To the Editor:—

We write to inform your readers about our experience with the configuration of the Dräger Apollo anesthesia machine (Dräger Medical, Inc., Telford, PA). We have had several instances where end-tidal carbon dioxide readings were skewed or undetected by the gas analyzer after successful tracheal intubation. Upon inspection of the source of the problem, it was found that the water trap (positioned just below the isoflurane vaporizer; fig. 1) was severely cracked and disfigured (fig. 2). This compromise of the water trap led to the inability to accurately detect and monitor end-tidal carbon dioxide. Upon replacement of the water trap, accurate carbon dioxide monitoring was once again possible.

It was discovered that during the filling process of the isoflurane vaporizer, a small amount of volatile anesthetic had dripped down on the water trap, leading to compromise of the integrity of the plastic outer shell of the trap and loss of the ability to accurately detect and monitor end-tidal carbon dioxide. These conditions were easily reproducible and always led to the same water trap disruption.

Further investigation revealed that inspired and end-tidal volatile anesthetic levels may be skewed as well. In a clean anesthesia circuit with gas flow consisting of 100% oxygen in the presence of a water trap disrupted by spillage of isoflurane, high levels of inspired and expired isoflurane were detected despite the vaporizer having never been turned to the “on” position.

Most anesthetic machines have a configuration that places the water trap above the vaporizers. The Dräger Apollo has a unique configuration that places the water trap directly below the vaporizers and at risk from spillage of volatile anesthetic agents during the filling process. Since these episodes, we have repositioned the isoflurane vaporizer into the position to the far left side of the machine, away from the water trap. So far, this change seems to have eliminated the issue. Incidentally, sevoflurane and desflurane seem to cause little to no disruption of the water trap based on our limited trials of direct exposure. Perhaps chronic exposure to these agents may lead to similar disruptions, but certainly not to the same degree as isoflurane. The filling system on the desflurane vaporizer also seems to be less prone to spillage, thereby making it a seemingly more appropriate choice for placement in the position above the water trap. Other possible solutions might include removal of the vaporizer before filling it and avoiding overfilling of the vaporizer to minimize dripping during the filling process.

Potential problems that can arise may include incorrect assessment of correct tracheal placement of the endotracheal tube, skewed or absent capnograms, and elevated inspired and end-tidal volatile anesthetic readings. It is hoped that this information will help practitioners have early recognition of these water trap disruptions to avoid misinterpretation of clinical situations. Practitioners should also consider avoiding the placement of the isoflurane vaporizer directly above the water trap and should have replacement water traps readily available so that patient care is not interrupted.

*Scott & White Memorial Hospital and Clinic, Temple, Texas.