اشتباهات شایع در بخش آی سی یو 7
Position the Tip of the Endotracheal Tube 4 Centimeters Above the Carina
Leo Hsiao DO
Establishment of the airway is an integral part of any resuscitative algorithm. In the acute setting it is often necessary to intubate a patient in order to secure a means of providing ventilation. To this end, the position of the endotracheal tube is paramount to its success. A malpositioned endotracheal tube can be detrimental and potentially life threatening (Fig. 111.1).
To briefly review, the upper airway begins at the nose and mouth and ends at the carina where the trachea divides into the left and right main-stem bronchi. The nose and mouth form a common passage posteriorly called the pharynx, which is divided into three parts: nasopharynx, oropharynx, and laryngopharynx. The pharynx leads to the trachea anteriorly and the esophagus posteriorly. The glottis is the inlet to the trachea. It is bordered by the vocal cords laterally and epiglottis superiorly. The trachea, which corresponds to the C6 vertebra posteriorly, is a tubular conduit supported by semicircular cartilaginous rings leading down to the carina, the branching point for the main-stem bronchi.
What to Do
In determining the proper placement of an endotracheal tube, the length of the segments through which the tube must pass should be considered. The distance from the teeth to the vocal cords is approximately 10 to 15 cm. Once through the glottic aperture, the trachea measures another 12 to 15 cm to its end at the carina. Because the tip of the endotracheal tube is optimally positioned at 4 cm above the carina, some authors advocate empiric insertion of the endotracheal tube to a depth of 23 cm and 21 cm, measured at the lips, for men and women, respectively. Auscultation of the bilateral lung fields and stomach should follow intubation. The presence of sustained end-tidal CO2 is confirmatory of tracheal placement. A chest radiograph then confirms the position of the tube and the need for subsequent repositioning. An improperly positioned endotracheal tube can be dangerous if left unchecked. Esophageal intubation is diagnosed by nonsustained or absent end-tidal CO2 and epigastric gurgling on ventilation. Ventilation should be terminated immediately to avert insufflation of the stomach, which can increase gastric pressures and the risk for aspiration.
Even when tracheal intubation is achieved, the position of the tube can be hazardous depending on its position within the trachea. If the endotracheal tube is too cephalad in position the danger of inadvertent extubation and vocal-cord injury becomes problematic. On the other hand, if the endotracheal tube is advanced too deeply, the risk of main-stem intubation is of concern. Because the right main-stem bronchus forms a more obtuse angle with the trachea than the left main-stem bronchus, it is more commonly intubated on deep advancement. Endobronchial intubation, regardless of side, is diagnosed by unequal or unilateral breath sounds, high peak airway pressures, and hypoxemia. If left unchecked there is a potential for bronchospasms, contralateral atelectasis, and ipsilateral tension pneumothorax.
Once the decision is made to reposition the endotracheal tube, the most accurate manner of determining proper positioning is with a fiberoptic bronchoscope. However, this is often impractical and typically the tube is retracted or advanced, with the cuff down, by 1-cm increments, taking care to reassess by auscultation over the bilateral lung fields. Alternatively, if there is a chest radiograph available, the degree of retraction or advancement can be estimated on film.
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