Size 2 ProSealTM laryngeal mask airway: a randomized, crossover investigation with the standard laryngeal mask airway in paediatric patients

K. Goldmann*,{dagger} and C. Jakob

Department of Anaesthesia and Intensive Care Therapy, Philipps University Marburg, 35033 Marburg, Germany

* Corresponding author. E-mail: kaigoldmann1{at}aol.com

Accepted for publication September 14, 2004.


    Abstract
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Background. One of the main concerns with the use of the standard laryngeal mask airway (SLMA) in small infants is that its low-pressure seal might be inadequate for positive pressure ventilation so that there is a risk of gas leakage into the stomach with the subsequent risk of regurgitation. The new ProSealTM LMA (PLMA) has been shown to form a more effective seal than the SLMA and to facilitate gastric tube placement in adults. The first paediatric size PLMA became available recently.

Methods. Thirty anaesthetized, non-paralysed children aged 46 (19) months, weighing 16 (10–21) kg, were studied. The SLMA and PLMA were inserted in random order into each patient. Airway leak pressure and maximum tidal volume were measured. Ease of insertion, quality of initial airway and fibreoptic position were also determined. Gastric tube placement was assessed for the PLMA.

Results. The airway leak pressure and maximum tidal volume were significantly higher for the PLMA (P=0.001). Ease of insertion and quality of initial airway were similar for both devices. Air entry into the stomach occurred more frequently with the SLMA (P=0.005). Gastric tube placement was possible in all patients.

Conclusions. The size 2 PLMA offered some advantages over the same size of SLMA in this crossover investigation. The high reliability of gastric tube placement and the significantly increased airway leak pressure might have important implications for use of this device for positive pressure ventilation in infants.

Keywords: anaesthesia, paediatric ; equipment, laryngeal mask airway ; monitoring, oropharyngeal sealing pressure


    Introduction
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
The laryngeal mask airway (LMA{ddagger}) has been used to secure the airway in paediatric patients during general anaesthesia for many years. Its safety and efficacy has been shown in several large studies.13 However, there are well known limitations of the standard LMA (SLMA) in paediatric patients, in particular size 1 and 2 SLMA.46 A main concern is that its low-pressure seal might be inadequate for positive pressure ventilation so that there is a risk of gas leakage into the stomach with the subsequent risk of gastric distension and regurgitation. This could potentially put the patient at risk of pulmonary aspiration since the SLMA, unlike the cuffed endotracheal tube, does not seal the trachea.

The ProSealTM LMA (PLMA), a new laryngeal mask airway with a modified double cuff and an oesophageal drainage tube was introduced in 2000 with the intention of providing a more secure airway for airway management in adults.7 Brain and colleagues showed that the PLMA formed a more effective seal than the SLMA and facilitated gastric tube placement. It is believed that these two features can contribute to improved protection against aspiration.810 The first paediatric size PLMA became available recently. This randomized crossover study was designed to test the hypothesis that in anaesthetized paediatric patients the size 2 PLMA forms a more effective seal, allows for higher tidal volumes than the size 2 SLMA and facilitates gastric tube placement.


    Patients and methods
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
After obtaining approval from the local ethics committee and written parental consent 30 patients, ASA physical status I and II, scheduled for elective genitourinary surgery were included into this study. Patients were excluded if they were ASA physical status greater than II, were at risk of aspiration, had a potential difficult airway or a mouth opening <1.5 cm.

Device description
The PLMA differs from the SLMA in several features. The two principal modifications are a drainage tube that travels from the tip of the mask through the bowl alongside the wire reinforced airway tube and a modified shape of the cuff (Figs 1 and 2). The purpose of the drainage tube is to separate the alimentary from the respiratory tract by forming a sealed junction against the upper oesophageal sphincter (UOS) and to allow gastric tube placement. The second important modification is the different shape of the cuff that is designed to form a more effective seal around the larynx. It consists of a larger proximal portion and a deeper bowl than the cuff of the SLMA. Both features are believed to push the ventral part of the cuff into the periglottic tissues and to plug potential gaps of the pharynx more effectively. In contrast to the adult version of the PLMA the size 2 does not contain an additional dorsal cuff. For detailed description of the evolution of the concept and the design of the PLMA the reader is referred to the original publication of the inventor.7



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Fig 1 Size 2 PLMA (bottom) and size 2 SLMA (top) seen from the front.

 


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Fig 2 Size 2 PLMA (bottom) and size 2 SLMA (top) seen from the back.

