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.
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Abstract |
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Methods. 240 consecutive ASA IIII children aged 116 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; 030) 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
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Introduction |
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Methods |
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Patients were fasted for at least 6 h for solids and 4 h for liquids. Pre-medication, midazolam 0.5 mg kg1 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 kg1 i.v. and pre-oxygenated for 2 min. Anaesthesia was then induced with remifentanil 0.1 µg kg1 min1 and propofol 3 mg kg1 along with lidocaine 0.5 mg kg1 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 kg1 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 1020, greater than 2030, 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 min1 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 2-test. Significance was taken as P<0.05.
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Results |
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Discussion |
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The cuff of the size 1.52.5 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.
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Acknowledgments |
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Footnotes |
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References |
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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: 6247[ISI][Medline]
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