High-flow nasal oxygen has been shown to provide effective pre-oxygenation and prolong apnoeic time during intubation attempts in non-pregnant patients. We aimed to compare pre-oxygenation using high-flow nasal oxygen (30-70 l.min À1 oxygen flow) via nasal prongs with standard 15 l.min À1 oxygen breathing via a tightfitting facemask. Forty healthy parturients were randomly allocated to these two groups, and furthermore each patient underwent the selected pre-oxygenation method with both 3-min tidal volume breathing and 30s tidal breathing followed by eight vital capacity breaths. With 3-min tidal volume breathing, the respective estimated marginal means for high-flow nasal oxygen and standard flow rate facemask pre-oxygenation were 87.4% (95% CI 85.5-89.2%) and 91.0% (95%CI 89.3-92.7%), p = 0.02; with eight vital capacity breaths the estimated marginal means were 85.9% (95%CI 84.1-87.7%) and 91.8% (95%CI 90.1-93.4%, p < 0.0001). Furthermore, high-flow nasal oxygen did not reliably achieve a mean end-tidal oxygen concentration ≥ 90% compared with the standard flow rate facemask. In this physiological study, high-flow nasal oxygen pre-oxygenation performed worse than standard flow rate facemask pre-oxygenation in healthy term parturients.

Summary Using biased‐coin sequential allocation, we sought to determine the effective time interval in 90% of healthy parturients to achieve a target endpoint end‐tidal oxygen of ≥ 90% using standard flow rate facemask and high‐flow nasal oxygen. Eighty healthy parturients were randomly assigned to standard facemask (n = 40) or high‐flow nasal oxygen (n = 40) groups; half of the parturients in the high‐flow nasal oxygen group also used a simple no‐flow facemask to minimise air entrainment. The effective time interval for 90% of parturients to achieve the target endpoint for standard facemask was 3.6 min (95%CI 3.3–6.7 min), but could not be estimated for the high‐flow nasal oxygen groups with or without an additional simple facemask, as eight minutes was insufficient to achieve the target endpoint for 55% and 92% of parturients, respectively. Furthermore, after three minutes, the target endpoint was reached by 71% in the standard facemask group vs. 0% in the high‐flow nasal oxygen groups. After four minutes, the target endpoint was reached by 100% in the standard facemask, 80% in the high‐flow nasal oxygen with simple facemask and 67% in the high‐flow nasal oxygen groups. Beyond four minutes, there was no improvement in pre‐oxygenation success using high‐flow nasal oxygen. In conclusion, under the conditions of our study, the effective time interval for 90% of parturients to achieve an end‐tidal oxygen ≥ 90% for standard flow rate facemask was estimated to be 3.6 min, but could not be estimated for high‐flow nasal oxygen groups even after eight minutes.

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(Anaesthesia. 2019;75:450–456) While preoxygenation is an important component of safe general anesthesia, it is often suboptimal for obstetric patients. This is due to several factors including air entrainment even with a tight-fitting mask, the need for rapid delivery of the fetus in many situations, and human factor issues. For obstetric patients, an end-tidal oxygen concentration (EtO2) ≥90% is recommended before initiating rapid sequence induction and tracheal intubation. The standard practice for preoxygenation in this population is usually either 3 minutes of tidal volume breathing or 8 vital capacity breaths with facemask administration of 100% oxygen at 15 L/min. Growing in popularity for nonobstetric patients, including children, is high-flow nasal oxygen (HFNO) to increase the time to desaturation during induction of general anesthesia; however, literature on HFNO for obstetric patients is sparse. This study aimed to determine whether preoxygenation with HFNO (30 to 70 L/min oxygen flow) via nasal prongs is as effective as the recommended preoxygenation using standard 15 L/min oxygen administered via a tight-fitting facemask in obstetric patients.

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