COMPARISON OF THE REINFORCED LARYNGEAL MASK AIRWAY AND TRACHEAL INTUBATION FOR ADENOTONSILLECTOMY

One hundred and four patients were allocated randomly to receiveanaesthesia for adenotonsillectomy via either a reinforced laryngealmask airway or a tracheal tube. Airway maintenance and protectionwere assessed during and after operation. The reinforced laryngealmask did not interfere with surgical access; it resisted compressionand protected the lower airway from contamination with blood.Four patients were withdrawn from the laryngeal mask airwaygroup: two because of difficulty with placement, and two becausethe laryngeal mask was obstructed distally when the Boyle Davisgag was opened fully. In children, recovery was less eventfulin the laryngeal mask airway group, with less airway obstruction(P < 0.001) and better airway acceptance (P < 0.05). Thereinforced laryngeal mask airway provided a clear, secure airwayuntil recovery of protective reflexes. (Br. J. Anaesth. 1993;70: 30–33)     

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)     

EFFECT OF THE LARYNGEAL MASK AIRWAY ON LOWER OESOPHAGEAL SPHINCTER PRESSURE IN PATIENTS DURING GENERAL ANAESTHESIA

We have studied the tone of the lower oesophageal sphincter(LOS) in 40 adults undergoing routine body surface surgery andallocated randomly to receive anaesthesia either by face maskand Guedel airway or by laryngeal mask airway. In the laryngealmask group there was a mean (SEM) decrease in barrier pressure(LOS minus gastric pressure) of 3.6 (1.4) cm H², compared witha mean increase of 2.2 (1.2) cm H2O in the face mask group (P< 0.005).     

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.      

THE LARYNGEAL MASK AIRWAY FOR INTRAOCULAR SURGERY: EFFECTS ON INTRAOCULAR PRESSURE AND STRESS RESPONSES

Tracheal intubation, performed routinely during general anaesthesiain patients undergoing intraocular surgery, may have adverseeffects on cardiovascular function and intraocular pressure.This study assessed the suitability of the laryngeal mask airway(LMA) as a substitute for tracheal; intubation. Intraocularand systemic pressor effects, heart rate changes and catecholamineconcentrations were measured in two groups of 10 patients receivingstandardized anaesthesia with either a trachealtube (TT) ora LMA. There were significantly smaller changes in the pressorresponses to insertion and in concentrations of catecholaminesat critical times in the anaesthetic sequence in the LMA group.Mean (SEM) rate-pressure product was significantly smaller inthe LMA group compared with the TT group after both insertion(8276 (730) vs 13307 (1348), P<0.01) and removal (10 152(595) vs 14 137 (1044). P < 0.07; of the airway device. Thechange in intraocular pressure was significantly less in theLMA group at all time points after airway instrumentation thanthat in the TT group, with the greatest difference after extubation(–2.3 (2.4) mm Hg vs 74.5 (3.4) mm Hg. P < 0.071 ^*Present address: Department of Anaesthetics, Victoria Infirmary,Glasgow.     

RESISTANCE TO CONSTANT AIR FLOW IMPOSED BY THE STANDARD LARYNGEAL MASK, THE REINFORCED LARYNGEAL MASK AND RAE TRACHEAL TUBES

The reinforced laryngeal mask airway (RLMA) has been introducedrecently for head and neck surgery. Its resistance to constantair flow has been measured and compared with that of the standardlaryngeal mask airway (LMA). The RLMA resistance has also beencompared with that imposed by the standard oral Ring-Adair-Elwyn(RAE) tube of a corresponding size for a given patient. Theresistance to gas flow of the new RLMA was approximately threeto five times that of the LMA at two flow rates (0.5 and 7.0litre s^-1). The resistance of the RLMA 4 was intermediate betweenthat of RAE tubes sizes 8 and 9 mm, and that of RLMA 2 intermediatebetween that of RAE tubes sizes 5 and 6 mm. (Br. J. Anaesth.1993; 71: 594–596)     

Comparison of fibrescope guided intubation via the classic laryngeal mask airway and i‐gel in a manikin*

