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High-flow humidified nasal preoxygenation in pregnant women: a prospective observational study - 17/1/2019

Br J Anaesth 2019; 122: 86-91


Obstetric airway guidelines recommend preoxygenation in preparation for general anaesthesia to achieve end-tidal oxygen concentrations (etO2) of =90%, and mention the potential use of high-flow humidified nasal oxygen (HFNO). These authors investigated the new HFNO technique (Optiflow™) in term pregnant women.


A total of 73 term participants underwent a 3-minute HFNO protocol (30 L/min for 30 seconds, and then 50 L/min for 150 seconds). The etO2 was assessed for the first four breaths after simulated preoxygenation. The primary outcome was the proportion who achieved etO2 =90% for the first expired breath. The secondary outcomes were the proportion who achieved etO2 =80%; fetal heart rate before and after the test; the association of body mass index (BMI) to etO2 achieved with preoxygenation; and comfort levels of, and preference for, nasal and face mask preoxygenation.



The proportion with first expired breath etO2 =90% was 60% (95% confidence interval [CI] 54% to 66%) and etO2 =80% was 84% (95% CI 80% to 88%). There was no change in fetal heart rate from before to after the test (p=0.34). There was a negative association of BMI to etO2 achieved with preoxygenation (Pearson correlation –0.26; p=0.027). There was no difference in comfort scores between nasal cannula and face mask (p=0.40). Forty-one (56%; 95% CI 35% to 47%) women preferred the nasal cannula to the face mask.



The authors conclude that, using this protocol, HFNO is inadequate to preoxygenate term pregnant women. They advise that, despite encouraging results in the literature reporting results in non-pregnant women, further work is required before justifying its use in pregnant women.

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