To the Editor:—
We would like to report an inadvertent vaporizer selection malfunction on the North American Dräger Narkomed 2C (Dräger Medical, Danvers, MA). This incident occurred during a routine elective outpatient surgical case. Standard anesthesia machine checkout was performed as per our routine before the start of the daily workload. After intravenous induction and before placement of the endotracheal tube, the supervising anesthesiologist actuated the desflurane vaporizer (Tec 6 Plus; Datex-Ohmeda Inc., Madison, WI) to deliver a 3% concentration. Immediately after placement of the endotracheal tube, the supervised certified registered nurse anesthetist reached behind herself and actuated the sevoflurane vaporizer (Drägerwerk Vapor 19.1; Dräger Medical) to deliver a 3% concentration. The certified registered nurse anesthetist did this while keeping her eyes on the patient and connecting the ventilator circuit to the recently placed endotracheal tube. The attending anesthesiologist noted that both of the vaporizers were activated, and the anesthesia gas analyzer confirmed that both vapor anesthetic agents were present in the inhalation phase of respiration.
One volatile agent was selected, and the other was discontinued. The conduct of the anesthesia proceeded without event. The anesthesia machine was briefly checked for any other problems. No other malfunction was determined, and the case was allowed to proceed with the same anesthesia machine. The patient did not experience any consequence as a result of unintentional momentary dual volatile agent anesthesia. At the conclusion of the anesthesia, the anesthesia machine was changed out, and the service maintenance department of North American Dräger (Dräger Technical Support, Telford, PA) was summoned to examine the machine.
The attached illustration in figure 1demonstrates that both vaporizers were activated and delivering the set concentrations. The photograph was taken after the case was completed. The set concentrations in the photograph do not reflect the concentrations used in the case. The Dräger service engineer corrected a faulty linkage in the lever system in the back bar support for the vaporizers.
It is fortuitous that the anesthesiologists at the Ambulatory Clinical Building Operating Suite selected to have only two vaporizers mounted, desflurane (Tec 6 Plus) and sevoflurane (Drägerwerk Vapor 19.1). The desflurane vaporizer was deliberately mounted downstream of the sevoflurane vaporizer. Cross-contamination of the downstream vaporizer does not occur in this instance. The desflurane vaporizer uses vapor injection technology via an electromechanical control system to deliver the set concentration.
As a result of this design, there is no part of the fresh gas flow entering the vaporizing chamber in the desflurane vaporizer. Therefore, the vaporizing chamber is completely isolated from the fresh gas flow. Our decision to place the vaporizers in this manner resulted in preventing contamination of the downstream vaporizer in this instance.
The downstream vaporizer would certainly have been contaminated if the position of the sevoflurane and the desflurane vaporizers were reversed. A portion of the desflurane-laden fresh gas flow would enter the downstream sevoflurane-vaporizing chamber because of the design of that vaporizer. Some of this desflurane would then dissolve into the sevoflurane solution in accordance with the solubility coefficient of desflurane in liquid sevoflurane. This would adulterate the sevoflurane vaporizer for subsequent use, because both sevoflurane and desflurane would be delivered when this vaporizer is actuated. This would have resulted in further delay due to the need to wash out the contaminant in the downstream vaporizer. As it was, the anesthesia machine was back in operation the next day.
The literature has reports of anesthesia vaporizer selection malfunction. Vaporizer failure has been reported after inversion or tilting of the vaporizer when filling the reservoir.1Vaporizer malfunction at low flow has been reported with the ADU desflurane vaporizer (Anesthesia Delivery Unit; Datex-Ohmeda, Stockholm, Sweden).2User-removable vaporizer malposition has been reported to result in vaporizer failure.3Understanding the technology behind new equipment and upgraded equipment is essential to understanding its limitations, as is seen in this report of the desflurane Tec6 Plus vaporizer.4
As far as we can determine, this is the first documented failure of the vaporizer-selection system in the Dräger Narkomed 2C. We publish this because this model is a common workhorse in American anesthesia practice. Our first delivery of this machine type was in September 1996. Our oldest machine is therefore 9 yr old and the youngest Narkomed 2C is 5 yr old at the time of this letter. All of our anesthesia machines are serviced and maintained as per manufacturer’s guidelines.
*University of Texas M. D. Anderson Cancer Center, Houston, Texas. firstname.lastname@example.org