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GENERAL ARTICLES

A Comparison of a Silicone Wire-Reinforced Tube with the Parker and Polyvinyl Chloride Tubes for Tracheal Intubation Through an Intubating Laryngeal Mask Airway in Patients with Normal Airways Undergoing General Anesthesia

From the American University of Beirut-Medical Center, Department of Anesthesiology, Beirut, Lebanon.

Address correspondence and reprint requests to Chakib M. Ayoub, American University of Beirut, P.O.Box 11–0236/Anesthesiology, Riad El-Solh/Beirut 1107 2020, Lebanon. Address e-mail to ca04{at}aub.edu.lb.

	Abstract

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BACKGROUND: The intubating laryngeal mask airway (ILMA) is used in the management of difficult intubation. Usually, a silicone wire-reinforced tube is inserted for tracheal intubation. Because the silicone wire-reinforced tube is expensive, alternatives, such as polyvinyl chloride (PVC) and posterior beveled Parker tubes, are worth considering. We compared the blind intubation success rates among the silicone wire-reinforced tube, the Parker tube, and the PVC tube, and identified laryngeal structures preventing tracheal intubations through the ILMA.

METHODS: Sixty-three adult patients were randomized into three groups: Group I (n = 20) silicone wire-reinforced tube, Group II (n = 21) Parker tube, and Group III (n = 22) PVC tube. Demographic and clinical continuous data were compared with the analysis of variance with the Scheffé test for post hoc analysis. Frequencies and percentages were compared with the ² test.

RESULTS: Tracheal intubation was successful from the first attempt in 18 of 20 patients in Group I (silicone wire-reinforced tube), which was significantly higher than the success rate in either Group II (12 of 22 patients) (Parker tube) or Group III (10 of 21 patients) (PVC tube). With clockwise or anticlockwise rotation of the tracheal tube, the number of successful intubations did not change in Group I, but it increased to 19 of 22 patients in Group II and to 12 of 21 patients in Group III. The rate of successful intubation between patients in Group I (90%) and Group II (86%) was not significantly different after manipulation of the tracheal tube (P = 0.72). However, the rate of successful tracheal intubations in patients of Group III (57%) was significantly lower in comparison to patients in both Group I (P = 0.02) and Group II (P = 0.03). In 3 of the 22 patients of Group II and in 9 of the 21 patients of Group III in whom blind intubation was not possible, the obstruction was due to the epiglottis tubercule.

CONCLUSIONS: Manipulation improved the success rate of intubation with the Parker tube through the ILMA rendering it a possible alternative to the silicone wire-reinforced tube.

	Introduction

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The intubating laryngeal mask airway (ILMA) is used in the management of difficult intubation.1 It features a silicone wire-reinforced tube for tracheal intubation.2 These tubes are expensive ($18) and not reusable. Polyvinyl chloride (PVC) tubes are significantly less expensive ($2.2), but their stiffness, lateral opening bevel, and curvature have made them more difficult to use with an ILMA. Reducing the curvature of a PVC tube by either warming it to make it more flexible, or by inserting it with its curvature facing backward, have made tracheal intubation possible with PVC tubes.3

The Parker tube ($3.75) is similar to a PVC tube, but it has an anterior curvature. However, in contrast to the PVC tube, the Parker tube has a posterior opening bevel4 (Fig. 1). It was designed so that the posterior bevel will decrease the incidence of the tube catching at the anterior or the lateral laryngeal structures during tracheal intubation. Baraka et al. have shown that a posterior beveled tube may facilitate tracheal intubation with fiberoptic bronchoscopy.4 The favorable characteristics of the Parker tube suggest that it may beneficial for blind intubation through the ILMA.

View larger version (106K): [in this window] [in a new window]   Figure 1. The three tracheal tubes used in the study. (A) The polyvinyl chloride tube, (B) the Parker tube, (C) the silicone wire-reinforced tube.

The purpose of this study was to compare the blind intubation success rates using the silicone wire-reinforced tube, the posterior bevel Parker tube, and the regular PVC tube. We also identified the laryngeal structures obstructing tracheal intubations through the ILMA when using these three endotracheal tubes.

	METHODS

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The IRB approved the study and a written informed consent was obtained from each patient preoperatively. Sixty-three ASA I and II adult patients undergoing elective surgery under general anesthesia were enrolled in the study. Exclusion criteria included patients with suspected difficult airway (Mallampati score > 3 and/or a thyromental distance < 5 cm) and gastroesophageal reflux.

All patients were premedicated with oral diazepam 5 mg. After administration of oxygen, anesthesia was induced with IV lidocaine 1 mg/kg, fentanyl 2–3 µg/kg, and propofol 2 mg/kg. Rocuronium 0.6 mg/kg was used for muscle relaxation. A size 3, 4, or 5, ILMA was used based on the weight of the patient and the discretion of the attending anesthesiologist. The patients' lungs were ventilated through the ILMA. The ease of ventilation was evaluated by monitoring of airway pressure, chest rise, and end-tidal CO₂ throughout the study. If ventilation was difficult, the ILMA was repositioned, removed and reinserted, or changed to a different size. If ventilation continued to be a problem, the study was aborted. A mixture of O₂/N₂O (34%/66%) and sevoflurane was used for maintenance of general anesthesia.

