Although “awake FOI” seems to be an ideal regime for managing a “difficult airway” in patients with high CICV-risk and severe comorbidities, clinical practice has shown that some sedation is needed by most patients. However, the use of intravenous drugs may lead to over-sedation with airway obstruction, apnea, and a lack of patient cooperation. Thus, the ideal sedation regime for FOI in these patients is still controversial. In our study, all patients had a relevant risk for a CVCI-scenario and relevant comorbidities. In all 29 procedures, the patients breathed spontaneously during FOI.
The use of SEVO for inhalational induction of anesthesia in children has been common practice for years, and it has also been used in patients with anticipated “difficult airways”. In 1997, Mostafa and Atherton reported about three patients undergoing head and neck surgery who breathed spontaneously during FOI. Studies by Pean et al. and Favier et al. investigated SEVO for FOI in patients with expected “difficult airway,” but they excluded patients with pathologies of the upper airway, reduced muscular tone, expected “difficult ventilation,” symptomatic gastro-esophageal reflux disease, seizure disorder, coagulopathy, or nasal injury.[18, 19] Bonnin et al. compared a target controlled propofol infusion with SEVO for FOIs but excluded all patients with any predictor of a “difficult airway.” Wang et al. investigated the effectiveness and safety of a new approach - the “fast difficult airway evaluation - FDAE-approach” – in 150 patients with anticipated potential difficult mask ventilation or tracheal intubation. Unfortunately they excluded patients with severe airway obstruction, external tracheal compression, or complicated respiratory diseases including asthma or chronic bronchitis. Consequently, an evaluation of the use of SEVO in patients with a high risk for “CICV” was missing, although the results were encouraging. An explanation might be that anesthesiologists are concerned about dose-dependent upper airway collapsibility and pharyngeal dysfunction. [21, 22] However, in this study, all patients breathed spontaneously and adequately throughout FOI (oxygen saturation ≥ 90% during 97% of all FOIs), although we used SEVO at a high concentration.
FOI failed in four patients (14%). This seems like a high failure rate, as other investigators reported failure rates of approximately 1–5%.[5, 7, 23] However, in three patients, the FOI failed because of a blocked nose. An oral FOI would have been possible, but video laryngoscopy was technically feasible and used instead. Front-of-neck access was performed in only one patient (3%). All patients breathed spontaneously until the trachea was intubated. Furthermore, all patients had severe airway pathologies (pharyngeal or laryngeal tumors), and a permanent tracheostomy was performed in 34% of patients. In contrast, Law et al. reported a failure rate of 2%, but only 26% of the patients were scheduled for head and neck surgery, and the reasons for the FOI remained unclear. However, in 22 patients, the FOI failed due to anesthesia-associated problems. Kim et al. published experiences of second-year anesthesiology residents learning nasal FOI. Failure rates were 5% in intravenously sedated patients and approximately 14% in awake patients. In this study, the FOI lasted 9 min on average. This is consistent with results from Pean et al. who reported a median duration of 8.6 min.
Changes in vital parameters during FOI were negligible. One patient suffered from epistaxis which is a typical complication even in healthy probands.[24, 25] In four patients, a moderate bronchial spasm occurred although SEVO is a potent bronchodilator. However, approximately 60% of our patients had COPD. Thus, the frequency of this side effect could have even been higher when using intravenous sedatives. Awareness did not occur, which is expected due to the high SEVO concentrations; this is an advantage against intravenous sedation strategies. [27, 28]
Although not formally assessed, medical staff noticed a smell of SEVO in some cases. This reflects that inhalational inductions are associated with SEVO pollution, and possibly, with anesthetic gas exposure of the medical staff.
Major limitations of this study were its retrospective nature and the small number of FOIs. Therefore, the results must be interpreted with caution. However, we tried to provide evidence for the use of SEVO in high-risk patients.