Effect of the laryngeal mask airway on oesophageal pH: influence of the volume and pressure inside the cuff

We studied gastro-oesophageal reflux (GOR) with a face mask and laryngeal mask airway (LMA), and the effects of inflation pressure and volume of the LMA cuff on oesophageal pH, in 60 patients. Patients were managed with either a face mask (group I) or LMA inflated to obtain a seal in the anaesthesia circuit at 7 cm H2O (group II) or 15 cm H2O (group III). A pH-sensitive probe with two electrodes, 10 cm apart, was placed in the oesophagus during anaesthesia and recordings were made continuously until patients awakened. There was a significant difference in the incidence of GOR between the face mask (group I) and the LMA (groups II-III) (P < 0.05) in the lower oesophagus but there was no difference in the mid-oesophagus. No correlation was found between pressure and volume inside the cuff and variations in oesophageal pH. We conclude that LMA use was associated with increased reflux in the low oesophagus but oesophageal pH was not influenced by variations in pressure or volume inside the LMA cuff.      

Developing a strategy to improve ventilation in an unprotected airway with a modified mouth-to-bag resuscitator in apneic patients

The strategies to ensure safety during ventilation of an unprotected airway are limiting airway pressure and/or inspiratory flow. In this prospective, randomized study we assessed the effect of face mask ventilation with small tidal volumes in the modified mouth-to-bag resuscitator (maximal volume, 500 mL) versus a pediatric self-inflatable bag versus automatic pressure-controlled ventilation in 40 adult apneic patients during induction of anesthesia. The mouth-to-bag resuscitator requires the rescuer to blow up a balloon inside the self-inflating bag that subsequently displaces air which then flows into the patient's airway. Respiratory variables were measured with a pulmonary monitor (CP-100). Mouth-to-bag resuscitator and pressure-controlled ventilation resulted in significantly lower (mean +/- sd) peak airway pressure (8 +/- 2 and 8 +/- 1 cm H(2)O), peak inspiratory flow rate (0.7 +/- 0.1 and 0.7 +/- 0.1 L/s), and larger inspiratory time fraction (33% +/- 5% and 47% +/- 2%) in comparison to pediatric self-inflating bag ventilation (12 +/- 3 cm H(2)O; 1 +/- 0.2 L/s; 27% +/- 4%; all P < 0.001). The tidal volumes were similar between groups. No stomach inflation occurred in either group. We conclude that using a modified mouth-to-bag resuscitator or automatic pressure-controlled ventilation with similar small tidal volumes during face mask ventilation resulted in an approximately 25% reduction in peak airway pressure when compared with a standard pediatric self-inflating bag.     

Gas leak and gastric insufflation during controlled ventilation: face maskversus laryngeal mask airway

Purpose

To compare two airway management techniques, face mask (FM) with oropharyngeal airway and laryngeal mask airway (LMA), with respect to the effectiveness of positive pressure ventilation and airway maintenance.

Methods

After induction of anaesthesia, two airway management techniques (FM or LMA) and three peak pressures (20, 25 and 30 cm H₂O) were randomly applied during controlled ventilation in 60 patients. Data collected included inspiratory and expiratory volumes and presence of gastro-oesophageal insufflation. Leak was calculated by subtracting the expiratory from the inspiratory volume, expressed as a fraction of the inspiratory volume.

Results

Expiratory volumes (mean ± SD) at 20, 25 and 30 cm H₂O for LMA ventilation were 893 ± 260, 986 ± 276 and 1006 ± 262 respectively, and for FM ventilation 964 ± 264, 1100 ± 268 and 1116 ± 261. Leak fractions at 20, 25 and 30 cm H₂O for LMA ventilation were 0.21 ± 0.15, 0.24 ± 0.18 and 0.26 ± 0.18 respectively, and for FM ventilation 0.14 ± 0.09, 0.14 ± 0.09 and 0.12 ± 0.08. The frequency of gastro-oesophageal insufflation was 1.6%, 5% and 5% for the LMA and 5%, 15% and 26.6% for the FM for ventilation pressures of 20, 25 and 30 cm H₂O respectively which was greater with LMA use.

