A randomized non-crossover study comparing the ProSealTM and ClassicTM laryngeal mask airway in anaesthetized children

M. Lopez-Gil1, J. Brimacombe2,*,{dagger} and G. Garcia3

1 Department of Anaesthesia and Reanimation, Maranon University Hospital, Madrid, Spain. 2 James Cook University, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Cairns, Australia. 3 Dental School, Department of Pharmacology School of Medicine, University Complutense, Madrid, Spain

* Corresponding author. E-mail: jbrimaco{at}bigpond.net.au

Accepted for publication August 1, 2005.


    Abstract
 Top
 Footnotes
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Background. We tested the hypothesis that ease of insertion, oropharyngeal leak pressure, fibreoptic position, gastric insufflation, and the frequency of mucosal trauma differ between the ProSeal laryngeal mask airway (PLMA) and the classic laryngeal mask airway (cLMA) in anaesthetized children. For the PLMA, we also assessed the ease of gastric tube placement via the PLMA drain tube and measure residual gastric volume.

Methods. 240 consecutive ASA I–III children aged 1–16 yr were randomized for airway management with the ProSeal or cLMA.

Results. The time taken to provide an effective airway, the number of insertion attempts, fibreoptic position of the airway tube and frequency of mucosal trauma were similar, but oropharyngeal leak pressure was higher (33 vs 26 cm H2O, P<0.0001) and gastric insufflation less common (0 vs 6%, P<0.01) for the PLMA. Gastric tube insertion was successful at the first attempt in 106 of 120, and at the second attempt in 14 of 120. The mean (SD; range) value for residual gastric volume was 2.2 (5.9; 0–30) ml. There were no differences in performance among sizes for the PLMA and the cLMA.

Conclusions. We conclude that ease of insertion, fibreoptic position, and frequency of mucosal trauma are similar for the PLMA and cLMA in children, but oropharyngeal leak pressure is higher and gastric insufflation less common for the PLMA. Gastric tube insertion has a high success rate, provided the PLMA is correctly positioned.

Keywords: airway, technique, complications ; children ; equipment, ProSeal laryngeal mask airway


    Introduction
 Top
 Footnotes
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The ProSealTM laryngeal mask airway (PLMA, Laryngeal Mask Company, Henley-on-Thames, UK) is a relatively new laryngeal mask device with a modified cuff to improve the seal and a drain tube to: (i) prevent gastric aspiration; (ii) prevent gastric insufflation; (iii) facilitate gastric tube insertion; and (iv) provide information about position.1 2 Recently, it has been shown that the drain tube can also function as a highly effective guide to insertion.3 Adult studies have shown that compared with the classicTM laryngeal mask airway (cLMA) the PLMA forms a better seal with both the respiratory4 5 and gastrointestinal tracts,6 provides easier access to the gastrointestinal tract,5 and exerts lower mucosal pressures for a given seal pressure,7 but is more difficult to insert at the first attempt.4 5 The paediatric sizes vary slightly from the adult sizes in that they lack a dorsal cuff and the drain tube is proportionally larger, but this does not appear to interfere with the performance.8 There are two studies comparing the ProSeal and cLMA in children. Shimbori and colleagues,9 in a non-crossover study of 60 children, showed that PLMA offered no advantages over the cLMA, other than a lower frequency of mucosal trauma, and that gastric tube insertion was possible in 90%. In contrast, Goldmann and Jakob,10 in a crossover study of 30 children, showed that the PLMA was a better ventilatory device and had a lower frequency of gastric insufflation than the cLMA, and gastric tube placement was possible in 100%. In the present non-crossover randomized study of 240 children, we have tested the hypothesis that ease of insertion, oropharyngeal leak pressure, fibreoptic position, gastric insufflation and the frequency of mucosal trauma differ between the PLMA and the cLMA in anaesthetized children. For the PLMA, we also assessed the ease of gastric tube placement and residual gastric volume.


    Methods
 Top
 Footnotes
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Ethical committee approval and written parental consent were obtained for all the patients. 240 consecutive ASA I, II, III children aged 1–16 yr undergoing minor surgery (excluding head and neck surgery) in the supine position were randomized for airway management with the PLMA or cLMA by opening an opaque envelope containing the computer-generated random assignments. Patients were excluded if they were at risk of aspiration.

Patients were fasted for at least 6 h for solids and 4 h for liquids. Pre-medication, midazolam 0.5 mg kg–1 by mouth, was given 30 min before induction of anaesthesia. A standard anaesthesia protocol was followed and routine monitoring applied, including an ECG, pulse oximeter, gas analyser, non-invasive arterial pressure monitor, tidal volume monitor, and airway pressure monitor. Patients were given atropine 0.01 mg kg–1 i.v. and pre-oxygenated for 2 min. Anaesthesia was then induced with remifentanil 0.1 µg kg–1 min–1 and propofol 3 mg kg–1 along with lidocaine 0.5 mg kg–1 given over 1 min. Facemask ventilation was performed until conditions were suitable for insertion of the laryngeal mask (loss of eyelash reflex, jaw relaxation, absence of movement). Additional boluses of propofol 1 mg kg–1 were given as required until an adequate level of anaesthesia was achieved for placement. The devices were inserted according to manufacturer's instructions with the cuff fully deflated using either the digital or introducer tool techniques, according to the preference of the clinician. The size 2, 2.5, and 3 were used in children weighing 10–20, greater than 20–30, and greater than 30 kg, respectively.

