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Anesth Analg 2003;96:600-605 © 2003 International Anesthesia Research Society
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Abstract |
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In this multicenter, randomized study, we compared ease of insertion, postinsertion hemodynamic repercussion, quality of ventilation, and the capacity to achieve a "hands-free" anesthesia delivery between two new devices: the ProSealTM laryngeal mask airway (PLMA) and the Laryngeal Tube® (LT). The incidence of postoperative laryngopharyngeal discomfort was examined after short surgical interventions in spontaneously breathing patients. After induction with fentanyl and propofol, the respective airways were inserted into 70 adult ASA physical status I and II patients (35 patients in each group). First-attempt insertion success rates were more frequent for the PLMA (77% versus 51%; P < 0.05), but success rates were similar (100% versus 97%) after 3 attempts. The anesthesiologists considered that insertion of the PLMA was easier (P < 0.001). Expired tidal volume was larger with the PLMA (404.9 versus 328.4 mL; P < 0.005) and the ability to achieve hands-free ventilation was more frequent with the PLMA (32 versus 21 cases; P < 0.004). Positional maneuvers with the LT to correct ventilation deficiencies were not always completely effective (5 of 13). There were no differences in the incidence of intolerance, sore throat, dysphagia, and/or dysphonia between the two devices. We conclude that the PLMA showed greater ease of insertion and reliability than the LT for use in nonparalyzed anesthetized patients.
IMPLICATIONS: In this prospective, randomized study, we found that the ProSealTM laryngeal mask airway was easier to insert and permitted a better delivery of hands-free anesthesia than the Laryngeal Tube®. The incidence of postoperative laryngopharyngeal discomfort was similar for both devices.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Two new devices for controlling the airway as an advantageous alternative to the face mask during spontaneous-breathing general anesthesia have recently been marketed: the ProSealTM laryngeal mask airway (PLMA) (Laryngeal Mask Company, Henley-on-Thames, UK) (1,2) and the Laryngeal Tube® (LT) (VBM Medizintechnik GmbH, Sulz a. N., Germany) (3,4).
The PLMA is a modification of the classic laryngeal mask airway (LMA) which features a double cuff that forms a better seal than the standard LMA, to which a drainage tube, designed to protect against regurgitation and facilitate passage of a gastric tube, has been added. The LT is a single-lumen silicone tube closed at the distal end with an esophageal balloon and a pharyngeal cuff that is used to seal the airway. The air is blown through a ventral outlet between the two cuffs.
One of the advantages of these devices versus ventilation with face masks is the possibility of achieving a clinically adequate airway that does not require manual support, i.e., "hands-free."
Our objective was to compare these two devices to prove or reject the hypothesis that both are equivalent in terms of ease of insertion, ventilation quality during anesthesia in spontaneously breathing patients, and capacity to achieve a hands-free anesthesia delivery, and to evaluate their impact on postoperative laryngopharyngeal discomfort.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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After approval was granted from the ethics committees of the three participating institutions, informed consent was secured from all the patients. The study objective was to include 164 fasted patients of both sexes, classified as ASA physical status I or II, aged 18–60 yr, and scheduled for elective surgery of expected duration of <30 min, and in whom the use of muscular relaxants was not needed.
Surgical interventions were selected in which the use of the LMA or LT were regarded as acceptable alternatives for airway maintenance. Patients weighing between 60 and 80 kg with a height between 1.60 and 1.80 m were included in the study. According to the respective instruction manuals, the correct size to be used within these ranges in the LT and the LMA is 4.
All participating anesthesiologists read the manufacturers’ instruction manuals (5,6) and had previous experience of 10 insertions with each device before the start of this prospective study.
Patients were excluded from the trial if they were pregnant, had a history of gastroesophageal reflux, or a known or predicted difficult airway. Random allocation into two groups (PLMA or LT) via a computer-generated random numbers table was achieved by using sealed opaque envelopes, which were opened by the investigator immediately before the induction of anesthesia.
Anesthetic management was standardized according to the following protocol: monitoring included an electrocardiograph, pulse oximeter, capnograph, automated blood pressure manometer, and in-line spirometer for tidal volume measurement. Noninvasive arterial blood pressure and physiological data including heart rate and arterial oxygen saturation were recorded before the induction of anesthesia, 1 min after induction, and 30 s after insertion of the device.