Conclusion

Ventilation was adequate in all patients using both techniques. Leak was pressure dependent and greater with LMA use. Most of the leak was vented to the atmosphere via the pharynx. Gastro-oesophageal insufflation was more frequent with ventilation using the face mask. LMA use with positive pressure ventilation would appear to be a better airway management method than the face mask.     

CRICOID PRESSURE MAY PREVENT INSERTION OF THE LARYNGEAL MASK AIRWAY

We have studied 42 female patients undergoing elective day-casesurgery allocated randomly to two groups. After induction ofanaesthesia an attempt was made to insert a laryngeal mask airwayafter application of cricoid pressure in one group or with nocricoid pressure in the other. The anaesthetist was unawareof the application, or not, of cricoid pressure. Successfulinsertion was achieved at the first or second attempt in 19of the 22 patients in the non-cricoidpressure group, but inonly three of the 20 patients in the cricoid pressure group(X² 18.62, P <0.001). The laryngeal mask airway was theninserted successfully in all 17 patients after removal of cricoidpressure. The implications of having to remove cricoid pressureif a laryngeal mask airway is to be inserted are discussed.(Br. J. Anaesth. 1992; 69: 465–467)     

REGURGITATION OF GASTRIC CONTENTS DURING GENERAL ANAESTHESIA USING THE LARYNGEAL MASK AIRWAY

We have investigated the incidence of regurgitation of gastriccontents during general anaesthesia administered via a laryngeaimask airway (LMA) or face mask and Guedel airway in 56 patientswith no risk factors for regurgitation. Patients swallowed agelatine capsule containing methylene blue 10 min before inductionof anaesthesia. Fibreoptic laryn–goscopy in the LMA groupor conventional laryn-goscopy in the face mask group was performedat the end of surgery. Dye was observed within the laryngeaimask in seven of 28 patients (25%). No patients in the facemask-Guedel airway group regurgitated dye (P = 0.005). Therewas no evidence of aspiration of dye.      

Work of breathing during spontaneous ventilation in anesthetized children: a comparative study among the face mask, laryngeal mask airway and endotracheal tube

Work of breathing (WOB) increases during general anesthesia in adults, but such information has been limited in pediatric patients. We studied WOB in 24 healthy children (mean age 2+/-1.9 yrs), during elective urogenital surgery under 1 minimum alveolar anesthetic concentration halothane-nitrous oxide anesthesia with a caudal block while breathing spontaneously. WOB was measured with an esophageal balloon, miniature flowmeter, and a computerized (Bicore) system. In each patient, WOB was computed under four conditions: a mask without oral airway (-AW), a mask with oral airway (+AW), a laryngeal mask airway (LMA), and an endotracheal tube (ETT). With each apparatus WOB was studied both with continuous positive airway pressure (CPAP) (5-6 cm H(2)O) and without CPAP (or zero end-expiratory pressure [ZEEP]). Under ZEEP, WOB (g x cm/kg) among the four apparatus were (mean +/- SEM): mask (-AW) (64 +/-19.2) > mask (+AW) (44+/-17.2), LMA (42+/-15.6) > ETT (25.4+/- 12.4) (P<0.05). WOB with CPAP significantly (P<0.05) decreased from WOB with ZEEP in three groups (mask [-AW], mask [+AW], and LMA), but not in the ETT group. Tidal volume (both ZEEP and CPAP) and end-tidal PCO(2) (with CPAP only) were significantly (P<0.05) decreased only in the ETT group, whereas no significant difference was found in respiratory rate or minute volume among the four airway apparatus groups, either with or without CPAP. The reduction in WOB, when breathing through ETT was primarily attributable to decreases in tidal volume and volume work. The finding that WOB decreases with CPAP in all groups except for the ETT group suggests that the decrease is a result of improved patency of the upper airway rather than of increases in functional residual capacity and lung compliance.     