 
Anaesthesia management
All patients were premedicated orally with 0.4–0.5 mg kg–1 midazolam and EMLATM cream was applied to the back of both hands 30 min before induction of anaesthesia. Standard monitoring consisted of a precordial stethoscope, an automated blood pressure monitor, electrocardiography, pulse oximetry and capnography. In most patients (n=18) general i.v. anaesthesia was induced with alfentanil 0.02 mg kg–1 followed by propofol 3–5 mg kg–1. In patients in whom i.v. access was thought to be difficult (n=12) general anaesthesia was induced by inhalation of sevoflurane 8% in nitrous oxide 66% with oxygen. After i.v. access was established, the level of anaesthesia was deepened by an injection of alfentanil 0.02 mg kg–1 followed by propofol 2–3 mg kg–1. Anaesthesia maintenance was with propofol 0.1–0.15 mg kg–1 min–1 and additional boluses of alfentanil 0.02 mg kg–1 if required. No neuromuscular blocking agents were used.

Airway management
After cessation of spontaneous ventilation the lungs of the patients were ventilated manually via a face mask until a sufficient depth of anaesthesia was reached as indicated by a heart rate 20% lower than the baseline value. The first LMA was then placed and measurements were made. After completion of measurements with the first mask it was removed, the second mask placed and the same measurements were recorded. The order of mask insertion in each patient was randomized before commencement of the trial, and was contained in a sealed envelope that was opened before induction of anaesthesia by a person not involved in the investigation. Both types of masks were placed using the standard technique recommended by Brain.11 The breathing tube was connected to a circle system of an anaesthesia machine (Primus, Draeger, Luebeck, Germany) and manual ventilation (ManV) commenced after the cuff had been inflated to an intracuff pressure (Pintracuff) of 60 mbar (VBM Cuff Pressure Gauge, VBM Medizintechnik, Sulz a.N., Germany). Auscultation of the epigastrium and larynx took place before the device was taped in the way recommended by Brain with the airway tube being flexed and taped over the chin.11 The head of the child was then placed in neutral position on a soft 3 cm high head-ring. During the initial study period the lungs of the patient were ventilated manually; once the measurements had been completed pressure-controlled ventilation (PCV) was used to ventilate the lungs throughout the procedure.

Measurements
The total doses of propofol and alfentanil given throughout the period of measurements were recorded. The number of attempts for placement of each mask was recorded. A maximum of two attempts was allowed for each device. Removal of the mask from the mouth was considered a failed attempt. Ease of placement was recorded from 0–10 on a visual analogue scale (VAS) and quality of airway judged as follows: ‘excellent’, no audible leak; ‘good’, a slight, but clinically irrelevant, audible leak; ‘poor/acceptable’, clinically relevant loss of air, but sufficient ventilation; ‘unacceptable’, clinically relevant loss of air and insufficient ventilation. Air entry into the stomach and abnormal airway sounds over the larynx were noted by auscultation. After placement of the PLMA, a drainage tube test, as described in the PLMA instruction manual, was conducted in order to confirm correct position of the mask.12 A small amount of lubricant jelly was used to close the proximal end of the drainage tube, a slight up and down movement of the lubricant conus was judged a ‘positive’ drainage tube test. After again confirming a sufficient level of anaesthesia the maximum tidal volume and the leak airway pressure (Pleak) were measured at three different head positions. The Pintracuff was checked before commencement of the measurements. If necessary it was adjusted to, and maintained at, 60 mbar. Maximum tidal volume was determined by squeezing the anaesthesia circuit bag until an audible leak was noted in the mouth of the patient and the highest expired tidal volume indicated by the anaesthesia machine was recorded. Pleak was measured after the fresh gas flow was set to 3 litre min–1 and the expiration valve closed.13 The airway pressure at which an audible leak in the mouth of the patient occurred was recorded as the Pleak. The expiration valve was opened if the Pleak reached 40 mbar without an audible leak. The Pleak value on the monitor of the anaesthesia machine was not visible to the observer of the audible leak. The order of the head position was neutral, maximum flexion and maximum extension. The lungs of the child were ventilated manually between the consecutive measurements. Fibreoptic examination of the position of the LMA was performed thereafter (2.8 mm flexible endoscope Karl Storz, Tuttlingen, Germany). The position of the LMA was graded in accordance with the fibreoptic scoring system described previously: 1, vocal cords not seen; 2, vocal cords+anterior epiglottis seen; 3, vocal cords+posterior epiglottis seen; 4, only vocal cords seen.14 When the PLMA was used first a 12 French gauge gastric tube was then placed and correct placement confirmed by auscultation of the epigastrium during injection of a small amount of air. Gastric fluid was aspirated using a syringe and the amount of fluid noted. The PLMA and gastric tube were removed and the same measurements took place for the SLMA, which was left in place for the rest of the procedure. When the PLMA was used second the gastric tube remained in place until the end of the case. It was removed under suction before the PLMA was removed once the child was fully awake. Both masks were inspected after removal for signs of blood. Any adverse event, apparent oropharyngeal injury or problem with the devices was documented. During the postoperative visit (6–8 h after the end of the anaesthetic) the parents were asked whether their child had complained about a sore throat (‘Has your child ever complained about a sore throat since you met him/her in recovery?’).

