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Intraoperative awareness due to malfunction of a Siemens 900B ventilator

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A case of intraoperative awareness during a thoracotomy is described. The patient’s recall coincided with an intraoperative period during which a Siemens 900B ventilator and a Siemens 952 isoflurane vaporiser were used. Subsequent assessment of this equipment with an anaesthetic agent analyzer revealed that, at the ventilator settings which had been used, the delivered anaesthetic vapour concentration varied greatly from the vaporizer settings. This problem eventually was traced to a malfunctioning inlet control valve on the ventilator. This complication may have been prevented if the end-tidal anaesthetic concentration had been monitored intraoperatively.


Nous décrivons un cas d’anesthesie insuffisiante non détectée, avec souvenirs des evenements perioperatoire, dûe a une valve d’entrée sur un ventilateur Siemens 900B ne fonctionnant pas. Ce problème aurait pu étre éviter en monitorant la concentration dagent volatile dans les gazs expirés.


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Correspondence to Peter D. Slinger.

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Slinger, P.D., Andrew, W., Scott, C. et al. Intraoperative awareness due to malfunction of a Siemens 900B ventilator. Can J Anaesth 37, 258–261 (1990).

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Key words

  • anaesthesia: depth, awareness
  • complications: awareness
  • equipment: ventilators, malfunction