Airway Management in Ambulatory Anesthesia

Greta Gormley 0 Stephen Mannion 0 0 G. Gormley S. Mannion (&) Department of Anaesthesiology , South Infirmary, Victoria University Hospital , Old Blackrock Road, Cork, Ireland Ambulatory surgery numbers are rising in the United States at a rapid pace. Between 1996 and 2006, procedures carried out in free-standing surgical centers rose by 300 %. Airway management is a key factor in time management, patient safety, and cost-effectiveness. For the anesthesiologist practicing in a free-standing or officebased unit, patient selection and preparation for all eventualities are essential. A combination of traditional skills and advances in technology and anesthetic research are discussed to outline what we believe is a guide to safe anesthetic practice and airway management in the ambulatory setting. Pre-assessment of the patient, the management of the uncomplicated airway, and management of the anticipated and unanticipated difficult airway are discussed in this article. - Ambulatory anesthesia is becoming increasingly more common worldwide as the result of advancing surgical technology, improved peri-operative care, and rising financial pressure. It is associated with improved patient quality of life [1]. In the United States of America (USA), ambulatory surgery can involve a patients admission for 23 h or less. All these factors combined have resulted in procedures with previously protracted hospital stays (e.g., thyroidectomy and total knee arthroplasty) being carried out in an ambulatory setting [2]. Ambulatory surgery may occur in one of three settings: (1) a day surgery unit as part of a large hospital, (2) a stand-alone ambulatory unit, or (3) an office-based practice. In the two latter environments, the anesthesiologist is working independently and may not have access to help or the necessary facilities should the unanticipated occur. In the USA in 2006, there were 34.7 million visits for ambulatory surgery, 19.9 million were to hospitals, and 14.9 million occurred in freestanding ambulatory surgery centers. In the decade between 1996 and 2006, there was a 300 % rise in visits to free-standing ambulatory centers [3]. There are many anesthetic factors necessary for safe and successful ambulatory surgery. Airway management is a key element. In the ambulatory surgery setting, patient turn-over is paramount. Rapid awakening and extubation allow for earlier operating room (OR) exit and shorter post-anesthesia care unit (PACU) stay. As we will see later, the choice of airway contributes to these parameters. The correct choice of anesthetic technique including airway, therefore, plays a pivotal role in maintaining the momentum required of ambulatory surgical lists. Airway management is also vital for patients both with anticipated and unanticipated difficult airways. Preassessment prior to anesthesia and surgery allows assessment of the patients airway and previous airway history thus guiding the anesthesiologists management throughout the peri-operative period. Finally, airway management of the unanticipated difficult airway in the ambulatory setting is a significant concern to the anesthesiologist, especially those practicing in stand-alone facilities. This article will explore and discuss these elements pre-assessment, day-to-day management, management of the anticipated and unanticipated difficult airwayand provide some recommendations on airway management in the ambulatory setting. The choice of patient for the ambulatory surgery setting is important. Patients with multiple co-morbidities may be found to be unsuitable for the ambulatory setting and must be excluded accordingly [4], [5]. Patients with elevated body mass index (BMI), a history of obstructive sleep apnea (OSA), and patients with a history of chronic obstructive pulmonary disease (COPD) are particularly pertinent co-morbidities with regard to predicting difficulties in airway management and difficulties in intubation and ventilation as well as extubation [4], [6, 7]. Patients with a history of head and neck cancer and in particular previous treatment with surgery or radiotherapy carry a high risk of failed intubation [8]. Pre-assessment allows the anesthesiologist to form an anesthetic plan and involves the patient in these decisions. There are multiple scoring systems, both new and more traditional (Table 1) for grading the airway. These can be useful tools, but none are without limitation. The Modified Mallampati Score is one of the commonest used classifications but should be used in combination with other methods of pre-operative airway assessment [9]. When used as a single predictor, it fails in detection of the difficult airway in up to 35.4 % of patients [10, 11]. Other methods of airway assessment such as thyromental distance, mouth opening, cervical spine movement, body habitus, BMI, and the Wilson Score (a score of 0-2 for each: weight; head and neck movement; lower jaw protrusion; receding mandible; prominent Table 1 Airway Pre-assessment overbite, with a maximum score of 10) provide us with an overall picture, but all carry significant weaknesses in terms of sensitivity and specificity [7, 12]. Some studies do show that the best predictor, when using the classical assessments of difficult intubation, is a combination of Modified Mallampati Score and thyromental distance assessment [7]. However, this still only has a specificity of 87 % with a very low sensitivity of 36 %. Newer computer-assisted models for prediction of difficult airway are promising [12] as well as more novel approaches such as sublingual ultrasound [13] are being piloted but are still in their infancy and cannot yet be recommended for everyday clinical ambulatory practice. These scoring systems are for predicting difficult laryngoscopy and therefore possible difficult intubation. For anesthesiologists, the fall back safe position for oxygenation is mask ventilation. Anesthesiologists need to be aware that this fall back position may fail even if intubation is not being considered for their patient. Kheterpal and colleagues reviewed 53,041 attempts at mask ventilation [14]. They found a 0.15 % incidence of failed mask ventilation with predictive factors being male sex, OSA, Mallampati 3 or 4, presence of a beard, or neck radiation changes. A further study of 176,679 cases of mask ventilation and attempted laryngoscopy demonstrated difficult mask ventilation and difficult laryngoscopy in 698 patients (0.4 %) [15]. One patient required emergency cricothyrotomy. Importantly, over 89 % were successfully intubated by another operator using direct laryngoscopy (DL), DL plus a bougie introducer, or using a videolaryngoscopy (23.4 %). Other predictive factors of both difficult mask ventilation and DL were age: 46 yr or more, BMI: 30 or more, neck mass, limited thyromental distance, presence of teeth, thick neck, limited cervical spine mobility, and limited jaw protrusion [15]. As can be seen, difficult mask ventilation com (...truncated)