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GENERAL ARTICLES

A Comparison of the Laryngeal Mask Airway ProSeal^TM and the Laryngeal Tube Airway in Paralyzed Anesthetized Adult Patients Undergoing Pressure-Controlled Ventilation

Joseph Brimacombe, MB ChB, FRCA, MD^*, Christian Keller, MD, and Lawrence Brimacombe, MB ChB^*

*Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns, Australia; and Department of Anaesthesia and Intensive Care Medicine, Leopold-Franzens University, Innsbruck, Austria

Address correspondence and reprint requests to Professor Joseph Brimacombe, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns 4870, Australia. Address e-mail to jbrimacombe{at}austarnet.com.au

	Abstract

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We compared the laryngeal mask airway ProSeal^TM (PLMA^TM) and the laryngeal tube airway (LTA), two new extraglottic airway devices, with respect to: 1) insertion success rates and times, 2) efficacy of seal, 3) ventilatory variables during pressure-controlled ventilation, 4) tidal volume in different head/neck positions, and 5) airway interventional requirements. One-hundred-twenty paralyzed anesthetized ASA physical status I and II adult patients were randomly allocated to the PLMA^TM or LTA for airway management. A standardized anesthesia protocol was followed by two anesthesiologists experienced with both devices. The criteria for an effective airway included a minimal expired tidal volume of 6 mL/kg during pressure-controlled ventilation at 17 cm H₂O with no oropharyngeal leak or gastric insufflation. First attempt success rates at achieving an effective airway were similar (PLMA^TM: 85%; LTA: 87%), but after 3 attempts, success was more frequent for the PLMA^TM (100% versus 92%, P = 0.02). Effective airway time was similar. Oropharyngeal leak pressure was larger for PLMA^TM at 50% maximal recommended cuff volume (29 ± 7 versus 21 ± 6 cm H₂O, P < 0.0001), but was similar at the maximal recommended cuff volume (33 ± 7 versus 31 ± 8 cm H₂O). Tidal volumes (614 ± 173 versus 456 ± 207 mL, P < 0.0001) were larger and ETCO₂ (33 ± 9 versus 40 ± 11 mm Hg, P = 0.0001) lower for the PLMA^TM. The number of airway interventions was significantly less frequent for the PLMA^TM. Airway obstruction was more common with the LTA. When comparing mean tidal volumes in different head/neck positions, the quality of airway was unchanged in 56 of 60 patients (93%) with the PLMA^TM and 42 of 55 (76%) with the LTA (P = 0.01). The PLMA^TM offers advantages over the LTA in most technical aspects of airway management in paralyzed patients undergoing pressure-controlled ventilation.

IMPLICATIONS: The laryngeal mask airway ProSeal^TM offers advantages over the laryngeal tube airway in most technical aspects of airway management in paralyzed patients undergoing pressure-controlled ventilation.

	Introduction

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The laryngeal mask airway ProSeal^TM (PLMA^TM) (1) and laryngeal tube airway (LTA) (2) are new reusable extraglottic airway devices intended for spontaneous and positive pressure ventilation. The PLMA^TM (Laryngeal Mask Company, Henley-on-Thames, UK) is a variation of the laryngeal mask airway with a modified cuff to improve the seal and a drainage tube to provide a channel for regurgitated fluid, gastric tube placement, prevention of gastric insufflation, and diagnosis of malposition (Fig. 1). The LTA (VBM Medizintechnik GmbH, Sulz, Germany) is a variation of the esophageal-tracheal Combitube with a large proximal cuff that inflates in the proximal pharynx and a distal conical cuff that inflates in the hypopharynx to prevent regurgitation and gastric insufflation (Fig. 2). Preliminary studies have shown that both the PLMA^TM (3) and LTA (4) are effective ventilatory devices with a small incidence of gastric insufflation, but there are no studies comparing the two devices. The aim of this randomized prospective study was to compare the PLMA^TM and LTA with respect to: 1) insertion success rates and times, 2) efficacy of seal, 3) ventilatory variables during pressure-controlled ventilation, 4) tidal volume in different head/neck positions, and 5) airway interventional requirements in paralyzed adult patients. We hypothesized that these devices were different based on their dissimilar designs.

View larger version (126K): [in this window] [in a new window]   Figure 1. The laryngeal mask airway ProSealTM.

View larger version (123K): [in this window] [in a new window]   Figure 2. The laryngeal tube airway.

