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Preliminary evaluation of a new prototype laryngeal mask in children
British Journal of Anaesthesia 82 (1): 132–4 (1999)
Preliminary evaluation of a new prototype laryngeal mask in children M. Lopez-Gil1, J. Brimacombe2* and A. I. J. Brain3 1Maranon
University Hospital, Department of Anaesthesia and Reanimation, Maranon University Hospital, Madrid, Spain. 2University of Queensland, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Cairns 4870, Australia. 3Royal Berkshire Hospital, Institute of Laryngology, University of London, London, UK *To whom correspondence should be addressed We have assessed a prototype laryngeal mask airway (pLMA) in 50 anaesthetized children for ease of insertion, oropharyngeal leak pressures, gastric insufflation and fibreoptic position. The pLMA has a second smaller mask, which rests against the upper oesophageal sphincter, and a second cuff to increase the seal pressure of the glottic mask. All insertions were graded as easy and an effective airway was achieved in all patients. Oropharyngeal leak pressure was .40 cm H2O in 49 of 50 patients. Gastric insufflation was not detected by epigastric auscultation. In 46 of 50 patients, the vocal cords were seen via a fibreoptic laryngoscope. One patient regurgitated clear fluid, but aspiration did not occur. On removal, blood staining was detected in three of 50 children. We conclude that the pLMA was easy to insert, facilitated high airway pressure ventilation and may provide some protection against gastric insufflation. Br J Anaesth 1999; 82: 132–4 Keywords: intubation tracheal; equipment, masks anaesthesia; ventilation, positive pressure; complications, regurgitation Accepted for publication: August 10, 1998
The laryngeal mask airway (LMA) is used widely in paediatric anaesthesia and has been shown to be safe and effective, and to offer some advantages over the face mask and tracheal tube.1 However, it has two main limitations: seal pressures are sometimes lower than required for positive pressure ventilation and it does not protect the lungs from regurgitated gastric contents. In 1994, a prototype LMA was designed with a second mask to isolate the upper oesophagus and a second dorsal cuff to increase the seal against the glottis. A within-patient comparison with the standard LMA showed that it isolated the glottic inlet and gave leak pressures greater than 50 cm H2O.2 However, it was considered too bulky and stiff for easy placement. The design was therefore refined by changing the size/shape of the dorsal cuff to reduce bulk and by placing the drainage tube alongside the breathing tube to increase flexibility. In this study, we have assessed this new prototype in children for ease of insertion, oropharyngeal leak pressures, gastric insufflation, fibreoptic position and utility for spontaneous and positive pressure ventilation.
Methods and results The new prototype LMA (pLMA) was constructed of identical materials to those used in the commercial device
(Fig. 1). The pLMA fits into the pharynx in a similar position to the LMA and can be regarded as a double mask forming two end-to-end junctions, one sealing around the opening into the entrance to the respiratory tract, the other sealing around the opening into the entrance to the digestive tract (Fig. 2). It has a second, smaller, trumpet-shaped mask which rests against the upper oesophageal sphincter, and a second cuff mounted on the dorsal surface to increase the seal pressure of the glottic mask and provide a firm anchor for the oesophageal mask. The interior of the dorsal cuff communicates with the ventral cuff so that the two cuffs inflate simultaneously via a single pilot balloon. The oesophageal mask and drain are formed by invaginating the tip and welding it to a soft tube, which is fixed to the backplate of the mask. The dorsal cuff forms a partial hemisphere covering the back of the mask and enclosing this drainage tube which is positioned posterolateral to the main breathing tube and welded to it. Two sizes of prototype were constructed for the study which were equivalent to sizes No. 2 and No. 2.5 of the LMA. After obtaining approval from the Ethics Committee and informed parental consent, we studied 50 consecutive ASA I–II paediatric patients, weighing 10–45 kg, for whom the LMA was considered suitable. Patients were excluded if they were at risk of aspiration or if they were not in the
© British Journal of Anaesthesia
Prototype LMA in children
supine position for surgery. A standard anaesthetic procedure was followed and routine monitoring applied. Patients were premedicated with midazolam 0.5 mg kg–1 orally, 30 min before operation and atropine 0.015 mg kg–1. Anaesthesia was induced with propofol 3–5 mg kg–1 and fentanyl
Fig 1 The prototype laryngeal mask airway.
