Performance of an active inspired hypoxic guard

Abstract

Current hypoxic guards systems fail to maintain the inspired O₂ concentration (F_IO₂) ≥ 21 % across the entire fresh gas flow (FGF) range when a second carrier gas is used (N₂O or air). We examined the performance of the Maquet O₂ Guard^®, a smart hypoxic guard that increases O₂ delivery if an inspired hypoxic mixture is formed. After obtaining IRB approval and informed consent, 12 ASA I-II patients were enrolled. During anesthesia with sevoflurane in O₂/air, the O₂ Guard^® was tested by administering O₂/air at the following delivered hypoxic guard limits [expressed as (total FGF in L min⁻¹; F_DO₂ in %)] for 4 min each: [0.3;67], [0.4;50], [0.6;34], [0.8;25], [1.0;21], [1.2;21], [1.5;21], [2;21], [3;21], and [5;21]. The following data were collected: (1) time from F_IO₂ = 30 to 20 %; (2) time from F_IO₂ = 20 % to O₂ Guard^® activation; (3) time from O₂ Guard^® activation to F_IO₂ = 25 %; (4) FGF and F_DO₂ used by the O₂ Guard. If SpO₂ was <90 % for 10 s or longer at any time, the patient was excluded. Three patients were excluded for low SpO₂. The incidence of F_IO₂ < 21 % was 100 % within the 1–2 L min⁻¹ FGF range. The O₂ Guard^® was activated within 20 s after F_IO₂ became 20 %, except in one patient where F_IO₂ oscillated between 20 and 21 %. F_DO₂ was increased to 60 % and FGF to 1 L min⁻¹ (the latter only if it was lower than 1 L min⁻¹ prior to activation of the O₂ Guard). F_IO₂ increased to 25 % within 55 s after O₂ Guard activation in all patients. The O₂ Guard^®, an active inspired hypoxic guard, rapidly reverses and limits the duration of inspired hypoxic episodes when the delivered hypoxic guard fails to do so.