Anesth Analg 2005;100:590-593
© 2005 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000144068.26632.B7
GENERAL ARTICLES
The ProSealTM Has a Shorter Life-Span than the ClassicTM Laryngeal Mask Airway
Sarah Doneley, MB BS*,
Joseph Brimacombe, MB ChB, FRCA, MD
,
Christian Keller, MD
, and
Achim von Goedecke, MD
*Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Australia; James Cook University, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, Australia; Department of Anaesthesia and Intensive Care Medicine, Leopold-Franzens University, Innsbruck, Austria
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Abstract
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We tested the hypothesis that the life-span of the ProSealTM laryngeal mask airway (LMA) is shorter than the ClassicTM LMA. We also compared residual cuff volumes and changes in elastance and permeability with use. Six new size 4 ProSealTM LMAs and 6 new size 4 ClassicTM LMAs were tested. Each LMA underwent a simulated clinical use cycle until it failed the pre-use check tests. The simulated clinical use cycle comprised: i) inflating the cuff to the maximum recommended volume for 1 h; ii) immersion in an enzymatic solution for 3 min; iii) washing the external and internal surfaces; iv) automatic washing for 14 min (
85°C); v) drying for 30 min (75°C); and vi) autoclaving at 134°C for 4 min at 206 kPa. Before the first cycle and every 10 subsequent cycles, the cuff was inflated with 40 mL air and the intracuff pressure was measured immediately and 3 h later. The initial intracuff pressure was taken to be an inverse measure of the elastance or resistance to deformation, and the intracuff pressure change were taken as a measure of the permeability. The residual cuff volume was determined for 10 ClassicTM and 10 ProSealTM size 4 LMAs using a gas dilution technique. The mean ± sd (range) longevity for the ProSealTM LMA and ClassicTM LMA was 82 ± 23 (45–109) uses and 133 ± 35 (76–176) uses, respectively. The ProSealTM LMA has a shorter life-span than the ClassicTM LMA (P = 0.01). For the ProSealTM LMA, there was no change in elastance or permeability with use. For the ClassicTM LMA, there was a decrease in elastance (P < 0.0001) and an increase in permeability (P < 0.0001) with use. The residual cuff volume was higher for the ProSealTM LMA (2.6 ± 1.3 mL versus 1.5 ± 0.9, P = 0.04). We conclude that the life-span of the ProSealTM LMA is shorter than the ClassicTM LMA, but both exceed the manufacturer’s recommendations of 40 uses. We recommend that reusable LMA devices be discarded when they fail the pre-use check tests, rather than after a specific number of uses.
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Introduction
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Reusable laryngeal mask airway (LMA) devices are constructed from medical grade silicone, as it has an indefinite shelf life, is heat resistant to 180°C, and has excellent elastic properties (1). However, repeated sterilization produces degradation of the silicone polymer chains, which manifests as a decrease in elastance or resistance to deformation, an increase in permeability, and hardening/discoloration of the tube (2). Autoclaving also damages the bond between the connector and tube, although this does not affect the airtightness of the junction (3). The clinical consequences of device failure include airway obstruction, loss of seal, aspiration of tube fragments, and failure to identify regurgitation early (1). The manufacturer recommends that all reusable LMA devices be discarded after 40 uses (4–6), but for the ClassicTM LMA there is in vitro evidence that the physical properties do not alter substantially until after 80 uses (2) and in vivo evidence that there is no change in clinical performance for at least 60 uses (7). The ProSealTM LMA is the newest and most complex of the reusable LMA devices and differs from the ClassicTM LMA in that it has a larger ventral cuff, a dorsal cuff, a drain tube, and a built-in bite block (8,9). An audit of our institute suggested that many of the ProSealTM LMAs were not lasting for 40 uses, despite strict adherence to the manufacturer’s guidelines for cleaning and sterilization. In the following study, we test the hypothesis that the life-span of the ProSealTM LMA is shorter than the ClassicTM LMA. We also compare residual cuff volumes and changes in elastance and permeability with use.