Statistics
The primary variable tested was Pleak. The mean Pleak values for various paediatric size SLMA in the literature vary from 12.5 mbar to 17 mbar depending on the study population, size of LMA used and intracuff pressure of the LMA.13 15 Pleak values for the paediatric PLMA have not been reported previously. A 20% higher Pleak for the PLMA was considered to be clinically relevant, therefore a sample size of 22 patients was calculated to detect a projected difference of 20% between the groups with respect to Pleak for a type I error of 0.05 and a power of 0.9. Allowing for possible dropouts attributable to inability to place one of the masks within 2 attempts, we chose to examine 30 patients. Results were analysed using the SPSS (SPSS Inc., Chicago, IL, USA) computer program. Unless otherwise stated, data are expressed as mean (SD) [95% confidence intervals] or mean (range). The distribution of data was determined using Kolmogorov–Smirnov analysis. Statistical analysis was performed using paired t-test, Wilcoxon test and {chi}2-test. Results were considered statistically significant when P<0.05.


    Results
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
Twenty-eight male and two female patients were included in the study; no patient had to be excluded from data analysis. The mean age, height and weight were 46 (18–81) months, 103 (75–120) cm and 16 (10–21) kg, respectively. The patients were anaesthetized for 98 (36) [84–112] min. Throughout the period of measurements a total amount of propofol 85 (28) [73–96] mg and alfentanil 0.8 (0.2) [0.7–0.9] mg were given, equalling propofol 5.3 (1.6) [4.7–6.1] mg kg–1 and alfentanil 0.05 (0.015) [0.047–0.058] mg kg–1, respectively. The heart rate dropped from 109 (21) [101–118] beats min–1 before induction to 91 (15) [85–96] beats min–1 during the period of measurements.

All devices were placed at the first attempt. Ease of insertion and initial quality of airway was similar for both devices (Table 1). Air entry into the stomach was more common with the SLMA than the PLMA (8 vs 0; P=0.005). The PLMA drainage tube test was positive in 28 patients and inconclusive in 2 patients. Maximum tidal volume and Pleak of all three positions tested were significantly higher for the PLMA (P<0.001; Table 2). Vocal cord visibility was more common with the PLMA than the SLMA (26 vs 21 patients), but there was no statistically significant difference in the fibreoptic score between the masks (P=0.3; Table 3). In three patients the vocal cords seemed compressed (PLMA; n=2) or supraglottic soft tissue/mucous membrane bulged into the airway and lead to some degree of airway obstruction (PLMA and SLMA; n=1). However, this anatomical alteration was not associated with a reduction of tidal volume. A gastric tube was placed without any difficulties in 30 patients at the first attempt. Gastric fluid was aspirated in 8 patients, the volume ranging from 1–12 ml. A trace of blood was seen after removal of the mask on one SLMA but on no PLMAs. None of the children complained about a sore throat afterwards. Mild adverse events were recorded in 3 patients. Two patients developed some degree of laryngospasm confirmed by fibreoptic examination that responded to an increased positive end expiratory pressure. Both patients had a history of a recent (within 2 weeks) respiratory tract infection. After removal of the LMA one patient developed a mild inspiratory stridor that resolved spontaneously.


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Table 1 Mean (SD) [95% CI] visual analogue scale (VAS) for placement and quality of initial airway: PLMA vs SLMA. There are no significant differences

 

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Table 2 Mean (SD) [95% CI] Pleak, maximum tidal volume, and maximum tidal volume kg–1: PLMA vs SLMA.

