Background. High-flow nasal oxygen (HFNO) has been shown to benefit oxygenation, ventilation and upper airway patency in a range of clinical scenarios, however its use in spontaneously breathing patients during general anaesthesia has not been described. Spontaneous respiration using i.v. anaesthesia is the primary technique used at our institution for tubeless airway surgery. We hypothesized that the addition of HFNO would increase our margin of safety, particularly during management of an obstructed airway. Methods. A retrospective observational study was conducted using a SponTaneous Respiration using IntraVEnous anaesthesia and High-flow nasal oxygen (STRIVE Hi) technique to manage 30 adult patients undergoing elective laryngotracheal surgery. Results. Twenty-six patients (87%) presented with significant airway and/or respiratory compromise (16 were stridulous, 10 were dyspnoeic). No episodes of apnoea or complete airway obstruction occurred during the induction of anaesthesia using STRIVE Hi. The median [IQR (range)] lowest oxygen saturation during the induction period was 100 [99–100 (97–100)] %. The median [IQR (range)] overall duration of spontaneous ventilation was 44 [40–49.5 (18–100)] min. The median [IQR (range)] end-tidal carbon dioxide (ETCO2) level at the end of the spontaneous ventilation period was 6.8 [6.4–7.1 (4.8–8.9)] kPa. The mean rate of increase in ETCO2 was 0.03 kPa min−1. Conclusions. STRIVE Hi succeeded in preserving adequate oxygen saturation, end-tidal carbon dioxide and airway patency. We suggest that the upper and lower airway benefits attributed to HFNO, are ideally suited to a spontaneous respiration induction, increasing its margin of safety. STRIVE Hi is a modern alternative to the traditional inhalation induction.

BACKGROUND: High-flow nasal oxygen (HFNO) is an emerging technology that has generated interest in tubeless anesthesia for airway surgery. HFNO has been shown to maintain oxygenation and CO2 clearance in spontaneously breathing patients and is an effective approach to apneic oxygenation. Although it has been suggested that HFNO can enhance CO2 clearance during apnea, this has not been established. The true extent of CO2 accumulation and resulting acidosis using HFNO during prolonged tubeless anesthesia remains undefined. METHODS: In a single-center trial, we randomly assigned 20 adults undergoing microlaryngoscopy to apnea or spontaneous ventilation (SV) using HFNO during 30 minutes of tubeless anesthesia. Serial arterial blood gas analysis was performed during preoxygenation and general anesthesia. The primary outcome was the partial pressure of CO2 (Paco 2) after 30 minutes of general anesthesia, with each group compared using a Student t test. RESULTS: Nineteen patients completed the study protocol (9 in the SV group and 10 in the apnea group). The mean (standard deviation [SD]) Paco 2 was 89.0 mm Hg (16.5 mm Hg) in the apnea group and 55.2 mm Hg (7.2 mm Hg) in the SV group (difference in means, 33.8; 95% confidence interval [CI], 20.6–47.0) after 30 minutes of general anesthesia (P < .001). The average rate of Paco 2 rise during 30 minutes of general anesthesia was 1.8 mm Hg/min (SD = 0.5 mm Hg/min) in the apnea group and 0.8 mm Hg/min (SD = 0.3 mm Hg/min) in the SV group. The mean (SD) pH was 7.11 (0.04) in the apnea group and 7.29 (0.06) in the SV group (P < .001) at 30 minutes. Five (55%) of the apneic patients had a pH <7.10, of which the lowest measurement was 7.057. No significant difference in partial pressure of arterial O2 (Pao 2) was observed after 30 minutes of general anesthesia. CONCLUSIONS: CO2 accumulation during apnea was more than double that of SV after 30 minutes of tubeless anesthesia using HFNO. The use of robust measurement confirms that apnea with HFNO is limited by CO2 accumulation and the concomitant severe respiratory acidosis, in contrast to SV. This extends previous knowledge and has implications for the safe application of HFNO during prolonged procedures.

We conducted a retrospective audit of 285 adult elective microlaryngoscopy cases in our institution over a three-and-a-half year period. Conventional anaesthesia with intubation and mechanical ventilation was the most common technique, used in 71% of cases. Tubeless spontaneous ventilation during total intravenous anaesthesia with a target-controlled infusion of propofol (SVTCI) was the most common alternative. Spontaneous ventilation with target-controlled infusion was used for 79 (27.7%) anaesthetic inductions and was continued through the maintenance phase for 60 patients (21.1%). Jet and intermittent ventilation were both used infrequently (1% each). The most common SVTCI technique since 2013 involved adjusting the target-controlled infusion rate during induction using a formula we developed based on intermittently increasing the target rate, such that the predicted plasma concentration minus the predicted effect site concentration was maintained at 1 μg/ml. We found that this method maintained ventilation during induction more reliably than other SVTCI strategies, and was associated with fewer complications than other spontaneous ventilation techniques or mechanical ventilation: it was associated with only one (3.1%) failed induction and one (3.9%) episode of apnoea. Jet ventilation was associated with the most severe complications, including two cases of barotrauma.

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