The patients were randomly assigned into three groups using a computer-generated list of random numbers. The first group (n = 20) was intubated with the 7.0-mm silicone wire-reinforced endotracheal tube. The second group (n = 21) was intubated with the 7.0-mm Parker endotracheal tube. The third group (n = 22) was intubated with the 7.0-mm PVC endotracheal tube (Fig. 1).

The endotracheal tubes were inserted through the ILMA with the curvature of the tube facing upwards. Chandy's maneuver,5 a useful maneuver to aid in the correct positioning of the ILMA and to facilitate blind intubation, was not used in our study. Intubation was considered successful if the endotracheal tube slid through the ILMA without any resistance and tracheal intubation was confirmed by fiberoptic bronchoscope and the detection of end-tidal CO₂. However, if resistance was felt, a 5-mm fiberoptic bronchoscope (Karl Storz 1130 1BN1) was inserted and the laryngeal structures preventing the passage were identified. Four areas were defined based on the glottic opening: the interarytenoid fold, the left and right aryepiglottic, the vestibular and vocal folds, and the tubercule of the epiglottis. If tracheal intubation was unsuccessful after the first attempt, the tube was pulled 2 cm, rotated clockwise, and then advanced. If this attempt was unsuccessful, the tube was pulled again 2 cm, rotated counterclockwise, and then advanced. If tracheal intubation was accomplished after either maneuver, this was considered a success and the maneuver used was documented. If both maneuvers failed, tracheal intubation was performed using fiberoptic guidance. The rationale for clockwise or counterclockwise manipulation of the tracheal tubes was to determine the potential benefit of the tracheal tube bevel when compared with the tracheal tube curvature. The successes and failures for tracheal intubations before and after manipulation, as well as the laryngeal structures obstructing the insertion of the tracheal tube, were documented.

Heart rate and oxygen saturation were continuously monitored throughout the study. Side effects such as bleeding, laryngospasm, or sore throat were documented.

Demographic and clinical continuous data were represented as mean ± sd and were compared with the analysis of variance with the Scheffé test for post hoc analysis. Frequencies and percentages were compared with the ² test. Statistical significance was considered at P < 0.05 level.

	RESULTS

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The patients' ages, weights, genders, Mallampati scores, and thyromental distances were not significantly different among the three groups (Table 1). The ILMA sizes used in the study were also comparable among the three groups (range, 3–5; median, 4). There were no adverse hemodynamic events after the placement of the ILMA. All patients were adequately ventilated and oxygenated throughout the intubation process and throughout the study.

Tracheal intubation was successful without manipulation in 18 of 20 (90%) patients in Group I and was significantly higher than the incidence of intubation in either Group II [12 of 22 (54%) patients] (P = 0.02) or Group III [10 of 21 (48%) patients] (P = 0.02). With clockwise or counterclockwise rotation of the tracheal tube, the number of successful intubations did not change in Group I, but it increased to 19 of 22 (86%) patients in Group II, and to 12 of 21 (57%) patients in Group III. The success rate of intubation between patients in Group I (90%) and patients in Group II (86%) was not significantly changed by the rotation of the tracheal tube (P = 0.72). However, the success rate of tracheal intubation in patients of Group III (57%) remained significantly lower in comparison to patients in both Group I (P = 0.02) and Group II (P = 0.03).

The sites of obstruction in 2 of the 20 patients of Group I in whom tracheal intubation failed were the interarytenoid fold and the right aryepiglottic. However, in 3 of the 22 patients of Group II and in 9 of the 21 patients of Group III in whom blind intubation was not possible, the site of obstruction was the tubercule of the epiglottis.

There were no statistically significant differences in the incidence of bleeding, laryngospasm, and/or sore throat among the three groups.

	DISCUSSION

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In this study, the success rate after the first attempt of tracheal intubation via an ILMA using the silicone wire-reinforced endotracheal tube, the posterior-beveled Parker tube, and the PVC lateral-beveled tube were 90%, 54%, and 48%, respectively. After manipulation, the success rates did not change for the silicone wire-reinforced tube, whereas it increased in the posterior-beveled and in the PVC lateral-beveled tubes to 86% and 57%, respectively.

The silicone wire-reinforced tube is a well designed, straight, soft, wire-reinforced silicone tube with a full silicone distal inch terminating in a conical Tuohy-like tip for use with the ILMA. The ILMA directs this flexible tube towards the plane of the glottis without distortion of the anatomy at an angle of 35 degrees.2 In our report, the success rate of the silicone wire-reinforced tube on the first attempt was 90%. Brain et al. and Kapila et al. assessed the ILMA and found a 99% and 95% success rate of intubation respectively, which is similar to our study.2,6 Despite manipulation, the success rate remains 90% because the silicone wire-reinforced tube lacks a curvature and a bevel.

