Supraglottic airway devices have been believed to be suitable for routine anaesthesia and emergency airway management. There is a wide range of supraglottic airway devices for airway management; these include the classic laryngeal mask airway (cLMA), Proseal laryngeal mask airway (pLMA), intubating laryngeal mask airway Fastrach, laryngeal tube, Combitube, Cobra perilaryngeal airway and so on.
The I-gel (Intersurgical, Wokingham, UK) has been introduced as a novel supraglottic airway device. The tip of the I-gel is composed of a soft, gel-like, transparent and thermoplastic elastomer and was designed to obviate the need for cuff inflation and provide a widened, flattened and semi-rigid stem for the stabilizer. Recent observational studies have demonstrated that the I-gel offered a good seal and effective ventilation during general anaesthesia.1–3 Furthermore, some reports have shown that the I-gel protects against aspiration,4,5 secures the airway during cardiopulmonary resuscitation6 and protects against unexpected difficult intubation.7–9 It is expected that the I-gel will be an effective supraglottic airway device and provide an alternative to the LMA. The aim of the present study was to compare the success rate of insertion, airway sealing effects and complications of the I-gel with those of the cLMA and pLMA for airway management in anaesthetized, paralysed patients.
Our study was performed in the two medical centres. After the approval by each Institutional Ethics Committee and written informed consent, 167 American Society of Anesthesiologists (ASA) I–II patients scheduled for lower-extremity orthopaedic surgery were included in the study. The exclusion criteria included presence of any significant acute or chronic lung disease, known airway problems, potential difficult intubation (history of difficult intubation, Mallampati score 3 or 4, thyromental distance <60 mm, mouth opening <35 mm, rheumatoid arthritis)10 and increased risk of aspiration (BMI >35 kg m−2, gastroesophageal reflux, neuromuscular disease, pharyngeal dysfunction).11 After enrolment, the patients were randomly assigned to the cLMA (n = 50), pLMA (n = 53) and I-gel (n = 64) groups. Randomization was performed by an envelope method.
Routine monitoring was used throughout the study, including electrocardiography, heart rate, pulse oximetry, noninvasive blood pressure and end-tidal CO2 (ETCO2). Anaesthesia was induced with intravenous propofol 2 mg kg−1 and remifentanil 1 μg kg−1. Rocuronium 0.6 mg kg−1 was administered as a muscle relaxant. I-gel, cLMA or pLMA was inserted when no response was obtained in the train-of-four stimulation. In accordance with manufacturer's manual, size selection of the I-gel depended on patient's weight: size 3 was used for patients less than 50 kg, size 4 was used for those between 50 and 90 kg and size 5 was used for those over 90 kg in weight. The sizes of cLMA and pLMA were also decided by the patient's size. All supraglottic airway devices were inserted by anaesthesiologists who have experience with the LMA approach. Anaesthesia was subsequently maintained with target-controlled infusion of propofol and remifentanil, at effect-site concentrations of 2–3 μg ml−1 and 5–7 ng ml−1, respectively. Patients were ventilated with tidal volume of 8–10 ml kg−1. Respiratory rate was controlled to obtain an ETCO2 between 30 and 35 mmHg. The inspiratory to expiratory ratio was set at 1: 2. In addition, we monitored the bispectral index (BIS; Aspect Medical system, Norwood Massachusetts, USA) to achieve a target BIS in the range 40–60. At the end of the surgical procedure, anaesthetic agents were discontinued. The device was removed when the patients were able to open their mouth to command.
Mean blood pressure, heart rate, success rate of the insertion of the device, the airway leak pressure and volume and complications were compared among the groups. We recorded the haemodynamic data before induction of anaesthesia, at 1, 3, 5, 7 and 10 min following insertion of devices. Successful placement was confirmed by bilateral chest wall movement, auscultation, normal capnograph curves and normal values for partial pressure of ETCO2. If an effective airway could not be obtained, the following manipulations were allowed: gentle pushing or pulling of the device, chin lift, jaw thrust, head extension or neck flexion. A failed insertion could be followed by two further attempts; however, if the third attempt failed, this was recorded as a failure of the device and then the patient underwent endotracheal intubation. The airway leak pressure was assessed by closing the expiratory valve of the circle system at a fixed gas flow of 3 l min−1, noting the airway pressure (maximum allowed was 40 cmH2O). At this time, gas leaks at the sealing pressure were evaluated by auscultation using a stethoscope placed at the patient's mouth. The leak volume was obtained by calculation of volume differences between the inspiration and expiration. Complications such as hypoxia, regurgitation, pulmonary aspiration, laryngospasm, bronchospasm, gastric insufflation, blood adhesion to the device, tongue or lip trauma or hoarseness were recorded by an anaesthesiologist. The postanaesthesia care unit nurse recorded the presence or absence of sore throat before discharge to the ward.