Patients were premedicated with fentanyl 100 µg and metoclopramide 10 mg. After breathing oxygen for 3 min, propofol 2.5 mg/kg was administered IV over 30 s. Manually assisted ventilation was permitted in the event of apnea. One minute after propofol was administered, the investigator inserted the corresponding device using the technique recommended by the manufacturers.
Each insertion attempt was recorded. Only one forward pushing movement, without backward movement, was allowed in each insertion attempt (7). When device insertion was unsuccessful or the device was badly positioned, additional boluses of propofol could be given at the discretion of the anesthesiologist and another attempt at insertion was attempted. If the anesthesiologist could not effectively establish an airway using the initial randomized device after three insertion attempts, the alternative device was used. If the anesthesiologist could not establish an effective airway using the alternative device within three attempts at insertion, the patient was subsequently treated as clinically indicated. The anesthesiologist assessed the overall ease of PLMA or LT insertion as easy, moderate, or difficult. The number of attempts was recorded, but ease of insertion was only assessed during the first attempt.
The cuff of the LT was inflated with a cuff pressure manometer (Laryngeal Cuff Pressure Gauge; VBM Medizintechnik) to an intracuff pressure of 80 cm H2O to accommodate it in the oropharyngeal cavity, whereupon pressure was reduced to 70 cm H2O. The PLMA was inflated to a pressure of 60 cm H2O, as recommended by both instruction manuals. No cuff pressure adjustments were made during the procedure.
After the insertion of the devices, the patients were connected to the breathing system. Airway permeability was judged by observing respiratory movement and a square wave capnograph trace in spontaneously breathing patients or during assisted breaths in patients with apnea. Airway manipulations (head tilt, cervical extension, chin lift, jaw thrust), including pushing the devices in or out to achieve a clinically adequate airway not requiring manual support, were used as necessary and recorded. If these maneuvers failed to achieve adequate ventilation within a maximal period of 5 min, a change to the other device was allowed and the event was considered device failure.
Anesthesia was maintained with sevoflurane in oxygen/air or with a propofol infusion (50–200 µg · kg-1 · min-1) as clinically indicated. The lungs of apneic patients were ventilated manually to maintain arterial oxygen saturation >92%. During steady-state conditions of anesthesia, the maximal expired tidal volume was measured and later related to each patient’s body surface area (Mosteller’s formula). The presence of gas leak was detected by auscultation at neck and mouth.
The devices were withdrawn when the patients awoke and were able to respond to spoken commands. Tolerance during emergence was estimated with a nominal scale: a) comfortable, b) minor signs of intolerance (cough, retching, hiccup, or biting on the airway), and c) major signs of intolerance (vomiting, or vagal reactions rendering it necessary to remove the instrument immediately). Immediately after withdrawal of the devices, the content of the oropharynx was aspirated and its nature determined (saliva, gastrointestinal, or bloody fluid). Dipyrone (30 mg/kg IV) or ketorolac trometamol (30 mg IV) every 8 h was used for postoperative analgesia.
All patients were assessed 24 h after surgery for postoperative complications including sore throat (severity was graded by the patients as nil, mild, moderate, or severe), hoarseness of voice, and dysphagia. Any additional comments were also recorded.
All data were collected and analyzed by using the SPSS statistical software program, version 10.0.6 (Chicago, IL). The primary statistical end point of the trial was to determine whether the difficulty on insertion rates in the two treatments (LT or PLMA) was equivalent. On the basis of a previous study (8) on the PLMA, we considered a probable first-attempt insertion success rate of 80%, and defined equivalence as ±20%.
The sample size was chosen to yield 80% power to detect nonequivalent event rates. However, according to the ethics committee’s guidelines, enrollment of patients was stopped after 14 days of statistical analyses revealed a significant disadvantage in any of the devices—a priori defined as the failure to achieve a correct insertion at the third attempt or adequate ventilation without manual assistance. Analyses were performed following the predefined grouping; if a change of device was necessary, the following data were excluded from further analysis.
The 
2 test and t-test were used to compare demographic and clinical details, the 2 test for conditions during devices insertion, the unpaired t-test for hemodynamic changes during the induction of anesthesia, and Fisher’s exact test for postoperative complications. A probability of <0.05 was considered significant.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In accordance with the provisions of the above statistical analysis, only 70 patients were required to find significant differences between the two devices. The demographic and clinical characteristics of the 70 patients are shown in Table 1. Both groups of patients were similar in age, body weight, height, ASA grade, sex ratio, Mallampati score and baseline heart rate, systolic blood pressure, and oxygen saturation.