3 µg kg–1 and maintained with 0.5–1% isoflurane and nitrous oxide in oxygen. Patients undergoing short procedures (,30 min) were allowed to breathe spontaneously, but in those undergoing longer procedures, neuromuscular block was produced with atracurium 0.5 mg kg–1 and the lungs ventilated mechanically. A single experienced paediatric LMA user (M. L. .1000 uses) inserted and fixed the pLMA. Ease of insertion was assessed. The insertion and fixation techniques were identical to the standard LMA. A size No. 2 was used in children weighing ,20 kg and a size No. 2.5 in children weighing ù20 kg. The cuff was inflated with air (size No. 2, 10–14 ml; size No. 2.5, 18–22 ml) to an intracuff pressure of 60 cm H2O, measured using a calibrated aneroid manometer. An adequate airway was assessed from thoracoabdominal movement and a satisfactory capnograph trace. When an effective airway was established, a fibreoptic scope was passed down the ventilatory lumen to determine the position of the pLMA. If the vocal cords were not visible, the pLMA was reinserted. Oropharyngeal leak pressure (maximum 40 cm H2O) was determined by closing the expiratory valve and observing the pressure at which an audible leak occurred into the mouth. Epigastric auscultation was also performed at the maximum oropharyngeal leak pressure to detect gastric insufflation. During maintenance of anaesthesia, a fibreoptic scope was passed down the drainage tube and into the upper oesophagus to determine if they were aligned correctly. The pLMA was removed when the child was awake and the device inspected for blood. Any hypoxic events (SaO2 ,95%) or problems were documented. Mean age and weight were 75 (range 13–144) months and 23 (SD 11, range 10–45) kg, respectively. The male: female ratio was 35:15. Fifteen patients breathed spontaneously and 35 patients underwent mechanical ventilation. Duration of surgery was 40 (SD 10, range 11–60) min in patients breathing spontaneously and 74 (30, 25–140) min
Fig 2 Location of the prototype laryngeal mask airway in the pharynx. AT5Airway tube, OT5oesophageal tube, PB5pilot balloon, E5epiglottis, L5 larynx, T5trachea, VC5ventral cuff, DC5dorsal cuff, O5oesophagus and OL5oesophageal lumen.
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in the mechanically ventilated group. All pLMA insertions were graded as easy and an adequate airway was achieved in all patients. The size No. 2 was used initially in 30 of 50 and the size No. 2.5 in 20 of 50 patients. In 46 of 50 patients, the vocal cords were seen fibreoptically. In four patients the epiglottis was completely folded down over the mask aperture bars and the pLMA was reinserted even though function was adequate. At the second attempt the degree of downfolding decreased and the vocal cords became visible. Oropharyngeal leak pressure was .40 cm H2O in 49 of 50 patients. One patient had an oropharyngeal leak pressure of 20 cm H2O with the size No. 2, but when this was changed for a size No. 2.5, leak pressure increased to .40 cm H2O. Gastric insufflation was not detected. Passage of the fibreoptic scope into the oesophagus was possible in all patients, including those in whom the epiglottis was downfolded. One spontaneously breathing patient regurgitated clear fluid during passage of the fibreoptic scope. This was visible in the drainage tube, but fibreoptic and pH testing down the ventilatory lumen revealed that aspiration did not occur. On removal, blood was detected in three patients. There were no episodes of SaO2 ,95%.
