The Augustine Guide[trademark symbol] (AG) is a premolded device designed to engage in the glossoepiglottic fold to facilitate blind orotracheal intubation. Kovac  first used the AG in cadavers and described its design, use, and potential advantages. Later, Carr and Belani  used the AG with a guiding stylet in 100 anesthetized and paralyzed adult patients and claimed a 94% success rate in performing rapid, blind orotracheal intubation. However, no large study of the AG has been performed to determine its success rate in relation to predicting a difficult airway. Hence, we performed a prospective study in 530 cases of orotracheal intubation using the AG to evaluate its success rate in relation to the Mallampati classification [3,4] and Cormack and Lehane's  laryngoscopic view of the upper airway.
The study was approved by our institution's ethical committee, and informed consent was obtained from each patient. We studied 530 patients, ASA physical status I or II, of either sex, aged 16-73 yr, who were undergoing elective surgical procedure under general anesthesia. A preanesthetic airway assessment was performed using Mallampati classification [3,4]. Induction of anesthesia was achieved with IV thiopental (5 mg/kg). Ease of manual ventilation and patency of airway were ensured by intermittent positive pressure ventilation via a face mask using 100% oxygen. Vecuronium (0.1 mg/kg) was administered IV, and the lungs were ventilated with 50% N2 O and 0.5% halothane in oxygen for 3 min. Laryngoscopy was performed with a curved blade Macintosh laryngoscope, and the view obtained was classified as described by Cormack and Lehane . The classification was as follows: grade I = most of the glottis visible, grade II = only the posterior extremity of glottis visible, grade III = no part of the glottis visible-only the epiglottis, grade IV = not even the epiglottis visible. The preanesthetic assessment of the airway and the laryngoscopic view grading under anesthesia were performed by the nonintubating anesthesiologist. The intubating anesthesiologist was blinded to the result of assessments.
While in the supine position, anesthetized, and paralyzed, the patient's head was held in neutral position. The mouth was opened, and a tooth block was placed between the upper and lower molars. An AG loaded with a well lubricated endotracheal tube and guide catheter (50 cm long, 16-French gauge soft, polyvinyl chloride suction catheter) was introduced into the oral cavity and advanced until its semilunar tip engaged the glossoepiglottic fold. The guide catheter was negotiated into the larynx and advanced 8-10 cm in the trachea. Absence of resistance to catheter insertion coupled with free and easy aspiration of air with a 50-mL syringe confirmed successful placement in the trachea. The endotracheal tube was detached proximally from the AG and advanced over the guide catheter into the trachea. The guide catheter and AG were then removed, and the endotracheal tube was connected with the breathing system after inflating the tracheal cuff. Correct placement of the endotracheal tube was confirmed by chest auscultation and capnography.
The tracheas of all patients were intubated with a 7-or 7.5-mm Portex cuffed endotracheal tube. A maximum of three attempts was conducted with the AG. First, two attempts were made without retracting the tongue; for the third attempt, the tongue was retracted out anteriorly. Between the attempts, the lungs were ventilated via a face mask, and SpO2 was maintained above 96%. After three failed attempts with the AG, the trachea was intubated under direct laryngoscopy with or without a stylet, bougie, or laryngeal mask airway. The difficulties encountered during the placement of the AG, advancement of the guide catheter into the larynx, negative air aspiration, or sliding over the endotracheal tube into the trachea were noted. After successful orotracheal intubation, the oral cavity was examined for orotracheal trauma.
Endotracheal intubation was successful in 93.6% of the cases. Among the successful intubations, 67.5% were in the first attempt, 29.1% in the second attempt, and 3.4% in the third attempt.
The overall success rate in repositioning of the AG and guide catheter were not significantly different among the Mallampati classes and Cormack and Lehane's laryngoscopic grades (Table 1 and Table 2). In 85 patients (16%), cricoid pressure or external laryngeal manipulation was required to facilitate insertion of the guide catheter or endotracheal tube. Among 34 patients (6.4%) in whom tracheal intubation was not possible with the AG, 25 met with resistance and the guide catheter could not be inserted into the trachea. In 9 patients, the guide catheter entered into the esophagus, as confirmed with negative aspiration of air. In 16% of patients, after successful placement of guide catheter into the larynx, passage of the endotracheal tube became obstructed by the guide itself or by the tongue. The endotracheal tube was placed successfully in the next attempt after good lubrication of endotracheal cuff and the AG with 5% lidocaine jelly. None of the patients had significant arterial desaturation (SpO2 < 95%) during the procedure.
