Securing the airway in patients for general anaesthesia is performed routinely by an anaesthesiologist using a laryngoscope. When a difficult airway is encountered, other tools need to be employed. Two options that have emerged are the GlideScope® video intubation system and the intubating laryngeal mask.
The GlideScope® (Saturn Biomedical System Inc., Burnaby, British Columbia, Canada) is a new video laryngoscope that is designed as an alternative for managing normal  and difficult airways . The GlideScope® incorporates a high-resolution digital camera located in the middle of the reusable plastic laryngoscope blade tip. It is inserted like a conventional Macintosh laryngoscope, but in the midline position without the need to sweep the tongue to the right. The glottis is visualized through a video cable, using a high-resolution LCD monitor . The blade design of the GlideScope® has several advantages: an embedded anti-fogging mechanism, a reduced overall thickness of 18 mm and a 60° curvature to view the anterior glottis without the need for direct line of sight.
The intubating laryngeal mask airway (ILMA; FastrachTM, Laryngeal Mask Company, Henley-on-Thames, UK) is a new device specifically designed to be an effective ventilatory device and blind intubation guide in patients with normal and abnormal airways. The principal features of the ILMA are an anatomically curved, rigid airway tube with an integral guiding handle, an epiglottic elevating bar replacing the LMA bars, and a guiding ramp to direct the tracheal tube anteriorly as it emerges from the mask aperture .
There is no study comparing the ease of intubation of these two devices. This prospective randomized study aimed to compare the effectiveness of the ILMA technique with the GlideScope® in aiding endotracheal intubation in Asian female patients with normal airways. As airway management is routine in anaesthetic practice, the option and availability of a reliable tool to secure the airway other than direct laryngoscopy is important to decrease morbidity in difficult airway situations. This trial comparing the ILMA and the GlideScope® allows an anaesthesiologist proficient in both devices to select the most effective device in anticipated and unanticipated difficult airways.
Materials and methods
After Ethics Committee approval and obtaining patients' written informed consent, we recruited 60 ASA I or II patients undergoing elective gynaecological surgery requiring intubation into our study. Exclusion criteria were patients with difficult airways (defined as patients with a history of impossible intubation, mouth opening (inter-incisor distance) less than 20 mm, or cervical spine fixed in flexion, Mallampati Class III or IV, thyromental distance less than 65 mm), ASA Grade III, IV or V, those with respiratory tract pathology or coagulation disorders, or at risk of regurgitation–aspiration (previous upper gastrointestinal tract surgery, known hiatus hernia, oesophageal reflux, peptic ulceration or not fasted). Randomization was performed using sealed opaque envelopes.
Before induction of anaesthesia, preoxygenation was performed in all cases (4 min by bag and mask with 100% O2). Each patient was routinely monitored during the entire procedure by electrocardiography, pulse oximetry, capnography and non-invasive blood pressure measurements. Anaesthesia was induced with fentanyl 1–2 μg kg−1, propofol 2.5 mg kg−1 intravenous (i.v.) and muscle relaxation with atracurium 0.5 mg kg−1 i.v. Patients were ventilated via a face-mask and maintained with sevoflurane 2% in oxygen and nitrous oxide 66% for 3 min and until the train-of-four count was zero. All tracheal intubations were performed by anaesthesiologists with considerable experience with both techniques of intubation (number of uses of each >30).
In the ILMA group, an ILMA was inserted using a single-handed rotational technique . If resistance was felt during bag ventilation or if the tracheal intubation had failed, a predetermined sequence of adjusting manoeuvres was performed as previously recommended: (a) performing an up–down manoeuvre to prevent the epiglottis from down-folding, by swinging the ILMA back outward a few centimetres without deflating the cuff and then repositioning the ILMA; (b) optimizing the airway by steering the ILMA with the handle and moving it in the horizontal plane from one side to the other or raising the mask upward, while squeezing the reservoir bag to obtain the lowest resistance during insufflation and a complete expiration and (c) removing the ILMA to change its size. Initial size selection for the ILMA was as follows: size 3 for patients less than 50 kg and size 4 for those greater than 50 kg. However, the anaesthesiologist was permitted to change the size during the study.
The cuff was inflated with air (size 3, 20 mL; size 4, 30 mL; size 5, 40 mL), and an anaesthesia circuit was connected. The position of the ILMA was adjusted until optimal ventilation was obtained. This position was maintained by holding the handle firmly. The tracheal tube was inserted through the ILMA and advanced to 9 cm beyond the epiglottic elevating bar if no resistance was felt. If resistance was felt through the tracheal tube, the ILMA was readjusted in the patient's mouth before the second attempt of tracheal tube insertion. If tracheal intubation was unsuccessful in the second attempt, the following adjusting manoeuvres were performed before a further attempt depending on the depth of resistance: 1.5–2.0 cm, withdrawal of the ILMA by 5 cm followed by reinsertion; 0–1.5 or >4 cm, a smaller size ILMA is used; and 2–4 cm, a larger size ILMA is used . In the ILMA group, ventilation using the ILMA was permitted between attempts, if required.