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Methods
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Six new size 4 ProSealTM LMAs and 6 new size 4 ClassicTM LMAs were tested. Each LMA was randomly assigned a number that was marked on the proximal connector with an indelible pen. Each LMA underwent a simulated clinical use cycle until it failed the manufacturer’s pre-use check tests (4,6). The simulated clinical use cycle comprised the following steps: i) inflating the cuff to the maximum recommended volume for 1 h in vitro; ii) immersion in an enzymatic solution for 3 min; iii) washing the external surfaces with a cloth; iv) washing the airway and/or drain tube with an appropriate sized soft bristled brush; v) placing the LMA in an automatic washer for 14 min, which included warm washing at 55°C with a disinfectant and hot washing at 85°C; vi) placing in a dryer for 30 min at 75°C; vii) autoclaving at 134°C for 4 min at 206 kPa. Before each of the last three steps, the cuff was fully evacuated using a syringe.
Before the first simulated clinical use cycle and every 10 simulated clinical use cycles thereafter, the cuff was fully deflated and then reinflated with 40 mL air from a calibrated plastic syringe and intracuff pressure was measured both immediately and 3 h later. The initial intracuff pressure was taken to be an inverse measure of the elastance or resistance to deformation, and the pressure change was taken as a measure of the permeability. Intracuff pressure measurements were made by attaching the pilot balloon to a pressure transducer via a three-way tap. The reason for failing the pre-use test was documented. All tests were performed at in room air at 20°C. A maximum of three simulated clinical use cycles was conducted each day.
The residual volume was calculated using a gas dilution technique. Ten size 4 ClassicTM LMAs and 10 size 4 ProSealTM LMAs matched for number of uses were assessed. These LMA devices were not used in the simulated clinical use tests. All were in clinical use, had passed the pre-use check tests and had no macro or micro leaks, as assessed by spontaneous deflation characteristics. Each device was flushed with oxygen, placed in the deflation tool, and then evacuated to a pressure of –25 mm Hg. The cuff was then immediately inflated with 40 mL air and the oxygen concentration measured using a Datex AS/3 gas analyzer (Datex-Ohmeda, Helsinki, Finland) that had been zeroed and calibrated. This was repeated on 5 occasions for each device and the average taken.
Sample size for the life-span study was based on a previous study about the ClassicTM LMA by Figueredo (2) and our own audit data about the ProSealTM LMA. The distribution of data was determined using Kolmogorov-Smirnov analysis (10). Statistical analysis was with paired and nonpaired Student’s t-tests (normally distributed data), one-way analysis of variance with post hoc Bonferroni correction and Friedman’s two-way analysis of variance (non-normally distributed data). The relationship between number of uses and other variables was determined using Pearson’s product-moment correlation coefficient (PPCC). Unless otherwise stated data are presented as mean ± sd (range). Significance was taken as P < 0.05.
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Results
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The mean± sd (range) longevity for the ProSealTM LMA and ClassicTM LMA was 82 ± 23 (45–109) uses and 133 ± 35 (76–176) uses, respectively. The ProSealTM LMA had a shorter life-span than the ClassicTM LMA (P = 0.01). All the ProSealTM LMAs failed the pre-use tests because of tears in the cuff. Two ClassicTM LMAs failed because of tears in the pilot balloon, three failed as the result of a defect in the pilot balloon valve, and one failed because of a tear in the cuff. Data for the initial intracuff pressure (inversely related to elastance) and the intracuff pressure change (related to permeability) are presented in (Table 1). The elastance and permeability was always greater for the ClassicTM LMA (both P < 0.0001). For the ProSealTM LMA, there was no change in elastance or permeability with use. For the ClassicTM LMA, there was a decrease in elastance (PPCC = –0.64, P < 0.0001) and an increase in permeability (PPCC = 0.603, P < 0.0001) with use. For the ClassicTM LMA, there was a significant decrease in the elastance (P = 0.01) and a significant increase in the permeability (P = 0.004) between 80–90 uses. The mean (range) number of uses of the ProSealTM LMA and ClassicTM LMA for residual volume testing was 18 (0–36) and 20 (0–39) uses, respectively. The residual cuff volume was higher for the ProSealTM LMA than and ClassicTM LMA (2.6 ± 1.3 mL versus 1.5 ± 0.9, P = 0.04).