	Methods

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Anesthetic management was standardized according to the following protocol. Anesthesia was induced with fentanyl 1 µg/kg and midazolam 0.05 mg/kg followed by propofol 2.5 mg/kg. Sevoflurane 1.5%–3% in 33% oxygen and air was used for maintenance. Neuromuscular blockade was achieved with atracurium 0.5 mg/kg and maintained with 0.15 mg/kg boluses to maintain a train-of-four count <1. Ventilation was controlled via a face mask for 3–5 min which was graded as easy (chin lift only), adequate (jaw thrust required), difficult (oral airway and jaw thrust required), or failed (no capnograph trace or chest wall movement).

A size 4 PLMA^TM/LTA was used for adults weighing 50–80 kg and a size 5 for adults weighing >80 kg. A clear, water-based gel without local anesthesia was used for lubrication. Both devices were inserted and fixed according to the manufacturer’s instructions (5,6). The PLMA^TM/LTA was connected to a circle breathing system and the cuff inflated with air until an effective airway was established or the maximal recommended inflation volume reached (size 4/5 PLMA^TM, 30/40 mL; size 4/5 LTA, 130/150 mL). The criteria for an effective airway included a minimal expired tidal volume of 6 mL/kg during pressure-controlled ventilation at 17 cm H₂O with no oropharyngeal leak or gastric insufflation. Malposition was determined with the PLMA^TM by testing for air leakage from the drainage tube and by passing a gastric tube to the distal end of the drainage tube to confirm that the distal cuff was not folded over (7). If the PLMA^TM was malpositioned, it was considered ineffective even if the criteria for an effective airway were met. The anesthesiologists intervened if the airway was not effective. An intervention was defined as any airway maneuver used to provide an effective airway. Airway interventions were graded as minor (adjusting head/neck position or changing depth of insertion) or major (applying jaw lift/changing device size/reinserting the device). If the anesthesiologist was unable to establish an effective airway using the initial randomized device after three insertion attempts, then three attempts were permitted with the alternative device. The number of insertion attempts was recorded. A failed attempt was defined as removal of the device from the mouth. If both randomized airway devices failed during the placement phase, or if the airway device failed after the placement phase, the anesthesiologist was free to manage the airway as clinically indicated. The time between picking up the PLMA^TM/LTA and obtaining an effective airway was recorded. The PLMA^TM was inserted without the introducer tool.

Once an effective airway was obtained, oropharyngeal leak pressure was determined at 50% and 100% of the maximal recommended cuff volumes 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 was 40 cm H₂O) at which equilibrium was reached (8). Any air entering the stomach was noted when measuring oropharyngeal leak pressure by listening over the epigastrium with a stethoscope (9).

During the maintenance phase, patients were ventilated with peak airway pressures set at 17 cm H₂O, a respiratory rate of 12/min, an inspiratory/expiratory ratio of 1:1.5, and a fresh gas flow of 3 L/min. Oropharyngeal leaks were monitored by listening over the mouth and drainage tube (8). Gastric leaks were monitored by listening over the epigastrium with a stethoscope (9). If the SpO₂ was <95% or the end-tidal CO₂ was >45 mm Hg, the FIO₂ and respiratory rate were increased respectively. Intracuff volume was adjusted and maintained to the minimum required to prevent oropharyngeal air leaks. At the end of surgery, and before discontinuing anesthesia/neuromuscular blockade, the stability of the airway device was determined in different head/neck positions with the cuff inflated to 50% of the maximal recommended volume. This involved placing the head/neck in four sequential positions (head on standard pillow, head rotated to side, chin lift, and head without a standard pillow) and recording five consecutive tidal volumes. A time gap was allowed for recovery between positions if the airway was ineffective.

Neostigmine 0.04 mg/kg and atropine 0.02 mg/kg were given. Anesthesia was not discontinued until the train-of-four count was 3. Patients were given 100% O₂ during emergence and were not physically disturbed except for the purposes of monitoring. The airway device was removed when the patient was able to open his or her mouth to command. Before leaving the postanesthesia care unit, the mouth was carefully inspected by a single blinded data collector for damage to the tongue, lips, and teeth by using a spatula.

Patients underwent a structured interview by a data collector blinded to the airway device used 18–24 h after surgery. Patients were asked about the following: sore throat (constant pain, independent of swallowing), sore neck, sore jaw, dysphonia (difficulty/pain on speaking), and dysphagia (difficulty/pain on swallowing). Symptoms were graded by the patient as mild, moderate, or severe. Patients were unaware of the airway device used.