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The PLMA proved easier to insert and required fewer attempts than the LT (Table 2). This did not impact hemodynamic variables, which showed no differences after the insertion of either device. In one case in the LT group, it proved impossible to insert at the third attempt and the switch was made to the PLMA; that insertion was easy at the first attempt. The sequence of events with the LT is shown in the flowchart of Figure 1. The frequency of events observed in the PLMA group (versus the LT group) is shown in Table 2.
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The expired tidal volume was significantly larger in the PLMA group. When spontaneous ventilation was unsuitable (LT = 13; PLMA = 3), corrective action was taken, proving to be effective in 46% (6 of 13) in the LT group and in the 3 cases of the PLMA group. Once the malpositioning of the devices had been corrected, the tidal volumes increased, showing no differences between either (in absolute values or related to body surface area).
In one case in the LT group, the maneuvers used to correct the device positioning were not wholly effective, but as surgery was nearing completion, the device was not replaced. In another patient in the LT group in whom ventilation was insufficient, an urgent tracheal intubation had to be performed because of the presence of lingual cyanosis and edema. In the remaining six patients, the PLMAs were successfully inserted at the first attempt, although one patient presented severe bronchospasm, and a tracheal intubation was therefore performed.
In one patient in the PLMA group in whom ventilation was insufficient, a gastric distension was observed by a visible increase in abdominal girth with air entry into the stomach detected at stethoscopy. The problem was solved by mobilizing the device, although the insertion of a gastric tube was impossible. When the PLMA was removed, gastric fluid was aspirated from the oropharynx.
With the patients awake, the tolerance of both devices was good and similar in both groups. Five patients in the LT group displayed minor signs of intolerance (retching 2, cough 2, and restlessness 1) and a further 5 in the PLMA group (hiccoughs 2, restlessness 2, and retching 1). On removal of the device, we detected swelling and cyanosis of the tongue in one patient from the LT group, whereby the LT was removed immediately.
The incidence of postoperative complications was similar for both groups (Table 3). One of the patients in whom we detected lingual cyanosis during emergence from anesthesia had paresthesias and lingual pain that disappeared 24 h postoperatively.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The PLMA was easier to insert at the first attempt than the LT. Moreover, not all the insertions of the LT at the first attempt were as easy as PLMA. Our first-time-right insertion rate with the PLMA was 77%, somewhat less than the rate obtained in 2 studies by Brimacombe et al. (2,8) (82%–86%). This difference may be attributed to the fact that the investigators involved in the aforementioned study had more previous experience (>20 insertions) with the device, which shows that there may be a learning curve (9,10). The investigators that participated in this study had considered that 10 uses of both devices (and broad experience with the classic LMA) would be enough to overcome the learning curve. Moreover, with the LT, our first-attempt success rate is ostensibly different from the 94%–100% (in 50 and 30 cases, respectively) observed in previous studies (4,11). Our experience before the study with the LT and the PLMA was similar, and although it has not been demonstrated, we have assumed that the learning curves for both devices must be deemed equivalent (8,12), and the results are therefore comparable. Regardless of the ease of insertion, both devices had frequent success after 3 attempts (97% versus 100%) in nonparalyzed patients.
As occurs with other airway devices in which no tracheal manipulation is involved, hemodynamic variables did not differ between groups (13).
Hands-free ventilation was achieved successfully in 62% versus 91.5% of patients in the LT and PLMA groups, respectively. The figures observed with LT do not differ from the 66% observed with the "cuffed oropharyngeal airway" (14). The maneuvers performed to correct ventilation deficiencies were mainly cervical extension and chin lift, although the latter did not permit a hands-free anesthesia delivery. When these failed devices were removed and replaced by the alternative device (PLMA), the latter proved to be successful in all patients except one, in whom a bronchospasm required tracheal intubation. Over-handling of the airway in this patient, with a probable inadequate depth of inhaled anesthesia, may have triggered this adverse reaction.