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Discussion
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The life-span of the ProSealTM LMA is shorter than the ClassicTM LMA. This is probably because the ProSealTM LMA cuff has a more complex shape with more folds and seams; in any inflatable structure, these are the areas that are most likely to fail. In addition, the cuff wall may be subject to greater stresses during autoclaving because of the larger residual volume; however, to some extent this will be mitigated by the larger cuff. A removable plug has recently been added to the pilot balloon of the ProSealTM LMA (Red PlugTM) to prevent damage from any residual air or fluid. After completion of the current study, we tested 3 ProSealTM LMAs fitted with the Red PlugTM and found that the life-spans were roughly similar to those without, at 69, 87, and 102 simulated use cycles.
There was no change in the elastance and permeability of the ProSealTM LMA, but there was a decrease in elastance and an increase in permeability of the ClassicTM LMA. At first glance this suggests that the ProSealTM LMA cuff deteriorates less rapidly than the ClassicTM LMA cuff; however, most of the changes in elastance and permeability for the ClassicTM LMA occurred after 80 uses and few data were collected for the ProSealTM LMA after 80 uses, as most had failed. That the ProSealTM LMA cuff tears before any change in elastance or permeability supports the hypothesis that its reduced life-span is related to localized areas of weakness. Identification and strengthening of these areas should increase the life-span of the ProSealTM LMA. Figueredo (2) also found a decrease in elastance between 80 and 90 uses and suggested that this could be considered the safe life-span of the ClassicTM LMA. However, our data suggest that the changes in elastance and permeability are not useful guides to life-span. Elastance was less for the ProSealTM than the ClassicTM LMA, as the cuff has a larger volume.
The etiology of failure differed between devices, with all the ProSealTM LMAs failing from tears in the cuff, whereas most ClassicTM LMAs failed from problems with the pilot balloon (two from tears and three from valve failure). This almost certainly reflects the increased weakness of the ProSealTM LMA cuff, as the inflation line and pilot balloon are identical for the ClassicTM LMA and the ProSealTM LMA.
The life-span of reusable LMAs not only depends on the number, temperature, and duration of autoclave cycles but also on damage during clinical use (from biting, overinflation, surgical instruments, and accidental introduction of fluid into the cuff), damage during cleaning and sterilization (failure to evacuate air/fluid from the cuff, inappropriate cleaning methods/materials and contact with sharp objects), deliberate discarding (ignorance or concerns about transmissible diseases) and, sadly, theft. The lifespan of LMA devices in clinical practice has only been documented by one group. Wat et al. (11) found that the mean life-span of the ClassicTM LMA was at least 92 uses. The authors also showed that the airway tubes of LMAs of this age were 50% weaker but that the cuffs, pilot balloons, and valves were functioning normally.
The manufacturer recommends that reusable LMAs should be discarded after a maximum of 40 uses; however, the published data suggest that the ClassicTM LMA and, to a lesser extent, the ProSealTM LMA, will pass all the pre-use check tests for considerably longer. There is some evidence that there is no deterioration in performance with age. Berry et al. (7) found no difference in ease of insertion, efficacy of seal, anatomic position for the ClassicTM LMA after 60–79 uses. Most institutes adhere to the manufacturer’s recommendations. Williams and Henderson (12), in a 2000 survey of 100 operating room suites in the United Kingdom, found that 70% of departments discarded the LMA at 40 uses, 7% after <40 uses, and 23% after more than 40 uses. The re-use rate has financial implications. Given the expensive capital cost of reusable LMAs and the variable life-span of each device, we consider that reusable LMAs should only be discarded when they fail the pre-use tests rather than after a specified number of uses. It should also be discarded if it has been exposed to nonapproved chemicals or has been used in a patient with prion disease (13).
