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  • Title: [Efficiency of a mobile oxygen concentrator for mechanical ventilation in anesthesia. Studies with a metabolic lung model and early clinical results].
    Author: Rathgeber J, Züchner K, Kietzmann D, Kraus E.
    Journal: Anaesthesist; 1995 Sep; 44(9):643-50. PubMed ID: 7485926.
    Abstract:
    Oxygen (O2) for clinical application is generally provided from either a central gas supply via a hospital pipeline system or is delivered to the working place in cylinders as compressed gas. An alternative source is the one-site generation of O2 from air using O2 concentrators based on molecular sieve technology. Whereas O2 concentrators for anaesthesia in remote areas or underdeveloped countries are wide-spread, in Germany their use is common in neither hospitals nor anaesthesiological practice. The maximum O2 content produced by concentrators is 96% with about 4% argon (Ar) and minimal amounts of nitrogen and other noble gases. The total O2 production is systematically limited, and therefore, the delivered concentration decreases with higher flows. There is also a potential possibility of Ar accumulation in rebreathing anaesthesia systems with reduced fresh gas flow. We investigated the efficiency and potential disadvantages of using O2 concentrators in anaesthesia and the influence of Ar on the accuracy of anaesthetic gas monitors. METHODS. The efficiency of the concentrator was characterised as O2 concentration depending on delivered gas flow. The degree of Ar accumulation in rebreathing anaesthesia systems was obtained with an O2-consuming and CO2-producing metabolic lung model consisting of a water-cooled burning chamber with an adjustable gas jet. The expiratory CO2 content was set to approximately 7%, representing an O2 consumption of 350 ml/min while ventilating the model with 500 ml tidal volume and 10 breaths/min. The inspiratory O2 concentration was adjusted to 35% or 70%; the fresh gas flow was set to 0.5 or 1 l/min. The accuracy of different types of anaesthesia monitors for O2, CO2, volatile anaesthetics, and nitrous oxide in the presence of Ar was checked in comparison with data obtained with a mass spectrometer. To evaluate the usefulness of O2 concentrators for anaesthetic practice, the function of a respirator-concentrator unit was investigated in clinical routine for 8 weeks. RESULTS. The efficiency of the concentrator is flow-rate dependent: O2 concentrations higher than 90% are only achieved with flow rates below 5 l/min and decrease to values lower than 50% at 12 l/min or more. Ar accumulation occurred in rebreathing circuits but exceeded values higher than 10% only under minimal-flow conditions (fresh gas flow 0.5 l/min). Ar did not influence the accuracy of common anaesthetic gas monitors. In clinical practice, the performance of anaesthesia using O2 from an O2 concentrator generated no additional problems. CONCLUSIONS. For the future, the use of O2 concentrators for anaesthesia seems to be a practicable alternative to compressed O2 from cylinders. The main application could be in small operating units or anaesthesia practices. The method is safe and without additional risk of hypoxia, even in rebreathing systems and closed circuits, when the O2 concentration in the inspired gas is measured.
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