The following preoperative data were collected: sex, age, height, weight, body mass index, smoking history (yes/no), dentition (own/partial/edentulous), type of surgical procedure, heart rate, mean blood pressure, SpO₂, and respiratory rate. The conduct of anesthesia was divided into 3 phases: 1) placement phase (commencement of propofol induction to establishment of an effective airway), 2) maintenance phase (effective airway to discontinuation of anesthesia), and 3) emergence phase (discontinuation of anesthesia until removal of the device). The following intraoperative complications were documented: aspiration/regurgitation, hypoxia (SpO₂ <90%), bronchospasm, airway obstruction, gastric insufflation, coughing/gagging/retching, hiccup, cough during removal, blood staining of the airway device, and tongue/lip/dental trauma. If a complication occurred, an explanation was given and the minimal SpO₂ documented. Any adjustments in FIO₂ or respiratory rate during the maintenance phase were noted. The following data were recorded every 5 min commencing at the start of each new phase until the device was removed: heart rate, mean blood pressure, minimal SpO₂, expired tidal volume, fraction of inspired oxygen, end-tidal CO₂ concentration, end-tidal sevoflurane concentration, and the presence/absence of oropharyngeal or gastric leaks. Heart rate, mean blood pressure, SpO₂, and respiratory rate were recorded 5 min after PLMA^TM/LTA removal with the patients breathing O₂ at 4 L/min via a Hudson mask.

The primary variables were: insertion success rates and times, efficacy of seal, ventilatory variables during pressure-controlled ventilation, tidal volume in different head/neck positions, and airway interventional requirements. Secondary variables were intraoperative and postoperative complications. Sample size was based on data from previous studies on the LTA/PLMA^TM (2,4,10–14), and a pilot study of 20 patients with the LTA. The sample size was selected to detect a projected difference of 15% or less between the groups for a type I error of 0.05 and a power of 0.9. If the randomized device failed and the alternative device succeeded, all variables (other than oropharyngeal leak pressure and tidal volume in different head/neck positions) were assigned to the initial randomized device (intention to treat). The distribution of data was determined by using Kolmogorov-Smirnov analysis. Statistical analysis was performed with paired t-test (parametric data), Kruskal-Wallis test, Mann-Whitney ranked sum test, and ² test with Yates correction (nonparametric data). Significance was taken as P < 0.05.

	Results

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There were no significant differences between the groups with respect to demographic and surgical details, face mask score, and time factors (Table 1). There were no inconsistencies among observers. The first-time success rates at achieving an effective airway were 51 of 60 (85%) for the PLMA^TM and 52 of 60 (87%) for the LTA; second-time success rates were 7 of 60 (11%) for the PLMA^TM and 2 of 60 (3%) for the LTA; third-time success rates were 2 of 60 (3%) for the PLMA^TM and 1 of 60 (2%) for the LTA. The failure rate for the LTA was more frequent than the PLMA^TM at 5 of 60 (8%) and 0 of 60 (0%), respectively (P = 0.02). The PLMA^TM was successful at the first attempt in all failed LTA cases. All failed LTA cases were attributable to persistent oropharyngeal leak. The time to achieve an effective airway was similar (PLMA^TM: 63 ± 35 versus LTA: 66 ± 47 s). Oropharyngeal leak pressure was larger for PLMA^TM at 50% maximal recommended cuff volume (PLMA^TM: 29 ± 7 versus LTA: 21 ± 6 cm H₂O, P < 0.0001), but was similar at the maximal recommended cuff volume (PLMA^TM: 33 ± 7 versus LTA: 31 ± 8 cm H₂O). During maintenance, expired tidal volumes (PLMA^TM: 614 ± 173 versus LTA: 456 ± 207 mL, P < 0.0001) were larger and ETCO₂ (PLMA^TM: 33 ± 9 versus LTA: 40 ± 11 mm Hg, P = 0.0001) was lower for the PLMA^TM, but otherwise cardiorespiratory variables were similar between devices during placement, maintenance, emergence, and postremoval. Oropharyngeal and gastric leaks were not detected. More patients required an increase in FIO₂ (7/60 versus 0/60, P = 0.006) and respiratory rate (7/60 versus 1/60, P = 0.03) with the LTA. The numbers of minor and major airway interventions were lower for the PLMA^TM during all phases (Table 2). The incidence of airway obstruction was less frequent with the PLMA^TM, but otherwise the incidence of adverse events was similar (Table 3). The incidence of postoperative complications was similar (Table 4). When comparing mean expired tidal volumes in different head/neck positions, the quality of airway was unchanged in 56 of 60 patients (93%) with the PLMA^TM and 42 of 55 (76%) with the LTA (P = 0.01). The mean expired tidal volume for the PLMA^TM was larger than the LTA when the head/neck was positioned with the standard pillow (620 ± 151 versus 453 ± 202 mL), with the head rotated to the side (599 ± 183 versus 396 ± 156 mL), and without the standard pillow (604 ± 203 versus 378 ± 108 mL) (all: P < 0.0001). Expired tidal volumes were similar for the PLMA^TM and LTA when chin lift was applied (PLMA^TM: 623 ± 131 versus LTA: 605 ± 140 mL). There was no evidence for skill acquisition with either device when comparing success rates, airway interventions, and complication rates between the first and last 15 uses for either investigator.

