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O.3 High-flow humidified nasal oxygen versus facemask oxygen for preoxygenation of pregnant women: A prospective randomised controlled crossover study
International Journal of Obstetric Anesthesia ; 46, 2021.
Article in English | EMBASE | ID: covidwho-1333478
ABSTRACT

Introduction:

Airway management guidelines recommend the preoxygenation of obstetric patients to an end-tidal oxygen (etO2) concentration of 90% or more prior to general anaesthesia. A previous study showed that despite a plausible role for high-flow humidified nasal oxygen (HFNO) in this context, only 60% of participants achieved this target after t hree minutes of HFNO.1 This was vastly lower than reported rates with face mask (FM) oxygen. We conducted a randomised controlled crossover trial to determine if HFNO is non-inferior to FM oxygen for increasing etO2 concentration after simulated preoxygenation of women in late pregnancy (gestational age [Formula presented]6 weeks).

Methods:

After ethics approval, trial registration and consent, 70 women underwent simulated preoxygenation protocols with HFNO and FM oxygen sequentially. They were randomised to receive HFNO first then FM oxygen or vice versa. Baseline variables were measured before each protocol including etO2 concentration to ensure adequate oxygen washout between protocols. Protocols were three minutes long and conducted with the women in a ramped position and left lateral tilt. HFNO was delivered at highest tolerable flow rate with a maximum of 70 L/min and FM oxygen was delivered at 10 L/min. The primary outcome was first etO2 concentration after each protocol with a chosen non-inferiority margin of 5%. Recruitment occurred prior to COVID-19 pandemic restrictions.

Results:

70 women were randomised. 62 women completed the study protocols without complications. Eight women were excluded due to technical faults or incomplete protocols. Participant characteristics were age (mean ± SD, 34.7 ± 4.6 years) and body mass index (BMI) (median (IQR), 28.5 (26.6–32.4 kg/m2). First etO2 concentration after HFNO protocol was non-inferior to first etO2 concentration after FM oxygen protocol (mean difference, 1.45;95% CI, 0.19–2.72;two-tailed [Formula presented]value, 0.025). 71% of participants achieved first etO2 concentration of [Formula presented]0% after the HFNO protocol versus 43.5% after the FM protocol. There was no evidence of correlation between first etO2 concentration after either modality and BMI or gestation. First etO2 concentration after HFNO was weakly correlated to percentage of time of mouth closure (Pearson’s coefficient, 0.287). First etO2 concentration after FM oxygen was moderately correlated to respiratory rate in the final protocol minute and minute ventilation (Pearson’s coefficient, 0.426 and 0.339 respectively).

Discussion:

HFNO was non-inferior to FM oxygen for increasing etO2 concentration after simulated preoxygenation of women in late pregnancy. These results suggest that HFNO may be a suitable alternative to FM oxygen for preoxygenation of pregnant women prior to general anaesthesia. Disclosure Fisher & Paykel Healthcare provided equipment for this trial.

Full text: Available Collection: Databases of international organizations Database: EMBASE Type of study: Experimental Studies / Observational study / Prognostic study / Randomized controlled trials Language: English Journal: International Journal of Obstetric Anesthesia Year: 2021 Document Type: Article

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Full text: Available Collection: Databases of international organizations Database: EMBASE Type of study: Experimental Studies / Observational study / Prognostic study / Randomized controlled trials Language: English Journal: International Journal of Obstetric Anesthesia Year: 2021 Document Type: Article