Randomized crossover comparison of the ProSealTM laryngeal mask airway with the Laryngeal Tube® during anaesthesia with controlled ventilation

T. M. Cook*, C. McKinstry, R. Hardy and S. Twigg

Royal United Hospital, Combe Park, Bath, UK

Corresponding author

Accepted for publication: June 25, 2003


    Abstract
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Potential conflict of interest
 References
 
Background. The Laryngeal Tube (LT®) performs similarly to the classic laryngeal mask airway during controlled ventilation but with an improved airway seal. We compared the laryngeal tube with the ProSealTM laryngeal mask airway (PLMA) throughout anaesthesia.

Methods. Thirty-two patients were studied using a randomized cross-over design. The primary outcome measure was airway seal pressure. Secondary outcome measures included peak and plateau airway pressures, time to achieve an airway, ease of insertion, airway manipulations required to achieve a patent airway and grade of fibre-optic laryngoscopy. The proportion of patients in whom good, fair or failed ventilation was achieved was also calculated.

Results. No significant difference was found in regard to seal pressure (PLMA, median 26.5 cm H2O, range 10–40; LT, median 24, range 6–40; P=0.7, 95% confidence interval of the difference 3.5 to –4.0). There were two failures of insertion or ventilation in the LT group and none in the PLMA group. The peak airway pressure with the PLMA was lower than with the LT but the difference was clinically unimportant (PLMA, mean 16.2 cm H2O, SD 3.52; LT, mean 17.9, SD 5.21; P=0.02, 95% confidence interval of the difference –3.1 to –0.28). The PLMA took significantly less time to insert than the LT (PLMA, median 18.5 s, interquartile range 14–26; LT, median 22, interquartile range 15–36.5; P<0.02, 95% confidence interval of the difference –21.5 to –1.0). The PLMA gave a significantly better view on fibre-optic laryngoscopy than the LT (P<0.001, 95% confidence interval of the difference in grade –2.0 to –1.0). In the 16 patients in whom the PLMA was used during maintenance of anaesthesia ventilation was good in 15, fair in none and failed in one. The equivalent figures for the LT were good in nine, fair in six and failed in one (P=0.009). There was no significant difference in the plateau airway pressure, ease of insertion of the devices, number of manipulations required to achieve or maintain an airway, or in overall complications.

Conclusion. The two devices performed equally well in terms of seal pressure. The PLMA was quicker to insert. Efficacy of ventilation was significantly better with the PLMA than the LT. The PLMA allowed a significantly better view of the larynx with a fibre-optic laryngoscope, and may therefore be of more use in cases where visualization of the larynx is required.

Br J Anaesth 2003; 91: 678–83

Keywords: equipment, masks laryngeal; equipment, tubes laryngeal


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Potential conflict of interest
 References
 
The ProSealTM laryngeal mask airway (PLMA) (Intavent Orthofix, Maidenhead, UK) and the Laryngeal Tube (LT®) (VBM Medizintechnik, Sulz, Germany) are two recently introduced devices for airway maintenance during general anaesthesia. The PLMA is a modification of the classic laryngeal mask airway that includes an oesophageal drainage tube, a deeper bowl and a posterior cuff. The latter two modifications create a better pharyngeal seal than the classic laryngeal mask airway. Like the classic laryngeal mask airway, the PLMA is re-usable 40 times.1 2 The LT has been designed to secure a patent airway during either spontaneous or controlled ventilation. It is re-usable 50 times. It consists of an airway tube with a distal balloon designed to sit in the oesophagus, and a larger, asymmetrical proximal cuff in the middle of the device which creates a seal in the pharynx (Fig. 1). The cuffs are inflated through a single pilot tube and balloon. There are two large distal apertures in the tube between the two cuffs, through which gas movement may take place.



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Fig 1 The laryngeal tube. (1 and 2) Distal and proximal airway orifices. (3 and 4) Lateral small orifices.

 
The current design of the LT was introduced in 2002. In contrast to earlier designs, it has one pilot tube, a soft silicone tip and indented lower cuff (to prevent the cuff obstructing the airway) and an increase in the number of ventilation orifices (Fig. 1).

While there have been several studies comparing the classic laryngeal mask airway and LT, until recently all have used versions of the LT that are now obsolete.35 We have recently compared the classic laryngeal mask airway with the current LT during controlled ventilation.6 Performance of the two devices was similar; however, the airway seal pressure with the LT was higher than with the classic laryngeal mask airway and comparable to those in published studies with the PLMA.1 2

The aim of this study was to compare the seal pressure of the LT with that of the PLMA in paralysed patients during the entire course of anaesthesia. Secondary outcome measures were designed to examine the relative clinical utility of each device.


