Correspondence  |   March 2004
Novel Breathing Circuit Architecture: New Consequences of Old Problems: In Reply
Author Notes
  • Draeger Medical Inc., Telford, Pennsylvania. .
Article Information
Correspondence   |   March 2004
Novel Breathing Circuit Architecture: New Consequences of Old Problems: In Reply
Anesthesiology 3 2004, Vol.100, 756. doi:
Anesthesiology 3 2004, Vol.100, 756. doi:
The letter by Sandberg and Kaiser describes the entrainment of room air through a hole in a reservoir bag placed on a Fabius GS anesthesia machine (Draeger Medical Inc., Telford, PA) after the machine check had been completed. Before any adverse event could occur, the problem was identified by noting that the reservoir bag was not filling with gas during mechanical ventilation and that the concentrations of oxygen and anesthetic in the circuit were less than the concentrations set to be delivered by the machine. This report underscores several important issues concerning the safe use of not only a new design of an anesthesia machine like that of the Fabius GS but also of all anesthesia machines.
Machine checkout is a fundamental aspect of the strategy to use any anesthesia machine safely. Having confirmed proper functioning of the anesthesia machine prior to induction, Sandberg and Kaiser made an appropriate decision to avoid exposing the latex-allergic patient to latex by changing to a bag that did not contain latex. Because the procedure was already under way when the bag was changed, they did not have an opportunity to repeat the machine checkout, which would have identified a leak in the system. Once the preuse checkout is completed, changing or disconnecting any components of the circuit should be avoided unless the checkout can be repeated prior to use.
Another important point is the value of training users to understand the proper functioning of the anesthesia machine. The Fabius GS is designed with the reservoir bag as part of the circuit during mechanical ventilation so that fresh gas can accumulate in the bag during inspiration. The intent of this design is to improve the accuracy and consistency of tidal volume delivery by eliminating the interaction between fresh gas flow and tidal volume characteristic of a traditional anesthesia machine design. The authors had been trained to understand that the reservoir bag on the Fabius GS is an indicator of adequate fresh gas flow, just as the bellows is on a traditional anesthesia machine. After the reservoir bag was changed they continued with mechanical ventilation, but they quickly recognized that a problem existed when the reservoir bag did not fill. User training has become especially important with the development of new anesthesia machine designs, because indicators of proper functioning are different from traditional machine technology.
The importance of monitoring technology to patient safety has been emphasized repeatedly in the literature, and this report is just one more example. Indeed, observation of oxygen and anesthetic vapor concentrations led Sandberg and Kaiser to suspect that air was entering the breathing circuit. No matter how advanced anesthesia delivery systems become, monitoring the concentration of gases and vapors delivered to the patient will remain fundamental to confirming that the patient is receiving what the anesthesia provider intends to deliver.
To understand how the Fabius GS design facilitated the identification of the hole in the reservoir bag, it is useful to speculate about the implications of a similar situation when using a traditional anesthesia machine design. On a traditional anesthesia machine, the reservoir bag is excluded from the breathing circuit during mechanical ventilation. Had the bag been changed after induction and the start of mechanical ventilation on a traditional anesthesia machine, the hole in the bag might not have been recognized until the end of the procedure, when manual positive pressure ventilation was needed to facilitate emergence. The Fabius GS design likely led to an earlier recognition of the problem, because the bag did not fill with gas as expected immediately after it was changed.