Endotracheal tube versus face mask with and without continuous positive airway pressure (CPAP)

Various ways of delivering continuous positive airway pressure (CPAP) have been extensively studied, with little attention, however, being paid to the effects of an intubation tube compared with breathing through a face mask, with or without CPAP. Pulmonary and cardiovascular variables were measured while 12 patients recovering from coronary artery bypass grafting were spontaneously breathing at ambient airway pressure, then at 7.4 mmHg (1 kPa) CPAP, and again at ambient pressure just before extubation. The same stages were repeated immediately after extubation, with patients breathing through a tight-fitting face mask. Arterial oxygen tension (Pao₂, mean ± s.d.) was better when the patients were breathing at ambient pressure through a face mask (11.7±2.8 kPa) than when they were intubated (10.6±2.4 kPa, P < 0.05). Compared with ambient pressure, CPAP (7.4 mmHg) (1 kPa) increased Pao₂ in both modes (13.4 ± 3.5 kPa with mask, and 12.6 ± 3.5 kPa when intubated, n.s.). The best arterial oxygen saturation was measured during CPAP with a face mask (96± 1%). Cardiac output remained unchanged in all the breathing modes. After coronary artery bypass grafting, spontaneous breathing with a face mask resulted in better Pao₂ than breathing through an endotracheal tube, both with and without 7.4 mmHg (1 kPa) CPAP. This study indicates that unnecessary delay in extubation should be avoided.     

Intra-ocular pressure changes following laryngeal mask airway insertion: a comparative study

We compared the effects of the Brain laryngeal mask airway with a tracheal tube on intra-ocular pressure. Propofol was used as induction agent and atracurium as relaxant. Twenty-six patients with normal intra-ocular pressure undergoing cataract surgery were randomly allocated to two groups. Group A ( n  = 13) had a laryngeal mask airway inserted and Group B ( n  = 13) had a tracheal tube inserted. Intra-ocular pressure was measured just before insertion of the airway, 20 s after insertion and at 2 min. In the laryngeal mask airway group there were no significant changes in mean intra-ocular pressure. In the tracheal tube group there was a significant rise in mean intra-ocular pressure at 20 s (p = 0.0056) which returned to pre-insertion levels at 2 min. We conclude that the laryngeal mask airway continues to have advantages over the tracheal tube for ophthalmic surgery despite the use of propofol and atracurium as anaesthetic agents.     

I-gel喉罩与普通喉罩在全麻乳腺手术中的应用比较

目的比较I-gel喉罩与普通喉罩用于全麻乳腺手术中的气道管理效果。方法全麻下行乳腺肿物切除术患者60例,ASAⅠ或Ⅱ级,随机均分为I-gel喉罩组(I组)和普通喉罩组(S组)。记录首次插入成功率、插入时间、气道密封压、纤维支气管镜检查分级情况、苏醒时间、拔出喉罩时间及喉罩插入成功后15、30、45、60min时HR、BP、SpO2、PETCO2及气道峰压(Ppeak)值;记录并发症的发生情况。结果 I组首次插入成功率为90%,高于S组的76%(P<0.05);插入时间为(15.2±5.6)s,短于S组的(26.5±8.3)s(P<0.05);气道密封压为(27.6±4.7)cmH2O,高于S组的(23.8±4.5)cmH2O(P<0.05);纤维支气管镜评级优于S组(P<0.05)。两组患者苏醒时间、拔除喉罩时间和各时点HR、BP、SpO2、PETCO2及Ppeak差异无统计学意义;两组患者拔除喉罩后并发症的发生率差异无统计学意义。结论 I-gel喉罩用于全麻乳腺手术气道管理的效果优于普通喉罩。     