    Methods
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Potential conflict of interest
 References
 
The local research ethics committee approved the study and all patients gave written informed consent before taking part in the study. We used a randomized crossover study design. We recruited 32 ASA I–III patients undergoing elective surgery in the supine or lithotomy position, in whom neuromuscular block and the use of a laryngeal mask airway was appropriate. Patients were excluded if they had any pathology of the neck, upper respiratory or upper alimentary tract, if they were at risk of pulmonary aspiration of gastric contents, if they weighed less than 50 kg or greater than 100 kg, or were less than 155 cm in height. Before operation, the view of the oropharynx on opening the mouth was scored by the method of Mallampati7 as modified by Samsoon and Young.8

Standard anaesthesia monitors were attached before induction of anaesthesia. The patient’s head was supported on a firm pillow. After preoxygenation, anaesthesia was induced with a target-controlled infusion of i.v. propofol at 4–7 µg ml–1 and fentanyl 1 µg kg–1. Neuromuscular block was produced by rocuronium 0.6–0.9 mg kg–1 and was confirmed using a peripheral nerve stimulator (train of four count=0) before airway manipulation. Anaesthesia was maintained with a continuous target-controlled infusion of propofol. The patients were then allocated randomly to one of two groups, in which the LT or the PLMA was used first for airway management. Randomization was by the use of 32 sequentially numbered, sealed opaque envelopes; 16 contained a slip of paper on which was written the letters PLMA and 16 the letters LT. These envelopes were opened after induction of anaesthesia and the indicated device was then used first.

Insertion of the device
The LT was inserted following the manufacturer’s instructions. Before insertion, cuffs were deflated and a water-soluble lubricant (KY jelly) was applied to the cuffs. The patient’s head was extended on the neck (‘sniffing position’). The tip of the LT was placed against the hard palate behind the upper incisors and the device was inserted in the centre of the mouth until resistance was felt. If no resistance was felt the LT was positioned with the second bold positioning line on the tube between upper and lower incisors. The cuffs were inflated using a cuff inflator (VBM, Medizintechnik, Sulz, Germany) until the intracuff pressure reached 80–90 cm H2O and was then reduced to 60– 70 cm H2O.9 A size 4 was used for those between 155 and 180 cm and a size 5 for those above 180 cm in height.9

The PLMA was inserted according to the manufacturer’s instruction manual.10 An introducer was used in all cases. The back of the cuff was lubricated with KY jelly. A size 4 mask was used in females and a size 5 in males.11 The cuff was inflated using the same cuff inflator until the intracuff pressure reached 60–70 cm H2O.10

Maintenance of the airway
In both groups, the breathing system was connected to the device. An initial assessment of airway patency and the ability to ventilate the lungs was made by gently squeezing the reservoir bag, observing the presence of end-tidal carbon dioxide waveforms and chest movement. If it was not possible to ventilate the lungs, the following airway manoeuvres were allowed: chin lift, jaw thrust, head extension or flexion on the neck. For the LT, the position was also allowed to be adjusted, by gently pushing or pulling the device as recommended by the manufacturer.9 After any manoeuvre, adequacy of ventilation was reassessed. If it was not possible to insert the device or ventilate through it, one more attempt at insertion was allowed. If placement failed after two attempts, study of that device was abandoned and the second device was studied.

The time for insertion of the airway (from the time of picking up the device to attaching it to the breathing system after inflation of the cuff) was measured in patients in whom it was possible to ventilate the lungs.

Fresh gas was insufflated at 5 litres min–1, the spill valve was occluded and the minimum airway pressure at which gas leaked around the airway device was determined. The peak airway pressure was not allowed to exceed 40 cm H2O.

Ventilation of the lungs
After securing the device, controlled ventilation in oxygen and air was started with a delivered tidal volume of 7 ml kg–1 and an inspiratory/expiratory ratio of 1:2. The respiratory rate was adjusted to maintain the end-tidal carbon dioxide concentration in the normal range. If the expired tidal volume was below 7 ml kg–1, the delivered tidal volume was increased up to 10 ml kg–1 in an attempt to achieve this level. Four tests of ventilation were applied: (i) adequate chest movement; (ii) an expired tidal volume of 7 ml kg–1; (iii) stable oxygenation; and (iv) square-wave capnography. If all tests were passed, ventilation was recorded as ‘optimal’. Ventilation was recorded as ‘suboptimal’ if any one test was not passed.

