Is There a Best Approach for Patients With Difficult Airways: Regional Versus General Anesthesia?

INTRODUCTION

Regional and general anesthesia techniques can individually offer advantages to a patient with a known difficult airway. The superiority of one technique over the other is hotly debated, and the complexities of study design, as well as potential ethical dilemmas, mean finding a definitive answer regarding the best approach is difficult. Multiple factors influence the choice of anesthesia provided and its outcome, including patient comorbidities and preferences, proposed surgical technique (laparoscopic versus open), and the skillset of both the anesthesiologist and the surgeon. In a patient with known complicated airway anatomy, regional anesthesia may appear to be the ideal option because it avoids instrumentation of the airway. A balance must be struck, however, between inviting the unnecessary risk of a difficult airway when regional anesthesia would likely suffice with the risk for potential intraoperative conversion to a general anesthetic under adverse patient conditions.

RESEARCH

Research into safe airway management is challenging to design. In general, anesthesia is safe, and significant adverse events occur infrequently. Therefore massive studies are needed to detect differences between techniques. Most efficacy studies specifically recruit low-risk patients to avoid the risk of patient complications and other adverse events; this does not suit a safety-based study. It can raise ethical concerns to seek out patients at high risk for complications, even when clinical equipoise exists. Randomized control trials (RCTs), the benchmark of high-quality research, are often not a suitable methodology for studies looking at the best anesthetic technique for patients with difficult airways. Impediments exist in performing high-quality studies in difficult airway management, including the fact that significant adverse events are infrequent and unpredictable. If events occur or are predicted in those who are not anesthetized, the clinical setting means the patient is often not able to give informed consent; the success of any technique is reliant on user experience and preference. Therefore we rely on prospective and retrospective data reviews and audits to assimilate our information and knowledge in this area.

There is no standard definition of the difficult airway, but the American Society of Anesthesiologists (ASA) Task Force defines a difficult airway as “the clinical situation in which a conventionally trained anesthesiologist experiences difficulty with mask ventilation, difficulty with tracheal intubation, or both.” The ASA suggests using four descriptors of difficult airway events: difficult face mask ventilation (not possible to provide face mask ventilation), difficult laryngoscopy (multiple attempts, unable to visualize any portion of the vocal cords during conventional laryngoscopy), difficult tracheal intubation (requiring multiple attempts), and failed intubation (unable to secure placement of the tracheal tube after multiple attempts). The Task Force further notes that the “difficult airway [represents] a complex interaction between patient factors, the clinical setting, and the skills and preferences of the practitioner.” They advise that any patient who may require airway support or airway intervention should have an airway evaluation. Patients undergoing a procedure under local or regional anesthesia should also have an airway assessment in case of local anesthetic toxicity, high block, anaphylaxis, or as a requirement for general anesthesia because of patient, surgical, or block complications. There is no defined preoperative airway assessment in practice guidelines. Any preoperative airway assessment should involve obtaining a detailed history, highlighting any conditions associated with airway difficulties such as ankylosing spondylitis or obstructive sleep apnea. It should also identify previous surgery or radiotherapy to the head, neck, or mediastinum and include interactive bedside tests to note the cricothyroid membrane’s accessibility. Examining the neck for potential ease of emergency surgical airway should also be included in the preoperative assessment. The ASA Practice Guidelines for Management of the Difficult Airway reviews some of the common findings of an anticipated difficult airway. There is insufficient published evidence to evaluate the predictive value of multiple features of an airway physical examination versus single features in predicting a difficult airway. Observational studies of nonselected patients report associations between certain anatomic features and the likelihood of a difficult airway. Additionally, interactive screening tools for identifying difficult airways have variable sensitivity ( Table 19.1 ). Nevertheless, their inclusion is beneficial to create a comprehensive airway assessment. ^{, ,} Both the ASA Practice Guidelines for Management of the Difficult Airway and the Difficult Airway Society (DAS) guidelines provide instructions for managing the difficult airway in general and in specific situations, such as failed intubation or “can’t intubate can’t ventilate” scenarios. ^,

Many procedures are amenable to regional or neuraxial anesthesia as the primary anesthetic, including orthopedic limb cases, lower abdominal surgeries, and gynecologic and urologic procedures. Particularly in obstetric care, neuraxial techniques are favored for lower section cesarean sections (CS), even with the knowledge that there is an increased risk for difficult airway in obstetric patients. Regional anesthesia may be an attractive option for some clinicians when faced with a patient with anticipated difficult intubation who is scheduled for an appropriate surgery and does not have other contraindications to regional anesthesia. If conversion to general anesthesia is required, however, patient positioning, a surgical procedure in progress, less space, a decompensating patient, and increased stress may present more problems to an already difficult situation. Some clinicians are quick to criticize the role of regional anesthesia in patients with difficult airways as the primary anesthetic. They advocate that, in the anticipated difficult airway, the patient’s airway must be electively controlled at the beginning of the case. Regional anesthesia should only be an adjunct in a combined regional–general technique.

This chapter reviews the evidence supporting the decision to initiate a regional or general anesthetic in patients with anticipated difficult airways scheduled for a surgical procedure. Patients in whom difficulty with airway management is not anticipated preoperatively and patients undergoing surgical procedures not amenable to regional anesthesia alone (e.g., intrathoracic or intracranial surgery) are not addressed in this chapter.