Prevention of atelectasis formation during induction of general anesthesia

General anesthesia promotes atelectasis formation, which is augmented by administration of large oxygen concentrations. We studied the efficacy of positive end-expiratory pressure (PEEP) application during the induction of general anesthesia (fraction of inspired oxygen [FIO(2)] 1.0) to prevent atelectasis. Sixteen adult patients were randomly assigned to one of two groups. Both groups breathed 100% O(2) for 5 min and, after a general anesthesia induction, mechanical ventilation via a face mask with a FIO(2) of 1.0 for another 5 min before endotracheal intubation. Patients in the first group (PEEP group) had continuous positive airway pressure (CPAP) (6 cm H(2)O) and mechanical ventilation via a face mask with a PEEP of 6 cm H(2)O. No CPAP or PEEP was applied in the control group. Atelectasis, determined by computed radiograph tomography, and analysis of blood gases were measured twice: before the beginning of anesthesia and directly after the intubation. There was no difference between groups before the anesthesia induction. After endotracheal intubation, patients in the control group showed an increase of the mean area of atelectasis from 0.8% +/- 0.9% to 4.1% +/- 2.0% (P = 0.0002), whereas the patients of the PEEP group showed no change (0.5% +/- 0.6% versus 0.4% +/- 0.7%). After the intubation with a FIO(2) of 1.0, PaO(2) was significantly higher in the PEEP group than in the control (591 +/- 54 mm Hg versus 457 +/- 99 mm Hg; P = 0.005). Atelectasis formation is prevented by application of PEEP during the anesthesia induction despite the use of large oxygen concentrations, resulting in improved oxygenation. IMPLICATIONS: Application of positive end-expiratory pressure during the induction of general anesthesia prevents atelectasis formation. Furthermore, it improves oxygenation and probably increases the margin of safety before intubation. Therefore, this technique should be considered for all anesthesia induction, at least in patients at risk of difficult airway management during the anesthesia induction.     

Pharyngeal mucosal pressures with the laryngeal tube airway versus ProSeal laryngeal mask airway

We tested the hypothesis that mucosal pressures are higher for the laryngeal tube airway trade mark than the ProSeal laryngeal mask airway. Fifteen fresh cadavers were studied. Microchip pressure sensors were attached to the laryngeal tube airway and ProSeal laryngeal mask airway at four similar anatomical locations (base of tongue, lateral pharynx, posterior pharynx and posterior hypopharynx) and three dissimilar locations (laryngeal tube airway trade mark, anterior and lateral hypopharynx; ProSeal laryngeal mask airway, pyriform fossa). The cuff volume (laryngeal tube airway, < or = 140 ml; ProSeal laryngeal mask airway, < or = 30 ml) was adjusted until the oropharyngeal leak pressure was 15 cm H2O and the mucosal pressures recorded. This was repeated at an oropharyngeal leak pressure of 20, 25 and 30 cm H2O. Mucosal pressures in the lateral pharynx were always similar. Mucosal pressures at the base of tongue and posterior pharynx were similar for the laryngeal tube airway and ProSeal laryngeal mask airway at 15 and 20 cm H2O, but were higher for the laryngeal tube airway at 25 cm H2O at 30 cm H2O. Mucosal pressures in the posterior hypopharynx were always higher for the laryngeal tube airway (all: p < 0.03). Mean mucosal pressures for the laryngeal tube airway ranged from 8-31, 2-13 and 15-41 cm H2O for the base of tongue, lateral pharynx and posterior pharynx (proximal cuff) respectively and 3-7, 3-7 and 7-18 cm H2O for the anterior, lateral and posterior hypopharynx (distal cuff) respectively. Mean mucosal pressures for the ProSeal laryngeal mask airway ranged from 6-23, 3-10, 8-25, 6-17 and 2-8 cm H2O for the base of tongue, lateral pharynx, posterior pharynx, pyriform fossa and posterior hypopharynx respectively. We conclude that mucosal pressures are higher for the laryngeal tube airway, particularly when oropharyngeal leak pressure greater than 25 cm H2O. This suggests that mucosal ischemic injury will be more common with the LTA than the PLMA.     

Mask lung ventilation by ambulance personnel: a performance assessment

We evaluated the ability of basic life support ambulance officers and anaesthetists to perform lung ventilation with a face mask. After induction of anaesthesia and institution of standardized airway conditions the ambulance officer or anaesthetist placed a mask on the patient’s face and lung ventilation was commenced. The order of hand grip (one vs two hands) was randomized. The mask was connected to a ventilator which had flow and pressure transducers in the inspiratory and expiratory breathing circuits. The output of these devices was sent to an electronic integrator to determine volumes. Calibration of the flow transducers was made against a spirometer while ventilating a test lung. Oesophageal insufflation was determined by listening over the epigastrium with a stethoscope. Data collected included presence of gastro-oesophageal insufflation, inspiratory and expiratory volumes. Expiratory volumes for ambulance officers and anaesthetists at 30 cm H₂O were greater than that of ambulance officers at 20 cm H₂O (P < 0.001) but profession of the mask holder or hand grip had no effect on expiratory volume. There was no difference in the mask leak when the professions were compared but ambulance officers had a lower mask leak with a two-handed grip at 20 cm H₂O (P < 0.001). Anaesthetists had a greater incidence of gastro-oesophageal insufflation when a two-handed mask grip was utilized (P < 0.05). In healthy relaxed patients there appeared to be little difference between the ambulance officers and qualified anaesthetists in airway maintenance or mask-holding ability.     