Fibre-optic inspection of airway position
A fibrescope was inserted to assess airway positioning. The fibre-optic view was assessed with the tip of the fibrescope in the bowl of the PLMA and at the orifice of the LT. In the case of the LT, the view from both ventilation orifices was inspected and the best view recorded. The view was graded from 1 to 4: 1=vocal cords fully visible; 2=vocal cords partially visible or arytenoid cartilages visible; 3=epiglottis visible; 4=no laryngeal structures visible.12

Crossover
After the above tests had been completed for the first device, neuromuscular paralysis was reconfirmed (train of 4 count=0). The first device was removed and the second device was studied as described above. If airway obstruction occurred during maintenance of anaesthesia, manoeuvring the position of the device or the patient’s head and neck or removal and reinsertion of the device was allowed. The number of manipulations of the device during insertion and maintenance of anaesthesia was recorded for each device.

Ventilation efficacy
The second device was used for the duration of anaesthesia and we investigated the success rate for each device in establishing and maintaining a patent airway allowing ventilation without complications (efficacy). ‘Ventilation efficacy’ was recorded as good, fair or failed with the following definitions: good=optimal ventilation without complications during anaesthesia; fair=optimal ventilation with complications or suboptimal ventilation without complications; and failed=failed insertion or abandonment of use.

Removal of the device
At the end of the operation, anaesthetic agents were discontinued while the device was left in place. The device was removed after the patient had regained consciousness and had responded to a verbal command to open the mouth. However, if necessary (e.g. airway obstruction or retching occurred), it could be removed before this point. Before removal, the cuffs of the LT were deflated, whereas the cuff of the PLMA was not (in accordance with the manufacturer’s recommendations).10 At removal, the presence or absence of secretions interfering with airway management and of blood on the device was recorded. Complications, defined a priori, that occurred during induction of, maintenance of and emergence from anaesthesia from the use of the device were recorded.

Postoperative period
After operation, each patient was questioned to determine whether airway complications were present. Because of the crossover design of the study, these data were not used for analysis.

Statistical analysis
The primary aim of the study was to compare the leak pressures between two groups. On the basis of the results of our previous studies, power analysis showed that the study had 80% power to detect a difference in seal pressure of 5 cm H2O. Secondary outcome measures included peak airway pressure, time taken to achieve an airway, ease of insertion, number of airway manipulations required to achieve an airway, ventilation efficacy and grade of view on fibre-optic inspection of the larynx.

Insertion time and seal pressure data were not normally distributed and the Wilcoxon signed rank test was used. The {chi}2 test or Fisher’s exact test was used as appropriate to compare the grade of fibre-optic view of the larynx, numbers of manipulations, complications and efficacy of ventilation between groups. The data for peak airway pressure, plateau pressure and device intracuff pressure were normally distributed and the paired Student’s t-test was used for analysis. Statistical analysis was performed using the statistical package Analyse-it (Analyse-It Software, Leeds, UK) and Microsoft Excel v6.0.


    Results
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Potential conflict of interest
 References
 
The details of the patients are recorded in Table 1. Because of an error during randomization, the PLMA was used as the first device on 17 occasions and the LT on 15. There were two failures to establish a patent airway in the LT group and none in the PLMA group. On one of the occasions that the LT failed it was the second device used and an airway could not be established, so a PLMA was reinserted and used for airway maintenance. As a result, an LT was used for maintenance for 16 cases and the PLMA for 16.


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Table 1 Details of the 32 patients studied
 
No significant difference was found in regard to seal pressure (PLMA, mean 26.5 cm H2O, range 10–40; LT, median 24 cm H2O, range 6–40; difference between medians 0.5 cm H2O; P=0.7, 95% confidence interval (CI) of the difference 3.5 to –4.0 (Wilcoxon signed rank test)). Peak airway pressure was lower in the PLMA group than the LT group: the difference was statistically significant but not clinically important (PLMA, mean 16.2 cm H2O, SD 3.52 cm H2O; LT, mean 17.9 cm H2O, SD 5.21 cm H2O; P=0.02, 95% CI of the difference –3.1 to –0.28 (paired samples t-test)). The PLMA took significantly less time to insert than the LT (PLMA, median 18.5 s, interquartile range 14–26 s; LT, median 22 s, interquartile range 15– 36.5 s, difference between medians –5.0; P<0.02, 95% CI of the difference –21.5 to –1.0 s (Wilcoxon signed rank test)). The PLMA gave a significantly better fibre-optic view of the larynx than the LT (P<0.001, {chi}2-test). Part of the laryngeal inlet was visible in 29 of 32 cases with the PLMA and in 13 of 31 cases with LT. There was no statistically significant difference in ease of insertion of the devices, plateau airway pressure, number of manipulations required to achieve or maintain an airway, or in overall complications. In the 16 patients in whom the PLMA was used during maintenance of anaesthesia, ventilation was good in 15, fair in none and failed in one. The equivalent figures for the LT were good in nine, fair in six and failed in one. These differences are statistically significantly different (P=0.009, {chi}2-test) and suggest that the efficacy of ventilation with the PLMA is better than that with the LT. During maintenance of anaesthesia, minor loss of airway patency or gas leakage led to 10 airway manipulations (in four patients using the LT and none using the PLMA; difference not significant). There were no other airway complications during maintenance. During emergence, the LT and the PLMA were both well tolerated in all patients except one from each group. Complications during recovery were infrequent; coughing occurred in two patients maintained with a PLMA and one maintained with an LT. Two patients had blood noted on a PLMA after removal and none after removal of an LT.