In the PLMA group, the three patients in whom ventilation was not initially successful, improved their performance with the corrective maneuvers used. These differences in reliability for hands-free ventilation had already been observed in a previous study comparing the standard LMA to an earlier model of the LT (with two independent pilot tubes) (14,15) and it has been suggested that they are related to anatomical positioning.
These two new devices were designed to provide protection from fluid regurgitation (4,16). Their protection mechanism is totally different; whereas the LT prevents this from happening by blocking the top end of the esophagus, the PLMA allows the gastric contents to evacuate via its drainage tube. Moreover, the PLMA permits an orogastric tube to be run through the drainage tube to empty the stomach during surgery. However, it proved impossible to insert it in one of our patients with gastric dilation. This is no surprise, because whereas in the preliminary crossover studies a gastric tube placement was always successful (1,2), it proved impracticable in a later study in 12% of the patients (8). The guarantee offered by these devices to "prevent" or "drain" gastric regurgitation of the airway has yet to be determined.
The incidence of postoperative laryngopharyngeal discomfort with the PLMA in our study closely matches the findings of previous studies with the classic LMA and with the PLMA (9,17). Some factors are fundamentally decisive in the incidence of postoperative sore throat: the number of attempts at insertion (18), and an increase in oropharyngeal mucosal pressure related to intracuff pressure (19). Judging by these factors, the PLMA has the necessary conditions to have a decreased incidence of sore throat; first, the LT group required more attempts at insertion, and second, the LT manufacturers recommend keeping the device inflated at a slightly higher pressure (between 60 and 80 cm H2O) than the one suggested for the PLMA. Nevertheless, the small sample size and the fact that seven patients from the LT group who required more handling during insertion and during anesthesia were excluded from final count, prevented us from observing differences between groups.
A special comment must be made with regard to congestion, edema, and cyanosis observed in two patients of the LT group. We observed this same situation on a further four occasions during the lead-in training period, which was solved by reducing intracuff pressure. Other authors have highlighted the importance of this issue with a device in which characteristics are similar to the LT (the Airway Management Device) (20). Although Asai and Kawachi (21) consider that the pressure exerted on the oropharynx is not excessive with the LT, their data come from a global formula, and they do not take variations of the different cuff shapes into account. In vivo intracuff pressure and calculated mucosal pressure are imprecise predictors of directly measured mucosal pressure (22). Evidently, the balloon that best adapts (anatomically) to the pharyngeal walls will distribute its transmitted pressure more evenly.
The two airway devices analyzed are different in the way the cuff fits the base of the tongue. Whereas the PLMA is an elliptic mask with an outer inflatable rim that exerts scant pressure on the base of the tongue (23), the LT has a large spherical cuff, proximal to the airway, which needs to exert its greater pressure precisely on the medial part of the base of the tongue to obtain good sealing of the pharynx. We hypothesized that high pressure on this site may compromise circulation of the tongue and produce a macroglossia. Anesthesiologists do not usually open patients’ mouths to check tongue integrity during the maintenance of anesthesia. This happened with one of our patients in whom we detected the problem on emergence from anesthesia when removing the device. If this adverse effect is not detected at the right time, it could lead to a life-threatening situation (24). Because it is temporarily irreversible, an urgent tracheotomy might be required in some cases.
In conclusion, this study confirms the already known characteristics of the PLMA in terms of its ease of insertion and feasibility for maintaining a permeable airway in a hands-free manner. The drawbacks observed with the LT render its use inadvisable for the maintenance of anesthesia in spontaneously breathing patients.
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Acknowledgments |
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We are grateful to VBM Medizintechnik, Sulz, Germany and to Laryngeal Mask Company, Henley-on-Thames, UK, who loaned us the devices and the Laryngeal Cuff Pressure Gauge to perform this study.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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- Brain AIJ, Verghese C, Strube PJ. The LMA ‘ProSeal’: a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4.
[Abstract/Free Full Text] - Brimacombe J, Keller C. The ProSeal laryngeal mask airway: a randomized, crossover study with the standard laryngeal mask airway in paralyzed, anesthetized patients. Anesthesiology 2000; 93: 104–9.[Web of Science][Medline]
- Agro F, Cataldo R, Alfano A, Galli B. A new prototype for airway management in an emergency: the laryngeal tube. Resuscitation 1999; 41: 284–6.[Web of Science][Medline]
- Dorges V, Ocker H, Wenzel V, Schmucker P. The laryngeal tube: a new simple airway device. Anesth Analg 2000; 90: 1220–2.