低套囊压力下ProSeal或Supreme喉罩用于腹腔镜手术患者气道管理的效果

目的 评价低套囊压力下ProSeal和Supreme喉罩用于腹腔镜手术患者气道管理的效果.方法 择期仰卧位腹腔镜手术患者60例,ASA分级Ⅰ或Ⅱ级,年龄20～70岁,体重50～80 kg,随机分为ProSeal喉罩组(P组)和Supreme喉罩组(S组),每组30例.喉罩置入成功后,用手持测压计监测套囊充气压力并维持其为35 cm H2O,记录气道密闭压及气腹前后机械通气时气道压峰值和平均气道压,记录术后并发症的发生情况.结果 两组气腹后机械通气时气道压峰值高于气腹前(P＜0.05),两组间比较差异无统计学意义(P＞0.05);术中气腹前后均无漏气现象发生;两组气道密闭压比较差异无统计学意义(P＞0.05);两组拔除喉罩后表面带有血丝及术后咽痛发生率比较差异无统计学意义(P＞0.05).结论低套囊压力(35 cm H2O)下ProSeal和Supreme喉罩通气效果均较好,可安全地用于腹腔镜手术患者的气道管理.     

Use of the laryngeal mask airway as an alternative to a face mask during outpatient arthroscopy.

The laryngeal mask airway (LMA) has recently become available in the United States, and several authors have suggested that it is superior to an anesthesia mask. To test this hypothesis, 64 patients undergoing outpatient arthroscopic knee surgery were randomly assigned to have anesthesia maintained via either a laryngeal mask airway (LMA) (n = 31) or a standard face mask (n = 33). Anesthesia was induced with fentanyl 1 microgram.kg-1 and propofol 2 mg.kg-1 and maintained with a variable-rate propofol infusion (50-180 micrograms.kg-1 x min) and nitrous oxide 67% in oxygen. The LMA was inserted without difficulty by inexperienced anesthesiologists in 90% of the patients. Problems associated with airway management were more common in patients in the face mask (control) group. Episodes of hemoglobin oxygen desaturation (< 95%) occurred in 52% of patients in the face mask group compared to only 13% in the LMA group (P < 0.05). Intraoperative airway manipulations were required in 15% of face mask patients (vs. 3% of the LMA group), and difficulties in maintaining an airway were reported by 24% of the resident anesthesiologists caring for patients in the face mask group (vs. none in the LMA group) (P < 0.05). Insertion of the LMA was not associated with any acute changes in hemodynamic values. Intraoperative hemodynamic values and anesthetic requirements did not differ significantly between the two treatment groups. There were no significant differences in the emergence and recovery times or in the incidence of postoperative sore throats between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Aerosol kinetics and bronchodilator efficacy during continuous positive airway pressure delivered by face mask

BACKGROUND: Rates of fresh gas flow (FGF) commonly used when continuous positive airway pressure (CPAP) is delivered by face mask theoretically reduce the delivery and availability of therapeutic aerosols. As it may be hazardous for patients with acute respiratory failure to interrupt mask CPAP, the effects of CPAP on aerosol kinetics and bronchodilator efficacy were investigated. METHOD: The effect of CPAP at 10 cm H2O at a FGF rate of 50 l/min on the delivery of technetium labelled aerosol generated from a readily available jet nebuliser was measured using a bench model of spontaneous respiration. In a separate clinical study the bronchodilator responses to incremental doses of nebulised salbutamol were measured in nine stable asthmatic subjects in a random sequence of conventional nebulisation (control) or nebulisation whilst receiving CPAP via a tight fitting face mask. Each patient acted as his or her own control. RESULTS: CPAP significantly reduced total aerosol delivery to the face mask from 6.85 (1.52)% to 1.3 (0.37)% of the initial nebuliser charge. In the clinical study a significant bronchodilator response to nebulised salbutamol was seen during both conventional nebulisation and nebulisation whilst receiving CPAP by face mask. The shape of the dose-response curves and the magnitude of the total increase in the forced expiratory volume in one second (FEV1) was identical for CPAP and control conditions. CONCLUSIONS: Despite a reduction in aerosol presented to the proximal airway, the bronchodilator response to inhaled beta 2 agonists in stable asthmatic subjects was not affected when CPAP was delivered by face mask. Despite a high rate of FGF, nebulised beta 2 agonists are effective when administered in conjunction with CPAP delivered by face mask.