In the GlideScope® group, the anaesthesiologist introduced the blade and the camera portion of the GlideScope® along the middle of the tongue. The glottic opening was observed on the LCD screen by advancing the blade down the posterior pharynx while following the path of advancement on the LCD screen. A stileted size 7 endotracheal tube forming a curve to follow the 60° angulation of the GlideScope® blade was introduced. Correct placement was confirmed with auscultation and capnography. If the anaesthesiologist failed to introduce the endotracheal tube through the glottic opening, the following manoeuvres were used to aid tracheal intubation: external laryngeal pressure, withdrawal and readjustment of the stilet, increased lifting force of the intubating device or withdrawal of the intubating device. The anaesthesiologist was asked to grade:
- best laryngeal view and score it using the 5-grade modified Cormack and Lehane system (Grade I–IV);
- ease of device insertion;
- difficulty of tracheal intubation using a visual analogue scale. The scale, a line 0–100 mm, was used for each attempt; the word ‘easiest' was described on the left side of the line, and ‘most difficult' on the right side.
An independent observer recorded the following:
- Time taken for successful tracheal intubation: measured from the time the anaesthesiologist picked up the assigned intubating device to the time capnography confirmed the correct placement of the tracheal tube.
- Success or failure of the tracheal intubation attempt (a failed attempt is defined as removal of the tracheal tube from the oral cavity or the ILMA).
- Number of attempts needed for successful tracheal intubation.
- Manoeuvres needed to aid tracheal intubation: e.g. external laryngeal pressure, readjustment or withdrawal of stilet, bougie assisted, increased lifting force of the intubating device or withdrawal of the intubating device.
- Complications associated with tracheal intubation: e.g. desaturation (SPO2 < 95%) of the patient, bleeding or oesophageal intubation, lips or dental injury, mucosal injury, postoperative sore throat.
- Haemodynamic response to intubation: preintubation and every 2.5 min post-intubation for the first 5 min.
The anaesthesiologist was allowed three attempts or up to 120 s to intubate the trachea successfully. More than three attempts or 120 s was regarded as failure of intubation. Failure to secure the airway with either device resulted in the use of direct laryngoscopy to secure the airway.
Our primary comparison measure was time to successful tracheal intubation. Based on our pilot study and a previous study , power analysis showed that in order to show a difference of more than 50% in both groups with 80% power at the 0.05 level of significance, 24 patients are needed in each group. We therefore recruited 30 patients in each group to account for drop-outs. Patients with failed intubation were not included in the analysis of the total intubation time. We used the t-test to analyse patient characteristics and parametric data. The U-test was used to compare ASA status, Mallampati scores, ease of insertion/intubation and number of attempts needed between the two groups. Fisher's exact test was used for comparison of side-effects, and the general linear model was used for repeated measures for haemodynamic variables. All statistical analyses were performed using SPSS 11.5 TM (SPSS Inc., Chicago, IL, USA) software. Data are expressed as mean (standard deviation) unless otherwise stated. A P value of <0.05 was considered statistically significant.
The patient characteristics profiles were similar between both groups (Table 1). All three investigators recruited patients into the trial. Placement of the ILMA and adequate ventilation were achieved in the first attempt in all patients. The initial choice of ILMA was size 3 in 13 patients and size 4 in 17 patients. Four patients in the GlideScope® group were intubated using the paediatric-sized GlideScope® blade and 26 patients using the adult blade.
The time taken for successful intubation was significantly shorter with the GlideScope® than the ILMA (Table 2). Successful tracheal intubation on the first attempt occurred in all patients using the GlideScope® compared to 19/27 for the ILMA, and more patients required more than two attempts to achieve successful tracheal intubation in the ILMA group (1/27 vs. 0/29; Table 2). One failed intubation occurred in the GlideScope® group and three in the ILMA group, and direct laryngoscopy had to be used, which revealed an unexpected Grade III larynx in these patients.
The mean difficulty score for insertion of the device was also significantly lower for the GlideScope® group than for the ILMA group (Table 2). Nineteen patients in the ILMA group required one or more manoeuvres prior to successful intubation: 10 patients required the up–down manoeuvre, two required steering, and seven required removal and then reinsertion. Sixteen patients in the GlideScope® group required additional manoeuvres as follows: one required removal and reinsertion, 10 required external laryngeal pressure, four required withdrawal of the blade and one required increased lifting force. Anaesthesiologists in either group did not have to change the size of the device used. There were also no significant differences between the blood pressure (BP) and heart rate (HR) changes before and after intubation (Table 2).
The complication rate was also significantly higher in the ILMA group, with seven patients in the ILMA group but none in the GlideScope® group (P < 0.05) having some blood-stained secretions after intubation, suggestive of trauma to the airway during intubation attempts. Oesophageal intubation occurred in seven patients in the ILMA group and none in the GlideScope® group (P < 0.05). The numbers of patients with postoperative sore throat were similar in both groups (four in the ILMA group and five in the Glidescope® group). There were no instances of difficulty ventilating through the ILMA or desaturation during insertion, severe soft tissue or dental trauma, aspiration or regurgitation related to the use of these devices. Oxygen saturation fell below 95% transiently for one patient in the GlideScope® group.
