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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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: 5349
Keywords: equipment, airway; equipment, masks anaesthesia; larynx
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Introduction |
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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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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 min1 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 Fishers 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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Discussion |
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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 1012 cm H2O higher than the airway seal pressure of 1719 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 811 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 9699.8% 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 020% 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 5.834%.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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References |
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