	Discussion

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We found that first-time insertion success rates were similar, but failure rates were more frequent for the LTA. The more frequent failure rates were not related to difficulty with insertion, but rather failure to form an effective airway. The success rate for the LTA was more frequent than that reported by Asai et al. (4), who found that 82% (41/50) of patients had an oropharyngeal leak pressure >16 cm H₂O compared with the current study in which 92% (45/50) had an oropharyngeal leak pressure 17 cm H₂O.

We found that the oropharyngeal leak pressure was higher for the PLMA^TM at 50% of the maximal recommended volume, but similar at the maximal recommended volume. This probably reflects the different mechanism of seal between the two devices: the PLMA^TM primarily forms a seal by adapting its shape to the variable contours of the pharynx, whereas the LTA primarily forms a seal by exerting pressure against the pharyngeal mucosa. The values for oropharyngeal leak pressure are similar to previous studies with the PLMA^TM (3) and LTA (4).

We found that expired tidal volumes were smaller for the LTA during pressure-controlled ventilation. This was related to an increase in resistance to gas flow with the LTA because no leaks occurred. Increased resistance to gas flow can be within the device, between the distal aperture of the device and the trachea, or within the lungs. We speculate that the increased resistance was between the distal aperture and trachea and caused by epiglottic downfolding glottic compression or malposition. It is not likely to be related to increased resistance to gas flow through the device because the LTA has a larger internal diameter than the PLMA^TM. It is not likely to be related to differences in pulmonary compliance because neither device penetrates the vocal cords to trigger an increase in pulmonary airway resistance (16). This also explains the frequent incidence of airway obstruction and the improvement in tidal volume with chin lift for the LTA. Chin lift and head extension raise the hyoid and epiglottis to lessen airway obstruction in the area of the larynx. The PLMA^TM does the same lifting by its design, thus mostly obviating the need for these maneuvers (17). Unfortunately, we did not assess the anatomic position of the LTA. The detection of gastric insufflation in two patients with the LTA during maximal oropharyngeal leak pressure testing also suggests that the LTA was occasionally malpositioned. One of the advantages of the PLMA^TM is that malposition can be identified. We selected pressure-control ventilation rather than volume-controlled ventilation because peak pressures are lower for a given tidal volume, and the risk of gastric insufflation is reduced (18,19).

We found that postoperative airway morbidity was similar, but our study was not powered to assess this issue. Our data do suggest, however, that the LTA and PLMA^TM exert similar mucosal pressures and/or cause similar amounts of trauma during insertion. Directly measured mucosal pressures for the PLMA^TM are generally smaller than pharyngeal perfusion pressure (11), but there are no published data about directly measured mucosal pressures with the LTA.

Our study has a number of limitations. First, although the investigators were experienced with both devices, prior experience with other laryngeal mask devices may have given the PLMA^TM an advantage. However, this will be the situation with most anesthesiologists using the LTA and PLMA^TM for the first time. Interestingly, there was no evidence for skill acquisition with either device during the trial. Second, we did not determine the anatomic position of either airway device and it is possible that the LTA was malpositioned more frequently. However, fiberoptic assessment of position is not conducted in a routine clinical setting. Third, our results may not be applicable to patients who are breathing spontaneously. Fourth, intraoperative data collection was by an unblinded observer and is a possible source of bias.

We conclude that the PLMA^TM offers advantages over the LTA in most technical aspects of airway management in paralyzed patients undergoing pressure-controlled ventilation.

	References

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Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999