• D W Lehmann, K Engelbrecht, and J Radke.
• Klinik für Anästhesiologie und operative Intensivmedizin, Martin-Luther-Universität Halle-Wittenberg.
• Anaesthesist. 1997 Sep 1;46(9):801-4.

AbstractUnnoticed, minor damage to the unidirectional respiratory valves of the Draeger respiratory circuit may lead to intermittent and unpredictable malfunction, resulting in rebreathing and hypercapnia. The damage may be so minor that normal visual and functional test routines may be insufficient to detect it. We report one case of a potential life-threatening malfunction of the inspiratory valve and also propose economical solutions utilizing altered construction, modified machine-check procedures, or a simple instrument that adds only one step to the machine-check procedure. The general problem of minor but functionally important damage to parts of ventilatory equipment--so-called borderline damage--may not be limited to this particular model or manufacturer. Most users of ventilatory equipment believe that equipment that goes through normal check procedures is either fully functional or nonfunctional. In reality, this is not the case. Intermittent malfunctions due to slightly damaged equipment may be missed with normal machine-check procedures. This problem results in a significant but incalculable increased in risk to patients. Because of unclear reproduceability of intermittent malfunctions caused by borderline damage, there also is an increased forensic risk for the anaesthesiologist. The risk of mechanical malfunction might be displaced by software problems in new-generation ventilators in the market.

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