Anesth Analg 2001;93:1351-1353
© 2001 International Anesthesia Research Society
BRIEF REPORT
Positive Pressure Ventilation with the ProSeal Versus Classic Laryngeal Mask Airway: A Randomized, Crossover Study of Healthy Female Patients
Joseph Brimacombe, MBChB FRCA, MD*,
Christian Keller, MD,
Michael Boehler, MD, and
Friedrich Pühringer, MD
Department of Anaesthesia and Intensive Care Medicine, Leopold-Franzens University, Innsbruck, Austria; and *Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns, Australia
Address correspondence to Prof. Joseph Brimacombe, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns 4870, Australia. Address e-mail to jbrimacombe@ austarnet.com.au.
Abstract
IMPLICATIONS: The ProSeal and classic laryngeal mask airways are equally effective ventilatory devices in healthy female patients at tidal volumes of 8 and 12 mL/kg with the cuff semi- or fully inflated, but leakage of small volumes of air from the mouth occurs more frequently with the laryngeal mask airway.
The ProSealTM laryngeal mask airway (PLMA) (Laryngeal Mask Company, Henley-on-Thames, UK) is a new laryngeal mask device with a modified cuff and a drainage tube (1). Preliminary trials have shown that the PLMA forms a more effective seal than the standard laryngeal mask airway (LMA) during a static oropharyngeal leak test and isolates the respiratory tract from the gastrointestinal tract when correctly positioned (1,2), but there is no evidence that it is a better ventilatory device. In the following randomized, cross-over trial, we tested the hypothesis that the PLMA is a more effective ventilatory device than the LMA in healthy anesthetized females at 8 and 12 mL/kg tidal volume with the cuff semi- or fully inflated.
Methods
We studied 30 consecutive female patients (ASA physical status I-II, 18–80 yr) undergoing nonintraabdominal gynecological surgery. Ethical committee approval and written informed consent were obtained. Patients were excluded if they had respiratory tract pathology, were at risk of aspiration, or were taking medication that might trigger bronchospasm. The ventilator and anesthesia circuit were tested for leaks before use by connecting them to an artificial lung and recording the difference between inspired and expired tidal volume over 20 breaths at similar tidal volumes to those used in patients. Patients were induced with fentanyl 2 µg/kg and propofol 2.5 mg/kg. Maintenance was with propofol 6 mg · kg-1 · h-1 in 30% O2 and air. A single experienced PLMA/LMA user (>100/1500 uses) inserted/fixed each device in random order according to the manufacturer’s instructions (3,4). The PLMA was inserted using the introducer tool (4). Patients were ventilated (Evita 4; Draeger Medizintechnik GmbH, Luebeck, Germany) for 10 min at the following 4 tidal volume/cuff volume settings in random order: 1) tidal volume 8 mL/kg, cuff volume 15 mL; 2) tidal volume 8 mL/kg, cuff volume 30 mL; 3) tidal volume 12 mL/kg, cuff volume 15 mL; 4) tidal volume 12 mL/kg, cuff volume 30 mL. The respiratory rate, inspiratory:expiratory ratio, and inspiratory flow rate were fixed at 15 breaths/min, 1:1, and 30 L/min respectively. Measurements were made during/ after surgery with the patient in the lithotomy position. The ventilator compliance was 2 mL/cm H2O and the pneumotachograph was connected directly to the proximal end of the airway tube. Airway pressure was measured at the pneumotachograph. The CO2 sampling port was sited above the flow transducer. Failed oxygenation and ventilation were defined as an inability to maintain oxygen saturation  95% at an inspired oxygen concentration of 33% and an inability to maintain end-tidal carbon dioxide  45 mm, respectively.
The following data were recorded by an unblinded observer once every 20 s for the last 5 min for each tidal volume/cuff volume setting and the average reading taken: peak airway pressure, inspired tidal volume, expired tidal volume, pulmonary compliance, oxygen saturation, end-tidal carbon dioxide, and heart rate. Mean arterial pressure was measured using a noninvasive blood pressure monitor at the start and end of the 5-min period and the average value was taken. Leak fraction was calculated by subtracting expired from inspired tidal volume. Epigastric auscultation was performed to detect air entering the stomach (5). Oropharyngeal leaks were detected by listening over the mouth with an ear (6). Drainage tube leaks were detected by placing a clear lubricant in the proximal 1 cm of the drainage tube and noting whether bubbling occurred during ventilation (2). When these measurements were complete, oropharyngeal leak pressure (6) and fiberoptic position (7) were determined at 15 mL and 30 mL cuff volume in random order. The alternative randomized device was then inserted and data collection repeated.
