[Disconnections in the breathing system]

Abstract

Modern anaesthesia is considered as relatively safe. Nevertheless, incidents happen which result in harm for the patient. Incidents which cause hypoxia are especially grave. One of the most frequent incidents in anaesthesia and intensive care is of this nature: disconnection in the ventilatory apparatus. DEFINITION. Unintentional separation--partial or complete--of two manually connected components in a ventilatory apparatus. INCIDENCE. About 5% of incidents during narcosis are likely to be caused by disconnections in the ventilatory apparatus. CAUSES. Axially directed force of as little as 15 N may cause disconnection. It may result from active or passive movements of the patient, high pressure in the apparatus or unintentional traction on the breathing hoses. Conically moulded couplings are mostly used for connections. The stability of these so-called taper fit connections is decisively determined by the effort and technique of the user when coupling the two components. On the other hand the use of unsuitable materials may lead to an inadequate connection. Another possibility is damage by mechanical, chemical or thermal influences. Additionally, differences from the standard specifications of the components may occur. MOST COMMON SITES. Disconnections are found predominantly (in around 70% of cases) at the connection between the tube connector and the adapter or Y-piece. This joint represents a weak point, especially during surgical treatment in the head and neck region, when it cannot be controlled and in most cases is not accessible by hand because it is covered. CONSEQUENCES. The consequences of disconnection depend on different factors: relaxation of the patient, depth of narcosis, duration and localization of the disconnection, constitution and current oxygenation of the patient. An undetected disconnection may lead to hypoxia within a few minutes and then to irreversible brain damage and finally death. Serious incidents have been decreased in number in recent years by the application of improved monitoring procedures. DETECTION. Measurements of airway pressure, minute volume and expiratory CO2 by capnography ensure rapid detection of disconnections using appropriate adjustments of alarm limits. A disconnection may not be detected by pulse oximetry before a latent period, i.e. after a significant decrease of the oxygenation saturation of the patient. PREVENTION. Standardized specifications exist for technical dimensions of connectors, but "reliability" of connectors has not yet been defined in terms of technical requirements. Disconnection is currently prevented by application of various mechanical methods and devices, not all of which fulfil the conditions required of an ideal system: (1) Simple and fast connection ("single-handed operation"); (2) connection independent of the torsional angle between the two parts; (3)safe connection which cannot be detached unintentionally; (4) 360 degrees torsion possible after connection; (5) tight connection; (6) fast and easy deliberate disconnection; (7) intentional disconnection possible independent of the torsional angle between the two parts; (8) compatibility with conventional systems; (9) user's comfort and convenience (when ventilating with mask, etc.) as good as with conventional systems. DISCONNECTION OR EXTUBATION? There is a heated debate on the theme "disconnection". Some authors suspect that the development of reliable locking connections could lead to an increased frequency of unwanted extubations. To prevent unwanted extubations with consequent harm to patients, some developers propose a mechanical fuse, i.e. a defined site of fracture with an additional adequate monitoring device for reliable detection of disconnections. CONCLUSIONS. There are many approaches to the "disconnection" problem. In principle the problem requires a fundamental decision for each connection in the breathing system: safe prevention of disconnection (lock connection) or reliable mechanical f