Loose adhesive in anaesthetic circuit

Abstract

During a routine anaesthetic machine check we found there was a leak between the common gas outlet and the patient end of the circuit (which included a circle absorber). All the connections were checked and tightened but the leak persisted and a test lung failed to inflate. On disconnecting the scavenging system attached to the APL valve we found that all the gases were exiting through it. Fully opening or closing the APL valve made no difference and we decided that the fault was with the APL valve. On inspecting the APL valve our Medical Physics staff found that there was some soft plastic material obstructing the diaphragm of the valve (Fig. 3) causing it to malfunction. It was suggested that the material was some excessive adhesive used to join the hard 22 mm plastic connector of the anaesthetic circuit tubing to the corrugated soft plastic. In this case the adhesive had broken free and become trapped in the APL valve. Further discussion with the Medical Physics staff revealed that a similar incident had occurred a few months previously, but they had been unable to identify the source of the plastic. A further incident came to light in a neighbouring hospital within NHS Highland, discovered by a service engineer during routine maintenance. Scottish Healthcare Supplies and the manufacturers of the anaesthetic circuit tubing (Armstrong Medical Ltd, Coleraine, N. Ireland) were contacted. All our stock of this particular type of circuit (A-100 anaesthetic circle absorber/breathing circuit) was withdrawn and replaced with non-bonded corrugated tubing as an interim measure, while further investigations and monitoring were undertaken by the company. However, customers outside the UK, constituting some 90% of total output, continue to be supplied with the suspect circuit. Loose adhesive trapped in APL valve. Thank you for the opportunity to reply to Dr Barker's observations. In the original hospital complaint, the debris found in the APL valve was referred to as a small piece of plastic and, indeed, this is how the material is described in Dr Barker's letter. The source of this debris could not be accurately determined due to the number of potential origins of such material, nor was the debris ever conclusively identified as adhesive from the Armstrong circuit. If the assumption is made that this debris was, indeed, a small, disc-shaped piece of adhesive, the likelihood of such a piece of material occluding gas flow must be considered to be low. In any event, inhalation or ingestion of this material would not be possible given the use of a patient-end bacterial and viral resistant breathing filter as per Association of Anaesthetists of Great Britain and Ireland guidelines. For such material to be present in the APL valve it would have to detach from the inner surface of the tubing or connector, negotiate a tortuous route through the head of the absorber without causing an obstruction and, presumably carried by the gas flow, become lodged in the APL valve. Its ability to cause a fully closed spring-loaded APL valve to remain open and vent gas should be further evaluated along with other possible reasons for valve malfunction. Despite the inconclusive nature of our findings, and the fact that many thousands of circuits of similar construction were sold globally by Armstrong Medical in the previous 12 months with no reports of similar occurrences, immediate preventative action was taken as described in Dr Barker's letter. In addition to this, due to the necessity of using adhesive in this particular design of circuit, an improved adhesive is now used on all such circuits. We have received no reports of any similar occurrences during the 10+ years of clinical use of our smooth bore circuits.