Comment We have shown that the pLMA was easy to insert and provided a patent airway for spontaneous and positive pressure ventilation, with a low incidence of gastric insufflation. The mean oropharyngeal leak pressure for the standard LMA in children is approximately 25 cm H2O,3 but in our study it was greater than 40 cm H2O, even though intracuff pressures were limited to 60 cm H2O. Mean airway pressure at which gastric insufflation occurs with the standard LMA is unknown in children, but one study reported no cases with peak pressures less than 20 cm H2O.4 The mean pressure at which air can be detected entering the stomach is approximately 30 cm H2O in adults.5 6 High oropharyngeal leak pressures are possible because the inflated dorsal cuff forces the oval-shaped ventral cuff more firmly against the periglottic tissues. In theory, the broader leading edge of the pLMA (containing the trumpet-shaped end of the drainage tube) compared with the standard LMA (deflated end of cuff) might lead to an increased incidence of epiglottic downfolding, but this was not apparent in our study. A degree of epiglottic downfolding is common in children and usually does not affect function.7 We used the size No. 2.5 pLMA in children weighing 20–45 kg, whereas the size No. 2.5 LMA is recommended for children weighing 20–30 kg. This was because of the lack of availability of a size No. 3 pLMA, but the size No. 2.5 functioned well in children weighing more than 30 kg. There has been no study assessing the accuracy of the size selection criteria in
children based on weight. In adults, weight-based selection criteria have been shown to be inaccurate.8 We did not determine if the pLMA effectively protected the airway from regurgitated stomach contents. However, it is likely that some protection is provided as high oropharyngeal leak pressures would not have been possible if the glottic inlet communicated with the oesophageal inlet or drainage tube. Also, there was no soiling of the respiratory tract in the patient who regurgitated and the oesophageal inlet was always correctly aligned with the drainage tube. There have been two reports of a similar prototype LMA preventing aspiration after regurgitation in adults.9 10 There was good anatomical alignment of the ventilatory tube and glottis, and drainage tube and oesophagus. Although not done in this study, passage of a nasogastric tube via the drainage tube should be achieved easily as the oesophageal lumen was always visible via the drainage tube. Pharyngolaryngeal damage was not adequately studied, but blood-stained mucosa was detected on removal of the device in 6% of patients. In summary, these data suggest that the pLMA is easy to insert, facilitates high airway pressure ventilation and provides some protection against gastric insufflation. These results suggest that the refinements in design were appropriate.
References 1 Brimacombe J, Brain AIJ, Berry A. The Laryngeal Mask Airway: Review and Practical Guide. London: WB Saunders, 1997 2 Brain AIJ, Verghese C, Strube P, Brimacombe J. A new laryngeal mask prototype—preliminary evaluation of seal pressures and glottic isolation. Anaesthesia 1995; 50: 42–8 3 Gursoy F, Algren JT, Skjonsby BS. Positive pressure ventilation with the laryngeal mask airway in children. Anesth Analg 1996; 82: 33–8 4 Selby IR, Morris P. Intermittent positive ventilation through a laryngeal mask in children: does it cause gastric dilatation? Paediatr Anaesth 1997; 7: 305–8 5 Weiler N, Latorre F, Eberle B, Goedecke R, Heinrichs W. Respiratory mechanics, gastric insufflation pressure, and air leakage of the laryngeal mask airway. Anesth Analg 1997; 84: 1025–8 6 Brimacombe J. Positive pressure ventilation with the size 5 LMA. J Clin Anesth 1997; 9: 113–17 7 Goudsouzian NG, Denman W, Cleveland R, Shorten G. Radiologic localisation of the laryngeal mask airway in children. Anesthesiology 1992; 77: 1085–9 8 Berry A, Brimacombe J, McManus KF, Goldblatt M. An evaluation of the factors influencing selection of the optimal size of laryngeal mask airway in normal adults. Anaesthesia 1998; 53: 565–70 9 Agro F, Brain A, Gabbrielli A, et al. Prevention of tracheal aspiration in a patient with a high risk of regurgitation using a new double-lumen gastric laryngeal mask airway. Gastrointest Endosc 1997; 46: 257–8 10 Brimacombe J. Airway protection with the new laryngeal mask prototype. Anaesthesia 1996; 51: 602–3
134
Preliminary evaluation of a new prototype laryngeal mask in children M. Lopez-Gil1, J. Brimacombe2* and A. I. J. Brain3 1Maranon