To estimate sample size, a pilot study was conducted measuring the leak pressure for the I-gel in anaesthetized patients. The standard deviation of the leak pressure in I-gel group was 6 cmH2O and a difference of 3 cmH2O (difference of 10%) in leak pressure was assumed to be clinically relevant.12,13 We needed more than 50 patients per group with α equal to 0.05 and β equal to 0.8. The data were analysed for normal distribution using the Kolmogorov–Smirnov test. Statistical analysis among the groups was performed by one-way analysis of variance (ANOVA), the Kruskal–Wallis test or the χ2 test. Haemodynamic data were analysed using two-way repeated measures ANOVA. Data analysis was performed using SigmaStat 3.10 software. Data were presented as mean ± SD. A P value less than 0.05 was considered to indicate statistical significance.
There were no differences among the three groups in demographic characteristics and in haemodynamic data (Table 1, Fig. 1). In all patients, cLMA, pLMA and I-gel were inserted within three attempts. The success rate of the first attempt was lower for the I-gel (78%) than for the pLMA and cLMA (89 and 84%, respectively); however, these differences were not statistically significant (P = 0.670). Airway leak pressure in the I-gel and pLMA groups, both had no difference, were significantly higher than that in the cLMA group (Table 2, Fig. 2). The leak volumes were not different among the groups (Table 2). There were no episodes of hypoxia, pulmonary aspiration, regurgitation, laryngospasm, bronchospasm or gastric insufflation. There was no difference in the incidence of blood adhesion to the device, but the number of patients with sore throat in the cLMA group was significantly larger than those in other two groups (Table 2).
The important finding of the present study was that the airway sealing pressure achieved with the I-gel was similar to that achieved with the pLMA and greater than that with cLMA. Additionally, incidence of sore throat in the I-gel was lower than that in the cLMA.
It has been shown that the bulky cuff design of the pLMA provides an excellent sealing effect for positive pressure ventilation. Indeed, many studies have shown that the oropharyngeal sealing pressure achieved with the pLMA is greater than that achieved with the cLMA both in patients and in cadaver models.12,14–16 Our results are consistent with their reports. The pLMA probably forms a better seal because the larger ventral cuff stops gaps in the proximal pharynx and the dorsal cuff pushes the ventral cuff more firmly into the periglottic tissues.12
The novel supraglottic airway device, I-gel, is designed to fit into the postcricoid cervical oesophagus and abut the aryepiglottic folds and pharyngoepiglottic folds, and the proximal portion of the bowl contacts the tip of the epiglottis and the base of the tongue.17 In our study, the mean airway leak pressure in the I-gel group was 27.1 cmH2O. This result is consistent with the results of earlier studies, reporting that the I-gel provides an airway leak pressure of 24–33 cmH2O.1–3 Airway leak pressure of I-gel was similar to that in the pLMA group but greater than that in the cLMA group in the present study. A recent study has also suggested that the I-gel could be an alternative to the cuffed tracheal tube with moderate airway pressure.18 Although airway sealing pressures were significantly different between I-gel and cLMA groups, around 24 cmH2O sealing pressure for cLMA is usually enough to ventilate adequately in general anaesthesia.
It was shown that the cLMA is easier and quicker to insert at the first attempt than the pLMA.12,16 The difficulty with pLMA insertion is probably caused by the larger cuff, the lack of a backplate, the precise tip positioning and the nonlinear leading edge formed by the drain tube.19 In the recent study, using various manikins, it was reported that the I-gel insertion was easier for beginners compared with LMA insertion.20 In our study, there were no significant differences in success rate among the three groups; however, success rate of first attempt in the I-gel group is likely lower than those of pLMA and cLMA. One of the reasons for this result might be that the anaesthesiologists in our study were familiar with the pLMA and cLMA but not with the I-gel.
A previous study has shown that sore throat after I-gel insertion was reported by 18% of patients and blood-tinged complications were reported to be in 1% of patients,2 whereas no case showed blood adhesion to the I-gel, in the present study. The pLMA and cLMA were associated with increased rates of postoperative blood staining compared with the I-gel, but the difference was not statistically significant. The inflatable cuffs of the pLMA and cLMA have the potential to cause complications such as mucosal injury, sore throat, airway obstruction and gastric insufflation,19 in contrast with the I-gel without an inflatable cuff. However, the I-gel could cause complications such as nerve injury, regurgitation and aspiration.4,21
One of the limitations of our study is that the data were collected by unblinded observers. In addition, the anaesthesiologists had much more experience with cLMA and pLMA than with the I-gel. These factors might have produced some bias in the results.
In conclusion, the I-gel has a similar airway sealing effect to that of pLMA, higher than that of cLMA and is not associated with adverse effects in anaesthetized, paralysed patients. The I-gel could be an effective alternative as a supraglottic airway device.
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Keywords:© 2010 European Society of Anaesthesiology
I-gel; laryngeal mask airway; supraglottic airway