Detection of oesophageal intubations using cuff pressures in a pig trachea–oesophagus model

Verification of endotracheal tube placement using electrical stimulation through electrodes placed on the endotracheal tube cuff

BACKGROUND

Current methods for verification of endotracheal intubation can fail, particularly in emergency settings. We investigated whether a verification method using electrical stimulation through electrodes placed on the endotracheal tube cuff could distinguish endotracheal and esophageal intubations in an experimental setting.

METHODS

During three sequential sessions simulating emergency intubation without paralysis, rapid sequence intubation (RSI) with neuromuscular blockade, and intubation during cardiopulmonary resuscitation, eight pigs were intubated with an endotracheal tube fitted with two electrodes exposed on the cuff of the tube, first in the esophagus and next in the trachea or in reverse sequence. Cuff pressure was monitored during a 5-s electrical stimulation (20 mA, 80 Hz, 500 μs), and delta pressure was calculated as the difference between baseline cuff pressure and maximum cuff pressure during the electrical stimulation.

RESULTS

Delta pressure was significantly higher in esophageal than in tracheal placements in all three sequential sessions (86.0 [78.3-89.7] vs. 6.5 [2.0-7.9] mmHg, P = 0.001; 16.6 [13.2-22.8] vs. 0.8 [0.3-2.6] mmHg, P = 0.004; 66.1 [60.0-84.7] vs. 2.7 [0.7-9.7] mmHg, P = 0.001). The delta pressure did not overlap between tracheal and esophageal intubations except for the session simulating RSI with neuromuscular blockade, in which one of eight esophageal placements showed a delta pressure within the delta pressure range of tracheal placements.

CONCLUSION

Electrical stimulation through electrodes placed on the endotracheal tube cuff produced remarkably greater increases in cuff pressure in esophageal intubations than in tracheal intubations in an experimental setting.

The lowest effective intracuff pressure of the esophagus obstruction tube to prevent reflux of gastric contents: a study on rabbits

PURPOSE

To determine the lowest effective cuff pressure of the esophageal obstruction tube to prevent reflux of gastric contents in rabbits.

METHODS

Twenty-two New Zealand white rabbits (2.0-2.5 kg) were anesthetized. An esophageal obstruction tube, an esophageal observation tube, and a gastric tube were inserted into the esophagus and stomach, respectively. Normal saline containing methylene blue was injected into the stomach for an animal model of gastric contents reflux. Possible saline reflux was observed through the esophageal observation tube. It was considered "regurgitation" when the saline flowed out, and "no regurgitation" when the saline did not. When a "regurgitation" result was obtained in a particular rabbit, the intracuff pressure was increased by 10 cm H(2)O in the following rabbit and vice versa. The trial was not terminated until six crossover points were observed from "no regurgitation" to "regurgitation." A probit regression model was used to analyze the effective intracuff pressure of the esophagus obstruction tube after 50 % and 95 % of the rabbits showed no reflux.

RESULTS

The lowest effective intracuff pressure to prevent reflux of gastric contents in 50 % of rabbits from the Dixon up-down method was 61.67 ± 8.16 cm H(2)O. The intracuff pressures at which there was 50 % and 95 % probability of lack of gastric contents reflux from a probit regression model were 61.95 and 74.39 cm H(2)O, respectively.

CONCLUSION

The insertion of an esophageal obstruction tube before endotracheal intubation can be an acceptable method for preventing the reflux of gastric contents in most rabbits under light anesthesia.

Comparison of Tracheal and Esophageal Compliance Curves in Human Cadaveric Subjects

We sought to derive compliance curves of the trachea and esophagus. 16 fresh human cadavers were intubated tracheally and esophageally and cuff pressures measured at equal air volumes. Tracheal compliance was statistically less than esophageal compliance for volumes of 1, 2, and 3 mL of air, (p = 0.002, p = 0.008, and p = 0.006, respectively) but not so for volumes beyond that. This physical property is therefore not robust enough for detecting esophageal intubation.

Analytic Review: Confirmation of Endotracheal Tube Position: A Narrative Review

Endotracheal tube (ETT) insertion is the primary method of definitive airway protection and control in critically ill patients. Detection of ETT malposition in a timely fashion is crucial in both elective and emergent intubation. In this review, we describe classic tests and highlight several new technologies that may assist the practitioner in determining ETT position within the esophago-tracheal complex, namely ultrasonographic and impedance-based methods. Strengths and weaknesses of particular methods are highlighted. Although many physical examination maneuvers have been described, reliance on the physical examination alone is insufficient for confirmation. Touted methods that appear failsafe, such as direct visualization of the ETT traversing the vocal cords have limitations, especially when dealing in the emergency setting accompanying a difficult to visualize airway. While carbon dioxide detection is an excellent confirmatory method, it is not infallible. Esophageal detection devices are useful as an alternative means of confirmation. New methods such as ultrasonic location of the ETT show promise but require further study. The clinician performing ETT insertion should have multiple confirmation methods that allow the practitioner to adapt to a variety of clinical situations, depending on local costs and availability. Finally, when the clinician still has uncertainty, or multiple tests give conflicting results, the availability of bronchoscopy at the bedside to visualize the carina through the ETT is useful.