We compared the classic laryngeal mask airway and i‐gel as adjuncts to fibrescope guided intubation in a manikin. Two methods of intubation were compared with each device: the tracheal tube directly over the fibrescope; and the tracheal tube over an Aintree Intubation Catheter. Thirty‐two anaesthetists took part in this randomised crossover study. Each anaesthetist performed two intubations with each method via each device. The mean (SD) time for the first intubation using the tracheal tube over the fibrescope was 43 (24) s with the classic laryngeal mask airway and 22 (9) s with the i‐gel (95% CI for the difference 12–30 s, p < 0.0001). The mean (SD) times for the first intubation when using the Aintree Intubation Catheter was 46 (24) s with the classic laryngeal mask airway and 37 (9) s with the i‐gel (95% CI for the difference 5–12 s, p < 0.0001). We recorded five (5/64, 8%) oesophageal intubations when using the classic laryngeal mask airway and none when using the i‐gel. The participants rated the ease of railroading of the tracheal tube and railroading the Aintree Intubation Catheter over the fibrescope to be significantly easier (p < 0.0001 and p = 0.002 respectively) when using the i‐gel than when using the classic laryngeal mask airway. Furthermore, 30/32 (94%) of anaesthetists reported preference for the i‐gel over the classic laryngeal mask airway for fibrescope guided tracheal intubation when managing a difficult airway. We conclude that the i‐gel is likely to be a more appropriate conduit than the classic laryngeal mask airway for fibrescope guided intubation irrespective of the intubation method used.     

Complications associated with removal of the laryngeal mask airway: A comparison of removal in deeply anaesthetised versus awake patients

The purpose of the study was to compare the incidence of complications (coughing, biting, retching, vomiting, excessive salivation and airway obstruction) associated with removal of the laryngeal mask airway. The laryngeal mask airway was used in 100 adults undergoing urological procedures. The patients were randomly assigned to two groups. In 50 patients the laryngeal mask was removed by a nurse when the patient responded to commands in the recovery area. In the other 50 patients it was removed by the anaesthetist with the patient deeply anaesthetized in theatre. The majority of patients were elderly men who had relatively short procedures. The incidence of gastric regurgitation was assessed by measurement of pH of secretions at the tip of the laryngeal mask airway. Complications occurred more frequently in the awake patients (P < 0.01). Most were minor and occurred before removal of the laryngeal mask airway during emergence in the recovery room. Airway obstruction occurred in three patients in whom the laryngeal mask was removed in the recovery room. In two of these patients the oxygen saturation decreased below 80% and the other to 90%. No decrease in arterial oxygenation occurred in the anaesthetised patients in whom the laryngeal mask was removed by the anaesthetist. In 14 patients in the awake group the pH of secretions at the tip of the laryngeal mask was ≤3 compared with only four patients in the anaesthetised group (P < 0.05). It is concluded that it may be safer to remove the laryngeal mask airway whilst the patients are deeply anaesthetised in the operating room than when they are awake in the recovery room.     

Placement of the intubating laryngeal mask is easier than the laryngeal mask during manual in-line neck stabilization

We have compared in 25 patients ease of placement of the conventional and intubating laryngeal masks while the patient's head and neck were stabilized by a manual in-line method, in a randomized, crossover study. After induction of anaesthesia and neuromuscular block, the masks were placed in turn. Adequacy of ventilation and ease of placement (using a 10-cm visual analogue scale (VAS)) were assessed; time for placement between removal of the face mask and connection of the laryngeal mask to the breathing system was measured. Adequate ventilation was always obtained after placement of the intubating laryngeal mask, whereas ventilation was adequate in 22 of 25 patients after placement of the conventional laryngeal mask. Placement of the intubating laryngeal mask was significantly easier (P < 0.001; 95% confidence intervals (CI) for median difference 8-31 mm in VAS) and faster (P << 0.001; 95% CI for mean difference 3.2-6.2 s) than that of the conventional mask.      

Patient response to laryngeal mask insertion after induction of anaesthesia with propofol or thiopentone

The response to insertion of the laryngeal mask airway (LMA) following either propofol 2.5 mg·kg^?1 or thiopentone 5 mg ·kg^?1 was assessed in two groups of patients. The purpose of the study was to ascertain which of these two induction agents provided the better conditions for insertion of the LMA. Anaesthesia was induced by propofol in 35 patients and by thiopentone in 37. Following induction, ventilation was assisted for two minutes using 50% oxygen and nitrous oxide and 2% isoflurane, before insertion of the LMA. The presence of gagging, coughing, laryngospasm and movement was noted and graded. Thiopentone was associated with an adverse response in 76% of patients, compared with propofol in 26% (P < 0.01). Gagging, laryngospasm and head movement were more common using thiopentone (P < 0.01, P < 0.05 and P < 0.05 respectively) and in 11% (P < 0.05) of the thiopentone group insertion of the LMA was impossible due to inadequate relaxation. We conclude that, using these doses, propofol is superior to thiopentone as an induction agent for insertion of the laryngeal mask airway.     

COMPARISON OF END-TIDAL AND ARTERIAL CARBON DIOXIDE MEASUREMENTS DURING ANAESTHESIA WITH THE LARYNGEAL MASK AIRWAY

We have confirmed the value of measurement of end-tidal carbondioxide concentration as an indicator of arterial carbon dioxidetension during the use of the laryngeal mask airway in healthypatients breathing spontaneously. The mean difference betweenarterial and end-tidal carbon dioxide tension was 0.52 kPa (range0–1.5 kPa), which is similar to the difference which hasbeen reported when a tracheal tube has been used. (Br. J. Anaesth.1993; 71: 734–735) ^*Present address, for correspondence: Department of Anaesthesia,St George's Hospital, Blackshaw Road, London SW17 OQT.     

COMPARISON OF THE EFFECTS OF THE LARYNGEAL MASK AIRWAY AND ENDOTRACHEAL INTUBATION ON VOCAL FUNCTION

We have compared changes in vocal function produced after insertionof a laryngeal mask airway (LMA) with those produced by trachealintubation in 20 patients. Using acoustic waveform analysis,we computed amplitude variability (AV), pitch variability (PV),harmonics-to-noise ratio (HNR) and additive noise level (ANL)before anaesthesia and at 1, 4, and 24 h after tracheal extubation.There were no significant changes in vocal function after extubationexcept for HNR ratio (P = 0.046) at 4 h in the LMA group. Therewere differences in all four variables at 1 h, 4 h, or both,after tracheal extubation compared with baseline in the trachealtube group. In both groups, all variables were the same as baselinevalues 24 h after extubation. We observed significant differencesin AV (4 h), PV and ANL (1, 4 h) values between the two groups.These observations suggest that the LMA causes less vocal changethan tracheal intubation (Br. J. Anaesth. 1993; 71: 648–650)     

Removal of the laryngeal mask airway in children: anaesthetized compared with awake

We studied 60 children, aged 12 months to 8 yr, undergoing plastic surgery under general anaesthesia supplemented by regional anaesthesia. Patients were allocated randomly to have the laryngeal mask airway removed either on awakening or while anaesthetized. Subsequent observation of respiratory factors and oxygen saturation showed a significant difference between the groups for coughing (P < 0.001), with a greater incidence (17 of 33) in the awake group compared with those from whom the laryngeal mask airway was removed while anaesthetized (two of 27). There were no differences in the incidences of laryngospasm, desaturation (< 95%) and excess salivation between the groups. Removed of the laryngeal mask airway during deep anaesthesia reduced coughing in the immediate postoperative period.      

Stability of the LMA-ProSeal and standard laryngeal mask airway in different head and neck positions: a randomized crossover study

BACKGROUND AND OBJECTIVE: The LMA-ProSeal laryngeal mask airway is a new laryngeal mask airway with a modified cuff and drainage tube. We compared oropharyngeal leak pressure, intracuff pressure and anatomical position (assessed fibreoptically) for the Size 5 LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway in different head-neck positions and using different intracuff inflation volumes. METHODS: Thirty paralysed anaesthetized adult male patients were studied. The LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway were inserted into each patient in random order. The oropharyngeal leak pressure, intracuff pressure, and anatomical position of the airway tube and drainage tube (LMA-ProSeal laryngeal mask airway only) were documented in four head and neck positions (neutral first, then flexion, extension and rotation in random order), and at 0-40 mL cuff volumes in the neutral position in 10 mL increments. RESULTS: Compared with the neutral position, the oropharyngeal leak pressure for both the LMA-ProSeal laryngeal mask airway and the classic laryngeal mask airway was higher in flexion and rotation (all P < or = 0.02), but lower in extension (all P < or = 0.01). Changes in head-neck position did not alter the anatomical position of the airway tube or the drainage tube. The oropharyngeal leak pressure was always higher for the LMA-ProSeal laryngeal mask airway (all P < or = 0.005) and anatomical position better for the classic laryngeal mask airway (all P < or = 0.04). CONCLUSIONS: The anatomical position of the LMA-ProSeal and the classic laryngeal mask airway is stable in different head-neck positions, but head-neck flexion and rotation are associated with an increase, and head-neck extension a decrease, in oropharyngeal leak pressure and intracuff pressure. The Size 5 LMA-ProSeal laryngeal mask airway is capable of forming a more effective seal than the Size 5 classic laryngeal mask airway in males.     

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)     

Manikin study of fibreoptic‐guided intubation through the classic laryngeal mask airway with the Aintree intubating catheter vs the intubating laryngeal mask airway in the simulated difficult airway*

In this randomised crossover manikin study of simulated difficult intubation, 26 anaesthetists attempted to intubate the trachea using two fibreoptic‐guided techniques: via a classic laryngeal mask airway using an Aintree intubating catheter and via an intubating laryngeal mask airway using its tracheal tube. Successful intubation was the primary endpoint, which was completed successfully in all 26 cases using the former technique, and in 5 of 26 cases using the latter (p < 0.0001). The former technique also proved quicker to reach the vocal cords with the fibrescope (median (IQR [range])) time 18 (14–20 [8–44]) s vs 110 (70–114 [30–118]) s, respectively; p = 0.008); and to first ventilation (93 (74–109 [52–135]) s vs 135 (79–158 [70–160]) s, respectively; p = 0.0038)]. We conclude that in simulated difficult intubation, fibreoptic intubation appears easier to achieve using a classic laryngeal mask airway and an Aintree intubating catheter than through an intubating laryngeal mask airway.     

