Flexible Laryngeal Mask Airway for Cleft Palate Surgery in Children: A Randomized Clinical Trial on Efficacy and Safety

Transcription

1 Flexible Laryngeal Mask Airway for Cleft Palate Surgery in Children: A Randomized Clinical Trial on Efficacy and Safety Pankaj Kundra, M.D., N. Supraja, M.D., K. Agrawal, M.S., M.Ch., M. Ravishankar, M.D. Objective: To evaluate the efficacy of a flexible laryngeal mask airway in children undergoing palatoplasty. Design: Prospective, randomized, single-center study. Setting: Jawaharlal Institute of Postgraduate Medical Education and Research. Patients: Sixty-six children (American Society of Anesthesiologists physical status 1 and 2) scheduled to undergo palatoplasty were assigned randomly to an endotracheal intubation group (RAE group, n = 33) and a flexible laryngeal mask airway group (FLMA group, n = 33). Main Outcome Measures: Peak airway pressure, inspired and expired tidal volume, end-tidal carbon dioxide, lung compliance, and airway resistance were continuously measured after placement of the assigned airway. The percentage leak around the airway was quantified as the leak fraction. Parametric data between groups were analyzed using an unpaired Student s t test and within groups using a one-way analysis of variance. Nonparametric variables were analyzed using the Fisher exact test. Results: In two children, the flexible laryngeal mask airway was displaced from its original position; whereas, one endotrachial tube advanced endobronchially. The leak fraction was significantly higher in the RAE group when compared with that in FLMA group (13.34% % versus 5.96% %, p,.05) until the throat pack was applied. Peak airway pressure and resistance were significantly higher in the RAE group compared with the FLMA group at all time intervals, p,.05. During emergence, frequency of coughing, desaturation, and laryngospasm were increased in the RAE group. Conclusion: A flexible laryngeal airway mask is suitable for maintaining the airway and helps in smooth emergence in children undergoing palatoplasty. KEY WORDS: cleft palate, flexible, laryngeal mask airway, palatoplasty Nothing short of an endotracheal tube (ETT) is typically considered for airway maintenance when oral surgeries are contemplated. This is because the ETT seems to be the only safe option for providing a secure and a definitive airway. However, there are concerns related to intubation, and problems are encountered frequently during emergence and extubation. Repeated attempts at intubation and use of a tight-fitting ETT can result in laryngeal edema; whereas, Dr. Kundra is Professor, Dr. Supraja is Senior Resident, Dr. Agrawal is Professor and Head, and Dr. Ravishankar is Former Professor and Head, Department of Anesthesiology and Critical Care and Department of Plastic Surgery, Jawaharlal Institute of Postgraduate Medical Education and Research, Pondicherry, India. Presented at the 6th Annual Conference of Indian Society for Cleft Lip, Palate and Craniofacial Anomalies at Chandigarh, February 16 18, 2007, and at the 6th Asian Pacific Cleft Lip & Palate Congress at Goa, September 2 5, Submitted July 2008; Accepted November Address correspondence to: Dr. Karoon Agrawal, Professor and Head of Plastic Surgery, Type VB/12, JIPMER Campus, Pondicherry , India. karoonaparna@gmail.com. DOI: / maintaining a minimal leak around the ETT can result in minor aspiration. On completion of oral surgery, extubation is attempted only after protective reflexes have completely returned. Coughing, breath holding, and occasionally laryngospasm occur following extubation and can pose a constant threat of hypoxia. A laryngeal mask airway (LMA) can be a suitable alternative. The use of a flexible laryngeal mask airway (FLMA) is well established for tonsillectomy and other shorter, less complex surgeries, but its place in longer, more complex surgeries in older patients undergoing cleft palate surgery has not been defined. The technique of cleft palate repair using an LMA was first described in a case report (Beveridge, 1989). It has a definitive advantage in securing the airway in children with Pierre Robin sequence where endotracheal intubation had failed (Beveridge, 1989) and can be left in place until the patient is fully awake without causing straining or coughing (Williams and Bailey, 1993). Consequently, the FLMA was designed to be used as an alternative to endotracheal intubation in adenotonsillectomies as well as intranasal, strabismus, and head and neck surgeries (Williams and Bailey, 1993; Nair and Bailey, 368

