To the Editor:
Joyal et al.1 recently presented an alarming case in which the Dräger Apollo system failed to detect an occlusion of the main exhaust valve during the routine self-calibration testing and missed an occlusion by a plastic wrapper which was discovered upon visual inspection. At our institution, Memorial Hermann Hospital-Texas Medical Center, we experienced the same system failure.
The incident occurred during the second case of the day. After the first case the machine was cleaned and reset as per protocol by the anesthesia technician. Pre-oxygenation, induction, and mask ventilation occurred uneventfully, but at commencement of mechanical ventilation the reservoir bag continued inflating, and the high peak pressures warning alarmed. Even reverting the machine to manual/spontaneous did not relieve the circuit’s excessive pressure. The next course of action was opening the Apollo’s valve/canister drawer, which rapidly resolved the pressure overload that had progressively exceeded 40 cm H2O. The acuity of the situation allowed only a momentary glance inside the drawer; nothing abnormal was appreciated at the time. While a replacement ventilator was being rushed to the room, the patient was ventilated by an AMBU bag and anesthesia was maintained via IV agents. The relief of the accumulating pressure was rapid enough that no adverse effects to the patient were noted for the remainder of the procedure nor postoperatively.
Determining the cause of the failure was difficult since the main exhaust outlet is deeply recessed within the drawer. Thorough inspection of the Dräger Apollo after the conclusion of the case revealed a transparent plastic wrapper which had occluded the machine’s main exhaust outlet, exactly as described by Joyal et al. Even in a normally lit room, supplemental lighting such as a flash light seems necessary to discover such a transparent obstruction.
In our opinion this case is disconcerting regarding not only the self testing procedure of the Apollo (the company’s response to Joyal’s letter did not recognize any failure of the self-test for the workstation), but also on the care in discarding any plastic covers we use in the operating room. Such covers may have less likelihood of presenting discreet problems if they had bright colored stripes or other elements which are opaque in nature.
Davide Cattano, MD,PhD
John W Henschel, MD
- Joyal JJ, Vannucci A, Kangrga I. High end-expiratory airway pressures caused by internal obstruction of the Dräger Apollo® scavenger system that is not detected by the workstation self-test and visual inspection. Anesthesiology 2012;116:1162-4; discussion 1164-6.