The conventional PVC regular tube is less expensive, readily available, and disposable. However, our study showed that the PVC success rate was a low 48% after the first attempt and increased to only 57% with manipulation. This can be attributed to the impingement of the tip of the endotracheal tube on the tubercule of the epiglottis, as the tube has a steep curvature and exits the ILMA with an angle higher than 45 degrees. The PVC tracheal tube is stiff and emerges from the ILMA with its distal end pointing too anteriorly to enter the glottis. This explains the overall low success rate (57%). Joo et al. examined the maximal in vitro forces and pressures exerted by the tip of various tracheal tubes as they exit the ILMA and found that the PVC endotracheal tube exerted 7–10 times higher forces and pressures than the silicone and armored endotracheal tubes.3 Although heating and introduction with reverse curvature of PVC endotracheal tubes increased the success rate, they did not decrease the pressure exerted by the endotracheal tube on distal objects. This could contribute to increased morbidity to a patient's airway and esophagus. Therefore, caution must be used with the passage of the PVC regular tube into the ILMA and the use of force must be avoided to prevent airway trauma.

Using the posterior bevel Parker tube, the success rate was similar to that of the PVC endotracheal tube after the first attempt (54% vs 48%). The success rate increased after manipulation of the Parker tube to 86% vs 57% for the PVC tube. Also, with manipulation, the success rate of intubation when using the Parker tube increased (86%), which was not significantly different from the success rate of intubation when using the silicone wire-reinforced tube (90%). This increase in success rate may be attributed to the posterior bevel of the Parker Flex-Tip tube and its anterior flexible tip, which was designed to pass easily through the glottis.4,7 Although the Parker tube has a similar curvature to the regular PVC tube as it exits the ILMA, its anterior flexed tip prevents its impingement on the epiglottis. In addition, the flexed tip also helps it slide gently past the anatomical structures of the airway, thereby minimizing intubation trauma.

The patient population included in this study consisted of patients with normal airways. Our current findings might not apply to patients with difficult airways. However, our current findings warrant future similar study on patients with difficult airways. Lack of blinding, a small sample size, and lack of visualization of the position of the ILMA in relation to the laryngeal structures are other possible limitations of the current study. The lack of blinding reflects the impossibility of concealing the tubes during insertion through the ILMA. In addition, a good mask–larynx relationship was ascertained clinically rather than from a fiberoptic view. Before attempting intubation, the adequacy of pulmonary ventilation was determined through manual ventilation, end-tidal CO₂, and airway pressure. The fiberoptic scope was used only after a failed intubation to recognize the obstructing structure.

In conclusion, our report shows that in patients with normal airways the success rate after the first attempt of blind tracheal intubation via an ILMA was 90% with the silicone wire-reinforced tube, whereas the success rate using the Parker tube or the PVC tube was much lower (54% and 48%, respectively). Manipulation improved the intubation success rate in the Parker tube to 86%, comparable to the silicone wire-reinforced tube, and making the Parker tube with minimal manipulation a possible alternative to the manufacturer-supplied silicone wire-reinforced tube.

	Footnotes

 
Accepted for publication April 24, 2008.

	REFERENCES

Top Abstract Introduction METHODS RESULTS DISCUSSION REFERENCES

 

1. Benumof JL. Laryngeal mask airway and the ASA difficult airway algorithm. Anesthesiology 1996;84:686–99[Web of Science][Medline]
2. Brain AIJ, Verghese C, Addy EV, Kapila A. The intubating laryngeal mask. I: development of a new device for intubation of the trachea. Br J Anaesth 1997;79:699–703[Abstract/Free Full Text]
3. Joo HS, Kataoka MT, Chen RJB, Doyle J, Mazer D. PVC trachel tubes exert forces and pressures seven to ten times higher than silicone or armoured tracheal tubes-an in vitro study. Can J Anaesth 2002;49:986–9[Web of Science][Medline]
4. Baraka A, Rizk M, Muallem M, Haroun-Bizri S, Ayoub C. Posterior-beveled vs. lateral-beveled tracheal tube for fiberoptic intubation. Can J Anaesth 2002;49:889–90[Web of Science][Medline]
5. Ferson D, Rosenblatt W, Johansen M, Osborne I, Ovassapian A. Use of the intubating LMA-Fastrach in 254 patients with difficult-to-manage airways. Anesthesiology 2001;95:1175–81[Web of Science][Medline]
6. Kapila A, Addy EV, Verghese C, Brain AIJ. The intubating laryngeal mask airway: an initial assessment of performance. Br J Anaesth 1997;79:710–13[Abstract/Free Full Text]
7. Hwan S, Joo D, Keith Rose. The intubation laryngeal mask airway with and without fiberoptic guidance. Anesth Analg 1999;88:662–6[Abstract/Free Full Text]

This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Kanazi, G. E. Articles by Ayoub, C. M. Search for Related Content PubMed PubMed Citation Articles by Kanazi, G. E. Articles by Ayoub, C. M. Related Collections Airway General