2 Kundra et al., FLEXIBLE LARYNGEAL MASK AIRWAY IN CLEFT PALATE SURGERY ; Williams et al., 1995). All comparative studies indicate a lower incidence of postoperative sore throat, coughing, and laryngospasm with the FLMA as compared with endotracheal intubation (Williams and Bailey, 1993; Williams et al., 1995). The current study was designed to test the hypotheses that use of FLMA would provide an effective airway control during cleft palate surgery and would serve to decrease the incidence of complications during emergence and airway removal. MATERIALS AND METHODS The study was conducted from July 2003 through June 2005 at Jawaharlal Institute of Postgraduate Medical Education and Research. Included were 66 children (American Society of Anesthesiologists physical status 1 and 2) weighing between 10 and 20 kg (appropriate for a size 2 FMLA; smaller sizes are not being manufactured) scheduled to undergo cleft palate surgery with or without previous surgery for cleft lip, with normal airway anatomy. Children suffering from upper respiratory tract infection were excluded. Approval from the hospital research and ethics committee was obtained for the study. After the procedure was explained, written informed consent was obtained from the parents of the children included in the study. Participants allocation sequence was accomplished according to a computer-generated list, and the children were assigned randomly into two groups by sealed-envelope technique by a person not involved in the study. In the control group (RAE group, n 5 33), the airway was maintained with Ring, Adair, and Elwin (RAE) tracheal tubes and in the study group (FLMA group, n 5 33) with FLMAs. All children were premedicated with oral midazolam (0.5 mg/kg) and atropine (0.04 mg/kg) 30 minutes before surgery. In the operation theatre, baseline measurements, namely, pulse rate, blood pressure, oxygen saturation (SpO 2 ), and end-tidal carbon dioxide (EtCO 2 ) were recorded using a Datex-Ohmeda S/5 compact anesthesia monitor (Datex-Ohmeda Inc., Tewksbury, MA). Intravenous or inhalational induction was done as found feasible with the child. Following induction and after verifying the ability to mask ventilate, vecuronium 0.1 mg/kg was used for insertion of the group-designated airway (RAE tube or FLMA). The size of the RAE tube was calculated using the modified Cole s formula for an uncuffed pediatric tracheal tube (Weiss et al., 2004), and a size 2 FLMA was used in all patients of the study group. Insertion of the FLMA was accomplished with the lateral, partially inflated technique (Kundra et al., 2003). The cuff was inflated, and the device was secured with an adhesive tape. The airway (RAE tube or FLMA) was first connected to Ayre s T-piece with Jackson Ree s modification, and successful placement was determined clinically by the ability to easily ventilate the lungs (as seen by chest movement) without any significant resistance or leak and without significant resistance to expiration with rapid refilling of the reservoir bag. In addition, a capnograph was used to verify endotracheal intubation and to assess the adequacy of ventilation. Ease of insertion was determined by the time taken for a successful insertion (from beginning of FLMA introduction till confirmation of adequate ventilation), and the numbers of attempts made before successful placement. An attempt was defined as insertion of the airway and its subsequent removal. Once satisfactory placement was confirmed, a throat pack was placed in the RAE group, and the airway was attached to the anesthesia ventilator incorporated into the anesthesia machine (Aestiva S/ anesthesia machine; Datex Ohmeda Inc., Tewksbury, MA) through a pediatric circuit. Analgesia was supplemented with 1 mcg/kg of fentanyl and was maintained with 0.5% to 1.5% halothane in a mixture of 40% oxygen and 60% nitrous oxide using a circle system at a fixed-flow rate of 2 L/min. The flow sensor (Pedi-lite flow sensor and gas sampler) of the spirometry module was attached near the patient end and provided the conduit for gas monitoring and lung mechanics. The ventilator was set to deliver mandatory breaths, and the high airway-pressure alarm limit was set at 25 cm H 2 O. Inspiratory tidal volume (V TI ) was increased sequentially to achieve an expiratory tidal volume (V TE )of 10 ml/kg and a minute volume (V E ) of 100 ml/kg at an inspiratory to expiratory ratio of 1:2. Peak airway pressures (Paw), inspiratory tidal volume (V TI ), expiratory tidal volume (V TE ), EtCO 2, compliance (C), and resistance (Raw) were measured continuously using a spirometry module. The percentage leak (LF) around the airway was quantified using the formula [(V TI 2 V TE )/V TI ] All the respiratory and hemodynamic parameters were recorded at the following time points: (1) after the insertion of airway, (2) after positioning the child in a hyperextended neck position for