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Original Article

Stability of the LMA-ProSeal® and standard laryngeal mask airway in different head and neck positions: a randomized crossover study

Brimacombe, J.*; Keller, C.

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European Journal of Anaesthesiology (EJA): January 2003 - Volume 20 - Issue 1 - p 65-69
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Abstract

The LMA-ProSeal® laryngeal mask airway (LMA North America, Inc, San Diego, CA, USA) is a new laryngeal mask airway device with a large wedge-shaped double cuff and a drainage tube parallel to a flexible airway tube. In a preliminary study, Brain and colleagues [1] showed that the Size 4 LMA-ProSeal® laryngeal mask airway formed a more effective seal than the standard laryngeal mask airway and facilitated gastric tube placement. The anatomical position of the standard and flexible laryngeal mask airway does not vary with head-neck position, but the oropharyngeal leak pressure increases with flexion and decreases with extension [2,3]. We considered that the differences in cuff shape/size and tube configuration compared with other laryngeal mask airway devices might influence the stability of the LMA-ProSeal® laryngeal mask airway in different head-neck positions. In addition, there are no published data about the Size 5 LMA-ProSeal® laryngeal mask airway. The following randomized crossover study compared the oropharyngeal leak pressure, the intracuff pressure and the anatomical position (assessed fibreoptically) for the Size 5 LMA-ProSeal® laryngeal mask airway and the laryngeal mask airway in different head-neck positions and intracuff volumes.

Methods

Device description

The LMA-ProSeal® laryngeal mask airway (Figs 1 and 2) is made from medical-grade silicone and has the following new or modified features (intended purpose): (a) a dorsal cuff (pushes the ventral cuff into the periglottic tissues to improve the seal); (b) a drainage tube that travels from the tip, through the bowl and alongside the airway tube (for passage of an ≤18-G gastric tube, for venting regurgitated fluid and to provide information about device position); (c) a built-in bite block; (d) a locating strap on the anterior distal tube (prevents the finger or introducer slipping off the tube); (e) the ventral cuff is larger proximally (to improve seal by plugging gaps) and contained posteriorly by a bucket-shaped section of the distal tube; (f) an accessory vent under the drainage tube in the bowl (prevents pooling of secretions and acts as an accessory ventilation port; (g) a double tube configuration (increases stability); (h) a wire-reinforced airway tube (prevents the double tube configuration from being too stiff); and (i) a deeper bowl than the standard laryngeal mask airway (facilitates a better fit in the pharynx). The LMA-ProSeal® laryngeal mask airway does not have a semirigid shield and does not have mask aperture bars; the drainage tube functions as a mask aperture bar for the accessory vent.

Figure 1
Figure 1:
LMA-ProSeal® laryngeal mask airway with the cuff inflated and deflated (upper and lower left windows), and the drainage tube travelling through the bowl to the tip (right lower window). A: Dorsal cuff; B: drainage tube; C: bite block; D: locating strap; E: ventral cuff; F: accessory vent; G: double-tube configuration; H: airway tube - wire reinforced; I: deeper bowl.
Figure 2
Figure 2:
LMA-ProSeal® laryngeal mask airwayin situ.