University Hospital, Department of Anaesthesia and Reanimation, Maranon University Hospital, Madrid, Spain. 2University of Queensland, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Cairns 4870, Australia. 3Royal Berkshire Hospital, Institute of Laryngology, University of London, London, UK *To whom correspondence should be addressed We have assessed a prototype laryngeal mask airway (pLMA) in 50 anaesthetized children for ease of insertion, oropharyngeal leak pressures, gastric insufflation and fibreoptic position. The pLMA has a second smaller mask, which rests against the upper oesophageal sphincter, and a second cuff to increase the seal pressure of the glottic mask. All insertions were graded as easy and an effective airway was achieved in all patients. Oropharyngeal leak pressure was .40 cm H2O in 49 of 50 patients. Gastric insufflation was not detected by epigastric auscultation. In 46 of 50 patients, the vocal cords were seen via a fibreoptic laryngoscope. One patient regurgitated clear fluid, but aspiration did not occur. On removal, blood staining was detected in three of 50 children. We conclude that the pLMA was easy to insert, facilitated high airway pressure ventilation and may provide some protection against gastric insufflation. Br J Anaesth 1999; 82: 132–4 Keywords: intubation tracheal; equipment, masks anaesthesia; ventilation, positive pressure; complications, regurgitation Accepted for publication: August 10, 1998
The laryngeal mask airway (LMA) is used widely in paediatric anaesthesia and has been shown to be safe and effective, and to offer some advantages over the face mask and tracheal tube.1 However, it has two main limitations: seal pressures are sometimes lower than required for positive pressure ventilation and it does not protect the lungs from regurgitated gastric contents. In 1994, a prototype LMA was designed with a second mask to isolate the upper oesophagus and a second dorsal cuff to increase the seal against the glottis. A within-patient comparison with the standard LMA showed that it isolated the glottic inlet and gave leak pressures greater than 50 cm H2O.2 However, it was considered too bulky and stiff for easy placement. The design was therefore refined by changing the size/shape of the dorsal cuff to reduce bulk and by placing the drainage tube alongside the breathing tube to increase flexibility. In this study, we have assessed this new prototype in children for ease of insertion, oropharyngeal leak pressures, gastric insufflation, fibreoptic position and utility for spontaneous and positive pressure ventilation.
Methods and results The new prototype LMA (pLMA) was constructed of identical materials to those used in the commercial device
(Fig. 1). The pLMA fits into the pharynx in a similar position to the LMA and can be regarded as a double mask forming two end-to-end junctions, one sealing around the opening into the entrance to the respiratory tract, the other sealing around the opening into the entrance to the digestive tract (Fig. 2). It has a second, smaller, trumpet-shaped mask which rests against the upper oesophageal sphincter, and a second cuff mounted on the dorsal surface to increase the seal pressure of the glottic mask and provide a firm anchor for the oesophageal mask. The interior of the dorsal cuff communicates with the ventral cuff so that the two cuffs inflate simultaneously via a single pilot balloon. The oesophageal mask and drain are formed by invaginating the tip and welding it to a soft tube, which is fixed to the backplate of the mask. The dorsal cuff forms a partial hemisphere covering the back of the mask and enclosing this drainage tube which is positioned posterolateral to the main breathing tube and welded to it. Two sizes of prototype were constructed for the study which were equivalent to sizes No. 2 and No. 2.5 of the LMA. After obtaining approval from the Ethics Committee and informed parental consent, we studied 50 consecutive ASA I–II paediatric patients, weighing 10–45 kg, for whom the LMA was considered suitable. Patients were excluded if they were at risk of aspiration or if they were not in the
© British Journal of Anaesthesia
Prototype LMA in children
supine position for surgery. A standard anaesthetic procedure was followed and routine monitoring applied. Patients were premedicated with midazolam 0.5 mg kg–1 orally, 30 min before operation and atropine 0.015 mg kg–1. Anaesthesia was induced with propofol 3–5 mg kg–1 and fentanyl
Fig 1 The prototype laryngeal mask airway.