palatoplasty, (3) after application of modified Kilner Dott mouth gag (Agrawal and Panda, 2005) and (4) at every 10-minute interval thereafter until the completion of surgery and the removal of the airway. Displacement of the airway was suspected if V TE decreased to less than 7 ml/kg or an audible leak producing bubbles in the pharynx was noticed. An attempt to correct the displacement was made by repositioning the FLMA. However, if a rise in Paw to.20 cm H 2 O was noticed, accompanied by increased resistance to ventilate the lungs with a bag, airway obstruction was suspected. The gag was withdrawn and reapplied after recording the peak airway pressures and V TE. Repositioning of the FLMA and reapplication of the gag was attempted only once, and if the leak or obstruction persisted, it was replaced by a RAE tube. After conclusion of the surgery, residual neuromuscular blockade was antagonized with a mixture of atropine (0.02 mg/kg) and neostigmine (0.05 to 0.07 mg/kg). Once the child was fully awake, the airway (FLMA or ETT) was removed in the head down position. Any episode of laryngospasm (mild 5 only O 2 required, moderate 5 requires jaw thrust or gentle continuous positive airway

3 370 Cleft Palate Craniofacial Journal, July 2009, Vol. 46 No. 4 TABLE 1 Demographic and Clinical Data Parameters RAE Group (n 5 33) FLMA Group (n 5 33) Age (mo) 16 (13 to 24) 17 (14 to 25) Weight (kg) 13 (10 to 16) 14 (10 to 17) Duration of surgery (min) * Airway insertion No. of attempts 1 30 (91%) 30 (91%) 2 3 (9%) 3 (9%) Insertion time to successful first * attempt (min) Airway displacement 1 (3%) 2 (6%) Postoperative complications Persistent cough{ 12 (36%) 5 (15%) SpO2, 95% 6 (18%) 0 Laryngospasm{ 3 (9%) 0 Laryngotracheal soiling 2 (6%) 2 (6%) Median (Range). * Mean 6 SD. { Persistent cough (2 or more episodes of stressful or violent coughing or SpO2 falling below 95% during coughing episode). { Laryngospasm (mild 5 only O 2 required, moderate 5 requires jaw thrust or gentle continuous positive airway pressure, severe 5 requires reintubation). pressure, severe 5 requires reintubation), desaturation (SpO 2, 95%), breath holding (causing SpO 2 to fall below 95%), persistent coughing (two or more episodes of stressful or violent coughing or SpO 2 falling below 95% during coughing episode), and vomiting were recorded. Laryngotracheal soiling was determined by the presence of blood on the surface of the ETT inside the glottis and on the undersurface (cup of the mask and tube) of the FLMA (Ahmed and Vohra, 2002) after removal. A preliminary trial was conducted on 100 children (1 to 12 years) undergoing intraoral surgery to calculate the incidence of respiratory complications during emergence from anesthesia after oral surgery (adenotonsillectomies, cleft palate repair, release of ankyloglossia, and dental procedures). A formal data-recording form was used to estimate the required number of children for the current study. Considering a 35% incidence of extubation complications (approximately 30% of the RAE group and 5% of the FLMA group), the sample size was estimated at an alpha level of 5% and power of 80%. The 35% incidence of respiratory complications observed during extubation (by the attending anesthetist) and in the recovery room (by the trained nurse) consisted of coughing/gagging (55%), desaturation (27%), laryngospasm (8%), breath holding (5%), and others (5%). Except for coughing, there was no other significant respiratory complication noticed in the recovery room. Statistical analysis of all parametric data between groups was done using the unpaired Student s t test and within groups using a one-way analysis of variance. Nonparametric variables were analyzed using the Fisher exact test. RESULTS Children who underwent cleft palate repair between July 2004 and July 2006 were recruited for the study. The FIGURE 1 Mean leak fraction (%) in both groups at various time intervals. MG App = after mouth gag application; MG Rem = after mouth gag removal. * p,.05 between the groups. physical characteristics of patients were comparable in both the groups (Table 1). Time taken for successful firstattempt insertion was similar in both the groups. In 2 out of 33 children in the FLMA group, the FLMA was displaced from its original position after successful insertion, and the mouth gag had to be realigned; whereas, the RAE tube advanced endobronchially in one child after gag application (Table 1). After airway insertion and on positioning of the children for palatoplasty, LF was significantly higher in the RAE group when compared with the FLMA group ( versus , p,.05) until a throat pack was applied; thereafter, it was comparable to the FLMA group at all time intervals (Fig. 1). Paw (Fig. 