Surgery under apnoeic conditions with the use of high-flow nasal oxygen is novel. Between November 2016 and May 2017, 28 patients underwent tubeless laryngeal or tracheal surgery under apnoeic conditions with high-flow nasal oxygen as the sole method of gas exchange. Patients received total intravenous anaesthesia and neuromuscular blocking agents for the duration of their surgery. The median (IQR [range]) apnoea time was 19 (15-24 [9-37]) min. Four patients experienced an episode of oxygen desaturation to a value between 85% and 90%, lasting less than 2 min in each case. Median (IQR [range]) end-tidal carbon dioxide (ETCO ) level following apnoea was 8.2 (7.2-9.4 [5.8-11.8]) kPa. The mean (SD) rate of ETCO increase was 0.17 (0.07) kPa.min from an approximated baseline value of 5.00 kPa. Venous blood sampling from 19 patients demonstrated a mean (SD) partial pressure of carbon dioxide (P CO ) of 6.29 (0.71) kPa at baseline and 9.44 (1.12) kPa after 15 min of apnoea. This equates to a mean (SD) P CO rise of 0.21 (0.08) kPa.min during this period. Mean (SD) pH was 7.40 (0.03) at baseline and 7.23 (0.04) after 15 min of apnoea. Mean (SD) standard bicarbonate was 26.7 (1.8) mmol.l at baseline and 25.4 (1.8) mmol.l at 15 min. We conclude that high-flow nasal oxygen under apnoeic conditions can provide satisfactory gas exchange in order to allow tubeless anaesthesia for laryngeal surgery.

Apnoeic oxygenation refers to oxygenation in the absence of spontaneous respiration or mechanical ventilation. It has been described in humans for over half a century and has seen a resurgence in interest given its potential to delay oxygen desaturation during airway management, especially with the advent of high-flow nasal cannulae. This narrative review summarises our current understanding of the mechanisms of gas exchange during apnoeic oxygenation and its diverse range of clinical applications, including its use at induction of anaesthesia and for the facilitation of 'tubeless anaesthesia'. Additional discussion covers use in critical care, obese, obstetric and paediatric sub-populations. The article also highlights current research efforts aiming to enhance the evidence base for the use of this technique.

The key healthcare challenge of the coronavirus disease 2019 pandemic is the safe delivery of respiratory support on a large scale. The care of critically ill COVID-19 patients is guided by our knowledge and experience with acute respiratory distress syndrome (ARDS), but this crisis is pushing patients and their clinicians into uncharted territories. One of the key decisions faced by healthcare systems is selecting the appropriate devices for oxygen administration. The use of high-flow nasal oxygen (HFNO) in COVID-19 is the subject of much debate, relating to the benefits and harms that may result for patients and healthcare workers alike.In recent years, HFNO has become a commonly used therapy for patients with acute hypoxaemic respiratory failure. Frat et al. conducted a multicentre randomised controlled trial (RCT) of 310 patients assessing the efficacy of HFNO, non-rebreather facemask or non-invasive ventilation (NIV) in the treatment of type 1 respiratory failure [1]. The primary outcome of tracheal intubation rate was 38% in the HFNO group, 47% in the non-rebreather facemask group and 50% in the NIV group (p = 0.18 for all comparisons). However, the study was only powered to demonstrate an absolute difference of 20% between groups. The hazard ratio for death at 90 days was 2.01 (95%CI 1.01-3.99) with facemask vs. HFNO and 2.50 (95%CI 1.31-4.78) with NIV vs. HFNO. The authors proposed that the lower mortality observed in the HFNO group resulted from the cumulative benefit of a lower tracheal intubation rate in those patients with severe hypoxaemia (P a O 2 :F I O 2 ≤ 200 mmHg), and a slightly lower mortality among intubated patients who were initially treated with HFNO. Rochwerg et al. published a systematic review and meta-analysis comparing HFNO with conventional oxygen therapy in patients with acute hypoxaemic respiratory failure [2]. Nine RCTs involving 2093 patients were reviewed, including the aforementioned Frat et al. study. No difference in mortality was observed in patients treated with HFNO (relative risk (RR) 0.94, 95%CI 0.67-1.31) compared with conventional oxygen therapy. The use of HFNO resulted in a decreased requirement for tracheal intubation (RR 0.85, 95%CI 0.74-0.99) and a lower risk of escalation of oxygen therapy (RR 0.71, 95%CI 0.51-0.98) when compared with conventional therapy. Escalation of oxygen therapy was defined as initiation of non-invasive ventilation or invasive mechanical ventilation in either group, and additionally as crossover to HFNO in the conventional therapy group. The authors declared a low level of certainty to both benefits.The extent to which these outcomes in ARDS populations of undifferentiated aetiology are applicable to COVID-19 patients is unknown. If the above benefits are attainable in this population, then HFNO would warrant consideration as an early method of respiratory support even if the provision of other forms of support was not limited. However, a narrative has emerged that HFNO use should be greatly restricted or even contra-indicated in the treat...

No abstract

High-flow nasal oxygen used before and during apnoea prolongs time to desaturation at induction of anaesthesia. It is unclear how much oxygenation before apnoea prolongs this time. We randomly allocated 84 participants to 3 minutes of pre-oxygenation by one of three methods: 15 l.min -1 by facemask; 50 l.min -1 by high-flow nasal cannulae only; or 50 l.min -1 by high-flow nasal cannulae plus 15 l.min -1 by mouthpiece. We then anaesthetised and intubated the trachea of 79 participants and waited for oxygen saturation to fall to 92%. Median (IQR [range]) times to desaturate to 92% after pre-oxygenation with facemask oxygen, high-flow nasal oxygen only and high-flow nasal oxygen with mouthpiece, were: 309 (208-417 [107-544]) s; 344 (250-393 [194-585]) s; and 386 (328-498 [182-852]) s, respectively, p = 0.014. Time to desaturation after facemask preoxygenation was shorter than after combined nasal and mouthpiece pre-oxygenation, p = 0.006. We could not statistically distinguish high-flow nasal oxygen without mouthpiece from the other two groups for this outcome. Median (IQR [range]) arterial oxygen partial pressure after 3 minutes of pre-oxygenation by facemask, nasal cannulae and nasal cannulae plus mouthpiece, was: 49 (36-61 [24-66]) kPa; 57 (48-62 [30-69]) kPa; and 61 (55-64 [36-72]) kPa, respectively, p = 0.003. Oxygen partial pressure after 3 minutes of pre-oxygenation with nasal and mouthpiece combination was greater than after facemask pre-oxygenation, p = 0.002, and after high-flow nasal oxygen alone, p = 0.016. We did not reject the null hypothesis for the pairwise comparison of facemask pre-oxygenation and high-flow nasal pre-oxygenation, p = 0.14.