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*Department of Anaesthesia, Pain Clinic, and Clinical Toxicology, Mito Saiseikai General Hospital, Ibaraki, Japan; and
University of Queensland, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Cairns, Australia
Address correspondence and reprint requests to J. Brimacombe, FRCA, MD, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns 4870, Australia. Address e-mail to jbrimaco{at}bigpond.net.au
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Abstract |
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IMPLICATIONS: When sex is used to select the appropriate size of the ProSealTM laryngeal mask airway, the Size 4 ProSealTM is preferable for women and the Size 5 ProSeal for men.
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Introduction |
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Methods |
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Anesthesia was induced with fentanyl 2 µg/kg and propofol 2.5 mg/kg and maintained with sevoflurane 2%–3% in 30% oxygen and air. Neuromuscular blockade was achieved with vecuronium 0.1 mg/kg and maintained with 0.05 mg/kg boluses to keep the train-of-four count <1. All male patients (comparing the Size 4 and 5; Group M4/5) and half the female patients (comparing the Size 4 and 5; Group F4/5) had a Size 4 or 5 PLMATM inserted in random order; the other half of the female patients (comparing the Size 3 and 4; Group F3/4) had the Size 3 or 4 PLMATM inserted in random order. Randomization was achieved with computer-generated numbers. All insertions were by a single experienced PLMATM user (SK; >100 uses), who used the index finger technique according to the manufacturer’s instructions (14). The introducer tool was not used. The cuff was inflated with air to an intracuff pressure of 60 cm H2O (14). The insertion time (from picking up the device to capnographic confirmation) and the number of insertion attempts (a failed attempt was defined as removal of the device from the oral cavity) were recorded.
Patients were ventilated for 15 min at the following settings: tidal volume, 10 mL/kg; respiratory rate, 10 breaths/min; and inspiratory/expiratory ratio, 1:1. Measurements were made before surgery with the patient in the supine position and the head resting on a pillow 7 cm thick. Tidal volume was measured by a constant-temperature hot-wire anemometer that was calibrated before each use. Airway pressure was measured by piezoresistive change of resistance in a membrane. Carbon dioxide and sevoflurane were sampled from the proximal end of the PLMATM shaft and measured by an infrared multigas analyzer. The following data were measured and recorded by the PM 8060 anesthesia monitor on the Cicero EMTM every 30 s for the last 5 min, and the average reading was taken: peak airway pressure, inspired tidal volume, expired tidal volume, pulmonary compliance, oxygen saturation, end-tidal carbon dioxide, and heart rate. Leak fraction was calculated by subtracting expired from inspired tidal volume. Epigastric auscultation was performed to detect air entering the stomach (15). Oropharyngeal leaks were detected by listening over the mouth (16). Drain tube leaks were detected by placing a clear lubricant in the proximal 1 cm of the drain tube and noting whether bubbling occurred during ventilation (2). Failed oxygenation and ventilation was defined as an inability to maintain oxygen saturation ≥95% at an inspired oxygen concentration of 30% and an inability to maintain end tidal carbon dioxide ≤45 mm Hg, respectively.
When these measurements were complete, oropharyngeal seal pressure and fiberoptic position were determined. OLP was measured by closing the expiratory valve of the circle system at a fixed gas flow of 3 L/min and noting the airway pressure (maximum allowed, 40 cm H2O) at which equilibrium was reached (16). The location (mouth, stomach, or drain tube) of any gas leak at OLP was determined by using the same methods as during positive pressure ventilation. The anatomic position of the airway tube was determined by passing a fiberoptic scope to a position just proximal to end of the airway tube and scoring the view (17). The anatomic position of the drain tube was determined by passing a fiberoptic scope to the end of the drain tube. The view was catalogued as mucosa (mucosa blocking the end of the drainage tube), open upper esophageal sphincter (a clear view down the esophagus), and glottis (any glottic structure visible). The first PLMATM was then removed, the alternative size was inserted, and data collection was repeated. After removal, the first PLMATM was inspected for visible blood. Mucosal injury was defined as the detection of visible blood.
An unblinded observer collected the data. Sample size was based on a crossover pilot study of five patients and was selected to detect a projected difference of 33% in leak fraction at 10 mL/kg between the devices for a Type I error of 0.05 and a power of 0.9. The distribution of data was determined with Kolmogorov-Smirnov analysis (18). Descriptive data were tested with paired Student’s t-tests. Categorical data were tested by the 
2 test. Significance was taken as P < 0.05.
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Results |
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Discussion |
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OLP was higher for the Size 5 than the Size 4 in men and women. Similar findings have been reported for the Classic LMATM in men (20,22) and women (22). However, one study found that OLP was similar for the Size 5 and the Size 4 Intubating LMATM in men and women (25). OLP was higher for the Size 4 than the Size 3 in women. Similar findings have been reported for the Classic LMATM (20) and Intubating LMATM (25). OLP probably increases with size because the surface area for the pharynx/cuff interaction is larger and because the larger proximal cuff forms a more effective proximal pharyngeal plug.
