Kinking of disposable anaesthetic circuits

Abstract

During an anaesthetic for hand surgery, the patient's lungs were ventilated via a laryngeal mask airway, using a Flextube™ Anaesthetic Circle Systems (Intersurgical Ltd, Wokingham, UK) to deliver the anaesthetic gases. Fifteen minutes into the procedure, a sudden increase in the inspiratory airway pressure was noticed as the ventilator started to alarm and attempts at manual ventilation proved to be difficult. Despite tracheal intubation, attempts at manual ventilation continued to be difficult. A new anaesthetic circuit was obtained and the obstruction disappeared. The anaesthetic circuit tubing had been secured with a Bristol board with a short loop of the inspiratory tube hanging underneath the board. This loop of the tube was found to be kinked, although the kink was not immediately visible when initially inspected from above. Closer inspection revealed that the kink had occurred at a junction of a straight segment of the tube with the corrugated one. The Flextube has been used widely during anaesthesia for around 15 years. These tubes and their congeners characteristically have straight segments (‘cuffs’) occurring at regular intervals of 40 cm. Although breathing tubes are at a risk of kinking if bent acutely, the corrugated tubes tend to resist kinking compared with straight ones when bent gently. The straight segments and their junctions with the adjacent corrugated segments of the Flextube, however, seem to be particularly vulnerable to kinking (Fig. 2). The reason for the sudden kinking of the tube remains unclear. It is possible that the kink occurred due to an inherent design weakness of the junction of straight segment with the corrugated section, presumably as the tubes warmed up during the procedure. Flextube™ Anaesthetic Circle System tube showing kinking at a junction of the straight and corrugated segments. The closely placed straight segments such as those found in the Flextube appear to be neither necessary nor safe. These tubes were originally designed to allow them to be easily cut to the desired lengths. It would therefore appear wise to switch to tubes which do not bear such straight segments. This will, hopefully, reduce the risk of kinking when anchoring and negotiating bends. According to the manufacturers this is the first time that such a problem has been identified. They have put measures in place to phase out the production and distribution of these circuits for use in anaesthesia.