All insertions were carried out by three experienced users of the cLMA and PLMA. Once inserted into the pharynx, the cuff was inflated with air until effective ventilation was established or the maximum recommended inflation volume reached. Fixation was according to the manufacturer's instructions.11 Effective ventilation was judged by observation of chest wall movement and a square wave capnograph trace. Three attempts were allowed before insertion was considered a failure. A failed attempt was defined as removal of the device from the mouth. Between attempts, the lungs were ventilated using the facemask. If insertion failed after three attempts, the alternative device was used.

The time between picking up the laryngeal mask device and obtaining an effective airway was recorded. Once insertion was successful, the intra-cuff pressure was set at 60 cm H2O using a digital manometer (Mallinckrodt Medical, Athlone, Ireland) and the oropharyngeal leak pressure was determined by closing the expiratory valve of the anaesthesia breathing system at a fixed gas flow of 3 litre min–1 and noting the airway pressure (maximum allowed, 40 cm H2O) at which equilibrium was reached.12 Gastric insufflation was assessed by listening with a stethoscope over the epigastrium during oropharyngeal leak pressure testing.13 Anatomic position of the airway tube was determined by passing a fibreoptic scope to a position just proximal to the end of the airway tube and scoring the view.14 Anatomic position of the drain tube was determined by passing a fibreoptic scope to the end of the drain tube and scoring the position, as described previously.4

A well-lubricated gastric tube (size 2 PLMA, Fr 10; size 2.5, Fr 10; size 3 PLMA, Fr 12) was inserted through the drain if there was no air leak up the drain tube. Correct gastric tube placement was assessed by suction of fluid or detection of injected air by epigastric stethoscopy. Two attempts were allowed before gastric tube insertion was considered a failure. The volume of gastric fluid was noted. Any episodes of hypoxia (<90%), airway reflex activation (coughing, gagging, retching, laryngospasm, bronchospasm) or aspiration/regurgitation/vomiting were documented. At the end of the procedure, the laryngeal mask device was inspected for any stains of blood. Data were collected by a second anaesthesiologist.

Sample size was selected for a type I error of 0.05 and a power of 0.95 and was based on a pilot study of 10 patients with a measured difference in oropharyngeal leak pressure of 10% between the groups. Statistical evaluation was with Student's t-test and {chi}2-test. Significance was taken as P<0.05.


    Results
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 Footnotes
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Data are presented in Table 1. There were no differences between the groups regarding patient characteristics. The digital technique was used in 64 children and the introducer tool technique in 56 children. The time taken to provide an effective airway, the number of insertion attempts, fibreoptic position of the airway tube and frequency of mucosal trauma were similar, but oropharyngeal leak pressure was higher (P<0.0001) and gastric insufflation less common (P<0.01) for the PLMA. Gastric tube insertion was successful at the first attempt in 106/120 and at the second attempt in 14/120. The mean (SD; range) value for residual gastric volume was 2.2 (5.9; 0–30) ml. There were no differences in performance among the sizes 2, 2.5, and 3 of either PLMAs or cLMAs. There were no differences in performance between the digital and introducer tool techniques. There were no differences in performance among users.


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Table 1 Comparative data for the PLMA and cLMA. Values are given as mean (SD; range). UOS, open upper esophageal sphincter;

 

    Discussion
 Top
 Footnotes
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The time taken to provide an effective airway, the number of insertion attempts, and fibreoptic position were similar between the devices. This is a similar finding to the studies in children by Shimbori and colleagues9 and Goldmann and Jakob,10 but contrasts with the studies in adult population,15 which show that PLMA insertion is more difficult and fibreoptic position inferior. Perhaps the PLMA is better suited to the paediatric airway. Oropharyngeal leak pressure was higher for the PLMA. This is a similar finding to the studies in adults15 and the crossover study in children by Goldmann and Jakob,10 but contrasts with the non-crossover study in children by Shimbori and colleagues.9

The cuff of the size 1.5–2.5 PLMAs differ from the adult sizes as they lack a dorsal cuff; this probably contributes to the improved seal by pressing the ventral cuff more firmly into the periglottic tissues. A previous study by our group detected no difference in oropharyngeal leak pressure between the size 2 and 3 for their respective age groups,8 suggesting that the dorsal cuff only plays a minor role in the improved seal. Perhaps, the biggest contribution to the improved seal comes from the wider proximal end, which forms a more effective plug in the proximal pharynx. Other features that may contribute to the improved seal are: (i) the larger distal cuff, which forms a more effective plug in the distal pharynx and thus prevents air leaking into the gastrointestinal tract; and (ii) the parallel arrangement of the airway and drain tubes, which allows the tongue to fall more efficiently over the proximal cuff.

