT scan cannot capture the dynamic changes of the airway space. Unless special techniques are applied, such as a second pass with breath holding during deep inspiration, the maximal airway space available at the tumor site, and therefore the appropriate tube size, cannot be determined ( Fig. 17.1 ). The interpretation of imaging findings must therefore be combined with clinical evaluation. Although a high-resolution ultrasound study may be used to assess vocal fold mobility and the maximal airway caliber, inadequate spatial resolution remains an issue for accurately measuring the airway space.

Guidelines and Cognitive Aids in Managing Difficult Airways

Globally, all the major societies of anesthesiology or airway management have published guidelines and algorithms for management of the airway in various situations. ^, These documents consist of fundamental elements in daily airway management and should be routinely applied to cancer airway management. Further, an appropriately designed cognitive aid is an important tool in the management of an unexpected airway event and should be routinely included in the cancer airway management strategy. A study showed that when appropriately implemented, a cognitive aid is effective for improving team communication and promoting situation awareness. A meta-analysis of outcome measures showed that the surgical safety checklist improves the effect on teamwork and communication by 1.2-fold and enhances heterogeneity. Effective implementation of a checklist requires that the entire team participate in the process, receive support from senior personnel, have appropriate education and training, and address the barriers to the implementation of the checklist. Implementing a safety checklist should consider the needs of the patient population, the procedures, and the practice environment.

Training and Education in Cancer Airway Management

Difficult or failed tracheal intubation due to inadequate skill in using advanced tools is not uncommon. Lack of skill curbs the efforts of managing an unexpected airway event. Training should emphasize the critical skills in managing cancer airway such as flexible scope intubation (awake or asleep) and lifesaving skills such as cricothyroidotomy (needle or scalp) that are not used as routine anesthesia practice. One survey from 147 directors of an anesthesiology residency program in the United States and Canada showed that approximately one-third of graduating residents were estimated to have performed 25 awake fiber optic intubations during their training. The skill level for preforming an awake flexible bronchoscopy will rapidly decay if it is not used in routine practice after residency. Cricothyroidotomy is a lifesaving technique. Correct identification of the cricothyroid membrane (CTM) is not only the key to success but also to reducing the risk of major complications. Inability to identify the CTM is a common issue among anesthesiologists and surgeons. One study showed that less than 50% of anesthesia providers and trauma surgeons were able to identify the CTM in nonobese females with optimized neck extension. Prior experience of emergency surgical airway did not improve the success rate, emphasizing the importance of training on a regular basis. Further, clinical data showed that in comparing elective cases, emergency airway management bears a significantly higher morbidity and mortality, suggesting that training should not be focused on clinical skills only but must be performed in different environments and situations.

Human Factor in Airway Management

The 4th National Audit Project (NAP4) studied the major complications of airway management in the UK and showed that the majority of the major complications of airway management in the emergency department would have been preventable through an improved system, better preparation, and good communication, suggesting that human factors impose significant adverse impacts in patient outcomes. The NAP4 also revealed that we are unable to effectively manage the difficult situations with our existing knowledge, “…the vast majority of the reports concerned events that are already well known to the anesthetic community but it seems that we have not learned from the past…” Acknowledging the human limits and inclusion of human factors in training and education curricula will enhance teamwork, communication, situation awareness, and the decision-making process.

Principles and Strategies of Managingan Unexpected Difficult Cancer Airway

Following the first airway management guidelines published in 1993 by the American Society of Anesthesiologists (ASA), all the major societies of anesthesiology or airway management have published their corresponding guidelines. These guidelines provide step-by-step approaches to managing the difficult airway in different clinical scenarios. The practice guideline for management of the difficult airway by the ASA (2013) proposed basic preparations for difficult airway management including:

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Availability of appropriate equipment with at least one portable storage unit containing specialized equipment for difficult airway management readily available,
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Informing the patient with a known or suspected difficult airway and procedures pertaining to managing a difficult airway,
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Ascertaining an assigned individual to provide assistance,
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Preanesthetic preoxygenation by mask before initiation of anesthetic induction, and
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Actively pursuing the chance to deliver supplemental oxygen throughout the process of managing the difficult airway.