    Discussion
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Potential conflict of interest
 References
 
We have shown that the LT and PLMA are similarly easy to insert and provide similar laryngeal seal pressure. We found statistically significant, but clinically unimportant, differences in time for insertion of the devices and peak airway pressure during controlled ventilation.

The crossover design of this study increased its power, allowing us to treat each patient as their own control and answer our clinical question while studying the minimum number of patients. The success rate of obtaining a patent airway through both the PLMA and the LT was high and in keeping with recent reports on both devices.6 Ventilation was also adequate in most cases. Both devices required few manipulations during anaesthesia and were tolerated well during emergence, but the numbers studied were too small to make robust conclusions about stability, tolerability or safety.

There have been several other studies of LT performance and indeed two in which the LT was compared with the PLMA.13 14 However, modifications to the design of the LT were carried out in September 2001 and only one study (currently in press) has used the LT that is now commercially available.6 Whether the results from previous studies using older devices and prototypes can be extrapolated to the current device is unknown.

Two recent studies have compared the performance of the LT with that of the PLMA. Brimacombe and colleagues13 compared the devices in similar conditions to this study, with controlled ventilation in paralysed patients. They found that the airway seal pressures were similar between the two devices, whereas expired tidal volumes were larger, end-tidal carbon dioxide concentration lower and the incidence of airway obstruction during anaesthesia lower for the PLMA than for the LT. Although these authors used the previous version of the LT, their results are in broad agreement with ours.

Figueredo and colleagues14 compared the two devices during anaesthesia in 70 patients breathing spontaneously. First-attempt insertion rates were poorer for the LT than for the PLMA (but low in both groups compared with our results) and the LT group showed a lower tidal volume and less frequent ‘hands-free’ ventilation. More airway manoeuvres were required in the LT group to maintain a patent airway. There are several criticisms of this study. First, the PLMA is a device primarily designed for use during controlled ventilation15 and it has been commented that in order for its performance to be optimized it should be used in this manner.16 Previous versions of the LT have performed particularly poorly during spontaneous ventilation,5 and while the new version probably performs better its role in patients breathing spontaneously has yet to be established.6 Compared with the large airway orifice of the PLMA, the small gas exchange orifices of the LT and the fact that these orifices are frequently not positioned directly over the laryngeal inlet are likely to increase the work of ventilation during spontaneous breathing.

In a recent study6 we noted that the peak airway pressure with the LT was higher than with the classic laryngeal mask airway. We speculated that this might be due to the higher resistance of the small airway orifices of the LT, or the possibility that the LT was not lying over the laryngeal inlet. A novel feature of this study is that the position of the airway devices was examined fibre-optically. The vocal cords were visible in 91% of cases with the PLMA and in only 42% of cases with the LT. The positioning of the PLMA is in keeping with or better than that reported in other studies.1 2 In a recent report, Genzwuerker and colleagues17 reported high levels of success with visualization of the larynx and airway instrumentation in 10 patients after practice on a mannekin. They suggested that the LT would be a useful device for catheter exchange tube insertion. Genzwuerker used a previous version of the LT and ‘minor’ manipulations were needed in four of 10 patients to optimize the view, whereas we used the currently available device and examined the position of the device once in a functional position. Our findings suggest that the PLMA will perform better than the LT when access to the trachea is required. The relatively narrow diameter of the PLMA (similar to that of the reinforced laryngeal mask airway) is against its use for directly instrumenting the trachea, but the lack of grille bars and of an epiglottic elevator (compared with the classic laryngeal mask airway and intubating laryngeal mask airway respectively) may offer advantages for catheter exchange techniques.

