In Reply:—
We would like to thank Drs. Krafft, Hartmann, Agro, Gaitini, and Vaida and Drs. Urtubia and Gazmuri for their interest in our study that demonstrated high pharyngeal and esophageal mucosal pressures with the esophageal–tracheal Combitube (ETC; Kendall-Sheridan Catheter Corp., Argyle, NY) in fresh cadavers and awake volunteers. 1We will respond to each point in turn, dealing with the former group first.
We were aware that our maximum cuff volumes exceeded those for the small-adult ETC. In clinical practice, recommended volumes are frequently exceeded, either by initial overinflation (both accidental and deliberate) or through nitrous oxide diffusion (and subsequent failure to limit intracuff pressure increases), and we wished to test these conditions. The maximum volumes we chose were those recommended for the normal-adult ETC. Our subjects, both living and dead, were adults of normal—not small—size.
Obviously, and as we showed in our study, an effective pharyngeal seal can be obtained at lower cuff volumes, but many patients still require the maximum volume. Krafft et al. seem to ignore the fact that we measured mucosal pressures over the full inflation range and found that even when cuff volume was reduced to the minimum required to form a pharyngeal seal of 30 cm H2O, mucosal pressures were still two or three times higher than mucosal perfusion pressure. A meta-analysis of data from similar studies suggests that when cuff volumes are reduced so that the pharyngeal seal is no greater than 30 cm H2O, pharyngeal mucosal pressures for the ETC are the highest among modern extraglottic airway devices (table 1).
Table 1. Composite Data for Directly Measured Mucosal Pressures in the Anterior (Base of Tongue), Lateral, and Posterior Pharynx for Six Modern Extraglottic Airway Devices at a Pharyngeal Seal Pressure of 30 cm H2O or at Maximum Seal
Units are cm H2O. Data from Keller et al. 1,2,21,23and Brimacombe et al. 22
* Laryngeal Mask Company, San Diego, CA.
† Maximum seal.
‡ Kendall-Sheridan Catheter Corp., Argyle, NY.
Krafft et al. suggest that a pharyngeal seal of 30 cm H2O can never be reached with use of an LMA-Classic™ (Laryngeal Mask Company, San Diego, CA) or an LMA-ProSeal™ (Laryngeal Mask Company) and quote a study by our group in which the mean pharyngeal seals were 16 and 27 cm H2O, respectively. 2However, if the authors had read the studies more carefully they would have realized that these results were from a mixed male and female population in which the size 4 laryngeal masks were used. The mean ± SD maximum pharyngeal seal for the size 4 LMA-Classic™ and LMA-ProSeal™ in women is 21 ± 3 cm and 36 ± 6 cm H2O, 3respectively, and the maximum pharyngeal seal for the size 5 LMA-Classic™ and LMA-ProSeal™ in men is 24 ± 5 cm 4and 32 ± 7 cm H2O, 4respectively. These values are by no means the highest reported in the literature, and both values for the LMA-ProSeal™ exceed 30 cm H2O.
Citing two studies, 5,6Krafft et al. state that the incidence of bleeding, dysphagia, and sore throat for routine anesthesia can be reduced by experienced users to 10–27%, 16%, and 8%, respectively. However, another study by experienced users showed that the incidence of bleeding, dysphagia, and sore throat was 36%, 68%, and 48%, respectively. Interestingly, in the former two studies the ETC was inserted with laryngoscopic guidance, 5,6and in the latter study it was inserted blindly. 7Perhaps it is the insertion technique rather than the experience level that reduces morbidity.
