In Reply:--I thank Alfery, Bapat, Ullman, and Burk for their thoughtful comments. Three of the authors suggested new methods to obtain either a greater depth of tracheal insertion and/or increase the size of the endotracheal tube (ETT) when performing tracheal intubation through a laryngeal mask airway (LMA), and the fourth author suggested yet another supraglottic ventilatory mechanism for the "cannot ventilate, cannot intubate" situation.
To gain a greater depth of tracheal insertion, Alfery suggested insertion of a 34-cm long, 6.0-mm-internal diameter (ID) cuffed nasal RAE ETT (Mallinkrodt Medical, St. Louis, MO) through a #3 and #4 LMA instead of a standard 29-cm long, 6.0-mm-ID cuffed ETT and a 36-cm-long, 7.0-mm-ID cuffed nasal RAE ETT through a #5 LMA instead of a standard 31-cm-long, 7.0-mm-ID cuffed ETT. I followed his suggestion several times and he is correct in all claims; a greater depth of tracheal insertion is obtained and with proper lubrication; the preformed curve does not present a problem in any respect. One needs to be cognizant of the depth of tracheal insertion (i.e., be aware of the centimeter marking at or near the incisor or LMA adaptor level) because a right mainstem bronchial intubation is possible.
To increase the safety of changing a small-bore ETT to a large-bore ETT, Bapat suggested the simultaneous use of both an appropriately sized fiberoptic bronchoscope (FOB) and reintubation guide (elastic bougie or tube exchanger) within the larger ETT when actually placing the larger ETT into the trachea. The concept is sound, and various permutations of using a FOB along with another guide for changing ETTs in other situations (e.g., all four permutations of interchanging oral and nasal ETTs) have been published. It would be helpful to interested readers if Dr. Bapat would publish a small table of different-sized ETTs and compatible-sized intraluminal guides and FOBs.
To increase the depth of tracheal insertion, Ullman suggests lengthening the 6.0-mm-ID ETT by splicing in a plastic connection (narrow "neck" of an ETT adaptor) that will allow attachment of another length of 6.0-mm-ID ETT. I came to the same idea a year ago and used both the hard plastic sheath that surrounds a 22-gauge spinal needle in an unopened sterile package and the plastic connectors that are used to lengthen wide-bore suction tubing in the operating room as the plastic connection. The method works fine, provided one does not want/need to remove the 6.0-mm-ID cuffed ETT from the #3 or #4 LMA. The problem with removal of the 6.0-mm-ID cuffed ETT from the #3 or #4 LMA is that the ridge created by the plastic connector-distal 6.0-mm-ID cuffed ETT interface can impact on or hang up on the ridge created by the LMA adaptor-LMA shaft interface. Forceful pulling on the proximal end of the 6.0-mm-ID ETT extension can cause the distal end of the 6.0-mm-ID cuffed ETT to separate from the plastic connector; the result is that the distal full length of the 6.0-mm-ID cuffed ETT is unattached and free within the LMA shaft and trachea, and is not necessarily retrievable. In fear of this complication, I stopped using this method to increase the depth of tracheal insertion.
Burk suggests using a nasotracheal tube (or an appropriately adapted soft nasopharyngeal airway; sometimes refered to as a "Nosworthy chimney") as a supraglottic ventilatory mechanism for the "cannot ventilate, cannot intubate" situation. I have often ventilated in this manner in elective situations, especially when teaching fiberoptic intubation (either orally or nasally), because the method works reasonably well, and for fiberoptic intubation, the method is visually noninterfering. However, for the "cannot ventilate, cannot intubate" situation, the method has two serious limitations. First, because the ventilation mechanism is supraglottic, it suffers from the same limitations I outlined in my article for the supraglottic ventilatory mechanisms of the LMA and Combitube (i.e., the ventilatory mechanism can be proximal to a periglottic pathologic obstruction). Second, use of the nasopharyngeal route may cause nasopharyngeal bleeding, a most unwelcome happenstance in a "cannot ventilate, cannot intubate" situation. Although Burk may be dismayed that the ASA Difficult Airway Algorithm does not specifically mention his first choice emergency ventilation method, and many other practitioners have reminded me of not-specifically-mentioned tricks they have, the ASA Difficult Airway Algorithm does not exclude these methods. It is appropriate to conclude by reminding the anesthesia community that the ASA Difficult Airway Algorithm states that the recommendations therein "may be adopted, modified, or rejected according to clinical needs and constraints" and that "the techniques chosen by the practitioner in a particular case will depend upon specific needs, preferences, skills and clinical constraints". 
Jonathan L. Benumof, M.D., Professor of Anesthesia, UCSD Medical Center, Department of Anesthesiology, 402 Dickinson Street, 8812, San Diego, California 92103-8812.
(Accepted for publication June 17, 1996.)