     

ProSeal laryngeal mask airway for cardiac surgery after airway rescue

We present the case of the successful use of a ProSeal laryngeal mask airway in a severe obese 41-year-old women with a difficult airway, scheduled to undergo cardiac surgery (off-pump coronary artery bypass). Two intubation attempts failed and face mask ventilation became impossible with rapidly falling peripheral oxygen saturation. A ProSeal laryngeal airway was railroaded over a tracheal tube guide, a gastric tube was inserted along the drain tube and the patient underwent positive pressure ventilation, resulting in normal gas exchange and an oropharyngeal leak pressure > 40 cm H2O. The decision was taken to proceed with the ProSeal as the airway during the surgical intervention. Surgery was uneventful and the ProSeal was removed on the ICU three hours later. This case reports illustrates the successful use of a guided insertion of the ProSeal laryngeal mask for airway rescue in cardiac surgery.     

Einsatz der ProSeal®-Kehlkopfmaske der Größe 3 bei Kindern

BACKGROUND: The low-pressure airway seal of the Classic laryngeal mask airway (CLMA) can be inadequate for positive pressure ventilation (PPV) in children. The ProSeal laryngeal mask airway (PLMA) forms a more effective seal of the airway than the CLMA and facilitates gastric tube placement in adults. The size 3 PLMA can be used in adults and children. METHODS: The CLMA and PLMA were studied in random order -- crossover -- in 30 anaesthetized, non-paralysed children (average age 10.6 years, average body weight 39 kg). Airway leak pressure, maximum tidal volume, ease of insertion, quality of initial airway and fiberoptic position were determined. Gastric tube placement was assessed for the PLMA. RESULTS: The mean airway leak pressure in neutral head position (27.0 vs. 16.8 cm H(2)O), maximum flexion (38.3 vs. 26.2 cm H(2)O) and maximum extension (21.1 vs. 14.2 cm H(2)O) as well as the mean maximum tidal volume (1432 vs. 1062 ml) were significantly higher (p<0.001) for the PLMA. Air insufflation into the stomach occurred with the CLMA but not with the PLMA. Gastric tube placement was possible in all patients. CONCLUSIONS: The high reliability of g-tube placement and the significantly increased airway leak pressure seem to make the size 3 PLMA a more suitable device for PPV in children than the same size CLMA.     

The influence of the tonsillar gag on efficacy of seal, anatomic position, airway patency, and airway protection with the flexible laryngeal mask airway: a randomized, cross-over study of fresh adult cadavers.

We conducted a randomized, controlled, cross-over cadaver study to test the hypothesis that the efficacy of seal for ventilation and airway protection, anatomic position, and airway patency with the flexible laryngeal mask airway (FLMA) are altered by the application of a Boyle Davis (B-D) gag. We also determined the airway sealing pressure (ASP) at which the FLMA prevents aspiration when large volumes of fluid are placed above the cuff. We studied 20 adult cadavers (6-24 h postmortem). Efficacy of seal for ventilation and airway protection, anatomic position, and airway patency were determined with and without a B-D gag (two blade sizes: 8 and 10 cm) for the size 3, 4, and 5 FLMA in random order. Efficacy of seal for ventilation was determined by measuring the ASP at an intracuff pressure of 60 cm H2O. Efficacy of seal for airway protection was determined by flooding the mouth with 55-135 mL of water, reducing intracuff pressure until aspiration was detected fiberoptically and measuring ASP at this intracuff pressure. Anatomic position and airway patency were determined with a fiberoptic scope at an intracuff pressure of 60 cm H2O. In addition, in vivo compliance and ASP for the FLMA were measured in 10 cadavers and 10 paralyzed, anesthetized patients. Efficacy of seal for ventilation and airway protection, anatomic position, and airway patency did not change with the application of a gag for any mask size. The mean (range) ASP at which aspiration occurred when large volumes of fluid were placed above the cuff was 11 (7-15) cm H2O. The ASP for ventilation was always higher than the ASP for airway protection (P<0.0001). The FLMA had similar in vivo compliance and ASP in cadavers and anesthetized patients. We conclude that efficacy of seal for ventilation and airway protection, anatomic position and airway patency for the FLMA are unaffected by the application of a B-D gag in adults. ASP should be >15 cm H2O if there is a maximal risk of aspiration from above the cuff. IMPLICATIONS: The flexible laryngeal mask airway forms an effective seal for ventilation and protection of the airway that is unaffected by the application of a mouth gag that provides surgical access to the oropharynx. The efficacy of the seal should be >15 cm H2O if there is a maximal risk of aspiration from above the cuff.     

