Editor:
We wish to report a potentially fatal critical incident that occurred during an elective operating theatre list. A similar problem [Reference Webb, Ringrose and Stone1] has been recently highlighted by the MHRA but without the emphasis of its potentially fatal nature (Fault in Draeger Vapor 2000/D-Vapor Vaporizer series with the interlocking device, MDA/2006/030) [2].
This series of vaporizers for isoflurane and sevoflurane has an interlocking safety system consisting of a hole with a nib in the coloured disk on the top of the vaporizer, at 180° to each other. This prevents the locking bar being inserted into the hole unless the vaporizer is turned off. It is known that damage to or loss of this plastic nib can result in two vaporizers being turned on simultaneously [3].
The presence of a unilateral nib at the 5% delivery mark masks the absence of the second nib at the 0% delivery mark due to the nature of the vaporizer position on the anaesthetic machine at the left-hand side (Fig. 1). This machine thus passed the routine AAGBI Recommendations for Checking Anaesthetic Equipment [4].
Figure 1 Damaged nib.
On transfer of the patient to the operating room, initially isoflurane was switched on to 1–2%. The desflurane vaporizer was then mounted as the anaesthetist’s agent of choice and switched on after switching off the isoflurane vaporizer – or so we thought. What happened next is shown in Figure 2. The vaporizer on the left is locked at 5% isoflurane. This was caused when the anaesthetist inadvertently turned the vaporizer dial anticlockwise to switch off instead of in a clockwise direction (i.e. the wrong way) and engaged the interlocking device, which then allowed operation of the desflurane vaporizer. We recognized this mistake a few seconds after it occurred preventing any harm to the patient. The interlocking device required considerable force to disengage from the isoflurane vaporizer.
Figure 2 Isoflurane vaporizer at 5% with interlocking device on and desflurane also switched on at 4%.
Two issues need to be addressed:
1. Awareness of this potential error as the number of general anaesthetics given daily with these agents is large, increasing the chances of a similar episode that might not be corrected so speedily.
2. The manufacturer needs to urgently rectify this problem.
This incident emphasizes the fact that despite repeated checking, errors can and do occur and it is necessary to be vigilant for new errors as our anaesthesia delivery systems become more complicated and modernized. We have informed Draeger and look forward to their comments.