The guidelines for management of unanticipated difficult intubation in adults by the Difficult Airway Society (DAS, 2015) proposed a simplified, single algorithm, including a four-plan strategy consisting of:

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Face mask ventilation and tracheal intubation as an initial step (Plan A),
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Maintaining oxygenation by a supraglottic airway device (SAD) after an unsuccessful initial intubation attempt (Plan B),
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Final attempt at face mask ventilation as the last effort of noninvasive intervention (Plan C), and
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Performing emergency front of neck access (FONA, Plan D).

These recommendations and step-by-step approaches comprise the fundamental components in management of the difficult airway in different clinical situations.

Techniques and Tools for Managementof the Difficult Cancer Airway

Ventilation and oxygenation of the lungs is the primary determinant of an urgent or emergency airway event. The tools that are commonly used to achieve effective lung ventilation and oxygenation include face mask and SAD. In recent years, application of heated, humidified high-flow oxygen devices such as Optiflow (Fisher & Paykel, Healthcare Ltd., Auckland, New Zealand) has increased in airway management and is reported to enhance oxygen delivery, counterbalance auto-PEEP (positive end-expiratory pressure), and increase ventilatory efficiency. One early study in 25 patients showed that at an oxygen flow rate of 70 L/min, the patients maintained oxygen saturation above 90% with a median apneic time of 14 min (range, 5–65 min). Another study on 21 healthy volunteers showed that Optiflow provided rapid oxygenation. With a flow rate of 70 L/min, patients achieved 72% end-tidal oxygen concentration (ETo ₂ ) in 30 s and reached the ETo ₂ peak level of 88% in 150 s. Use of a nasal oxygen cannula as a machine-human interface increases patient tolerance and compliance during the course of preoxygenation, especially for patients with claustrophobia. Current studies favor its usage in airway management although the benefits for cancer airway management need to be further studied.

Due to significant risk of airway bleeding after failed airway intubation, the initial intubation technique should be carefully selected based on the anesthesiologist’s previous experiences. In general, videolaryngoscope is a preferred tool for an unobstructed airway, and flexible scope remains the most popular tool to intubate a partially obstructed airway. Multiple randomized controlled trials (RCTs) have compared the outcomes of direct laryngoscopy and videolaryngoscopy intubation. Tracheal intubation by videolaryngoscopy had higher success rates on the first attempt in patients with predictors of difficult airway (C-MAC; Karl Storz, Tuttlingen, Germany) in patients with restricted neck mobility (Pentax-AWS; Pentax Corporation, Tokyo Japan), or in simulated difficult airway (GlideScope, Bothell, MA, USA).

Comparing videolaryngoscopes, the flexible scope remains a nonreplaceable tool in managing various levels of obstructive airways. However, performing flexible scope intubation demands an experienced hand, a clean field, and is time-consuming. Further, the flexible scope is limited during a time-sensitive event. Inability to maintain adequate oxygenation during the procedure due to various causes is a common problem and curbs the success of flexible scope intubation. The tube impinging on laryngeal structure during the flexible scope intubation resulting in difficulty or impossibility in sliding the ETT into the trachea is also a common issue. This may be especially true when intubating the trachea via a partially obstructed pathway at the tumor site. It is important to select an appropriate ETT for flexible scope intubation in cancer airway management. One RCT on 80 patients compared outcomes of flexible scope oral intubation using a Parker Flex-Tip tube (PFT) (Parker Medical, Highlands Ranch, CO, USA) ( Fig. 17.2 ) and a standard-tip tube and found that use of the PFT resulted in a two-thirds reduction in the rate of resistance to passage of the tube into the trachea. Another randomized study on 40 individuals during transnasal fiber optic intubation reported that PFT significantly reduced the incidence of traumatic nose bleeding when compared with using a standard-tip tube during nasal intubation.