[Free Full Text] - LMA ProSealTM instruction manual. Henley-on-Thames: The Laryngeal Mask Company, 2000.
- Laryngeal-Tube (LT). Instructions for use. Sulz a. N., Germany: VBM Medizintechnik GmbH, 2000.
- Dingley J, Baynham P, Swart M, Vaughan RS. Ease of insertion of the laryngeal mask airway by inexperienced personnel when using an introducer. Anaesthesia 1997; 52: 756–60.[Web of Science][Medline]
- Brimacombe J, Keller C, Fullekrug B, et al. A multicenter study comparing the ProSeal and classic laryngeal mask airway in anesthetized, nonparalyzed patients. Anesthesiology 2002; 96: 289–95.[Web of Science][Medline]
- Genzwuerker HV, Hilker T, Hohner E, Kuhnert-Frey B. The laryngeal tube: a new adjunct for airway management. Prehosp Emerg Care 2000; 4: 168–72.[Medline]
- López-Gil M, Brimacombe J, Cebrian J, Arranz J. The laryngeal mask airway in pediatric practice: a prospective study of skill acquisition by resident anesthesiologists. Anesthesiology 1996; 84: 807–11.[Web of Science][Medline]
- Asai T, Murao K, Shingu K. Efficacy of the laryngeal tube during intermittent positive-pressure ventilation. Anaesthesia 2001; 55: 1099–102.
- Miller DM, Youkhana I, Pearce AC. The laryngeal mask and VBM laryngeal tube compared during spontaneous ventilation: a pilot study. Eur J Anaesthesiol 2001; 18: 593–8.[Web of Science][Medline]
- Heringlake M, Doerges V, Ocker H, Schmucker P. A comparison of the cuffed oropharyngeal airway (COPA) with the laryngeal mask airway (LMA) during manually controlled positive pressure ventilation. J Clin Anesth 1999; 11: 590–5.[Web of Science][Medline]
- Dounas M, León O, Bonnet V, et al. Learning placement of a new oropharyngeal intubation (COPA). Ann Fr Anesth Reanim 1999; 18: 309–12.[Web of Science][Medline]
- Genzwuerker HV, Kuhnert-Frey B. Modification of the laryngeal tube. Prehosp Emerg Care 2000; 4: 371–2.
- Keller C, Brimacombe J, Kleinsasser A, Loeckinger A. Does the ProSeal laryngeal mask airway prevent aspiration of regurgitated fluid? Anesth Analg 2000; 91: 1017–20.
[Abstract/Free Full Text] - Figueredo E, Vivar-Diago M, Muñoz-Blanco F. Laryngo-pharyngeal complaints after use of the laryngeal mask airway. Can J Anaesth 1999; 46: 220–5.[Web of Science][Medline]
- Keller C, Sparr HJ, Brimacombe J. Laryngeal mask lubrication: a comparative study of saline versus 2% lignocaine gel with cuff pressure control. Anaesthesia 1997; 52: 592–6.[Web of Science][Medline]
- Burgard G, Mollhoff T, Prien T. The effect of laryngeal mask cuff pressure on postoperative sore throat incidence. J Clin Anesth 1996; 8: 198–201.[Web of Science][Medline]
- Mandal NG. A new device has to be safe and reliable too. Anaesthesia 2001; 56: 382–3.
- Asai T, Kawachi S. Pressure exerted by the cuff of the laryngeal tube on the oropharynx. Anaesthesia 2001; 56: 911–2.
- Keller C, Brimacombe J, Benzer A. Calculated versus measured pharyngeal mucosal pressures with the laryngeal mask airway during cuff inflation: an assessment of four locations. Br J Anaesth 1999; 82: 399–401.
[Abstract/Free Full Text] - Keller C, Brimacombe J. Mucosal pressure and oropharyngeal leak pressure with the ProSeal versus laryngeal mask airway in anaesthetized paralysed patients. Br J Anaesth 2000; 85: 262–6.
[Abstract/Free Full Text] - Figueredo-Gaspari E, Fredes-Kubrak R, Canosa-Ruiz L. Macroglossia after surgery of the posterior fossa. Rev Esp Anestesiol Reanim 1997; 44: 157–8.[Medline]
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