From the Literature: Does Esophageal Detector Device Really Work?

Ian Ehrenwerth, M.D.

Zaleski L, Abello D, Gold M. The Esophageal Detector Device Does it work? Anesthesiology 1993:79; 244-247.

The detection of an endotracheal tube that has been mistakenly placed into the esophagus is of prime concern to the anesthesiologist. The current American Society of Anesthesiologists Standards for Basic Intraoperative Monitoring require that ‘the correct positioning of an endotracheal tube in the trachea must be verified by clinical assessment and by identification of carbon dioxide in the expired gas.’ However, this may not always be possible. Electronic equipment for measuring end-tidal C02 may malfunction, the anesthesiologist may be in a location outside the operating room where this equipment is unavailable or the patient may not have a cardiac output sufficient to deliver carbon dioxide to the lungs. Therefore, an alternative means of reliably detecting esophageal intubations would be highly desirable. In 1988, Wee described what he called an esophageal detector device (EDD). This consisted of a 60 ml catheter syringe which was fitted to a catheter mount and attached to the endotracheal tube. If gas could be aspirated into the syringe, the endotracheal tube was felt to be in the trachea. If no gas could be aspirated, then the tube was thought to be in the esophagus. The accuracy of the device is ascribed to the fact that the esophagus is a fibromuscular organ that will collapse when subjected to a negative pressure. However, the trachea has a cartilaginous structure that allows gas to be easily aspirated when a negative pressure is applied. In 1989, Williams and Nunn tested a modified device that used an evacuator bulb and enabled the procedure to be a one-handed operation. They studied 100 patients and were able to correctly identify tracheal or esophageal placement 100% of the time.

Zaleski et al. studied 500 patients to determine the accuracy of an EDD that consisted of an inflatable rubber bulb that was made from an ear/ulcer syringe that was tightly fitted with a plastic 15 mm fitting. The study was divided into three sections. The first group, which consisted of 300 patients, had a standard anesthesia induction and then both the EDD device and capnography were used to determine whether the endotracheal tube was in the esophagus or the trachea. The second group consisted of 100 patients in which the endotracheal tube was purposely placed into the esophagus. Again the accuracy of the EDD was compared with capnography. The third group involved another 100 patients in which a double-blind randomized trial was conducted in which approximately half of the patients had their trachea intubated and the other half had the esophagus intubated. A blinded observer was then asked to use the EDD and capnogram to determine whether the trachea or esophagus had been intubated.

The analysis of the results showed that in all three parts of the study, the EDD correctly identified either tracheal or esophageal intubation and correlated with capnography 100% of the time. Thus, the total sensitivity, specificity and predictive values of this test were 100%. When the endotracheal tube was in the trachea, the bulb usually reinflated in less than 5 seconds. However, in a small percentage of cases, the bulb took up to 30 seconds to fully reinflate. If the bulb did not reinflate by 30 seconds, the tube was deemed to be in the esophagus. The reasons for the delayed reinflation were not clear. The authors speculated that perhaps the bevel of the endotracheal tube impinged on the carina or the wall of the main stem bronchus. The authors cautioned that the device must be tested prior to use on each patient to make sure that it is air tight.

It is indeed rare that a scientific study encompassing some 500 subjects with a total of 681 intubations (500 tracheal and 181 esophageal) produced such dramatic results. Indeed, the fact that the authors had no false positives and no false negatives is truly remarkable. The authors designed an interesting and comprehensive study to demonstrate the utility of this device. Not only is it simple and easy to use, but it can be easily constructed from materials commonly found in the operating room. Although this device is unlikely to replace capnography, it clearly can provide the anesthesiologist the ability to detect esophageal intubations when capnography is not available or in cases where capnography might not be useful such as a cardiac arrest. It seems that this is a device that every anesthesiology department ought to have readily available.

Reviewed by Ian Ehrenwerth, M.D., Professor of Anesthesiology, Yale University School of Medicine, and a member of the Newsletter Editorial Board.