Airway Management in Special Situations

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:

• 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.

• 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.

• 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.

• 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.

• 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.