Among 34 failures, the tracheas of 28 patients were intubated under Macintosh curved blade laryngoscopy with or without a stylet, 2 with a gum elastic bougie, and 3 via a laryngeal mask airway and bougie. For 1 patient in whom tracheal intubation was not possible, surgery was successfully performed via laryngeal mask anesthesia. Overall, 3% of patients had minor injuries to oropharyngeal mucosa and 2.5% to the frenulum or tongue. Twenty-two patients presented with loose upper teeth. Three suffered dental injury.
AG-aided blind orotracheal intubation was successful in 93.6% of anesthetized, paralyzed patients. Our overall success is comparable with that of Carr and Belani , who used the AG with a guiding stylet after retraction of the tongue anteriorly and reported successful endotracheal intubation in 94% of patients. Our study shows a greater rate of successful intubations (70%) in Mallampati class IV than did Carr and Belani  (50%). Unlike Carr and Belani , in our first two attempts, we did not retract the tongue anteriorly, but used this option in a third attempt. The overall incidence of trauma to the frenulum and tongue was less (2.5%) in our study compared with that of Carr and Belani (7%). Because we could intubate the tracheas of most patients, the retraction of the tongue anteriorly did not seem necessary. The use of a soft suction catheter in place of a rigid guiding stylet decreased the incidence of trauma to oral cavity soft tissues and helped in suctioning the oropharyngeal secretions. Like those of Carr and Belani, all of our patients were relaxed and received positive pressure bag mask ventilation before AG-assisted intubation was attempted. None of our patients showed a false-positive aspiration test when the guide catheter was in the esophagus. The possibility of false-positive aspiration can further be minimized by attempting quick aspiration through a 50-mL syringe, because the possibility of that amount of air collecting in the esophagus seems negligible.
We found no significant correlation between Mallampati class and Cormack and Lehane's  grading of the laryngoscopic view, with or without retraction of tongue, with patients who had failed intubation with the AG. It is well known that Cormack and Lehane's grades III and IV patients are at risk of difficult or failed intubation because the larynx is not visible under direct laryngoscopy. Unfortunately, this cannot be known preanesthetically. Because of the diversity of factors involved, the desire for a simple bedside test to predict all cases of difficult intubation may be unduly optimistic . It is axiomatic that a careful preanesthetic assessment, which results in the prediction of a potentially difficult airway, represents the best method for avoiding problems. Yet even the most scrupulous preanesthetic assessment [7,8] does not predict every case of difficult intubation. Sia and Edens  estimated that 90% of cases of difficult intubation could be predicted, whereas 10% could still pose unexpected problems. On the other hand, no single method or device guarantees 100% success in tracheal intubation. In our experience, the AG is a safe, handy, light-weight, and effective tool for blind orotracheal intubation in most anesthetized and paralyzed patients.
1. Kovac AL. Augustine Guide: a new device for blind orotracheal intubation. Anesthesiol Rev 1993;1:25-9.
2. Carr RJ, Belani KG. Clinical assessment of Augustine Guide[trademark symbol] for endotracheal intubation. Anesth Analg 1994;78:983-7.
3. Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J 1985;32:929-34.
4. Samsoon GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987;42:487-90.
5. Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984;39:1105-11.
6. Charters P. What future is there for predicting difficult intubation? Br J Anaesth 1996;77:309-11.
7. Sia RL, Edens ET. How to avoid problems when using the fibreoptic bronchoscope for difficult intubation. Anaesthesia 1981;36:74-7.
© 1998 International Anesthesia Research Society
8. Wilson ME, Speiglhalter D, Robertson JA, Lesser P. Predicting difficult intubation. Br J Anaesth 1988;61:211-6.