 

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Table 3 Fibreoptic score: PLMA vs SLMA. 1=vocal cords not seen; 2=vocal cords+anterior epiglottis seen; 3=vocal cords+posterior epiglottis seen; 4=only vocal cords seen. There are no significant differences

 

    Discussion
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
The LMA has gained wide popularity in paediatric anaesthesia since its introduction into clinical practice in 1990. Although first only used as a replacement for the face mask, it is now used in areas where the endotracheal tube was formerly used.1519 Although its safety and efficacy has been shown in several large studies there are limitations of its use in paediatric patients, in particular with the size 1 and 2 SLMA.46 A principal concern is that its low-pressure seal might be inadequate for positive pressure ventilation so that there is a risk of gas leakage into the stomach with the subsequent risk of gastric distension and regurgitation. This limitation seems to be more relevant in children since it was found that the SLMA forms a less effective seal in children than in adults as indicated by lower Pleak.13 20

The first paediatric size ProSealTM LMA became available recently. Various authors have shown that the adult PLMA forms a more effective seal than the SLMA and facilitates gastric tube placement.7 21 The results of this investigation indicate that this is also true for the size 2 PLMA. We found that the Pleak of the size 2 PLMA was significantly higher than that of the SLMA in all three positions studied. The fact that the Pleak in maximum flexion was significantly higher and in maximum extension significantly lower than in neutral position for both types of masks is in accordance with the findings of Okuda and colleagues for the SLMA.22 The maximum tidal volume generated by manual ventilation in the neutral position was also significantly higher with the PLMA than with the SLMA. The first objective of our study was to investigate the Pleak of this new LMA. However, as there are reports that in adults the greater invasiveness of the PLMA can lead to some degree of upper airway obstruction,23 24 we wanted to determine whether an increased Pleak was associated with a higher tidal volume or might lead to compression of the soft cartilage of the paediatric larynx with a consequent reduction in tidal volume. Our results indicate that a higher airway leak pressure actually allows a greater tidal volume and does not result in clinically relevant upper airway compression when the Pintracuff is limited to 60 mbar. Air entry into the stomach was not noted with the PLMA in any case but occurred in eight cases with the SLMA. This finding and the ability in all cases to place a gastric tube in the stomach through the drainage tube of the PLMA at the first attempt suggest that the PLMA might provide protection against aspiration by avoidance of gastric insufflation and the potential of emptying the stomach. This aspect certainly requires further assessment before any conclusion about protection against pulmonary aspiration can be drawn.

In contrast to the studies conducted in adult patients we did not find that placement of the mask was more difficult or that fibreoptic position of the airway tube in relation to the laryngeal structures was worse for the PLMA than the SLMA. In fact, the incidence of an obstructed view of the larynx was lower in the PLMA group, although not statistically significant. Brimacombe and colleagues21 speculated that the larger cuff of the PLMA was responsible for difficulties in placement and a higher likelihood of epiglottic downfolding. However, the design of the size 2 PLMA is not just a scaled-down version of the adult PLMA. The main difference is that it does not contain a large dorsal cuff so that the device is less bulky than the adult version. This might explain why placement of the paediatric PLMA was as easy as the SLMA and the fibreoptic view of the larynx was slightly better than that achieved with the SLMA.

The main limitation of our investigation is that we did not study positive pressure ventilation with the PLMA. Therefore we cannot draw any definitive conclusion about the feasibility of the PLMA for this purpose. However, all but two patients who underwent a relatively short procedure were ventilated with PCV without any problem with either the PLMA or SLMA. Another difference from most studies investigating Pleak with the LMA is that we did not use neuromuscular blocking agents. The preserved neuromuscular function could influence the Pleak measurements. However, meticulous attention was paid to the level of anaesthesia at all times as indicated by the amount of propofol and alfentanil given. The fact that most patients were male could mean that the size 2 PLMA might perform differently in a predominant female population.

In conclusion we were able to show that the size 2 PLMA offers some advantages over the same size of SLMA in this crossover investigation. The high reliability of gastric tube placement and the increased Pleak might have important implications for the use of this device for positive pressure ventilation in paediatric patients. The unique design of the paediatric PLMA seems to be beneficial as indicated by a high first placement success rate and a high rate of anatomically correct position.


    Acknowledgments
 
The authors wish to thank Dr John Henderson for reviewing the manuscript critically.