Sample size was based on a cross-over pilot study of 5 patients and was selected to detect a projected difference of 33% in leak fraction at 12 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 using Kolmogorov-Smirnov analysis. Statistical analysis was with one-way analysis of variance with Bonferroni post hoc test for multiple comparisons paired and  2 test. Significance was taken as P < 0.05.
Results
The mean (range) age, height and weight were 41 (19–61) yr, 163 (150–172) cm and 61 (50–74) kg respectively. Ventilator and circuit leaks were always <1 mL at the preuse test. All PLMA and LMAs were inserted at the first attempt. Leak fraction was always lower for the PLMA (by 0.3–0.6% at 8 mL/kg, P < 0.001; and by 2.0–2.1% at 12 mL/kg, P < 0.0001), but otherwise respiratory mechanical and cardiorespiratory data were almost identical. Gastric insufflation was not detected with either device. Audible oropharyngeal leaks were not detected with either device at 8 mL/kg tidal volume but were more commonly detected with the LMA at 12 mL/kg tidal volume (15 mL cuff volume: 8/30 v 1/30, P = 0.01; 30 mL cuff volume: 7/30 v 1/30, P = 0.02). Drainage tube leaks were not detected. Oropharyngeal leak pressure was higher for the PLMA at 15 mL (29 ± 7 vs 20 ± 3) and 30 mL (36 ± 6 vs 21 ± 3) cuff volumes (all P < 0.0001). The median fiberoptic position was higher for the LMA at 15 mL (3.1 vs 2.7) and 30 mL (3.3 vs 2.7) cuff volumes (both P < 0.02). Failed oxygenation and ventilation did not occur with either device.
Discussion
The LMA and PLMA are equally effective ventilatory devices at 8 mL/kg and 12 mL/kg tidal volume with the cuff semi- or fully inflated (Table 1). We selected these values for tidal volume and cuff volume to represent the range of values used in clinical practice. The manufacturer currently recommends a tidal volume of up to 8 mL/kg for the LMA (3) and the PLMA (4). We recommend 12 mL/kg for healthy female patients. The leak fraction was always higher for the LMA. This is primarily related to the LMA having a less effective seal than the PLMA, because peak airway pressures (hence, resistance to gas flow) were similar. The oropharyngeal leak pressure was 9–15 cm H2O higher for the PLMA; this confirms previous findings (1). The fiberoptic score was higher for the LMA because there was less epiglottic downfolding; this also confirms previous findings (2). The differences in leak fraction, oropharyngeal leak pressure and fiberoptic position were of no clinical significance because oxygenation and ventilation were unimpeded, gastric insufflation did not occur, and hemodynamic variables were similar. Interestingly, an audible oropharyngeal air leak was often not heard despite a gas loss of up to 15 mL. Perhaps this is the limit of audible detection of oropharyngeal leak.
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Table 1. Pulmonary Mechanical and Cardiorespiratory Data for the Laryngeal Mask Airway (LMA) and ProSeal Laryngeal Mask Airway (PLMA) at 8 and 12 mL/kg Tidal Volume (TV) and With the Cuff Semi- and Fully Inflated
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Our study has a number of limitations. First, we studied healthy patients with normal lungs. In situations where higher peak airway pressures would be required, such as intraabdominal/intrathoracic surgery, in morbidly obese patients, or in patients with restrictive lung disease, it is possible that the PLMA would be a superior ventilatory device because of the better seal. Second, we only studied female patients; the results might not be applicable to males. Finally, the PLMA was inserted by an experienced LMA/PLMA user. Our data may not necessarily apply to the inexperienced user.
We conclude that the PLMA and LMA are equally effective ventilatory devices in healthy female patients at tidal volumes of 8 and 12 mL/kg with the cuff semi- or fully inflated, but leakage of small volumes of air from the mouth occurs more frequently with the LMA.
References
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Verghese C. LMA ProSeal instruction manual. Henley-on-Thames: The Laryngeal Mask Company Ltd, 2000.
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Brimacombe J, Keller C, Kurian S, Myles J. Reliability of epigastric auscultation to detect gastric insufflation. Br J Anaesth. In Press.
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Accepted for publication July 5, 2001.
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