Nitrous oxide diffusion into the cuffs of disposable laryngeal mask airways

The aim of this study was to investigate cuff pressure changes found in disposable size 3 laryngeal mask airways (LMAs) from different manufacturers during nitrous oxide exposure and to compare the results with the re-usable Classic LMA. In an in vitro experiment, laryngeal mask airway cuff pressures starting from a baseline pressure of 40 cm H(2)O were recorded using a pressure transducer for 60 min with the laryngeal mask airway cuff exposed to 66% N(2)O in oxygen. Cuff pressure increases within 5 min of nitrous oxide exposure were > 250% in the Classic LMA and were not significantly different from those found in the Marshall laryngeal mask airway. However, they were significantly greater than those in the Soft Seal, the Unique, the AMBU, and Intersurgical laryngeal mask airways, all of which demonstrated stable cuff pressure levels within the first 5 min. The cuff pressure increase following 60 min of nitrous oxide exposure was 13.0 +/- 1.1 and 14.6 +/- 0.7 cm H(2)O in the Intersurgical and Unique laryngeal mask airways, respectively, which was significantly lower than the cuff pressure increase in the Soft Seal and in the Ambu laryngeal mask airways (28.3 +/- 2.9 and 30.9 +/- 1.2 cm H(2)O, respectively). Unlike the re-usable Classic LMA and the disposable Marshall laryngeal mask airway, which have silicone cuffs, the disposable Ambu, Intersurgical, Portex Soft Seal and Unique laryngeal mask airways have cuffs constructed from PVC, which seems to be less susceptible to hyperinflation caused by nitrous oxide diffusion.     

Clinical comparison of the reusable LMA Classic laryngeal mask and the disposable Soft Seal mask in adult patients

OBJECTIVES: To compare the clinical behavior of the disposable Soft Seal laryngeal mask to the behavior of the reusable LMA Classic mask. METHODS: Patients were randomly assigned to 2 groups in which either the LMA Classic or the Soft Seal mask would be used. We assessed time required for positioning and number of attempts, seal pressure, fiberoptic bronchoscopic image, and complications. The masks were inserted by 2 anesthesiologists who were inexperienced in the use of laryngeal masks. We also compared compliance of the cuff in the laboratory. RESULTS: Sixty patients were enrolled. There were no differences in time required for insertion or number of attempts (first-try success, 83%). The mean (SD) seal pressure was greater in the Soft Seal group at 23 (4) cm H2O than in the LMA Classic group at 20 (4) cm H2O. There were no significant differences in the fiberoptic bronchoscopic images, ventilation, incidence of intraoperative complications, presence of blood on the cuff (LMA Classic, 6 out of 30 vs Soft Seal, 11 out of 29), or postoperative sore throat. In 3 patients in the Soft Seal group the laryngeal mask had to be replaced by an orotracheal tube. Cuff compliance in the laboratory was lower for the LMA Classic than for the disposable mask for all sizes assessed. CONCLUSIONS: Although the results suggest that the clinical behavior of the 2 masks is similar, the LMA Classic allowed for effective airway management in all of the cases assigned to it, whereas management was effective in 90% of the cases in which the Soft Seal mask was used. The inflatable cuff of the Soft Seal is more compliant in vitro and it provides a higher airway seal pressure than does the LMA Classic.