The authors imply that inflation of the distal cuff to the maximum recommended volume is safe because it “almost never blindly enters the trachea.” This statement is astonishing given that one of the authors (Dr. Agro) recently wrote a review on the ETC. 8A more careful analysis of the literature reveals that the mean incidence of tracheal placement when it is inserted blindly is 9% (range, 3–17%). 9–12Furthermore, accidental tracheal placement can occur even in an attempt to insert the distal cuff into the esophagus with laryngoscopic guidance, as demonstrated by yet another one of the authors (Dr. Gaitini). 5
Krafft et al. state that the ETC provides aspiration prophylaxis when used properly in the esophageal position, but they cite no evidence. Two studies have addressed this issue. One revealed no evidence of gastroesophageal reflux, as determined by swallowed dye, but the other showed that the incidence of aspiration was 12% with the ETC in the esophageal position, as determined by tracheal pH changes. Other evidence that the esophageal cuff does not always seal off the esophagus is that gastric insufflation can still occur. One recent study showed an incidence of 2.5%. 13In addition, gastric rupture 14,15has been reported to occur with the esophageal obturator airway, which also uses an esophageal cuff. The most likely explanation for failure of the esophageal seal is that the recommended volumes are too low.
We were unable to find any data about the cuff volume required to seal off the human esophagus. The only data we could find come from a 1974 study in which a canine model was used, which showed that inflation of a Foley catheter cuff with 30 ml prevented pharyngeal regurgitation of fluid. 16The implication is that the manufacturer's recommended cuff volume of 12–20 ml may be below that which is needed to provide protection. Interestingly, our study suggested that esophageal mucosal blood flow might be impeded at cuff volumes as low as 6 ml. 1
Drs. Urtubia and Gazmuri imply that it was unethical to insert the ETC into awake volunteers because the manufacturer considers it contraindicated for patients with intact gag reflexes. However, these recommendations relate to its use in semicomatose patients and not awake volunteers. We believe that using the ETC was entirely ethical for two reasons. First, numerous studies have been conducted on other airway devices in awake volunteers with potentially intact gag reflexes; for example, Benumof 17used 60 such volunteers to test a new airway device. Second, all volunteers understood the risks involved, topical anesthesia was applied, the efficacy of topicalization was tested with a spatula, and none of the subjects (as it happened) gagged with the ETC. We used only four volunteers to minimize risk.
Urtubia and Gazmuri are somewhat contradictory in their comments, claiming on the one hand that it was unethical to use awake volunteers and claiming on the other that we should have studied more. We agree that data from only four patients should be interpreted cautiously, but the main findings of our study were based on data from 20 fresh cadavers. In our study we presented evidence that a fresh cadaver is a reasonable model of the anesthetized, paralyzed patient. 1
Urtubia and Gazmuri state that 12 ml is usually sufficient to achieve an airtight seal with the esophagus. However, as mentioned earlier, little is known about the volumes required to form an airtight seal in the esophagus. Furthermore, the distal cuff volume cannot be reduced to the minimum required to form an effective seal since there is no easy way of measuring the esophageal seal, unlike the pharyngeal seal.
Urtubia and Gazmuri state that the ETC is safe for elective surgery. To date there have been only three studies in which the ETC was used for elective surgery, and, indeed, there have been no major complications in a metapopulation of 275 patients. 5–7However, these numbers are too small to claim that a technique is safe. In addition, Klein et al. 18reported that in a patient undergoing elective surgery with the ETC as part of a clinical trial, an esophageal tear occurred after difficult blind placement. Direct trauma or increased intraluminal pressure distal to the cuff may have caused the tear. The patient underwent a thoracotomy for esophageal repair and fortunately survived. The patient was only the ninth enrolled in the study. The incidence of esophageal tearing according to data collected so far is therefore 0.4% (1 of 284), a figure that could hardly be considered to confirm the safety of use of the ETC in patients undergoing elective surgery.
Urtubia and Gazmuri state that esophageal lesions associated with the ETC are incidental cases involving paramedics in out-of-hospital emergency settings and that according to the criteria of evidence-based medicine, these reports form a poor base for analysis. However, the case of Klein et al. 18occurred in a prospective study performed by anesthetists presumably adhering to the guidelines. The out-of-hospital evidence of major trauma is not just incidental. One such study showed that 0.7% of patients (8 of 1,139) developed subcutaneous emphysema, 19and another showed that major tissue trauma occurred in 0.6% (10 of 1,563). 20
Finally, we take offense to the authors’ suggestion that our study lacked good design in terms of randomization and blinding. There was nothing to randomize and nothing to blind other than perhaps the volume of air in the cuff. Blinding with respect to whether the subject was a cadaver or an awake volunteer would have been difficult.
