Cable Trapped Under Dräger Fabius Automatic Pressure Limiting Valve Causes Inability to Ventilate

I would like to report a problem with the Dräger Fabius anesthesia machine (Telford, PA) that caused the inability to ventilate. After the inhalational induction of a 2,100-g infant presenting for abdominal surgery, a muscle relaxant was given to facilitate intubation. As paralysis developed, a large circuit leak was discovered, making manual ventilation impossible. The machine had passed its preoperative checkout, and a further rapid check of the circuit did not uncover any disconnections, breaks in the circuit, or obvious explanation for the inability to generate positive pressure. During this check, the automatic pressure limiting (APL) knob was rotated back and forth through its range several times, but this did not correct the inability to ventilate. A self-inflating ventilation bag was used to ventilate the patient while we continued to troubleshoot the system. It was discovered that the temperature monitoring cable had become trapped between the knob and the base of the APL Valve (fig. 1A).

During normal operation, the APL dial of the Dräger Fabius anesthesia machine is lifted 4 mm from the base into the “open” position, releasing any positive pressure within the circuit. Closure of the APL Valve requires turning the control knob in a clockwise direction and descent of the knob onto its base, to generate positive pressure within the circuit. If the knob is manually lifted off its base, or prevented from descending by a foreign object, the APL Valve reverts to the “open” position and positive pressure cannot be generated, regardless of rotation of the knob.

Patient monitor cables are often run behind the carbon dioxide absorber arm to keep them free of the breathing circuit, placing them to the rear of the APL. In this position, the APL screens the cables from the view of the anesthetist (fig. 1B). Elevation of the knob is subtle and easily missed during a cursory inspection of the APL Valve. Merely rotating the APL Valve is not sufficient to free a cable trapped beneath.

This cause of APL Valve failure could easily be corrected by adding a skirt or lip to the APL knob extending over the base of the valve to prevent foreign objects from becoming wedged between the knob and the base. Anesthetists who work with the Dräger Fabius anesthesia machine should be aware of this potential problem and closely examine the APL Valve in the event of inability to generate positive pressure.

Cincinnati Children's Medical Center, Cincinnati, Ohio. michael.kibelbek@cchmc.org