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

Abstract

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.

Gastric insufflation and high‐flow nasal oxygenation in obstetric patients: a reply

“…However, we learned from our two recent studies that even when instructed, most parturients were unable to tolerate high‐flow nasal oxygen of 50–70 l.min ‐1 with closed mouth breathing 100% of the time . In fact, we found that only 37.5% of parturients were able to breathe high‐flow nasal oxygen with their mouths closed . Expiratory pharyngeal pressure is significantly lowered when breathing with the mouth open .…”

“… found high‐flow nasal oxygen at 50 and 70 l.min ‐1 resulted in nasopharyngeal airway pressures as high as 6.8 and 10.1 cmH 2 O, respectively, in healthy volunteers when breathing with their mouth closed. However, we learned from our two recent studies that even when instructed, most parturients were unable to tolerate high‐flow nasal oxygen of 50–70 l.min ‐1 with closed mouth breathing 100% of the time . In fact, we found that only 37.5% of parturients were able to breathe high‐flow nasal oxygen with their mouths closed .…”

“…We thank Dr Parida for his interest in our study and for drawing attention to the potential impact of high‐flow nasal oxygen on gastric insufflation and functional residual capacity. First, to clarify our original study finding, we did not find that it took more than 8 min to achieve the primary outcome of end‐tidal oxygen concentration ≥ 90% in 90% of parturients with high‐flow nasal oxygen pre‐oxygenation.…”

High‐flow nasal oxygen for pre‐oxygenation in obstetrics

“…I compliment Au et al. for their recent publication on the role of high‐flow nasal oxygenation in obstetric patients . They call attention to the fact that it took more than 8 min for 90% of parturients to attain an end‐tidal oxygen saturation of ≥ 90%.…”

The power of marginal gains in obstetric anaesthesia

“…The recent focus of attention on preventing hypoxia during induction of general anaesthesia has been on defining a role for high-flow humidified oxygen, but benefits of this equipment as a preoxygenation tool in obstetric patients have not been demonstrated. 7,8 Considering the cost implications and lack of evidence, it would be unjustified presently to recommend this as a standard of care in resource-constrained settings. However, several simple low-cost strategies should always be undertaken when providing general anaesthesia to an obstetric patient.…”