3 µg kg–1 and maintained with 0.5–1% isoflurane and nitrous oxide in oxygen. Patients undergoing short procedures (,30 min) were allowed to breathe spontaneously, but in those undergoing longer procedures, neuromuscular block was produced with atracurium 0.5 mg kg–1 and the lungs ventilated mechanically. A single experienced paediatric LMA user (M. L. .1000 uses) inserted and fixed the pLMA. Ease of insertion was assessed. The insertion and fixation techniques were identical to the standard LMA. A size No. 2 was used in children weighing ,20 kg and a size No. 2.5 in children weighing ù20 kg. The cuff was inflated with air (size No. 2, 10–14 ml; size No. 2.5, 18–22 ml) to an intracuff pressure of 60 cm H2O, measured using a calibrated aneroid manometer. An adequate airway was assessed from thoracoabdominal movement and a satisfactory capnograph trace. When an effective airway was established, a fibreoptic scope was passed down the ventilatory lumen to determine the position of the pLMA. If the vocal cords were not visible, the pLMA was reinserted. Oropharyngeal leak pressure (maximum 40 cm H2O) was determined by closing the expiratory valve and observing the pressure at which an audible leak occurred into the mouth. Epigastric auscultation was also performed at the maximum oropharyngeal leak pressure to detect gastric insufflation. During maintenance of anaesthesia, a fibreoptic scope was passed down the drainage tube and into the upper oesophagus to determine if they were aligned correctly. The pLMA was removed when the child was awake and the device inspected for blood. Any hypoxic events (SaO2 ,95%) or problems were documented. Mean age and weight were 75 (range 13–144) months and 23 (SD 11, range 10–45) kg, respectively. The male: female ratio was 35:15. Fifteen patients breathed spontaneously and 35 patients underwent mechanical ventilation. Duration of surgery was 40 (SD 10, range 11–60) min in patients breathing spontaneously and 74 (30, 25–140) min
Fig 2 Location of the prototype laryngeal mask airway in the pharynx. AT5Airway tube, OT5oesophageal tube, PB5pilot balloon, E5epiglottis, L5 larynx, T5trachea, VC5ventral cuff, DC5dorsal cuff, O5oesophagus and OL5oesophageal lumen.
133
Lopez-Gil et al.
in the mechanically ventilated group. All pLMA insertions were graded as easy and an adequate airway was achieved in all patients. The size No. 2 was used initially in 30 of 50 and the size No. 2.5 in 20 of 50 patients. In 46 of 50 patients, the vocal cords were seen fibreoptically. In four patients the epiglottis was completely folded down over the mask aperture bars and the pLMA was reinserted even though function was adequate. At the second attempt the degree of downfolding decreased and the vocal cords became visible. Oropharyngeal leak pressure was .40 cm H2O in 49 of 50 patients. One patient had an oropharyngeal leak pressure of 20 cm H2O with the size No. 2, but when this was changed for a size No. 2.5, leak pressure increased to .40 cm H2O. Gastric insufflation was not detected. Passage of the fibreoptic scope into the oesophagus was possible in all patients, including those in whom the epiglottis was downfolded. One spontaneously breathing patient regurgitated clear fluid during passage of the fibreoptic scope. This was visible in the drainage tube, but fibreoptic and pH testing down the ventilatory lumen revealed that aspiration did not occur. On removal, blood was detected in three patients. There were no episodes of SaO2 ,95%.
