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After ETI, verification of endotracheal tube placement is essential [64]. Tube placement verification is particularly important given the uncontrolled nature of the prehospital environment and the risks of unrecognized tube dislodgement or misplacement [65–68]. Because of the amount of patient movement during prehospital care, EMS personnel must frequently, and preferably continuously, verify correct tube positioning. In addition to visualizing the endotracheal tube passing through the vocal cords into the trachea, endotracheal tube placement should be confirmed using multiple techniques.

Auscultation is the most common method for verifying endotracheal tube placement. The rescuer auscultates both lung fields to verify the presence of breath sounds, and auscultates the epigastrium to verify the absence of gastric sounds. It is possible to be misled by transmitted sounds, however.

Some low‐tech innovations have been helpful in the past. The esophageal intubation detector consists of a Toomey syringe with a special adaptor for the endotracheal tube. The esophageal detector device is a large, bulb‐type device (Figure 3.11). Both of these devices are based on the concept that the esophagus will collapse, producing resistance to a vacuum, while the trachea will not collapse and will therefore not produce any resistance as the bulb or plunger produces suction.

Figure 3.11 Esophageal detector device.

The most important technique for verifying endotracheal tube placement is detection of exhaled, or end‐tidal, carbon dioxide. There are currently three types of devices used for detecting end‐tidal carbon dioxide: 1) colorimetric end‐tidal carbon dioxide detector, 2) digital capnometer, and 3) waveform end‐tidal capnography.

Figure 3.12 Colorimetric carbon dioxide detector.

The colorimetric end‐tidal carbon dioxide detector uses a chemically treated paper detector that changes color from purple to yellow when exposed to carbon dioxide (Figure 3.12). If the paper color remains purple, this suggests esophageal tube placement. Designed for single use, these devices can be used for only a limited duration (<2 hours). Exposure to liquid (for example, vomitus or blood) may render these devices nonfunctional.

Digital end‐tidal carbon dioxide capnometry samples exhaled gases, measuring and displaying the carbon dioxide level. A positive carbon dioxide level connotes correct endotracheal tube placement.

Waveform end‐tidal capnography is similar to digital capnometry, except that the exhaled carbon dioxide level is depicted continuously in graphical form (Figure 3.13). The “waveform” on the display makes it easier to observe changes in the exhaled carbon dioxide level. This also enables measurement of ventilation rate.

There are two primary designs for capnometers and waveform capnography: sidestream and mainstream [69]. Sidestream devices draw a sample of the exhaled gases from a port attached to the endotracheal tube. For mainstream capnography the sensor is placed in the gas delivery line near the endotracheal tube. In general, with sidestream devices there is a short (<1 second) delay between gas sampling and display of a carbon dioxide level. In contrast, in‐line devices provide instant carbon dioxide readings. The sensor for an in‐line device is placed near the endotracheal tube. The sensors for newer in‐line devices are light, compact, and less bulky and awkward than their predecessors. Sidestream devices may be more prone to condensation. EMS personnel may use sidestream devices with a nasal cannula in spontaneously breathing patients, broadening their potential application.

Waveform end‐tidal capnography is the most accurate tracheal tube placement verification and monitoring technique. However, waveform capnographers are expensive (over $3,000 per unit). Multiparameter cardiac monitors have options for integrated capnography. In situations with low perfusion (e.g., cardiopulmonary arrest) there may be inadequate circulation of carbon dioxide to the lungs. In these situations, carbon dioxide detectors may incorrectly indicate a misplaced endotracheal tube

Figure 3.13 Waveform carbon dioxide detector.

An essential consideration is that prehospital patients undergo considerable movement during field care, which may heighten the risk for tube dislodgement. Many EMS medical directors have emphasized the need for frequent reverification or continuous monitoring of endotracheal tube placement, especially after each patient movement; for example, after moving the patient onto the stretcher or loading into an ambulance. Only capnometers and waveform capnography are currently capable of providing continuous tube placement information. Whenever it is available, continuous waveform capnography should be standard all intubated patients.

While some clinicians rely on fogging of the endotracheal tube to indicate its correct placement, a well‐executed animal study demonstrated the inaccuracy of this technique [70]. Ultrasonography has been proposed as a method for confirming endotracheal tube placement, but this technique has not been tested in large series in the prehospital setting [71].