    Footnotes
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
{dagger} Declaration of interest. K.G. has received an honorarium for lecturing at regional meetings from LMA Vertriebs-GmbH, the German distributor of the PLMA. Back

{ddagger} LMA® is the property of Intavent Limited. Back


    References
 Top
 Footnotes
 Abstract
 Introduction
 Patients and methods
 Results
 Discussion
 References
 
1 Mason DG, Bingham RM. The laryngeal mask airway in children. Anaesthesia 1990; 45: 760–3[ISI][Medline]

2 Braun U, Fritz U. Die Kehlkopfmaske in der Kinderanästhesie. Anasthesiol Intensivmed Notfallmed Schmerzther 1994; 29: 286–8[Medline]

3 Lopez-Gill M, Brimacombe J, Alvarez M. Safety and efficacy of the laryngeal mask airway—a prospective survey of 1400 children. Anaesthesia 1996; 51: 969–72[ISI][Medline]

4 Bagshaw O. The size 1.5 laryngeal mask airway in paediatric practice. Paed Anaesth 2002; 12: 420–3[CrossRef][ISI][Medline]

5 Harnett M, Kinirons B, Heffernan A, Motherway C, Casey W. Airway complications in infants: comparison of laryngeal mask airway and the facemask-oral airway. Can J Anaesth 2000; 47: 315–18[Abstract/Free Full Text]

6 Goudsouzian NG, Denman W, Cleveland R, Shorten G. Radiologic localization of the laryngeal mask airway in children. Anesthesiology 1992; 77: 1085–9[ISI][Medline]

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

8 Mark DA. Protection from aspiration with the LMA-ProSealTM after vomiting: a case report. Can J Anaesth 2003; 50: 78–80[Abstract/Free Full Text]

9 Evans NR, Llewellyn RL, Gardner SV, James MFM. Aspiration prevented by the ProSealTM laryngeal mask airway: a case report. Can J Anaesth 2002; 49: 413–16[Abstract/Free Full Text]

10 Keller C, Brimacombe J, Kleinsasser A, Loeckinger A. Does the ProSealTM laryngeal mask airway prevent aspiration of regurgitated fluid? A cadaveric study. Anesth Analg 2000; 91: 1017–20[Abstract/Free Full Text]

11 Brimacombe JR, Brain AIJ, Berry AM. The Laryngeal Mask Airway: a Review and Practical Guide. London: W.B. Saunders, 1997

12 LMA-ProSeal Instruction Manual. San Diego: LMA North America, 2002

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16 Paterson SJ, Byrne PJ, Molesky MG, Seal RF, Finucane BT. Neonatal resuscitation using the laryngeal mask airway. Anesthesiology 1994; 80: 1248–53[ISI][Medline]

17 Ferarri LR, Goudsouzian NG. The use of the laryngeal mask airway in children with bronchopulmonary dysplasia. Anesth Analg 1995; 81: 310–13[Abstract]

18 Yazbeck-Karam VG, Aouad MT, Baraka AS. Laryngeal mask airway for ventilation during diagnostic and interventional fiberoptic bronchoscopy in children. Paed Anaesth 2003; 13: 691–4[CrossRef][ISI][Medline]

19 Keidan I, Berkenstadt H, Segal E, Perel A. Pressure versus volume-controlled ventilation with the laryngeal mask airwayTM in paediatric patients. Paed Anaesth 2001; 11: 691–4[CrossRef][ISI][Medline]

20 Keller C, Brimacombe J, Keller K, Morris R. Comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients. Br J Anaesth 1999; 82: 286–7[Abstract/Free Full Text]

21 Brimacombe J, Keller C. The ProSeal laryngeal mask. A randomized, crossover study with the standard laryngeal mask airway in paralysed, anesthetized patients. Anesthesiology 2000; 93: 104–9[ISI][Medline]

22 Okuda K, Inagawa T, Miwa T, Hiroki K. Influence of head and neck position on cuff position and oropharyngeal sealing pressure with the laryngeal mask airway in children. Br J Anaesth 2001; 86: 122–4[Abstract/Free Full Text]

23 Brimacombe J, Richardson C, Keller C, Donald S. Mechanical closure of the vocal cords with the laryngeal mask airway ProSealTM. Br J Anaesth 2002; 88: 296–7[Abstract/Free Full Text]

24 Stix MS, O'Conner CJ, Jr. Maximum minute ventilation test for the ProSeal laryngeal mask airway. Anesth Analg 2002; 95: 1782–7[Abstract/Free Full Text]