Case Reports: Case Report
Critical incidents in anesthesia are frequently related to problems with the anesthesia workstation.1 In this issue of A & A Case Reports, Vinay et al.2 describe an unusual and previously unreported cause of ventilator failure in a contemporary electronic Dräger Fabius GS anesthesia workstation (Dräger Medical, Inc., Telford, PA). Fortunately, the critical incident described did not result in an adverse outcome, because of recognition and timely action by the authors and the safety features of the Fabius workstation.
The report is noteworthy because it describes a case of equipment failure that occurred in a properly serviced workstation, after normal function in the previous surgical case, and following a reportedly normal preuse checkout before the procedure in which failure occurred. The American Society of Anesthesiologists Closed Claims study of 72 anesthesia gas delivery system adverse outcomes found that equipment failure was one-fourth as frequent as use(r) error.3 A recent closed claims update, based on review of 40 adverse outcomes, found provider error in 68%, equipment failure in 13% and both in 18%.4 The authors of the update considered that 35% were preventable by a preanesthesia check.
Modern anesthesia workstations are more complex and less intuitive than their simpler pneumatic ancestors. Optimal use of these workstations demands a better-educated caregiver who understands the principles of operation of his/her equipment. This case highlights the importance, for normal ventilator function, of the Fabius’ pneumatic circuit and a pneumatic pump that generates both negative (vacuum) and positive pressures.5 The Fabius GS uses a piston ventilator driven by an electric motor (in contrast to the gas-powered bellows design ventilators). The cylinder in which the piston moves is lined by 2 flexible rolling seal diaphragms, an upper and a lower, that together enclose a sealed chamber that contains the anesthetic gas mixture to be delivered to the patient on the next positive pressure breath. When the workstation is in ventilator mode, the pneumatic pump creates a vacuum that holds the rolling diaphragms tightly against the moving piston and its housing. The vacuum also operates the adjustable pressure limit “pop-off” bypass valve so that gas cannot leave the breathing system via the adjustable pressure limit valve. The positive pressure generated by the pneumatic pump is used in operating the electronically controlled positive end-expiratory pressure (PEEP) valve. To ensure correct function of the pneumatic circuit, the vacuum is monitored and maintained between certain limits. Blocking (the filter to) the pneumatic pump air inlet results in an abnormally high vacuum. This generates an alarm condition and shuts down mechanical ventilation to prevent damage to the workstation and harm to the patient.
The source and nature of the membrane that obstructed the filter in this case unfortunately were not determined. Foreign material obstructing gas pathways in anesthesia gas delivery equipment is certainly not unknown as a cause of critical incidents and adverse outcomes. Fortunately, ventilation of the patient’s lungs was possible in manual mode. Filter obstruction is a most unusual occurrence; therefore, it is not surprising that it is not listed in the troubleshooting section of the operator’s instruction manual.6
James B. Eisenkraft, MD
Department of Anesthesiology
Icahn School of Medicine at Mount Sinai
New York, New York
1. Cassidy CJ, Smith A, Arnot-Smith J. Critical incident reports concerning anaesthetic equipment: analysis of the UK National Reporting and Learning System (NRLS) data from 2006-2008*. Anaesthesia. 2011;66:879–88
2. Vinay B, Sringanesh K, Redhu S. Dräger Fabius GS ventilator failure: an unusual cause. A & A Case Reports. 2014;2:138–9
3. Caplan RA, Vistica MF, Posner KL, Cheney FW. Adverse anesthetic outcomes arising from gas delivery equipment: a closed claims analysis. Anesthesiology. 1997;87:741–8
4. Mehta SP, Eisenkraft JB, Posner KL, Domino KB. Patient injuries from anesthesia gas delivery equipment: a closed claims update. Anesthesiology. 2013;119:788–95
5. Yoder JM Understanding Modern Anesthesia Systems. 2009 Telford, PA Dräger Medical Inc.:173–180
6. Fabius GS Operator’s Instruction Manual. 2003 Telford, PA Dräger Medical, Inc.:116