2a) and Raw (Fig. 2b) were significantly higher in the RAE group compared with the FLMA group at all time intervals, p,.05. Normocapnia was maintained in both the groups throughout surgery (Fig. 3a), and the lung compliance (Fig. 3b) did not reveal any significant deviation from normal. Following removal of the airway, desaturation, coughing, and laryngospasm were noticed more frequently in RAE group; whereas, laryngotracheal soiling had similar distribution in both groups (Table 1). DISCUSSION Our study has demonstrated that the FLMA is suitable for use in children undergoing cleft palate repair. In spite of choosing an appropriately sized RAE tube, the LF was significantly higher in the RAE group until the supraglottic area was packed with wet ribbon gauze after mouth gag application. Thereafter, LF was similar for both the groups. Snugly fitting tracheal tubes are avoided in children due to the fear of causing glottic edema; hence, uncuffed ETTs were chosen to allow leak at pressures of 15 to 20 cm H 2 O (Gal, 2005). None of the children in our study had a leak that required replacement with a larger ETT. Cuffed

4 Kundra et al., FLEXIBLE LARYNGEAL MASK AIRWAY IN CLEFT PALATE SURGERY 371 FIGURE 2A Mean peak airway pressure in both the groups at various time intervals. Insert = after insertion of flexible laryngeal mask airway; Posit = after surgical position; Gag App = after mouth gag application; Gag Rem = after mouth gag removal. * p,.05 between the groups. FIGURE 2B Mean airway resistance in both the groups at various time intervals. Insert = after insertion of flexible laryngeal mask airway; Posit = after surgical position; Gag App = after mouth gag application; Gag Rem = after mouth gag removal. * p,.05 between the groups. FIGURE 3A Mean end-tidal carbon dioxide in both the groups at various time intervals. Insert = after insertion of flexible laryngeal mask airway; Posit = after surgical position; Gag App = after mouth gag application; Gag Rem = after mouth gag removal. * p,.05 between the groups. FIGURE 3B Mean airway compliance in both the groups at various time intervals. Insert = after insertion of flexible laryngeal mask airway; Posit = after surgical position; Gag App = after mouth gag application; Gag Rem = after mouth gag removal. * p,.05 between the groups. ETTs that are now available for this age group can be a good choice, allowing the use of low, fresh gas flow and reduction of the concentration of anesthetics detectable in the operating room (Khine et al., 1997). However, the cuffed pediatric ETTs are 10 times more expensive and therefore not always readily available in many centers. The LMA has been shown to provide equally effective positive pressure ventilation with a low-flow circle system in children (Heath and Sinnathamby, 1994; Engelhardt et al., 2006), and the efficacy of the seal for ventilation remains unaltered by application of the mouth gag (Brimacombe et al., 1999). Instead, opening of the mouth gag pushes the FLMA rim tightly against the glottis, resulting in a more effective seal. As a result, an increase in V TE was noticed that became almost equal to the V TI value in the FLMA group after mouth gag application. Insertion of FLMA by the midline technique (Brain s method) can be difficult in children having large defects of the palate. First, the FLMA cuff is often caught within the defect of the palate and, second, when it is pushed down, the cuff tends to fold back on itself after touching the posterior pharyngeal wall. Considering these limitations, FLMA insertion was successfully accomplished in all children using the lateral approach with a partially inflated cuff (Kundra et al., 2003). FLMA displacement was noticed in two children before the start of surgery. As soon as FLMA displacement was detected, manual ventilation with 100% oxygen was performed and maneuvers to optimize ventilation were undertaken (restoration of the head to neutral position from hyperextension, repositioning the FLMA, and removal of the mouth gag if applied). As a result of early detection and application of rescue measures, the minimum