Clinical study

Thirty male adult patients (aged 18-80 yr) ASA I-II participated in this randomized crossover trial. Ethics Committee approval and informed consent were obtained. Patients were excluded if they were at risk of pulmonary aspiration, had limited head-neck movement or were otherwise unsuitable for the LMA-ProSeal® laryngeal mask airway or the laryngeal mask airway. A standard anaesthesia protocol was followed. Anaesthesia was induced with propofol 2.5 mg kg−1, and was maintained with sevoflurane 1-2% in oxygen. Muscle relaxation was achieved with rocuronium 0.6 mg kg−1. A Size 5 device was used for all patients [4]. All LMA-ProSeal® laryngeal mask airways and laryngeal mask airways had been through at least 10 autoclave cycles, and had passed their pre-use check tests. The LMA-ProSeal® laryngeal mask airway and laryngeal mask airway were inserted into each patient's pharynx in random order (by opening a sealed envelope). A single experienced LMA-ProSeal® laryngeal mask airway (>100 uses) and laryngeal mask airway user (>1500 uses) inserted/fixed each device. The insertion technique for the LMA-ProSeal® laryngeal mask airway included full deflation of the cuff, careful placement of the cuff flat against the hard palate and a single-handed rotational technique using the introducer tool. The insertion technique for the laryngeal mask airway included full deflation of the cuff, careful placement of the cuff flat against the hard palate, and pushing the device into and along the posterior palatopharyngeal curve using the index finger. Both devices were fixed by taping the airway tube over the chin. The number of attempts taken to place the device was recorded. A failed attempt was defined as removal of the device from the mouth. The intracuff pressure was adjusted to 60 cmH2O using a digital cuff pressure monitor (Mallinckrodt Medical, Athlone, Ireland) with the head-neck in the neutral position before each measurement. Care was taken to avoid displacement of the LMA-ProSeal® laryngeal mask airway or laryngeal mask airway or transmission of any force along the tube during testing. The oropharyngeal leak pressure, intracuff pressure and fibreoptic position were documented by a trained assistant with the head-neck in four randomly selected positions: neutral (occiput resting on standardized firm pillow 7 cm in height); maximum flexion; maximum extension; and maximum right rotation. The cuffs were inflated to a volume of 0-40 mL in the neutral position in 10 mL increments. The assistant was blinded to the position of the head-neck during the oropharyngeal leak pressure measurements. Readings were taken 30-60 s after adjustment of the head-neck position. The oropharyngeal leak pressure was measured by closing the expiratory valve of the circle anaesthetic breathing system at a fixed gas flow of 3 L min−1, and noting the airway pressure at which the dial on a calibrated aneroid manometer (accurate to ±0.5 cmH2O) reached equilibrium [5]. The anatomical position of the airway tube was scored as: 4 (only vocal cords visible); 3 (vocal cords plus posterior epiglottis visible); 2 (vocal cords plus anterior epiglottis visible); and 1 (vocal cords not seen) [6]. The degree of rotation of the airway tube was scored by noting the angle between the anteroposterior plane of the airway tube and the vocal cords: nil (<10°), mild (10-45°), moderate (46-90°) and severe (>90°). For the LMA-ProSeal® laryngeal mask airway, the anteroposterior plane was identified by two marks inside the distal airway tube. The anatomical position of the drainage tube (LMA-ProSeal® laryngeal mask airway only) was determined by passing a fibreoptic endoscope down the drainage tube to a position just proximal to the end of the tube. The view was catalogued as: closed hypopharynx (mucosa blocking the end of the drainage tube); open hypopharynx (short conical tube of mucosa visible from drainage tube); open upper oesophageal sphincter (a clear view down the oesophagus); and others (glottis, epiglottis, arytenoids).

The sample size was selected to detect a projected difference of 25% between the groups with respect to oropharyngeal leak pressure for a Type I error of 0.01 and a power of 0.9. The power analysis was based on data from a pilot study of 10 patients in which oropharyngeal leak pressures were measured for the LMA-ProSeal® laryngeal mask airway in flexion and extension and compared with [3]. The distribution of data was determined using Kolmogorov-Smirnov analysis. Statistical analysis was by paired t-test (normally distributed data) and χ2-test (non-normally distributed data). Unless otherwise stated, data are mean ± SD. Significance was taken as P < 0.05.

Results

The mean (range) age, height and body weight were 37 (18-67) yr, 175 (159-188) cm and 72 (56-90) kg, respectively. All airway devices were inserted at the first attempt. Data are presented in Tables 1 and 2. The oropharyngeal leak pressure was always higher for the LMA-ProSeal® laryngeal mask airway than the laryngeal mask airway (all P ≤ 0.005). Compared with the neutral position, oropharyngeal leak pressure for the LMA-ProSeal® laryngeal mask airway and the laryngeal mask airway was higher in flexion and rotation (all P ≤ 0.02), but lower in extension (all P ≤ 0.01). Intracuff pressure was similar for the LMA-ProSeal® laryngeal mask airway and the laryngeal mask airway in all head-neck positions and increased with cuff volume (P < 0.001). Compared with the neutral position, intracuff pressure for the LMA-ProSeal® laryngeal mask airway and the laryngeal mask airway was higher in flexion and rotation, but lower in extension (all P < 0.001). The anatomical position of the airway tube of the LMA-ProSeal® laryngeal mask airway was better than the laryngeal mask airway in all head-neck positions (all P = 0.005) and cuff volumes (all P ≤ 0.02). Rotation of the airway tube was more common with the LMA-ProSeal® laryngeal mask airway than the laryngeal mask airway in all head-neck positions and cuff volumes (all P ≤ 0.04). An open hypopharynx was seen in two patients, and an open oesophagus in two patients. There were no changes in the anatomical position of the airway tube, the degree of rotation of the airway tube or the anatomical position of the drainage tube in different head-neck positions or cuff volumes for the LMA-ProSeal® laryngeal mask airway or the laryngeal mask airway.