Our study has a number of limitations. First, our findings reflect the maximum life-span of reusable LMA devices, as our study was conducted in vitro and under optimal conditions. Second, the frequency of damage might be different for the ClassicTM and ProSealTM LMA in clinical practice; for example, the larger cuff of the ProSealTM LMA is more likely to get damaged by teeth than the ClassicTM LMA. Third, our findings may be less applicable in situations where different cleaning and sterilization procedures are followed. Finally, our data may be less applicable to ProSealTM LMAs that have been fitted with the Red PlugTM; however, our additional work suggests that this is not the case.
We conclude that the lifespan of the ProSealTM LMA is shorter than the ClassicTM LMA, but both exceed the manufacturer’s recommendations of 40 uses. We recommend that reusable LMA devices be discarded when they fail the pre-use check tests rather than after a specific number of uses.
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Footnotes
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Accepted for publication August 18, 2004.
Address correspondence to Prof. J Brimacombe, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns 4870, Australia. Address e-mail to jbrimaco{at}bigpond.net.au. This project was supported solely by departmental resources. Drs Brimacombe and Keller have worked as a consultants for the Laryngeal Mask Company, manufacturer of the ProSealTM and ClassicTM laryngeal mask airways.
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References
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- Brimacombe J. Laryngeal mask anesthesia: principles and practice, 2nd ed. London: WB Saunders, 2004.
- Figueredo E. Changes in the intracuff pressure of the laryngeal mask airway caused by repeated use. Can J Anaesth 2001;48:409–12.[Abstract/Free Full Text]
- Preis C, Hartmann T, Preic I, et al. Autoclaving impairs the connector-tube bond of the laryngeal mask airway but not its airtightness. Br J Anaesth 1998;81:795–6.[Abstract/Free Full Text]
- Verghese C. LMA-ClassicTM, LMA-FlexibleTM LMA-UniqueTM. Instruction Manual. Henley-on-Thames: The Laryngeal Mask Company Ltd., 1999.
- Verghese C. LMA-FastrachTM Instruction Manual. Henley-on-Thames: Laryngeal Mask Company Ltd., 2000.
- LMA ProSealTM Instruction manual, 1st ed. San Diego: LMA North America Inc., 2000.
- Berry AM, Brimacombe J, McManus KF, Goldblatt M. An evaluation of the factors influencing selection of the optimal size of laryngeal mask airway in normal adults. Anaesthesia 1998;53:565–70.[ISI][Medline]
- Brain AIJ, Verghese C, Strube PJ. The LMA "ProSeal": a laryngeal mask with an oesophageal vent. Br J Anaesth 2000;84:650–4.[Abstract/Free Full Text]
- Brimacombe J, Keller C. The ProSeal laryngeal mask airway. a randomized, crossover study with the standard laryngeal mask airway in paralyzed, anesthetized patients. Anesthesiology 2000;93:104–9.[ISI][Medline]
- Gaddis GM, Gaddis ML. Introduction to biostatistics. Part 5: statistical inference techniques for hypothesis testing with nonparametric data. Ann Emerg Med 1990;19:1054–9.[ISI][Medline]
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- Williams S, Henderson K. A survey into the number of times laryngeal masks are used. Anaesthesia 2000;55:700–1.
- Clery G, Brimacombe J, Stone T, et al. Routine cleaning and autoclaving does not remove protein deposits from re-usable laryngeal mask devices. Anesth Analg 2003;97:1189–91.[Abstract/Free Full Text]
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Abstract
Introduction
