Letter to the Editor: In Response
We would like to thank Drs. Dunn and Mushlin for taking the time to read our case report . They appear to have missed the major problem we encountered, which was incomplete and possibly variable obstruction of the breathing circuit. Complete obstruction is easily detected by the current Food and Drug Administration checkout guidelines. As stated in our report, the most rational approach to correcting this problem is to redesign the packaging of the CO2 absorber canister so that a wrapped canister is either physically impossible to place into the absorber or so that it looks completely different from a canister with the wrapping removed.
We apologize for puzzling Drs. Dunn and Mushlin with our preoxygenation methods. It is our standard practice to have all adult patients breathe 100% oxygen immediately upon entering the operating room while other preparations for induction are being performed. This is not meant to be a formal "denitrogenation" procedure, and we do not insist on a tight mask seal. In contrast, we certainly do require an appropriate mask seal in patients having a rapid sequence induction or significant respiratory disease. It is possible that even with a tight mask fit our patient may not have voiced any complaints due to the incomplete nature of the breathing circuit obstruction and/or the administration of preoperative sedation.
The suggestion that a new Food and Drug Administration requirement for machine checkout require observation of CO2 waveforms and reservoir bag excursions generated by the patient before induction is interesting. While this may be a useful practice in many adults, difficulties would certainly arise in performing these procedures in uncooperative children or critically ill patients who have received muscle relaxants before entering the operating room. Although we agree that these procedures should be performed when possible, they should be considered primarily ancillary tests. With the busy operating room schedules present in most hospitals today, any procedures performed just before induction have the potential of being accomplished in a hurried and less than optimal manner. We thus believe that it is most prudent to ensure that the anesthesia apparatus is completely checked before the patient is brought into the operating room. To this end, an experienced anesthesiologist breathing through a circuit should be able to detect a faulty circuit by observing, among other things, the movements of the reservoir bag and the CO2 waveform.
Peter H. Norman, MD, FRCPC
M. Denise Daley, MD, FRCPC
Department of Anesthesiology; Baylor College of Medicine; Houston, TX 77030
1. Norman PH, Daley MD, Walker JR, Fusetti S. Obstruction due to retained carbon dioxide absorber canister wrapping. Anesth Analg 1996;83:425-6.