5 372 Cleft Palate Craniofacial Journal, July 2009, Vol. 46 No. 4 FIGURE 4 Modified Kilner Dott mouth gag. Two metal blocks fixed to the tongue blade with adequate space to house the endotracheal tube or flexible laryngeal mask airway. SpO 2 recorded in both the children was 97%. Low expired tidal volume with inadequate chest expansion and an audible leak are the first signs of FLMA displacement. In addition, an abrupt fall in Paw results from loss of the seal between the cuff and periglottic tissues; whereas, its sudden increase may suggest airway obstruction, which might occur after gag application. Displacement of the FLMA occurred during surgical positioning in one child with a large defect in the palate when head and neck extension was applied. Change in pharyngeal geometry following hyperextension of the head can reduce the efficacy of the seal by distorting the interface between the cuff and the periglottic tissues (Brimacombe et al., 1999). In addition, the FLMA has a straight reinforced shaft, and once the FLMA shaft is secured with adhesive tape below the lower lip, a curve is created on the shaft inside the oropharynx. The portion of the FLMA distal to the fixation has a natural tendency to straighten out but is retained in position by the palate. Palate support is lost when there is a cleft of the palate; hence, when the defect is large (as in a bilateral cleft palate), FLMA displacement is likely to occur during positioning of the child for surgery. In another child, FLMA displacement was noticed after application of the mouth gag. The mouth gag was released immediately, the FLMA was slightly pulled out until the ventilation was once again satisfactory, and the mouth gag was reapplied. The possibility exists of a discrepancy between the size of the FLMA prescribed for the child s weight and that which works best in practice. A one-size smaller FLMA might have been more appropriate in this child weighing 10 kg, but currently FLMA sizes smaller than 2 are not being manufactured. Use of an oversize FLMA may result in the placement of the cuff in the oropharynx, causing the blade of the mouth gag to rest on the mask. This can result in displacement and/or obstruction of the FLMA during manipulation of the gag by the surgeon. The surgeon, while applying the mouth gag, has to take care not to push the FLMA inside. This will prevent displacement of the FLMA. The surgeon should stabilize the FLMA with a forceps in the nondominant hand, position the tongue blade over the tube without pushing it in, and then open the gag. Correct FLMA position is confirmed if the cuff of FLMA is not seen in the oral cavity once the mouth gag is fully opened (Nair and Bailey, 1995). Endobronchial migration of the ETT occurred after mouth gag application in one child belonging to the RAE group. Because of the fixed length of RAE tracheal tubes, accidental endobronchial intubation can occur even when an appropriately sized tube is used for a given age group (Black and Mackersie, 1991). It should be noted that cleft palate repairs are usually performed in infants, and the FMLA technique would not be applicable to the majority of cleft palate patients for whom there is not an appropriately sized FLMA. However, if a smaller size FLMA becomes available, it could be considered during palatoplasty in infants. Nevertheless, a significant number of patients still present for palatoplasty at a later age in developing nations; hence, FLMA still remains a useful device in a large number of patients (Uetani et al., 2006; Morioka et al., 2007). Paw and Raw were significantly higher in the RAE group at all time intervals due to the significantly narrower lumen of RAE tubes when compared with the FLMA (mean internal diameter of RAE tube being 4.1 mm compared with the mean internal diameter of 5.1 mm in FLMA size 2). The resistance to ventilation encountered by a size 2 FLMA is between that of 5- and 6-mm size RAE tubes at 0.5 to 1 L/min flow of gases (al-hasani, 1993). There was a marginal increase in the Paw and Raw in both groups after application of a mouth gag. These changes in Paw and Raw were not of any clinical significance because the EtCO 2 remained similar in both groups throughout the surgery. Yet, because a majority of the changes in airway parameters occurred after the application of the mouth gag, a close scrutiny of the airway parameters is required during this time. The FLMA resists kinking on application of the mouth gag (Webster et al., 1993; Williams and Bailey, 1993; Williams et al., 1993), but there does exist a possibility of the spirals collapsing sideways when the tube is bent into a curve (Engelhardt et al., 2006). The modified Kilner Dott mouth gag s tongue blade has a safeguard to prevent compression of the FLMA. There are two metal blocks fixed to the tongue blade with adequate space to house the larger diameter FLMA. These blocks rest over the mandible and prevent compression. These modified tongue blades have been used in all the patients in both groups (Agrawal and Panda, 2005). The ability to retain the FLMA without excessive straining until the child is fully awake is the major benefit associated with its use (Daum and O Reilly, 1992; Williams et al., 1993). Consequently, the incidence of coughing, laryngospasm, desaturation, and laryngotracheal soiling is much lower when the FLMA is used in oral surgeries