The frequency of mucosal trauma was similar between devices. This is a similar finding to the studies in adult population,15 but contrasts with the non-crossover study in children,9 which showed more blood-staining for the cLMA. Our data for ease of insertion, oropharyngeal leak pressure and fibreoptic position for the PLMA were similar to a previous study by our group8 and the studies in adults.15 We found that gastric tube insertion was successful in all patients after two attempts. The first attempt failures were related to the distal cuff being folded over or inadequate lubrication.

We found that gastric insufflation was more common with the cLMA. This supports the findings of Goldmann and Jakob.10 The risk of gastric insufflation should be higher with the cLMA, as the seal with the hypopharynx is less effective,6 and malposition, which predisposes to gastric insufflation by exposing the upper oesophageal sphincter to positive pressure ventilation,16 is less easy to detect. We found that the upper oesophageal sphincter was open in 9% of children with the PLMA, a similar finding to our previous study in children8 and the studies in adults.15 The clinical importance of this finding is unknown.

Our study has three limitations. First, the number of patients managed with each size was different between devices, particularly for the size 3; however, we found no differences in performance among subgroups and a previous study suggested there were no differences in performance between the size 2 and 3.8 Secondly, all the devices were inserted by experienced personnel, and our data may not be applicable to those with less experience. Thirdly, there was no blinding in the data collection, a possible source of bias.

We conclude that ease of insertion, fibreoptic position, and frequency of mucosal trauma are similar for the ProSeal and cLMA in children, but oropharyngeal leak pressure is higher and gastric insufflation is less common with the PLMA. Gastric tube insertion has a high success rate, provided the PLMA is correctly positioned.


    Acknowledgments
 
This project was supported solely by departmental resources.


    Footnotes
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 Footnotes
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
{dagger} Declaration of interest. Dr Brimacombe has worked as a consultant for the Laryngeal Mask Company, who manufacture the ProSealTM laryngeal mask airway. Back


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

2 Howarth A, Brimacombe J, Keller C. Gum elastic bougie-guided insertion of the ProSeal laryngeal mask airway. A new technique. Anaesth Intens Care 2002; 30: 624–7[ISI][Medline]

3 Brimacombe J, Keller C, Vosoba Judd D. Gum elastic bougie-guided insertion of the ProSealTM laryngeal mask airway is superior to the digital and introducer tool techniques. Anesthesiology 2004; 100: 25–9[CrossRef][ISI][Medline]

4 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[CrossRef][ISI][Medline]

5 Brimacombe J, Keller C, Fullekrug B, et al. A multicenter study comparing the ProSeal with the Classic laryngeal mask airway in anesthetized, nonparalyzed patients. Anesthesiology 2002; 96: 289–95[CrossRef][ISI][Medline]

6 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]

7 Keller C, Brimacombe J. Mucosal pressure and oropharyngeal leak pressure with the Proseal versus the classic laryngeal mask airway. Br J Anaesth 2000; 85: 262–6[Abstract/Free Full Text]

8 Lopez-Gil M, Brimacombe J. The ProSeal laryngeal mask airway in children. Paed Anaesth 2005; 15: 229–34[CrossRef][Medline]

9 Shimbori H, Ono K, Miwa T, Morimura N, Noguchi M, Hiroki K. Comparison of the LMA-ProSeal and LMA-Classic in children. Br J Anaesth 2004; 93: 528–31[Abstract/Free Full Text]

10 Goldmann K, Jakob C. Size 2 ProSeal laryngeal mask airway: a randomized, crossover investigation with the standard laryngeal mask airway in paediatric patients. Br J Anaesth 2005; 94: 385–9[Abstract/Free Full Text]

11 LMA ProSealTM Instruction Manual, 1st Edn. San Diego: LMA North America Inc., 2000

12 Lopez-Gil M, Brimacombe J, Keller C. A comparison of four methods for assessing oropharyngeal leak pressure with the laryngeal mask airway in paediatric patients. Paed Anaesth 2000; 11: 319–21[ISI]

13 Brimacombe J, Keller C, Kurian S, Myles J. Reliability of epigastric auscultation to detect gastric insufflation. Br J Anaesth 2002; 88: 127–9[Abstract/Free Full Text]

14 Keller C, Brimacombe J, Puehringer F. A fibreoptic scoring system to assess the position of laryngeal mask airway devices. Interobserver variability and a comparison between the standard, flexible and intubating laryngeal mask airways. AINS 2000; 35: 692–4[Medline]

15 Brimacombe J. ProSeal LMA for ventilation and airway protection. Laryngeal Mask Anesthesia. Principles and Practice, 2nd Edn. London: WB Saunders, 2005; 505–38

16 Latorre F, Eberle B, Weiler N, et al. Laryngeal mask airway position and the risk of gastric insufflation. Anesth Analg 1998; 86: 867–71[Abstract]





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