Comment We have shown that the pLMA was easy to insert and provided a patent airway for spontaneous and positive pressure ventilation, with a low incidence of gastric insufflation. The mean oropharyngeal leak pressure for the standard LMA in children is approximately 25 cm H2O,3 but in our study it was greater than 40 cm H2O, even though intracuff pressures were limited to 60 cm H2O. Mean airway pressure at which gastric insufflation occurs with the standard LMA is unknown in children, but one study reported no cases with peak pressures less than 20 cm H2O.4 The mean pressure at which air can be detected entering the stomach is approximately 30 cm H2O in adults.5 6 High oropharyngeal leak pressures are possible because the inflated dorsal cuff forces the oval-shaped ventral cuff more firmly against the periglottic tissues. In theory, the broader leading edge of the pLMA (containing the trumpet-shaped end of the drainage tube) compared with the standard LMA (deflated end of cuff) might lead to an increased incidence of epiglottic downfolding, but this was not apparent in our study. A degree of epiglottic downfolding is common in children and usually does not affect function.7 We used the size No. 2.5 pLMA in children weighing 20–45 kg, whereas the size No. 2.5 LMA is recommended for children weighing 20–30 kg. This was because of the lack of availability of a size No. 3 pLMA, but the size No. 2.5 functioned well in children weighing more than 30 kg. There has been no study assessing the accuracy of the size selection criteria in
children based on weight. In adults, weight-based selection criteria have been shown to be inaccurate.8 We did not determine if the pLMA effectively protected the airway from regurgitated stomach contents. However, it is likely that some protection is provided as high oropharyngeal leak pressures would not have been possible if the glottic inlet communicated with the oesophageal inlet or drainage tube. Also, there was no soiling of the respiratory tract in the patient who regurgitated and the oesophageal inlet was always correctly aligned with the drainage tube. There have been two reports of a similar prototype LMA preventing aspiration after regurgitation in adults.9 10 There was good anatomical alignment of the ventilatory tube and glottis, and drainage tube and oesophagus. Although not done in this study, passage of a nasogastric tube via the drainage tube should be achieved easily as the oesophageal lumen was always visible via the drainage tube. Pharyngolaryngeal damage was not adequately studied, but blood-stained mucosa was detected on removal of the device in 6% of patients. In summary, these data suggest that the pLMA is easy to insert, facilitates high airway pressure ventilation and provides some protection against gastric insufflation. These results suggest that the refinements in design were appropriate.
References 1 Brimacombe J, Brain AIJ, Berry A. The Laryngeal Mask Airway: Review and Practical Guide. London: WB Saunders, 1997 2 Brain AIJ, Verghese C, Strube P, Brimacombe J. A new laryngeal mask prototype—preliminary evaluation of seal pressures and glottic isolation. Anaesthesia 1995; 50: 42–8 3 Gursoy F, Algren JT, Skjonsby BS. Positive pressure ventilation with the laryngeal mask airway in children. Anesth Analg 1996; 82: 33–8 4 Selby IR, Morris P. Intermittent positive ventilation through a laryngeal mask in children: does it cause gastric dilatation? Paediatr Anaesth 1997; 7: 305–8 5 Weiler N, Latorre F, Eberle B, Goedecke R, Heinrichs W. Respiratory mechanics, gastric insufflation pressure, and air leakage of the laryngeal mask airway. Anesth Analg 1997; 84: 1025–8 6 Brimacombe J. Positive pressure ventilation with the size 5 LMA. J Clin Anesth 1997; 9: 113–17 7 Goudsouzian NG, Denman W, Cleveland R, Shorten G. Radiologic localisation of the laryngeal mask airway in children. Anesthesiology 1992; 77: 1085–9 8 Berry A, Brimacombe J, McManus KF, Goldblatt M. An evaluation of the factors influencing selection of the optimal size of laryngeal mask airway in normal adults. Anaesthesia 1998; 53: 565–70 9 Agro F, Brain A, Gabbrielli A, et al. Prevention of tracheal aspiration in a patient with a high risk of regurgitation using a new double-lumen gastric laryngeal mask airway. Gastrointest Endosc 1997; 46: 257–8 10 Brimacombe J. Airway protection with the new laryngeal mask prototype. Anaesthesia 1996; 51: 602–3
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