Table 1
Table 1:
Oropharyngeal leak pressure and intracuff pressure for the LMA-ProSeal® laryngeal mask airway and standard laryngeal mask airway in different head-neck positions and at 0-40 mL cuff volumes in the neutral position. Interdevice statistics are detailed and intradevice statistics are summarized below.
Table 2
Table 2:
Airway tube position and the degree of rotation for the LMA-ProSeal® laryngeal mask airway and standard laryngeal mask airway, and drainage tube for the LMA-ProSeal® laryngeal mask airway in different head-neck positions and at 0-40 mL cuff volumes in the neutral position.

Discussion

The data show that the anatomical position of the LMA-ProSeal® laryngeal mask airway is stable in different head-neck positions, but head-neck flexion and rotation are associated with an increase - and head-neck extension a decrease - in oropharyngeal leak pressure and intracuff pressure. These findings are similar to the standard and flexible laryngeal mask airway [2,3], suggesting that the differences in cuff shape and tube configuration do not influence the stability of the LMA-ProSeal® laryngeal mask airway. The changes in oropharyngeal leak pressure are clinically important since they amount to an increase or decrease of approximately 25%. The mechanism of these changes is probably a reduction in pharyngeal volume during flexion and rotation, and an increase in pharyngeal volume during extension. Thus, during flexion and rotation, the cuff presses more firmly into the periglottic tissues and the intracuff pressure is higher, the converse occurring during extension.

The data confirm that the oropharyngeal leak pressure is higher for the LMA-ProSeal® laryngeal mask airway than for the laryngeal mask airway [1]. The oropharyngeal leak pressure is probably higher either because (a) the wedge-shaped ventral cuff plugs gaps in the proximal pharynx, or (b) the dorsal cuff pushes the ventral cuff more firmly into the periglottic tissues or (c) the cuff shape better matches the pharyngeal anatomy. Brain and colleagues [1] found that the oropharyngeal leak pressure for the Size 4 device in females was 30 cmH2O at an intracuff pressure of 60 cmH2O [1] and we found that it was 26 cmH2O for the Size 5 in males at an intracuff pressure of 60 cmH2O. Further studies are required to determine the appropriate size of LMA-ProSeal® laryngeal mask airway in males and females.

The data show that anatomical position is worse with the LMA-ProSeal® laryngeal mask airway. We speculate that this is because of the high incidence of epiglottic downfolding and it may be caused by the larger cuff catching the epiglottis during insertion. We do not consider this to be a clinical problem since the accessory vent should allow good airflow to continue, and the larger bowl and lack of a mask aperture bars means that epiglottic trapping is unlikely [7]. We found that the glottic inlet was more commonly rotated with the LMA-ProSeal® laryngeal mask airway compared with the laryngeal mask airway. This may be related to residual rotation of the LMA-ProSeal® laryngeal mask airway in the sagittal plane or the larger cuff distorting the anatomy of the glottis. Interestingly, Brain and colleagues [1] found no difference in anatomical position between the laryngeal mask airway and the LMA-ProSeal® laryngeal mask airway. This interstudy difference may be related to the use of different scoring systems.

We conclude that the anatomical position of the LMA-ProSeal® laryngeal mask airway is stable in different head-neck positions, but head-neck flexion and rotation are associated with an increase and head-neck extension a decrease in oropharyngeal leak pressure and intracuff pressure. The Size 5 LMA-ProSeal® laryngeal mask airway is capable of forming a more effective seal than the Size 5 laryngeal mask airway in males.

References

1. Brain AIJ, Verghese C, Strube PJ. The LMA 'ProSeal' - a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650-654.
2. Keller C, Brimacombe J. The influence of head and neck position on oropharyngeal leak pressure and cuff position with the flexible and the standard laryngeal mask airway. Anesth Analg 1999; 88: 913-916.
3. Buckham M, Brooker M, Brimacombe J, Keller C. A comparison of the reinforced and standard laryngeal mask airway: ease of insertion and the influence of head and neck position on oropharyngeal leak pressure and intracuff pressure. Anaesth Intens Care 1999; 27: 628-631.
4. Berry AM, Brimacombe J, McManus KF, Goldblatt M. An evaluation of the factors influencing selection of the optimal size of laryngeal mask airway in normal adults. Anaesthesia 1998; 53: 565-570.
5. Keller C, Brimacombe J, Keller K, Morris R. A comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients. Br J Anaesth 1999; 82: 286-287.
6. Brimacombe J, Berry A. A proposed fiber-optic scoring system to standardize the assessment of laryngeal mask airway position. Anesth Analg 1993; 76: 457.
7. Miller AC, Bickler P. The laryngeal mask airway. An unusual complication. Anaesthesia 1991; 46: 659-660.
Keywords:

EQUIPMENT AND SUPPLIES; INTUBATION, INTRATRACHEAL, laryngeal masks

© 2003 European Academy of Anaesthesiology