High-flow humidified nasal preoxygenation in pregnant women: a prospective observational study

Background: Obstetric airway guidelines recommend preoxygenation in preparation for general anaesthesia to achieve end-tidal oxygen concentrations (etO(2)) of >= 90%, and mention the potential use of high-flow humidified nasal oxygen (HFNO). We investigated the new HFNO technique (Optiflow (TM)) in term pregnant women. Methods: Seventy-three term participants underwent a 3 min HFNO protocol (30 L min(-1) for 30 s, and then 50 L min(-1) for 150 s). The etO(2) was assessed for the first four breaths after simulated preoxygenation. The primary outcome was the proportion who achieved etO(2) >= 90% for the first expired breath. The secondary outcomes were the proportion who achieved etO(2) >= 80%; fetal heart rate before and after the test; the association of body mass index (BMI) to etO(2) achieved with preoxygenation; and comfort levels of, and preference for, nasal and face mask preoxygenation. Results: The proportion with first expired breath etO(2) >= 90% was 60% [95% confidence interval (CI): 54-66%] and etO(2) >= 80% was 84% (95% CI: 80-88%). 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 etO(2) 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: 35-47%) women preferred the nasal cannula to the face mask. Conclusions: HFNO using this protocol is inadequate to preoxygenate term pregnant women. Despite encouraging results in the literature reporting results in non-pregnant women, further work is required before justifying its use in pregnant women.