In his letter entitled “With Technology comes Responsibility: Intraoperative Failure of an Anesthetic Vaporizer,”1Dr. Kimatian describes a situation where a Datex-Ohmeda D-Tec “Plus” (Datex-Ohmeda Inc., Madison, WI) vaporizer mounted to a Julian anesthesia workstation (Draeger Medical Inc., Telford, PA) ceased to deliver Desflurane because of the fresh gas decoupling feature of the Julian, which stops fresh gas flow during inspiration. This problem occurred despite certification of an earlier model Desflurane vaporizer (Datex-Ohmeda D-Tec Desflurane vaporizer) with the Julian anesthesia system.
After retesting both of the vaporizers, it was determined that under certain ventilation settings, the D-Tec Plus would indeed cease output because of the fresh gas decoupling feature of the Julian anesthesia system. As a result, Datex-Ohmeda modified the D-Tec Plus software to make it equivalent to the original D-Tec software. Subsequent testing revealed that at higher respiratory rates, it is still possible for fresh gas decoupling to cause the vaporizer to cease output. Draeger has revised the operator's manual to caution against the use of respiratory rates greater than 30 breaths/min when using a D-Tec vaporizer with the Julian in volume ventilation mode. Pressure ventilation and manual ventilation will not affect the Desflurane vaporizer.
Dr. Skimatian is absolutely correct that clinicians should understand the features of anesthesia delivery equipment that might lead to patient injury. Indeed, new anesthesia workstations offer new features and capabilities that require training to be used effectively. It is not clear, however, that in this case such knowledge would have avoided the incident described, because the Julian with fresh gas decoupling had been shown to work with an earlier model Desflurane vaporizer. Although the incident is described as a failure, the vaporizer was actually working as it was designed, that is, to detect when output from the vaporizer ceases. The new model of the vaporizer was more sensitive to cessation of vaporizer output than the earlier model, hence the incompatibility.
It is notable, however, that despite a failure of the vaporizer, there was no adverse effect on the patient. This positive outcome underscores the importance of design features that minimize the potential for patient injury. In this case, the “no output” alarm on the Desflurane vaporizer alerted the anesthetist to the malfunction, which initiated corrective action. Had the problem continued for any length of time, low anesthetic agent concentration alarms would have also alerted the anesthetist to a problem.
Anesthesia delivery system manufacturers pursue rigorous testing and thorough risk analysis in the process of designing equipment. Despite these high standards, equipment malfunctions will occur in the process of delivering anesthesia. Patient injury can be avoided, as it was in this case, by using equipment with appropriate alarm technology, recognizing a problem when it occurs, having a backup plan, and taking corrective action in timely fashion.