Current hypoxic guards systems fail to maintain the inspired O2 concentration (FIO2) ≥ 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; FDO2 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 FIO2 = 30 to 20 %; (2) time from FIO2 = 20 % to O2 Guard® activation; (3) time from O2 Guard® activation to FIO2 = 25 %; (4) FGF and FDO2 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 FIO2 < 21 % was 100 % within the 1–2 L min−1 FGF range. The O2 Guard® was activated within 20 s after FIO2 became 20 %, except in one patient where FIO2 oscillated between 20 and 21 %. FDO2 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). FIO2 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.
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Conflict of interest
The authors declare that they have no conflict of interest, but Jan Hendrickx received lecture support, travel reimbursements, equipment loans, consulting fees and/or meeting organizational support from a number of companies involved with inhaled agent delivery (alphabetically): AbbVie, Acertys, Air Liquide, Allied healthcare, Armstrong Medical, Baxter, Draeger, GE, Hospithera, Heinen und Lowensein, Intersurgical, Maquet, MDMS, MEDEC, Micropore. Molecular, NWS, Philips, Quantum Medical. The FLOW-i tested in this study has been provided by Maquet on a temporary basis.
Jan Hendrickx, Sofie De Cooman, Rik Carette, Philip Peyton, and Andre De Wolf are members of the NAVAt group.
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Ghijselings, I.E., De Cooman, S., Carette, R. et al. Performance of an active inspired hypoxic guard. J Clin Monit Comput 30, 63–68 (2016) doi:10.1007/s10877-015-9684-9
- Machine standards
- Hypoxic guard system
- Hypoxic mixtures