Leak fraction and leak volume were higher for the Size 4 than the Size 5 in men and for the Size 3 than the Size 4 in women. Leak fraction was similar for the Size 4 and 5 in women even though OLP was lower for the Size 4 because peak airway pressures were on average 11 cm H2O lower than OLP. Interestingly, despite the differences in OLP and leak fraction among sizes, there were no differences in gas exchange. Perhaps gas exchange would be better for the larger sizes in situations in which pulmonary compliance was increased, such as gross obesity and carboperitoneum. The increased leak with smaller sizes may have implications for operating room pollution.
Mucosal injury was similar for the Size 4 and 5 in men and for the Size 3 and 4 in women but was more frequent for the Size 5 than the Size 4 in women. Two groups have compared airway morbidity among sizes. Nott (27) found that the Size 3 Classic LMATM (among Sizes 2.5, 3, and 4) in women or the Size 4 (among Sizes 3, 4, and 5) in men was associated with the least incidence of sore throat. Grady et al. (24) compared the frequency of airway morbidity of smaller (Size 4 in men; Size 3 in women) and larger (Size 5 in men; Size 4 in women) LMAs and found that larger LMAs were associated with an increased incidence of sore throat in both sexes and a more frequent incidence of dysarthria in male patients. One explanation is that larger masks exert higher mucosal pressures; however, Asai et al. (20) and Brimacombe and Keller (22) both found that mucosal pressures were uninfluenced by size. Another explanation is that larger masks cause more trauma during insertion. Our study lends support to the latter explanation, because insertion was more difficult and trauma more common with the Size 5 than the Size 4 in women.
The location of the gas leak was similar among sizes during OLP testing and positive pressure ventilation. This suggests that that the degree of isolation of the respiratory tract from the gastrointestinal tract was uninfluenced by size. The anatomic position was similar among sizes, suggesting that insertion of instrumentation into the respiratory and gastrointestinal tracts would be uninfluenced by size. It also suggests that the increased difficulty with placement for the Size 5 in women did not influence its final position.
Taking all of these variables into consideration, the Size 5 is better than the Size 4 for men, and the Size 4 is better than the Size 3 for women. In women, selecting a Size 4 or 5 is less clear-cut, because insertion is easier and mucosal injury less common for the Size 4, but OLP is higher for the Size 5. However, in patients with normal lung compliance, insertion success and mucosal injury are more important considerations than OLP, suggesting that, on balance, the Size 4 is better for women than the Size 5. Further studies are required to determine whether these sex-based recommendations are superior to the manufacturer’s weight-based recommendations (14).
Our study has a number of limitations. First, we did not assess the ease of insertion of a gastric tube or tracheal intubation. However, the anatomic positions were similar, and it is unlikely that there would have been any differences among sizes. Second, although we documented mucosal injury for the first device, we did not compare pharyngolaryngeal discomfort among devices. A large, noncrossover study is required to determine any differences, given the infrequent incidence of pharyngolaryngeal discomfort (5). Third, we did not assess the frequency of the cuff protruding into the oropharynx. A possible disadvantage of larger sizes is that the proximal cuff may protrude into the oropharyngeal inlet and interfere with the surgical field (21,28). However, the ProSeal LMATM is generally unsuitable for oropharyngeal surgery. Fourth, a single experienced user conducted all insertions, and our results may not be applicable to inexperienced users. We believe that our findings can be extrapolated to other experienced users because the success rates, insertion times, and OLPs were similar to data from other experienced users (2,5,6). Fifth, all insertions used the digital manipulation technique, and our results may not be applicable to insertion with the introducer tool (5) or to bougie-guided (26) techniques. Sixth, our study was conducted in paralyzed patients, and our findings may be less applicable to the unparalyzed patient who is inadequately anesthetized. There is indirect evidence from mucosal pressure studies that pharyngeal muscle tone is similar in the paralyzed and unparalyzed patient (29). Finally, the data were collected by an unblinded observer, a potential source of bias.
We conclude that if size is selected by sex, the Size 4 ProSealTM is preferable for women and the Size 5 ProSealTM for men.
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Acknowledgments |
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This article has been cited by other articles:
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  A. Lallo, P. Drolet, and M. Lacroix Performance of the PAXpressTM vs the ProSealTM laryngeal mask airway during general anesthesia: [Efficacite du PAXpressTM et du masque larynge ProSealTM durant l'anesthesie generale] Can J Anesth, January 1, 2007; 54(1): 28 - 33. [Abstract] [Full Text] [PDF]
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T. M. Cook, G. Lee, and J. P. Nolan The ProSealTM laryngeal mask airway: a review of the literature: [Le masque larynge ProSealTM : un examen des publications] Can J Anesth, August 1, 2005; 52(7): 739 - 760. [Abstract] [Full Text] [PDF]
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C. J. O'Connor Jr, M. S. Stix, and D. R. Valade Glottic insertion of the ProSealTM LMA occurs in 6% of cases: a review of 627 patients: [L'insertion glottique du ML ProSealTM survient dans 6 % des cas : une revue de 627 patients] Can J Anesth, February 1, 2005; 52(2): 199 - 204. [Abstract] [Full Text] [PDF]
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