There have been many studies comparing the use of ILMA or GlideScope® with conventional or other intubation techniques. But to our knowledge, this is the first study comparing the use of ILMA vs. the GlideScope®. We showed that the GlideScope® was easier to insert and significantly shortened the time for successful intubation. The time taken for successful intubation using the GlideScope® was comparable with our previous study. The improvement of intubation time of 33 s seen with the GlideScope® may be clinically significant in influencing our choice of airway adjuncts for use in patients with difficult airways, in which the instrument that allows a faster intubating time will decrease the apnoeic period, reducing the risk of hypoxia in difficult intubations.
We found that the first-time success rate for blind ILMA-guided intubation was lower than that for GlideScope®-guided intubation, which is comparable to studies carried out by Bilgin and Kihara [8,9]. The difficulty scores were also higher when using the ILMA compared to the GlideScope® in our patients. The ease of intubation and mean time taken for successful intubation via the ILMA is comparable with earlier studies [6,10,11]. This is probably because intubation with the ILMA is a two-stage process of placement and then intubation compared with the GlideScope® technique.
The incidences of postoperative airway complications are similar between the groups . Being a blind technique, the chances of failed intubation or oesophageal intubation will be higher in the ILMA group as shown in our study. Our incidence of oesophageal intubation rate (23.3%) in the ILMA group is comparable to the study carried out by Kihara . The high incidence of oesophageal intubation in our study suggests that early confirmation of successful tracheal intubation via the ILMA is mandatory. Direct visualization of the glottic area via a fibreoptic technique, or even the use of the C-trach , will help to decrease frequency of oesophageal intubation. Other complications such as airway trauma and postoperative sore throat for the ILMA group were comparable with previous studies [13-15]. This may perhaps be due to the high mucosal pressures exerted by the ILMA  or as a result of easier detection of bleeding with the ILMA, because of the cuff collecting supra-cuff material. Although this result is significant, our study was not powered to detect the risk of complications associated with the use of each device. On the other hand, the video monitor of the GlideScope® helps the anaesthesiologist performing the tracheal intubation and the assistant in providing the right laryngeal manipulation to improve their co-ordination, causing less trauma.
We enrolled only patients with normal airways in our study. Intubation success rates with the ILMA may be higher in patients with abnormal airways  (perhaps owing to the tube being better directed towards a higher anterior larynx) and our results may not be applicable in this situation. Nevertheless, the role of the ILMA seems promising for difficult airways [18,19], especially those requiring ventilation in between intubation attempts, e.g. difficult airway algorithm. Even if blind intubation fails, we still have the option of securing the airway with the ILMA without the tube. Being able to provide ventilation provides the anaesthesiologist with precious time to make alternative plans for securing the airway should intubation be deemed necessary, e.g. fibreoptic-guided intubation through the ILMA.
Both devices are useful adjuncts to intubation for use in difficult airways [7,20], with less potential for haemodynamic stimulation. The use of the intubating laryngeal mask is associated with minimal haemodynamic changes , which was also shown in our study. The GlideScope® operates on a video laryngoscope system, which shows a good haemodynamic profile . It was proven to be safe in a large prospective trial and the results are comparable with routine direct laryngoscopic intubation . One advantage of the ILMA over the GlideScope® is that it can provide effective ventilation between intubation attempts , avoiding hypoxia in the patient with a potentially difficult airway or in multiply-injured patients with head injuries where hypoxia would be detrimental . Other than allowing ventilation in between attempts, blind intubation through the ILMA offers few advantages over the GlideScope® for adult patients requiring intubation for elective surgery with normal airways, but it is a feasible alternative.
Our study has a few limitations. Our study population consisted of only young Asian females who did not have difficult airways, whose airway characteristics such as anterior larynx and smaller airways may differ from other populations . Our results may not apply to those of different age groups, different ethnic descent, or males or patients with difficult airways. Our patients were healthy, and haemodynamic responses may be different in patients with cardiovascular disease. The intubation was performed by several anaesthesiologists who were relatively experienced in the use of these two devices. Our findings may not apply to those with less skill with the particular airway device, with a learning curve involved.
In conclusion, the GlideScope® is a more effective technique in aiding endotracheal intubation in patients with normal airways. It improved intubation times and achieved lower difficulty scores for tracheal intubation as compared with the ILMA. Blind intubation through the ILMA offers few advantages over the GlideScope® for adult patients with normal airways requiring intubation for elective surgery. However, it can provide effective ventilation between intubation attempts and an intubation guide with potential for use in patients who may present difficulty in tracheal intubation. Despite its limitations, the ILMA is a valuable adjunct to the airway management armamentarium, especially in cases of difficult airway management, when it can provide ventilation in between intubation attempts. However, the longer intubation time and greater risk of oesophageal intubation must be taken into consideration.
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