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Transient sevoflurane output failure in a Datum vaporiser with concurrent foreign body.

We recently encountered a transient loss of output from a Blease Datum sevoflurane vaporiser (Spacelabs, Issaquah, USA) during surgery for insertion of prostatic brachytherapy rods. Following an uncomplicated intravenous induction, sevoflurane was introduced at 3% via an Aestiva/5 anaesthetic machine (Datex-Ohmeda, GE Healthcare, Bucks, UK). Shortly after the initial normal increase at flows of 4 l/minute, the end-tidal sevoflurane concentration was noted to drop rapidly from 1.6% to 1.1%. We increased the dialled settings. The inspired sevoflurane fraction continued to decrease despite a dialled percentage of up to 8% and oxygen flow of 8 l/minute. Over the next 45 seconds the inspired fraction decreased further to 0.6%. A check of the vaporiser reservoir indicator window showed a small yellow foreign body had appeared (Figure 1). At the same time, the inspired fraction began to rise rapidly, allowing us to decrease gas flows and dialled percentage to the original settings. The foreign body was not present during the preoperative equipment check.

The vaporiser in question is leased by Abbott Australasia Pty Ltd (Botany, NSW), the supplier of sevoflurane. The service agents for the vaporiser are General Anaesthetic Services Australia (Adelaide, SA). When the service agents dismantled the vaporiser, they confirmed that the foreign body, 6x1 mm, was most likely a fragment of plastic material from the cap on a sevoflurane bottle. They reported that it is not uncommon to observe fragments of yellow plastic in similar, but normally functioning, vaporisers returned for routine service. The vaporiser was noted to be under-delivering by 20% across all gas flows, but this did not explain the precipitous decline in inspired gas. Two bench top tests using introduced plastic shavings failed to replicate a sudden drop in output. The vaporiser was also assessed by the manufacturers and found to be functioning within normal tolerance. They found two more plastic shavings and felt these were unrelated to the apparent output failure.

Sevoflurane bottles have a tamper proof cap. When the tamper proof cap is unscrewed for the first time it separates via perforations from a plastic collar. This is a potential source of a foreign body, but there was no obvious defect in the plastic on the bottle most recently used to refill the vaporiser. The Blease Datum vaporiser has an upward pointing port for connection of the sevoflurane bottle, which may promote inadvertent contamination with foreign material. A foreign body may fall in when the filling port cap is removed and be washed in unnoticed as the bottle is connected. In contrast, the Desflurane Tec 6 (Datex-Ohmeda, Wisconsin, USA) has a filling port that faces downward and is then inverted when the bottle is connected.

We were concerned the sudden drop in inspired sevoflurane represented a temporary blockage which resolved when the plastic sliver dislodged to appear in the sight glass. However, on examining a diagram of the vaporiser's internal components it is hard to see how such a small sliver could have interrupted gas flow.


There are no reported cases of vaporiser malfunction caused by a foreign body. Of the few reports of delivery failure, most were detected following the patient's physiological response to lack of anaesthesia (13). Given the short duration of apparent delivery failure in this case, it may have passed unnoticed had it not been for gas analysis and vigilance. Loss of anaesthetic delivery risks awareness and potential patient movement. Decreased inspired volatile concentration is detected only by regular observation of the monitor. Appropriately set volatile concentration alarms may be considered, but these are generally unhelpful during induction and emergence from general anaesthesia. Alternatively, some vaporisers, like the Desflurane Tec 6 have 'no output' alarms that could alert one to failure sooner.

We cannot conclusively state the foreign body caused the output failure. We have considered other causes. Transient entrainment of room air could cause a dilution of sevoflurane but this is unlikely in a ventilated patient. We cannot exclude transient failure of gas analysis, but the pattern of progressive decline in inspired and expired gases and then gradual increase was more in keeping with a temporary output failure. When we have experienced fluctuations in gas analysis previously, they have tended to be sudden and short lived. We would be interested to hear if anyone else has experienced a similar apparent output failure and any possible explanations. However, foreign bodies within vaporisers are not ideal. When filling Datum vaporisers, anaesthetists and technicians should take care to check the port to ensure there are no foreign bodies that could be washed in. Vaporiser designers could consider similar filling strategies to the Desflurane Tec 6 in order to reduce the chance of this problem occurring.




Perth, Western Australia


(1.) Fernando PM, Peck DJ. An uncommon cause of vaporiser failure. Anaesthesia 2001; 56:1009-1010.

(2.) MacLeod DM, McEvoy L, Walker D. Report of vaporiser malfunction. Anaesthesia 2002; 57:299-300.

(3.) Kimatian SJ. With technology comes responsibility: intraoperative failure of an anesthetic vaporizer. Anesthesiology 2002; 96:1533-1534.
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Title Annotation:Correspondence
Author:Penney, J.A.; Hocking, G.; Weightman, W.M.
Publication:Anaesthesia and Intensive Care
Geographic Code:8AUST
Date:Mar 1, 2011
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