Determining the effective pre-oxygenation interval in obstetric patients using high-flow nasal oxygen and standard flow rate facemask: a biased-coin up-down sequential allocation trial.

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.

High-flow nasal oxygen vs. standard flow-rate facemask pre-oxygenation in pregnant patients: a randomised physiological study.

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-1 oxygen flow) via nasal prongs with standard 15 l.min-1 oxygen breathing via a tight-fitting 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.