Letters to the Editor: Letters & Announcements
To the Editor:
We have several questions regarding the methodology in the recent article by Larson et al. (1) testing anesthesia providers' ability to detect anesthesia machine faults.
A more concise description of the study population would assist interpretation of the results and generalizability of the conclusions. Were the participants physicians or nurses, and were any still in training? Also helpful in describing the participants would be the type of professional meeting at which this study was conducted. There is also discrepancy in the description of the study participants. In the Methods section it is stated, “The volunteers were attending an anesthesia meeting that drew attendance from throughout the United States.” While in the Discussion it is noted that “The study was performed predominantly at an anesthesia meeting site.” Were all of the subjects (Methods section) or only some of the subjects (Discussion section) drawn from the meeting?
There is an ambiguity in the description of one machine fault. The Methods describe an induced failure of the “oxygen/nitrous oxide fail-safe linkage.” Standard reference texts (2,3) and Ohmeda's user manual describe the fail-safe mechanism as a device that serves to interrupt nitrous oxide flow if the oxygen supply pressure falls below a critical threshold. This contrasts with the oxygen/nitrous oxide proportioning device (Link 25 Proportion Limiting Control System) meant to prevent flow meters from delivering a hypoxic mixture. This system is often referred to simply as the “chain link” or “Link 25” mechanism. Thus the mixed use of terminology for their machine fault “fail-safe linkage” makes it unclear which fault was tested. One relevance to this matter lies in how test subjects utilized elements from the FDA anesthesia apparatus checkout recommendations in their personal machine check. The 1986 version of the checkout would be expected to detect both types of fault, whereas the 1993 version eliminated the check (Step 10 in the 1986 version) that would have detected the fault of the fail-safe mechanism. Only the failure of the oxygen/nitrous oxide proportioning would be detected by the current 1993 checkout (Step 7b). Understanding which fault was utilized in the present study is necessary if this study is to be used as a future benchmark.
As the subjects “… were asked to list faults on a data collection tool …” we are curious as to the frequency of the finding of false positive (nonexistent) faults. Did any list faults that were not present on the machine?
Charles Schrock, MD
Assistant Professor of Anesthesiology
St. Louis Children's Hospital
St. Louis, MO
Joseph Kras, MD
Associate Professor of Anesthesiology
St. Louis, MO
Alex Visuara, MD
Resident in Anesthesiology
St. Louis, MO
1. Larson ER, Nuttall GA, Ogren BD, Severson DD, Wood SA, Torsher LC, Oliver WC, Marienau ME. A prospective study on anesthesia machine fault identification. Anesth Analg 2007;104: 154–6
2. Ehrenwerth J, Eisenkraft JB, eds. Anesthesia equipment, principles and practice. St. Louis: Mosby, Year Book, 1993:37–8
3. Dorsch JA, Dorsch SE, eds. Understanding anesthesia equipment. Baltimore: William and Wilkins, 1999:93, 109