6 Kundra et al., FLEXIBLE LARYNGEAL MASK AIRWAY IN CLEFT PALATE SURGERY 373 REFERENCES FIGURE 5 Surgical field after completion of surgery with the FLMA beneath the mouth gag. The surgical position keeps the oropharynx at a lower level than the trachea and prevents laryngotracheal soiling. (Webster et al., 1993; Williams and Bailey, 1993; Nair and Bailey, 1995; Williams et al., 1995; Ahmed and Vohra, 2002). The presence of the ETT during emergence, on the other hand, predisposes to coughing and bucking that increase oozing from the surgical site and result in airway complications after extubation. Examination of the ETT and the undersurface of the FLMA revealed the presence of a similar quantity of blood in 4 out of 66 children (Table 1). None of these children with soiled airways had any significant complication or aspiration on postoperative follow-up. The surgical position of the hyperextended neck for palatoplasty keeps the oropharynx at a lower level than the glottis and thereby prevents trickling of blood into the trachea during surgery (Fig. 5). Soiling is likely to occur during emergence after children are repositioned for airway removal because the glottis comes back to the level of the oropharynx. It might be prudent to retain children in the same surgical position and reposition laterally for extubation only when the swallowing reflex returns. In conclusion, FLMA is a useful device for maintaining the airway and achieving smooth emergence in children undergoing cleft palate surgery. The use of the FLMA is safe. The modified Kilner Dott mouth gag further helps in use of the FLMA in palate surgery. The FLMA remains under the tongue blade and does not compromise the volume of the oral cavity available for surgical activity. However, both the surgeon and the anesthetist need to acquaint themselves with its use. Agrawal K, Panda KN. Modified palate mouth gag tongue blade to prevent endotracheal tube compression. Plast Reconstr Surg. 2005;116: Ahmed MZ, Vohra A. The reinforced laryngeal mask airway protects the airway in patients undergoing nasal surgery. Can J Anaesth. 2002;49: al-hasani A. Resistance to constant air flow imposed by the standard laryngeal mask, the reinforced laryngeal mask, and RAE tracheal tubes. Br J Anaesth. 1993;71: Beveridge ME. Laryngeal mask anaesthesia for repair of cleft palate. Anaesthesia. 1989;44: Black AE, Mackersie AM. Accidental bronchial intubation with RAE tubes. Anaesthesia. 1991;46: Brimacombe JR, Keller C, Gunkel AR, Pühringer F. The influence of tonsillar gag on efficacy of seal, anatomic position, airway patency, and airway protection with flexible laryngeal mask airway: a randomized, cross-over study of fresh adult cadavers. Anesth Analg. 1999;89: Daum RE, O Reilly BJ. The laryngeal mask airway in ENT surgery. J Laryngol Otol. 1992;106: Engelhardt T, Johnston G, Kumar MM. Comparison of cuffed, uncuffed tracheal tubes and laryngeal mask airways in low flow pressure controlled ventilation in children. Pediatr Anesth. 2006;16: Gal TJ. Airway Management. In: Miller RD, ed. Miller s Anesthesia. 6th ed. Philadelphia: Elsevier Churchill Livingstone; 2005:1630. Heath ML, Sinnathamby SW. The reinforced laryngeal mask airway for adenotonsillectomy. Br J Anaesth. 1994;72: Khine HH, Corddry DH, Kettrick RG, Martin TM, McCloskey JJ, Rose JB, Theroux MC, Zagnoev M. Comparison of cuffed and uncuffed endotracheal tubes in young children during general anesthesia. Anesthesiology. 1997;86: Kundra P, Deepak R, Ravishankar M. Laryngeal mask insertion in children: a logical approach. Paediatr Anaesth. 2003;13: Morioka D, Yoshimoto S, Udagawa A, Ohkubo F, Yoshikawa A. Primary repair in adult patients with untreated cleft lip-cleft palate. Plast Reconstr Surg. 2007;120: Nair I, Bailey PM. Review of uses of the laryngeal mask in ENT anaesthesia. Anesthesia. 1995;50: Uetani M, Jimba M, Niimi T, Natsume N, Katsuki T, Xuan le TT, Wakai S. Effects of a long-term volunteer surgical program in a developing country: the case in Vietnam from 1993 to Cleft Palate Craniofac J. 2006;43: Webster AC, Morley-Foster PK, Dain S, Ganapathy S, Ruby R, Au A, Cook MJ. Anesthesia for adenotonsillectomy: a comparison between tracheal intubation and the armoured laryngeal mask airway. Can J Anaesth. 1993;40: Weiss M, Dullenkopf A, Gysin C, Dillier CM, Gerber AC. Shortcomings of cuffed paediatric tracheal tubes. Br J Anaesth. 2004;92: Williams PJ, Bailey PM. Comparison of the reinforced laryngeal mask airway and tracheal intubation for adenotonsillectomy. Br J Anaesth. 1993;70: Williams PJ, Thompsett C, Bailey PM. Comparison of the reinforced laryngeal mask airway and tracheal intubation for nasal surgery. Anaesthesia. 1995;50: