British Journal of Anaesthesia, 2002, Vol. 88, No. 4 534-539
© 2002 The Board of Management and Trustees of the British Journal of Anaesthesia
Clinical Investigations |
The ProSeal laryngeal mask: results of a descriptive trial with experience of 300 cases
1Department of Anaesthesia, University of Cape Town, Groote Schuur Hospital, Observatory, Cape Town 7925, South Africa. 2Department of Anaesthesia, Edendale Hospital, Pietermaritzburg, Natal, South Africa*Corresponding author
Declaration of interest. Marland Medical South Africa funded the salary of a research assistant and provided the masks. AstraZeneca (South Africa) provided the propofol used for this study. 
LMA® is the property of Intavent Limited.
Accepted for publication: October 31, 2001
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Abstract |
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Background. The ProSeal laryngeal mask airway (PLMA) is a new laryngeal mask device with a modified cuff and a drainage tube.
Methods. We assessed the PLMA in 300 anaesthetized adults either paralysed or breathing spontaneously. We assessed insertion characteristics, airway seal pressures, haemodynamic response to insertion, ease of gastric tube placement, gastric insufflation, and postoperative sore throat.
Results. Insertion was successful in 294 patients (98%) and graded as easy in 274 patients (91%). We found no difference in ease of insertion or success rate with either the introducer or the finger insertion method, or in paralysed or non-paralysed patients. Mean airway seal pressure was 29 cm H2O, and 59 patients (20%) had seal pressures greater than 40 cm H2O. No gastric insufflation was detected. Gastric tube placement was successful in 290 of 294 patients (98.6%). There was no cardiovascular response to insertion, with a small reduction in heart rate 5 min after insertion and significant decreases in mean arterial pressure at 1 and 5 min after insertion. Sore throat was noted in 23% patients after operation and in 16% of patients after 24 h, with 90% of the sore throats described as mild.
Conclusions. The PLMA is a reliable airway management device that can give an effective glottic seal in paralysed and non-paralysed patients. The device allows the easy passage of a gastric tube, causes a minimal haemodynamic response to insertion, and an acceptable incidence of sore throat.
Br J Anaesth 2002; 88: 534–9
Keywords: equipment, airway; equipment, masks anaesthesia; larynx
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Introduction |
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The ProSeal laryngeal mask (PLMA; Intavent, Orthofix, Maidenhead, UK) is a new laryngeal mask device with a cuff modified to improve the seal around the glottis and a drainage tube to provide a bypass channel for regurgitated gastric contents, prevent gastric insufflation, and allow the passage of a gastric tube. These features are designed to improve the safety of the mask and broaden its scope, especially when used with positive pressure ventilation (Fig. 1).1 2
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Two randomized crossover trials1 2 compared the PLMA with the classic laryngeal mask (LMA
) in anaesthetized, paralysed, adults. The PLMA was as easy to insert as the LMA when the introducer tool was used and the airway sealing pressure was 8–11 cm H2O greater. Gastric tube placement was successful in all the patients. In both trials only size 4 masks were used. We set out to assess the performance of sizes 4 and 5 PLMA in 300 anaesthetized adults, either paralysed or breathing spontaneously.
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Methods |
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We studied 300 ASA I–III adult patients over 5 month periods. Research and ethical committee approval was obtained and all patients gave informed written consent. We studied patients undergoing routine elective surgery where a classic LMA would normally be used. Patients were excluded if they were at risk of aspiration. There were eight investigators who were consultants and senior registrars all of whom had more than 5 yr anaesthetic experience and had been trained to insert the PLMA as directed by the manufacturer. They carried out 10 insertions on a model and 10 insertions in patients before commencing the trial. Premedication consisted of oral temazepam 10 or 20 mg depending on body weight 1–2 h before surgery. Standard monitoring was applied before induction of anaesthesia. Anaesthesia was induced with fentanyl 1 µg kg–1 followed 2 min later by propofol 2–3 mg kg–1 until the eyelash reflex was abolished. In spontaneously breathing patients the PLMA was inserted immediately after this, when adequate jaw relaxation had been achieved. In patients to be paralysed and ventilated, an appropriate dose of a non-depolarizing agent was given and the PLMA inserted 2–3 min later. The decision to use neuromuscular blocking drugs depended on the surgical requirement for muscular relaxation. Anaesthesia was maintained with isoflurane and 66% nitrous oxide in oxygen using a circle absorber system. With the patient supine and the head in the neutral position resting on a pillow 7 cm in height, a PLMA (size 4 in females and size 5 in males) was inserted using either the index finger or the introducer tool. At the discretion of the investigator, a size 5 PLMA could be used in females taller than 165 cm or weighing more than 70 kg; in males less than 70 kg or shorter than 165 cm, a size 4 PLMA could be used. The index finger insertion method was identical to that recommended by the manufacturer for the classic LMA,3 and the insertion method with the introducer tool was that described for the intubating laryngeal mask.4 The cuff was inflated to obtain an intracuff pressure of 60 cm H2O, measured with a calibrated anaeroid manometer (Carron Medical® Control instruments RSA). The volume of air required was noted. The intracuff pressure was maintained at this pressure throughout the procedure. Arterial pressure (systolic, diastolic, and mean) and heart rate were recorded before induction, and at 1 and 5 min after insertion. After insertion and cuff inflation, manual ventilation of the lungs was carried out with the circuit closed to determine (i) whether an expired volume of more than 8 ml kg–1 could be achieved and (ii) whether leak occurred up the drainage tube when airway pressure was less than 20 cm H2O. This pressure was chosen as leaks with a pressure less than 20 cm H2O suggest malposition of the device.1 Leak was detected by placing a 1 ml bolus of lubricant jelly in the proximal orifice of the drainage tube to seal it. The airway pressure at which this bolus was ejected was noted. If a leak occurred with an airway pressure less than 20 cm H2O, malposition was assumed and the mask repositioned or reinserted. The number of insertion attempts required to achieve these criteria were recorded—a failed insertion attempt was defined as removal of the device from the mouth. Three insertion attempts were allowed before a failure of insertion was recorded. If the PLMA could not achieve a satisfactory airway within three insertions either a classic LMA was inserted or the trachea was intubated conventionally. A satisfactory placement was noted if the expired tidal volume was more than 8 ml kg–1 and there was no drainage tube leak. Once a satisfactory placement had been achieved, the PLMA was fixed in place by taping the tube over the chin. Ease of insertion was noted. An easy insertion was defined as insertion within the pharynx without resistance in a single manoeuvre. A difficult insertion was one in which there was resistance to insertion or where more than one manoeuvre was required to seat the device within the pharynx.
The airway sealing pressure was then determined as described previously5 by closing the expiratory valve of the breathing system. With a fresh gas flow rate set to 3 litre min–1 the pressure in the circuit was allowed to increase until no further increase in pressure occurred. The airway pressure was not allowed to exceed 40 cm H2O. The location of gas leak when the pressure became stable was determined as mouth (audible), stomach (epigastric auscultation), or drainage tube (bubbling of lubricant).
In 102 patients, a fibre optic bronchoscope (Olympus BF 240®) was passed down the airway to a position 1 cm proximal to the end of the tube and the view graded using an established scoring system:6 4=only vocal cords visible; 3=vocal cords and posterior epiglottis visible; 2=vocal cords and anterior epiglottis visible; 1=vocal cords not seen.
A lubricated size 16 or 18 French gauge gastric tube was inserted down the drainage tube. Gastric contents were aspirated with a 50 ml catheter tipped syringe; the volume measure and the pH were tested with litmus paper. The gastric tube was left in situ for the duration of the procedure and the total volume drained noted. The tube was removed at the end of the procedure while the patient was still anaesthetized. The duration of the surgery was noted. Once the patient was awake the mask was removed and the pH of the back and front of the mask tested by litmus paper sensitive to changes of 1 pH unit from pH 1 through to 10. (Duotest® Macherey-Nagel Duren, Germany). The patients were asked in the recovery room and 24 h later whether they had a sore throat. If a positive answer was obtained, they were asked to grade the sore throat as mild, moderate, or severe.
Statistics
For statistical analysis, we used Statistica for Windows® program running on an IBM compatible machine under Windows 98. Categorical data were analysed with Fisher’s exact test for two comparisons, or the chi-squared test for more categories, with Yates correction where appropriate. Quantitative data were analysed after exclusion of upper limits (e.g. maximum seal pressure) where appropriate by analysis of variance with post-hoc testing using 95% confidence intervals. We compared seal pressures between males and females and between paralysed and non-paralysed patients, and the method of insertion. These comparisons were not of randomly allocated groups and were not primary end-points of the study design. The analysis was to allow the development of hypotheses for future testing.
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Results |
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The characteristics of the 300 patients and details of anaesthesia are shown in Tables 1 and 2. Insertion was successful in 294 patients (98%), required one attempt in 243 patients (81%), and was graded as easy in 274 patients (91%) (Table 3). Of the six failed insertions, insertion of a classic LMA was possible in two patients but unsuccessful in two others, while in the other two failures, classic LMA insertion was not attempted and the trachea intubated conventionally. Table 4 lists the insertion failures by investigator and technique. The individual choices among investigators for the use of the introducer or finger insertion technique are shown in Table 5. There did not seem to be a difference in ease of insertion or success rate using either the introducer or the finger technique, or in paralysed vs non-paralysed patients (Table 6). However, as neither the insertion technique nor the use of neuromuscular blocking drugs was randomized, no firm conclusions can be drawn. Power analysis using our data shows that a sample size of approximately 500 randomized subjects would be needed to compare the insertion techniques.
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The mean (range) volume of air required to achieve an intracuff pressure of 60 cm H2O was 28 (14–45) ml for the size 4 mask and 37 (18–63) ml for the size 5 mask. Airway seal pressures are shown in Table 7. Where a size 4 PLMA was used in males (16 patients), seal pressure was similar to that of the whole group (29.5 cm H2O) and when a size 5 PLMA was used in females (16 patients) seal pressure was slightly higher (34.9 cm H2O). Significantly more females than males achieved a seal pressure of 40 cm H2O or greater (P=0.012). In those whose seal pressures were less than 40 cm H2O, the seal pressure was statistically significantly greater in females than in males (P=0.05) but this difference was not clinically important. There were no differences in the number of patients achieving seal pressures greater than/equal to 40 cm H2O between those paralysed and not paralysed; there was a statistically significant (P=0.01) but clinically unimportant difference in seal pressure in those whose seal pressure was less than 40 cm H2O. Gas leakage at airway sealing pressure was from the mouth in 290 cases (98.2%) and from the drainage tube in four patients (1%). Gastric insufflation was not detected in any patient. In the patients studied with the fibre optic bronchoscope the view ratings were four in 47 cases, three in 31 cases, two in 16, and one in eight. Vocal cords were seen in 94 of 102 patients (92%). Gastric tube placement was successful in 290 patients (97%), graded as easy in 286 of these patients (98%), and difficult in four. Gastric tube placement failed in four patients. Fluid was aspirated from the gastric tube initially in 193 patients (67%) and in 225 patients (76%) by the end of the procedure, with a mean (range) initial volume of 20 (0–120) ml and a final volume of 24 (0–180) ml.
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Haemodynamic measurements were incomplete in 32 patients and these values were not analysed. Complete haemodynamic data were available for 268 patients. Mean heart rate did not change at 1 min after insertion and decreased to 78 beats min–1 at 5 min after insertion (P=0.13) (Fig. 2). There was a significant decrease in mean arterial pressure at 1 min after insertion compared with before induction (77 vs 102 mm Hg, P<0.001) and at 5 min after insertion compared with the values after 1 min (71 vs 77 mm Hg, P=0.01) (Fig. 3).
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Litmus paper showed a pH less than 6 in one patient only, who tested pH 4 on the back of the mask only. Sore throat was reported by 60 of the 265 (23%) patients in the recovery room, 54 of whom (90%) described the sore throat as mild and six (10%) described it as moderate. The following day 41 out of 255 (16%) patients had a sore throat; 38 patients (92%) described the sore throat as mild and three (8%) described it as moderate. There were no reports of a severe sore throat.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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We studied the PLMA in 300 adult patients and found the following.
1. The PLMA was easy to insert with a high success rate.
2. There was no apparent difference in ease of insertion or success rate using either the introducer or the finger insertion method, or in paralysed compared with non-paralysed patients.
3. Mean airway sealing pressure was 10–12 cm H2O higher than the airway seal pressure of 17–19 cm H2O described for a classic LMA.5 7 13
4. No gastric insufflation was detected.
5. Gastric tube placement was successful in most patients (98.6%).
6. There was minimal haemodynamic response to insertion.
7. About 20% of patients had a mild sore throat.
The two small previous trials on the PLMA showed successful mask insertion and gastric tube placement in all patients, with airway sealing pressures 8–11 cm H2O greater than the classic LMA.1 2 We confirm in a larger study that the PLMA is a reliable airway device with a better glottic seal than the classic LMA, and that it allows the reliable placement of a gastric tube. The volume of the larger posterior cuff can make mask insertion difficult, with an insertion success rate of 92%.8 This may have played a role in the failures of mask insertion that occurred in our trial, although our overall success rate of 98% is similar to the rates of 96–99.8% described previously for the classic LMA.9 10 Brimacombe2 reported that the introducer makes insertion easier. Some investigators preferred the introducer technique, but no apparent difference in ease of insertion or success rate to the finger insertion method was found in the sample as a whole. Neuromuscular block confers no advantage over propofol alone in providing optimum conditions for classic LMA insertion11 and this seems to be the same for the PLMA. Neuromuscular block does not affect the directly measured mucosal pressures exerted by a classic LMA.12 We found similar airway seal characteristics and performance in paralysed vs non-paralysed patients for the PLMA, but we did not do a randomized study. Greater seal pressures for females have been found previously for the PLMA2 where size 4 masks were used for both females and males. Using predominantly a size 4 in females and a size 5 in males as recommended previously,13 we found marginally greater seal pressures in females. A size 6 PLMA may be useful in tall men in whom a size 5 may be too small to achieve an adequate seal. Our failure to detect gastric insufflation agrees with the findings of Brimacombe,2 although the sensitivity of epigastric auscultation has been questioned.14 We observed that auscultation using an epigastric microphone is still required. Fibre optic view showed epiglottic down folding on occasions, possibly related to the larger proximal cuff bringing the epiglottis down during insertion. Failure of gastric tube placement can occur if the tip of the mask folds during insertion, so that the distal orifice of the drainage tube is occluded. This can occur if the mask is inserted at an acute angle to the oropharynx allowing the tip of the mask to fold against the posterior oropharyngeal wall before passing into the hypopharynx, and is more likely during light anaesthesia when muscle tone is greater. Insertion of the classic LMA causes a 0–20% increase in heart rate and mean arterial pressure,15 which is less than laryngoscopy.16 17 The larger size of the PLMA and the rigid introducer could cause a greater haemodynamic response. A recent report found the rigid intubating laryngeal mask produced a similar haemodynamic response to laryngoscopy.18 We found that the PLMA caused no detectable response to insertion during propofol anaesthesia, with the heart rate and mean arterial pressure decreasing after insertion.
No regurgitation of gastric contents into the mask was found using the litmus paper technique. A single test at the end of the procedure may not be a sensitive way to detect this and further study with continuous measurement by pH probes down the drainage tube and into the bowl of the mask would be interesting. The incidence of sore throat after classic LMA insertion varies from 5.8–34%.19 Brimacombe20 recently showed that there was no difference between the PLMA and the LMA in directly measured mucosal pressures, so postoperative pharyngolaryngeal morbidity may be similar between the two devices. The incidence of sore throat in this trial supports a recent study on postoperative laryngopharyngeal morbidity with the classic LMA using low cuff volumes.21 In conclusion, the PLMA is a reliable airway capable of achieving an improved seal with the glottis and allowing the passage of a gastric tube in both paralysed and non-paralysed patients, with minimal haemodynamic response to insertion and a similar incidence of sore throat to the classic LMA.
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Acknowledgements |
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The authors wish to thank our contributors, particularly Dr J. A. King, for her enthusiastic assistance, Dr S. Fischer, Dr C. Caldwell, and Chris Goslin of Olympus (SA).
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References |
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Keller C, Brimacombe J, Keller K, Morris R. Comparison of four methods for assessing airway sealing pressure with the laryngeal mask airway in adult patients. Br J Anaesth 1999; 82: 286–7
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Keller C, Brimacrombe J. Mucosal pressure and oropharyngeal leak pressure with the proseal vs laryngeal mask airway in anaesthetized paralysed patients. Br J Anaesth 2000; 85: 262–6
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11
Brimacombe J, Berry A, Yaddanapudi LN, Kashyap L. Neuromuscular blockade and insertion of the laryngeal mask airway. Br J Anaesth 1993; 71: 166–7
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Keller C, Brimacombe J. Influence of neuromuscular block, mode of ventilation and respiratory cycle on pharyngeal mucosal pressures with the laryngeal mask airway. Br J Anaesth 1999; 83: 480–2
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Brimacombe J, Keller C. Laryngeal mask airway size selection in males and females: ease of insertion, oropharyngeal leak pressure, pharyngeal mucosal pressures and anatomical position. Br J Anaesth 1999; 82: 703–7
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21 Brimacombe J, Holyoake L, Keller C, et al. Emergence characteristics and postoperative laryngopharyngeal morbidity with the laryngeal mask airway: a comparison of high versus low initial cuff volume. Anaesthesia 2000; 55: 338–43[Web of Science][Medline]
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