THE advancement of the endotracheal tube (ETT) over a flexible fiberoptic bronchoscope (FOB) is often impeded by obstruction at the epiglottis or the arytenoids. 1–3This is usually attributed to the creation of a cleft along the ETT bevel by the difference in the outer diameter (OD) of the FOB and the internal diameter of the ETT. Inability to pass the tube into the trachea leaves the airway unprotected and may also result in injuries to the larynx.
Various maneuvers and endotracheal tube designs have been described to overcome this problem. The current report was designed to assess the feasibility and ease of passing the ETT over the FOB by using a Cook® airway exchange catheter. 2–4
With institutional review board approval and patients’ consent, 50 patients aged 20–76 yr, scheduled to undergo elective general anesthesia with tracheal intubation, were enrolled in the study. Patients included 23 women and 27 men, with ASA physical status I–III. Patients weighting more than 90 kg, patients having a history or signs of difficult airway, diabetics, and patients at risk for aspiration of gastric content were excluded from the study.
Anesthesia was induced with intravenous fentanyl 1 μg/kg, midazolam 1–2 mg, propofol 1–2 mg/kg, and vecuronium 0.1 mg/kg. After complete neuromuscular block was achieved as monitored by a peripheral nerve stimulator, a Berman intubating airway was inserted. One investigating anesthesiologist performed all of the tracheal intubations by advancing the FOB (3.8 mm Olympus LF2) through the oral airway, pharynx, larynx, and trachea until the carina was visualized. Mallinkrodt 7.5 and an 8.0 mm inner diameter (ID) endotracheal tube (ETT) were used for women and men respectively.
The lubricated ETT was then advanced into the oral airway with the preformed concavity oriented anteriorly (12 o'clock). If insertion was impeded, a lubricated 2.3 mm Cook® airway exchange catheter was inserted via the ETT beside the FOB until the tip of the catheter was visualized near the carina; the ETT was then advanced over the bronchoscope and the Cook® exchange catheter. If this maneuver failed to pass the tube into the trachea after two or three attempts, both the FOB and ETT were removed and tracheal intubation was performed by direct rigid laryngoscopy. In each case, the ease of ETT advancement was graded as follows: grade I indicates successful advancement of the ETT over the FOB; grade II indicates successful advancement of the ETT over the FOB by using a Cook® airway exchange catheter; and grade III indicates that ETT passage was unsuccessful despite the use of the Cook® airway exchange catheter, and intubation was performed by direct laryngoscopy. Also, the incidence of successful advancement of the tube over the FOB and the Cook® airway exchange catheter passage into the trachea was compared with the incidence of failure to pass the tube. Each patient served as her or his own control.
Chi-square was used to compare the incidence of successful passage of the ETT over the FOB with the incidence of success after the use of the Cook® exchange catheter. P < 0.05 was considered statistically significant.
Fifty patients were enrolled in the study. There was no significant difference in age, sex, height, and score between grade I patients 3,4and grade II and grade III patients. 1,6The ETT was successfully advanced over the FOB in 68% of the patients (34 out of 50). The Cook® airway exchange catheter was used to treat the remaining 32% of patients (16 of 50 patients). Out of the 16 patients who used a Cook® catheter, successful intubation was 94% (15 of 16 patients). The incidence of success after the two techniques, i.e ., 68%versus 94%, was statistically significant (P < 0.05).
The resistance to passage of the 7.5 mm and the 8.0 mm ETT using the Cook® exchange catheter and the FOB was not different. Passing the tube was accomplished at the first attempt in 9 out of the 16 patients, after two to three attempts in 6 patients, and was unsuccessful in the last patient (table 1).
The value of the flexible bronchoscope in the management of difficult tracheal intubation is well established. However, successful advancement of the FOB and visualization of the carina does not ensure successful advancement of the ETT over the FOB into the trachea. This was attributed to the “hanging up” of the tip of the conventional preformed plastic tubes (Murphy's tip) on the epiglottis during nasal fiberoptic intubation, or the arytenoids during oral fiberoptic intubation. 1,2The cause of this hanging up is the creation of a cleft along the ETT bevel by the difference in the OD of the FOB and the internal diameter of the ETT. This situation may leave the airway unprotected, and may also result in airway bleeding, damage to the arytenoid cartilages or epiglottis, or swelling of the airway, making subsequent tracheal intubation attempts more difficult.
To overcome this obstruction, rotating the ETT 90° counterclockwise has been advocated. 2This will allow the Murphy's tip to realign from the horizontal to the vertical plane, making it less likely to encounter any laryngeal structures. 5Brull recommended using a spiral-wound wire reinforced ETT. 4The greater side-to-side flexibility and the more obtuse angle at the distal end makes it less likely to impinge on pharyngeal structures, epiglottis, or the arytenoid cartilages during its advancement into the trachea. Marsh 6and Rosenblatt 7proposed the double setup tubes; they have shown that when the tip of an uncuffed lubricated pediatric ETT protrudes beyond the tip of the ETT to be used during fiberoptic intubation, it will fill the space that otherwise exists between the latter tube and the FOB. This minimizes the difference in diameters and allows the tube to be easily threaded into the trachea.
In the current report, we have found that inserting a Cook® airway exchange catheter beside the FOB facilitates the advancement of the ETT into the trachea, without the need for external laryngeal manipulation of the neck or 90° counterclockwise rotation of the tube, or both. This may be explained by the fact that the presence of the FOB and the Cook® airway exchange catheter together within the lumen of the ETT may decrease the size of the cleft and consequently centralize the ETT in front of the glottis. As a result, the likelihood of impingement on the arytenoid cartilages will decrease, and the chances of passing the ETT into the trachea without resistance will increase.
The presence of the FOB in the trachea allows the visualization of the tip of the Cook® airway exchange catheter, which will confirm its proper positioning and prevents its overinsertion, and hence will minimize the possible risks associated with the use of these catheters. 8
In conclusion, the current report shows that advancing the endotracheal tube into the trachea over the FOB may fail in almost one-third of patients. In these patients, successful tracheal intubation can be achieved by introducing a Cook® airway exchange catheter beside the FOB. The successful passage may result from centralizing the tube by both the FOB and the Cook® catheter in front of the glottis, which decreases the likelihood of impingement on the arytenoids.