While it was not a primary aim of our study to determine the quality of ventilation, we found that our ability to achieve a patent airway and optimal ventilation without subsequent complications (which we call ventilation efficacy) was higher using the PLMA than with the LT. While this finding is potentially important and the difference did reach statistical significance, we believe the finding should be interpreted with caution as it was not the primary aim of this study to examine this aspect of performance. Further studies, appropriately powered, may confirm or refute this.

Two of 18 LTs broke during the study, as has happened in our previous work. No PLMA failed. The durability of the LT would be usefully examined in a longitudinal study of its use.

The recently introduced Laryngeal Tube Sonda (LTS), like the PLMA, incorporates a drain tube to allow separation of the gastrointestinal and respiratory tracts. In future it would be useful to compare the performance of the PLMA and LTS.

We conclude that the LT and PLMA performed equally well in terms of laryngeal seal pressure. The PLMA was slightly quicker to insert. Ventilation was significantly more reliable with the PLMA. The PLMA allowed a significantly better view of the larynx with a fibre-optic laryngoscope, and may therefore be of more use in cases where visualization or access to the larynx is required.


    Potential conflict of interest
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Potential conflict of interest
 References
 
The LTs used in this study were provided by VBM, Medizintechnik, free of charge. TMC has received a small honorarium from Intavent Orthofix, the distributors of the PLMA.


    References
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Potential conflict of interest
 References
 
1 Cook TM, Nolan JP, Verghese C, et al. A randomised crossover comparison of the Pro-Seal with the classic laryngeal mask airway in unparalysed anaesthetized patients. Br J Anaesth 2002; 88: 527–33[Abstract/Free Full Text]

2 Evans NR, Gardner SV, James MFM, et al. The ProSeal LMA: results of a descriptive trial with experience of 300 cases. Br J Anaesth 2002; 88: 534–9[Abstract/Free Full Text]

3 Asai T, Kawashima A, Hidaka I, Kawachi S. The laryngeal tube compared with the laryngeal mask: insertion, gas leak pressure and gastric insufflation. Br J Anaesth 2002; 89: 729–32[Abstract/Free Full Text]

4 Ocker H, Wenzel V, Schmucker P, Steinfath M, Dörges V. A comparison of the laryngeal tube with the laryngeal mask airway during routine surgical procedures. Anesth Analg 2002; 95: 1094–5[Abstract/Free Full Text]

5 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[CrossRef][ISI][Medline]

6 Cook TM, McCormick B, Asai T. Randomized comparison of the laryngeal tube and the classic laryngeal mask airway during anaesthesia with controlled ventilation. Br J Anaesth. 2003; (In press)

7 Mallampati SR, Gatt SP, Gugino LD, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J 1985; 32: 429–34[ISI][Medline]

8 Samsoon GLT, Young JRB. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42: 487–90[ISI][Medline]

9 VBM Medizintechnik. Laryngeal tube LT®. Instructions for Use. VBM Medizintechnik GmbH, Sulz, 2001

10 Intavent Limited. LMA ProSeal Instruction Manual. Intavent Limited, 2002

11 Asai T, Brimacombe J. Cuff volume and size selection with the laryngeal mask. Anaesthesia 2000; 55: 1179–84[CrossRef][ISI][Medline]

12 Verghese C, Berlet J, Kapila A, Pollard R. Clinical assessment of the single use laryngeal mask airway—the LMA-Unique. Br J Anaesth 1998; 80: 677–9[CrossRef][ISI][Medline]

13 Brimacombe J, Keller C, Brimacombe L. A comparison of the laryngeal mask airway ProSealTM and the laryngeal tube airway in paralyzed anesthetized adult patients undergoing pressure-controlled ventilation. Anesth Analg 2002; 95: 770–6[Abstract/Free Full Text]

14 Figueredo E, Martinez M, Pintanel T. A comparison of the ProSealTM Laryngeal Mask and the Laryngeal Tube® in spontaneously breathing anesthetized patients. Anesth Analg 2003; 96: 600–5[Abstract/Free Full Text]

15 Brain AIJ, Verghese C, Strube PJ. The LMA ‘ProSeal’—a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4[Abstract]

16 Brain A. Esophageal breathing and upper airway obstruction with the ProSeal laryngeal mask airway. Anesth Analg 2002; 94: 1669–70[Free Full Text]

17 Genzwuerker HV, Vollmer T, Ellinger K. Fibreoptic tracheal intubation after placement of the laryngeal tube. Br J Anaesth 2002; 89: 733–8[Abstract/Free Full Text]