Laryngeal mask and anaesthetic waste gas exposure

In recent years there has been a growing awareness of the possible hazards caused by anaesthetic gases in operating theatres. The laryngeal mask airway provides an alternative both to tracheal intubation and the face mask although the implications for operating theatre contamination have not been quantified. This paper describes the incidence and magnitude of exposure of theatre personnel to waste anaesthetic gases during laryngeal mask airway anaesthesia. The leakage of anaesthetic gases to the anaesthetist's breathing zone was monitored using a Bruel & Kjaer Multi Gas Monitor, Type 1302 during 50 general anaesthetics employing either spontaneous (n = 24) or controlled (n = 26) ventilation. All patients were anaesthetised with propofol, alfentanil and nitrous oxide. There was no statistically significant association between the amount of anaesthetic gas leakage and ventilation method. The laryngeal mask airway meets occupational safety requirements on nitrous oxide concentrations in the operating theatre environment.     

Re-evaluation of appropriate size of the laryngeal mask airway

We have assessed 32 males and 31 females in a randomized, crossover study to see if there was any difference in the correct positioning of the laryngeal mask, optimal ventilation (defined as no gas leak around the mask at an airway pressure of 18 cm H2O) and cuff visibility between sizes 4 and 5 masks in males and sizes 3 and 4 in females. The position of the mask in relation to the glottis was assessed using a fibreoptic bronchoscope. There was no significant difference in correct positioning between the two sizes in either sex. Gas leak was significantly less frequent for a larger than a smaller mask (P < 0.01 for both sexes), whereas the cuff was more often seen in the mouth with larger masks (P < 0.02 for males and P < 0.01 for females). Therefore, larger masks (size 4 in females and size 5 in males) provided a better seal than smaller sizes without worsening the relative position of the mask to the glottis; however, the larger mask came up within the mouth more often, which could interfere with tonsillectomy and could increase the risk of sore throat or lingual nerve damage.      

Fibreoptic views through the laryngeal mask and the intubating laryngeal mask.

BACKGROUND AND OBJECTIVE: The intubating laryngeal mask (intubating laryngeal mask airway) was designed to facilitate blind intubation. Its value as an adjunct to fibreoptic laryngoscopy has not been evaluated. This study compares the intubating laryngeal mask airway with the standard laryngeal mask airway as conduits for fibreoptic laryngoscopy. METHODS: The fibreoptic view of the laryngeal inlet was graded via both devices in 60 anaesthetized patients. The fibreoptic view through the intubating laryngeal mask airway was assessed after the central epiglottic elevator bar had been lifted out of the field of vision by an 8-mm Euromedical tracheal tube, which was inserted to a depth of 18 cm. The fibreoptic view from the aperture bars of the laryngeal mask was recorded. RESULTS: The vocal cords were viewed less frequently through the intubating laryngeal mask airway (52%) than through the laryngeal mask airway (92%) [difference = 40% (95% CI = 26% to 54%), P < 0.0001]. CONCLUSION: The view of the laryngeal inlet is better through the laryngeal mask airway than through a tracheal tube inserted to 18 cm in the intubating laryngeal mask.     

A comparison of fibreoptic‐guided tracheal intubation through the Ambu®Aura‐i™, the intubating laryngeal mask airway and the i‐gel™: a manikin study

We compared the Aura‐i ^? , intubating laryngeal mask airway and i‐gel ^? as conduits for fibreoptic‐guided tracheal intubation in a manikin. Thirty anaesthetists each performed two tracheal intubations through each device, a total of 180 intubations. The median (IQR [range]) time to complete the first intubation was 40 (31–50 [15–162]) s, 37 (34–48 [25–75]) s and 28 (22–35 [14–59]) s for the Aura‐i, intubating laryngeal mask airway and i‐gel, respectively. Tracheal intubation through the i‐gel was the quickest (p < 0.01). Resistance to railroading of the tracheal tube over the fibrescope was significantly greater through the Aura‐i compared with the intubating laryngeal mask airway and the i‐gel (p = 0.001). There were no failures to intubate through the intubating laryngeal mask airway or the i‐gel but six intubation attempts through the Aura‐i were unsuccessful, in five owing to a railroading failure and in one owing to accidental oesophageal intubation. We conclude that the Aura‐i does not perform as well as the intubating laryngeal mask airway or the i‐gel as an adjunct for performing fibreoptic‐guided tracheal intubation.